U.S. patent application number 11/027598 was filed with the patent office on 2005-06-23 for flexible lead for digital cardiac rhythm management.
Invention is credited to Eigler, Neal L., Mann, Brian, Whiting, James S..
Application Number | 20050136385 11/027598 |
Document ID | / |
Family ID | 34738632 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050136385 |
Kind Code |
A1 |
Mann, Brian ; et
al. |
June 23, 2005 |
Flexible lead for digital cardiac rhythm management
Abstract
A cardiac rhythm management apparatus includes a proximal
housing, a distal housing and a lead. The proximal housing includes
a first energy storage device. The distal module is implantable
within a patient's heart, and includes a second energy storage
device, at least one electrode, and a control module. The control
module controls the delivery of at least one electrical stimulus
from the second energy storage device to a location in
communication with the patient's heart. The lead connects the
proximal housing to the distal module and is configured to
communicate one or more digital signals between the proximal
housing and the distal module.
Inventors: |
Mann, Brian; (Edgartown,
MA) ; Whiting, James S.; (Los Angeles, CA) ;
Eigler, Neal L.; (Pacific Palisades, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
34738632 |
Appl. No.: |
11/027598 |
Filed: |
December 30, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11027598 |
Dec 30, 2004 |
|
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11015336 |
Dec 17, 2004 |
|
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60531238 |
Dec 19, 2003 |
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Current U.S.
Class: |
434/320 |
Current CPC
Class: |
A61N 1/057 20130101;
A61N 1/37211 20130101; G09B 23/288 20130101; A61N 1/056 20130101;
A61N 1/025 20130101; A61N 1/37254 20170801; A61N 1/37229
20130101 |
Class at
Publication: |
434/320 |
International
Class: |
A61N 001/375; G09B
005/04 |
Claims
What is claimed is:
1. A flexible lead for implantation within a human body,
comprising: a lead length, wherein said lead length extends from a
first end to a second end, wherein said first end is coupled to a
proximal housing implanted at a first location within a human body,
and said second end is coupled to a distal module implanted at a
second location within a human body; and at least two conductors,
wherein said at least two conductors extend from the first end to
the second end, and wherein said at least two conductors are in
electrical communication with at least three electrodes, and
wherein said at least three electrodes are greater in quantity than
said at least two conductors.
2. The lead of claim 1, further comprising a shielding, wherein
said shielding extends from said first end to said second end,
covering at least one of said at least two conductors over said
lead length.
3. The lead of claim 1, wherein said first location is proximate a
shoulder, and said second location is in inside of a heart.
4. The lead of claim 1, wherein said at least three electrodes
comprise an indifferent electrode, a pacing electrode, and a
sensing electrode.
5. The lead of claim 1, wherein said at least two conductors
comprise no more than two conductors.
6. The lead of claim 1, wherein at least one of said at least two
conductors comprises a shielding.
7. The lead of claim 1, wherein said at least three electrodes
comprise no more than three electrodes.
8. The lead of claim 1, wherein said lead is adapted to communicate
digital signals between said proximal housing and said distal
module.
9. The lead of claim 8, wherein said digital signals comprise a
control instruction to deliver an electrical stimulus to the second
location.
10. The lead of claim 8, wherein said digital signals comprise a
power pulse.
11. An implantable lead, said lead comprising: An elongate body,
said elongate body having a first end, a second end, at least one
first conductor extending from the first end to the second end, at
least one second conductor extending from the first end to a
midportion located between the first end and the second end, and at
least one shielding layer extending from the first end to the
second end and covering the at least one first conductor between
the first end and the second end, wherein said first end is adapted
to be coupled to a proximal housing implanted at a first location
within a human body, and said second end is coupled to a distal
housing implanted at a second location within a human body, wherein
said at least one first conductor is coupled to at least two
electrodes, and wherein said at least one second conductor is
coupled to an indifferent electrode.
12. The lead of claim 111, wherein said first location is proximate
a shoulder, and said second location is in inside of a heart.
13. The lead of claim 11, wherein said at least two electrodes
comprise a pacing electrode and a sensing electrode.
14. The lead of claim 11, wherein said at least one first
conductors comprises no more than one conductor.
15. The lead of claim 11, wherein said at least two electrodes
comprise no more than two electrodes.
16. The lead of claim 111, wherein said lead is adapted to
communicate digital signals between said proximal housing and said
distal module.
17. The lead of claim 16, wherein said digital signals comprise a
control instruction to deliver an electrical stimulus to the second
location.
18. The lead of claim 16, wherein said digital signals comprise a
power pulse.
Description
[0001] This application claims priority from U.S. application Ser.
No. ______ filed Dec. 17, 2004, which claims priority from U.S.
Provisional No. 60/531,238 filed Dec. 19, 2003, both of which are
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to systems and methods for
detecting, diagnosing and treating cardiovascular disease in a
medical patient using cardiac rhythm management devices and methods
that use novel digital electrode technology.
[0004] 2. Description of the Related Art
[0005] The optimum management of patients with chronic diseases
requires that therapy be adjusted in response to changes in the
patient's condition. Ideally, these changes are measured by daily
patient self-monitoring prior to the development of symptoms.
Self-monitoring and self-administration of therapy forms a closed
therapeutic loop, creating a dynamic management system for
maintaining homeostasis. Such a system can, in the short term,
benefit day-to-day symptoms and quality-of-life, and in the long
term, prevent progressive deterioration and complications.
[0006] In some cases, timely administration of a single dose of a
therapy can prevent serious acute changes in the patient's
condition. One example of such a short-term disease management
strategy is commonly used in patients with asthma. The patient
acutely self-administers an inhaled bronchodilator when daily
readings from a hand-held spirometer or flowmeter exceed a normal
range. This has been effective for preventing or aborting acute
asthmatic attacks that could lead to hospitalization or death.
[0007] In another chronic disease, diabetes mellitus, current
self-management strategies impact both the short and long term
sequelae of the illness. Diabetic patients self-monitor blood
glucose levels from one to three times daily and correspondingly
adjust their self-administered injectable insulin or oral
hypoglycemic medications according to their physician's
prescription (known as a "sliding scale"). More "brittle" patients,
usually those with juvenile-onset diabetes, may require more
frequent monitoring (e.g., 4 to 6 times daily), and the readings
may be used to adjust an external insulin pump to more precisely
control glucose homeostasis. These frequent "parameter-driven"
changes in diabetes management prevent hospitalization due to
symptoms caused by under-treatment (e.g., hyperglycemia with
increased hunger, thirst, urination, blurred vision), and
over-treatment (e.g., hypoglycemia with sweating, palpitations, and
weakness). Moreover, these aggressive management strategies have
been shown to prevent or delay the onset of long-term
complications, including blindness, kidney failure, and
cardiovascular disease.
[0008] There are approximately 60 million people in the U.S. with
risk factors for developing chronic cardiovascular diseases,
including high blood pressure, diabetes, coronary artery disease,
valvular heart disease, congenital heart disease, cardiomyopathy,
and other disorders. Another 10 million patients have already
suffered quantifiable structural heart damage but are presently
asymptomatic. Still yet, there are 5 million patients with symptoms
relating to underlying heart damage defining a clinical condition
known as congestive heart failure (CHF). Although survival rates
have improved, the mortality associated with CHF remains worse than
many common cancers. The number of CHF patients is expected to grow
to 10 million within the coming decade as the population ages and
more people with damaged hearts are surviving.
[0009] CHF is a condition in which a patient's heart works less
efficiently than it should, and a condition in which the heart
fails to supply the body sufficiently with the oxygen-rich blood it
requires, either during exercise or at rest. To compensate for this
condition and to maintain blood flow (cardiac output), the body
retains sodium and water such that there is a build-up of fluid
hydrostatic pressure in the pulmonary blood vessels that drain the
lungs. As this hydrostatic pressure overwhelms oncotic pressure and
lymph flow, fluid transudates from the pulmonary veins into the
pulmonary interstitial spaces, and eventually into the alveolar air
spaces. This complication of CHF is called pulmonary edema, which
can cause shortness of breath, hypoxemia, acidosis, respiratory
arrest, and death. Although CHF is a chronic condition, the disease
often requires acute hospital care. Patients are commonly admitted
for acute pulmonary congestion accompanied by serious or severe
shortness of breath. Acute care for congestive heart failure
accounts for the use of more hospital days than any other cardiac
diagnosis, and consumes in excess of 20 billion dollars in the
United States annually.
[0010] Cardiac rhythm management devices such as pacemakers, are an
important tool in the treatment of cardiovascular diseases.
Typically, an implantable pacemaker uses a minimum of two
electrodes to stimulate tissue. At least one of these electrodes is
in contact with the heart tissue to be stimulated, and is called a
pacing electrode. The required second electrode need not be in
contact with tissue being stimulated, in which case it is called an
"indifferent" electrode. The indifferent electrode does not even
have to be in the heart. Cardiac pacemakers in commercial use today
all have the same basic configuration in which stimulating
electrical pulses are produced by a pulse generator located outside
the heart, typically in a subcutaneous pocket in the upper chest
near one shoulder. The stimulating electrical pulses are applied to
the electrodes via one or more electrical conductors within an
insulated flexible cable, or "lead", which is connected at its
proximal end to the pulse generator. The distal end of the lead is
placed within the heart at a desired pacing location, for example
in the apex of the right ventricle. Some pacemaker leads, called
"unipolar" leads, have only a pacing electrode, typically at the
distal end of the lead. In this case, the required indifferent
electrode may be provided by the metallic housing of the generator,
or conceivably could be located on another lead. Commonly, unipolar
pacemaker leads have a single conductor connecting the generator to
a single pacing electrode located at its distal end. Bipolar
pacemaker leads have two conductors, one connected to a pacing
electrode located at or near the distal end of the lead, the other
connected to an "indifferent" electrode, usually configured as a
ring electrode, located on the lead some distance proximal to its
distal end.
SUMMARY OF THE INVENTION
[0011] Several embodiments of the present invention relates to
systems and methods for detecting, diagnosing and treating
cardiovascular disease in a medical patient using cardiac rhythm
management devices and methods that use novel digital electrode
technology.
[0012] As discussed above, some cardiac rhythm management devices
apply electrical stimuli to the heart. In addition to applying
electrical stimuli to the heart, cardiac pacemakers also commonly
measure, or "sense," the natural electrical activity within the
heart in order to adjust, withhold, or apply stimulation in
response to specific electrophysiological conditions. Sensing
electrodes are commonly incorporated on pacing leads. In most
cases, the same electrode used for pacing is also used for sensing.
Although sharing of electrodes for pacing and sensing is common, it
does have limitations. The sensed electrical signals are much
weaker than the pacing pulses, and must be highly amplified before
being used in various ways to control the operation of the
pacemaker. An ideal sensing electrode should have a large surface
area for this very reason, while an ideal pacing electrode should
have a small surface area to minimize power requirements. Moreover,
following each pacing pulse there is a time interval during which
sensing cannot take place because the relatively high pacing pulse
voltage persists for some time due to capacitance in the lead.
Thus, potentially important electrophysiological data may be lost
during this interval with presently available pacemaker technology.
One example of such data is the evoked response to the pacing
stimulus. It would be beneficial to provide a lead with separate
sensing and pacing electrodes. However, in some cases, such a lead
would conventionally require separate sensing and pacing conductors
as well, which would disadvantageously require the lead diameter to
be increased. Thus, conventional combination sensing/pacing
electrodes represent a compromise between optimal pacing
performance and optimal sensing performance, and conventional
pacemaker leads represent a compromise between optimal electrode
performance and lead size, complexity, and reliability, as
discussed further below.
[0013] In some pacemakers, the lead further incorporates one or
more physiological sensors. The lead must then also provide the
electrical connections required to power the sensor(s) and to
return the physiological sensor signal back to the pacemaker
generator. One disadvantage with such multiple function pacemaker
leads is the that increased number of electrical conductors
required within the lead forces the lead to be larger in diameter
and less flexible, or that the conductors become smaller. Smaller
conductors in pacemaker leads may break more often over time,
resulting in lower lead reliability. Smaller conductors have higher
electrical resistance, resulting in an undesirable voltage drop
between the generator and the pacing electrode(s). An increased
number of conductors also increases the complexity of the connector
that plugs into the pacemaker generator housing.
[0014] Conventional cardiac pacemakers in clinical use, although
employing digital electronics in the pacemaker generator, use
analog voltages for pacing, sensing and physiological measurements.
As such, the sensing signals in particular are subject to noise due
to muscular activity, radiofrequency (RF) interference, and
potential cross-talk between physiological and electrical sensing
signals. Pacemaker lead conductors carrying analog signals act as
antennas for RF noise and for induced voltages due to RF energy
used in magnetic resonance imaging (MRI) scanners. RF noise on the
sense conductor may cause erroneous pacing, even with sophisticated
digital filtering algorithms commonly used in pacemaker sensing
systems. Voltages induced by RF and changing magnetic fields are a
primary reason why MRI scanning is contra-indicated for patients
with implantable cardiac pacemakers.
[0015] In general, incorporation of a sensor within a unipolar
pacing lead typically requires plural conductors that run the
length of the lead. This arrangement provides the proper electrical
connection between the implanted pacemaker and the sensor, and
between the pacemaker and the tip electrode. For a bipolar lead, an
additional conductor is typically required. One disadvantage of
these arrangements is that the more electrical conductors that are
required in a lead, the greater potential for lead unreliability.
See U.S. Pat. Nos. 5,843,135, 4,791,935, 4,497,755, 4,485,813,
4,432,372, all herein incorporated by reference. Lead reliability
is an important consideration, and several embodiments of the
present invention minimize the number of conductors required to run
the length of the pacing lead. Accordingly, several embodiments of
the present invention maximize lead reliability. Several
embodiments of the present invention also provide a lead which
incorporates a pressure sensor or similar transducer positioned
toward the distal end for sensing a heart parameter, the lead
having a safe arrangement enabling the use of only one or two
conductors for providing a connection to both the sensor and a
pacing/sensing electrode positioned at or about the distal tip of
the lead.
[0016] In one embodiment, a cardiac rhythm management (CRM)
apparatus is provided. In one embodiment, the CRM comprises: a
proximal housing, wherein the proximal housing comprises a first
energy storage device; a distal module implantable within a
patient's heart, wherein the distal module comprises a second
energy storage device, at least one electrode and a control module,
wherein the control module controls the delivery of at least one
electrical stimulus from said second energy storage device to a
location in communication with said patient's heart; and a lead,
wherein the lead connects the proximal housing to the distal module
and is configured to communicate one or more digital signals
between the proximal housing and the distal module.
[0017] In one embodiment, the control module controls the transfer
of energy from the first energy storage device to the second energy
storage device. In another embodiment, the proximal housing
controls the transfer of energy from the first energy storage
device to the second energy storage device.
[0018] In a further embodiment, an implantable therapeutic
apparatus is provided. In one embodiment, the implantable
therapeutic apparatus comprises: a proximal housing, wherein the
proximal housing comprises an energy storage device; a distal
module, wherein the distal module comprises an electrode and a
control module, wherein the control module controls the delivery of
at least one electrical stimulus to the patient via said electrode;
and a lead, wherein the lead connects the proximal housing to the
distal module and is configured to communicate one or more digital
signals between the proximal housing and the distal module. The
electrical stimulus, in one embodiment, comprises one or more
electrical pulses.
[0019] In one embodiment, the therapeutic apparatus comprises a
cardiac rhythm management (CRM) device. In one embodiment, the CRM
device comprises a cardiac pacemaker and/or a cardiac
defibrillator.
[0020] In one embodiment, the implantable therapeutic apparatus
comprises one or more of the following: a neurological stimulator,
a muscle stimulator device, a drug infusion pump, a ventricular
assist device, a brain stimulator.
[0021] In one embodiment, the implantable therapeutic apparatus
comprises a proximal housing that is implantable near the patient's
shoulder.
[0022] In a further embodiment, the implantable therapeutic
apparatus comprises a lead, wherein the lead comprises one or more
conductors. In one embodiment, two conductors are used. In another
embodiment, three conductors are used.
[0023] In one embodiment, the implantable therapeutic apparatus
comprises a first energy storage device that comprises a battery or
capacitor. In another embodiment, the distal module comprises a
battery or capacitor.
[0024] In one embodiment, the implantable therapeutic apparatus
comprises a pacing electrode. In one embodiment, the implantable
therapeutic apparatus comprises at least one sensing electrode and
at least one pacing electrode, wherein said sensing electrode has a
larger surface area than said pacing electrode.
[0025] In a further embodiment, the implantable therapeutic
apparatus comprises a distal module that comprises at least one
physiological sensor. In one embodiment, the physiological sensor
includes a pressure sensor and/or a thermometer. In another
embodiment, the electrical stimulus comprises one or more
electrical pulses. In another embodiment, the implantable
therapeutic apparatus also includes a sensing amplifier. In yet
another embodiment, the one or more digital signals comprises a
sense-detect signal.
[0026] In yet another embodiment, a cardiac rhythm management
apparatus for delivering one or more electrical pulses to a
patient's heart is provided. In one embodiment, this apparatus
comprises: a proximal housing, wherein said proximal housing is
configured to be implanted within a medical patient, and wherein
said proximal housing is configured to store electrical energy; a
distal module configured to be implanted within a heart, wherein
the distal module comprises a first energy storage device and a
control module; an electrode, operable to deliver one or more
electrical pulses from the first energy storage device to the
heart; and a lead, wherein said lead is configured to communicate
one or more digital signals between said proximal housing and said
distal module, and wherein said control module controls
communication of said digital signals on the lead.
[0027] In one embodiment, the distal module further comprises a
second energy storage device. In another embodiment, said one or
more digital signals are used to charge the second energy storage
device. In another embodiment, said second energy storage device
provides power to said control module. In another embodiment, said
second energy storage device stores provides energy to said first
energy storage device by using a charge pump. In another
embodiment, said distal module further comprises a sensing
amplifier. In another embodiment, said distal module further
comprises a sensor configured to provide a sensor signal, and said
distal module controls delivery of a therapy based at least in part
on said sensor signal.
[0028] In one embodiment, said distal module further comprises a
processor, said processor is configured to generate a processed
signal based at least in part on the sensor signal, and the distal
module is configured to communicate the processed signal to said
proximal housing using said lead. In another embodiment, said
distal module further comprises at least one sensing electrode. In
another embodiment, said lead further comprises a conductor, and
said at least one sensing electrode is indirectly connected to said
conductor. In yet another embodiment, the lead further comprises a
conductor, and the electrode is indirectly connected to the
conductor.
[0029] In another embodiment, an apparatus for treating
cardiovascular disease in a medical patient is provided. In one
embodiment, this apparatus comprises: a housing, a distal module
comprising a sensor, operable to generate a sensor signal
indicative of a fluid pressure within a left atrium of a heart; a
lead, wherein the lead is configured to communicate one or more
digital signals between the housing and the distal module; a signal
processor, operable to generate a processor output indicative of a
treatment, wherein said processor output is based at least in part
on the sensor signal; and a signaling device, operable to generate
a treatment signal indicative of a therapeutic treatment, wherein
said treatment signal is based at least in part on said processor
output.
[0030] In one embodiment, the distal module further comprises at
least one electrode. In another embodiment, the at least one
electrode is operable to sense a physiological parameter. In
another embodiment, the physiological parameter comprises
electrical depolarization. In yet another embodiment, the at least
one electrode is operable to deliver an electrical stimulus to a
location in the heart.
[0031] In one embodiment, a method of managing a cardiac rhythm in
a medical patient is provided. In one embodiment, this method
comprises: implanting a proximal housing in a location external to
the patient's heart wherein said proximal housing stores energy;
implanting a distal module in the patient's heart; implanting a
lead in the patient to couple said proximal housing and said distal
module; transferring at least a portion of said stored energy from
said proximal housing to said distal module through one or more
digital signals; storing said transferred energy in the distal
module; and using at least a portion of the transferred energy in
the distal module to deliver one or more electrical pulses to the
heart, thereby managing a cardiac rhythm in the patient.
[0032] In one embodiment, the method comprises storing said at
least a portion of said energy in said distal module. In another
embodiment, the method comprises sensing the electrical activity of
the medical patient's heart with a sensing electrode. In one
embodiment, the method comprises delivering said one or more
electrical pulses to the heart using a pacing electrode. In a
further embodiment, the method comprises recharging the energy
stores in the proximal housing. In one embodiment, the method
comprises further comprising the step of measuring a pressure
signal indicative of a pressure within the left atrium.
[0033] In one embodiment of the present invention, a method of
managing a cardiac rhythm in a medical patient is provided. In one
embodiment, this method comprises: implanting a proximal housing, a
distal module, and a lead coupling said proximal housing and said
distal module in a patient; transferring energy from said proximal
housing to said distal module through one or more digital signals;
and delivering one or more electrical pulses to the heart from said
distal module, wherein said one or more electrical pulses comprise
at least a portion of the energy received from the proximal
housing, thereby managing a cardiac rhythm in the patient.
[0034] In yet another embodiment, a physiologic monitoring
apparatus is provided. In one embodiment, the physiologic
monitoring apparatus comprises: an implantable first component
operable to connect to an implantable therapeutic device (ITD),
wherein said implantable first component comprises a transducer and
a communicator, wherein said transducer is operable to convert a
physiologic signal to an electrical signal, and wherein said
communicator is operable to communicate with an external second
apparatus component receiver; and a removable telemetry antenna
operable to be removed and replaced with said ITD. In one
embodiment, the ITD comprises a cardiac rhythm management
device.
[0035] In another embodiment, a physiological monitoring device is
provided. In one embodiment, the physiological monitoring device
comprises: a proximal housing adapted to be implanted within a
patient at a location external to an organ to be monitored; a
distal module adapted to be implanted within the patient at a
location at least partially internal to the organ to be monitored;
a lead, said lead having at least a first end, a second end, and a
connector attached to said first end, wherein said lead is
connected to said distal module at said second end, and wherein
said lead is configured to conduct power and data signals between
the distal module and the proximal housing, and wherein the
connector is adapted to interchangeably connect to an antenna coil
or a cardiac rhythm management device provided within said proximal
housing.
[0036] In one embodiment, the cardiac rhythm management device is
configured to provide said power and data signals. In another
embodiment, the antenna coil is configured to provide said power
and data signals. In another embodiment, the distal module is
configured to automatically operate under a first mode of operation
when said connector is connected to said antenna coil, and said
distal module is configured to automatically operate under a second
mode of operation when said connector is connected to said cardiac
rhythm management device.
[0037] In another embodiment, a cardiac rhythm management device is
provided. In one embodiment, the cardiac rhythm management device
comprises: a proximal housing, wherein said proximal housing is
configured to be implanted within a patient, wherein said proximal
housing is configured to store electrical energy, and wherein said
proximal housing is adapted to be implanted at a location external
to a heart; a distal module adapted to be implanted within the
heart, and to provide electrical energy received from said proximal
housing to said heart, wherein said distal module is configured to
provide defibrillation protection to said heart; and a lead,
wherein said lead electrically couples said proximal housing and
said distal module, and wherein said lead provides said electrical
energy from said proximal housing to said distal module.
[0038] In one embodiment, a flexible lead for implantation within a
human body, is provided. In one embodiment, the flexible lead
comprises: a lead length, wherein said lead length extends from a
first end to a second end, wherein said first end is coupled to a
proximal housing implanted at a first location within a human body,
and said second end is coupled to a distal housing implanted at a
second location within a human body; and at least two conductors,
wherein said at least two conductors extend from the first end to
the second end, and wherein said at least two conductors are in
electrical communication with at least three electrodes, and
wherein said at least three electrodes are greater in quantity than
said at least two conductors.
[0039] In one embodiment, the lead further comprises a shielding,
wherein said shielding extends from said first end to said second
end, covering at least one of said at least two conductors over
said lead length. In another embodiment, the first location is
proximate a shoulder, and said second location is in inside of a
heart. In another embodiment, the at least three electrodes
comprise an indifferent electrode, a pacing electrode, and a
sensing electrode.
[0040] In one embodiment, an implantable sensor apparatus is
provided, wherein said sensor apparatus is capable of being powered
externally by RF at one frequency or powered by an ITD at a
different frequency. In one embodiment, the device is externally
powered by an RF sine wave or powered by monophasic pulses from an
ITD.
[0041] In an alternative embodiment, an implantable device that
provides one or more electrical stimuli is provided. In one
embodiment, a remote distal electrode for delivering stimuli
co-located with an output switch, a capacitor and defibrillator
protection is provided.
[0042] In one embodiment, an implantable device that provides one
or more electrical stimuli, comprising a remote distal electrode
co-located with sensing amplifier and detector, is provided.
[0043] In one embodiment, a system wherein the communication
between a CRM and a digital electrode comprises digital
communication is provided. In one embodiment, the digital
communication comprises a digital sense detect signal sent from the
digital electrode to the proximal housing (module). In another
embodiment, the digital communication comprises a digital pace
trigger command sent from the proximal housing (module) to the
digital electrode. In a further embodiment, the digital
communication comprises a digitized sense signal sent from the
digital electrode to the proximal housing (module).
[0044] In one embodiment, a system having separate pace and sense
electrodes without separate conductors in the lead for sensing and
pacing is provided.
[0045] In a further embodiment, a system comprising a digital
electrode that automatically detects whether it is powered
externally or from an ITD, and automatically switches to the
external or ITD configuration, is provided. In one embodiment, the
power pulses from the ITD are used by the digital electrode to
synchronize the digital electrode (and/or sensor, if present) clock
and/or communication.
[0046] In one embodiment, an apparatus having an electrode with its
conducting surface area reduced by coating a portion of the surface
with an insulating material is provided. In one embodiment,
reflective impedance is used to communicate information to an
external device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] The structure and operation of the invention will be better
understood with the following detailed description of embodiments
of the invention, along with the accompanying illustrations, in
which:
[0048] FIG. 1 depics apparatus suitable for practicing at least one
embodiment of the invention.
[0049] FIG. 2 depicts an implantable apparatus suitable for
practicing another embodiment of the invention.
[0050] FIG. 3 is a schematic of one embodiment of the electronics
located within the implantable housing of the implantable apparatus
illustrated in FIG. 2.
[0051] FIG. 4 is a system for treating cardiovascular disease.
[0052] FIG. 5 is a block diagram of an external patient
advisor/telemetry module for use in one embodiment of the present
invention.
[0053] FIGS. 6A-6C provide a list of examples by which signals may
be interpreted to facilitate diagnosis, prevention and treatment of
cardiovascular disease.
[0054] FIG. 7 shows a table of cardiac and non-cardiac diagnostic
states derivable from measurements at the intra-atrial septum.
[0055] FIG. 8 shows the flexible lead of FIG. 13. The sheath has
been withdrawn to deploy the proximal distal anchors on the right
and left atrial sides of the atrial septum, and a pressure sensing
transducer is in fluid contact with the patient's left atrium.
[0056] FIG. 9 depicts a method for anchoring a flexible electrical
lead within the patient's heart.
[0057] FIG. 10 is a schematic sectional view of a patient's heart
illustrating an atrial septal puncture for implanting one
embodiment of the current invention.
[0058] FIG. 11 shows another method for anchoring a lead within the
heart, which includes a helical screw for advancement into the
patient's atrial septum.
[0059] FIG. 12 shows the apparatus depicted in FIG. 11, with a
pressure sensing transducer in place in the patient's left
atrium.
[0060] FIG. 13 is a schematic sectional view of a patient's heart
showing a part of an embodiment of the invention positioned
therein.
[0061] FIG. 14 shows the flexible lead of FIG. 15 and FIG. 16, with
a pressure sensing transducer in place inside the patient's left
atrium.
[0062] FIG. 15 depicts a flexible lead including deployable anchors
carried inside a removable sheath and placed through the atrial
septum.
[0063] FIG. 16 shows the flexible lead of FIG. 15 with the sheath
withdrawn to deploy the anchors on opposite sides of the atrial
septum.
[0064] FIG. 17 shows the correlation between the pulmonary
capillary wedge pressure (PCW) referenced to atmospheric pressure
(abscissa) and the differential pressure between the right atrium
and PCW (PCW-RA).
[0065] FIG. 18 illustrates typical normal pressure tracings.
[0066] FIG. 19 provides a table of normal hemodynamic values.
[0067] FIG. 20 shows a combination of one embodiment of the present
invention with an implantable cardiac pacemaker, in which the
sensor is a left atrial pressure sensor implanted in the
intra-atrial septum, and the sensor lead also serves as the atrial
lead of the pacemaker. A separate ventricular pacing lead is also
provided.
[0068] FIG. 21 shows the relationships between the
electrocardiogram and the left atrial pressure tracing.
[0069] FIG. 22 is a sensor package or module in accordance with one
embodiment of the present invention.
[0070] FIG. 23 is another sensor package or module in accordance
with another embodiment of the present invention.
[0071] FIG. 24 is a pulse timing diagram showing one embodiment for
sensing one or more physiological parameters and performing cardiac
pacing using a two-conductor digital sensor/pacemaker lead.
[0072] FIG. 25 is a schematic showing one embodiment of circuitry
that provides both pacing and physiological monitoring over a
two-conductor pacemaker lead.
[0073] FIGS. 26A-D are schematics showing circuitry within a sensor
module in accordance with another embodiment of the present
invention.
[0074] FIG. 27 is a schematic diagram depicting digital circuitry
suitable for use in one embodiment of the invention.
[0075] FIG. 28 is an implantable housing in accordance with one
"Stand-Alone" embodiment of the invention.
[0076] FIG. 29 is an implantable housing in accordance with one
"CRM Combination" embodiment of the invention.
[0077] FIG. 30 is a pacemaker using an analog lead.
[0078] FIG. 31 is a pacemaker with a digital-electrode comprising
sense amplifier, pacing/sensing electrode, and defibrillation
protection in accordance with one embodiment of the present
invention.
[0079] FIG. 32 is a pacemaker with a digital electrode as in FIG.
31, wherein the electrode module additionally comprises the charge
pump and pacing pulse capacitor in accordance with one embodiment
of the present invention.
[0080] FIG. 33 is a pacemaker in accordance with one embodiment of
the present invention, in which the defibrillation protection is
provided within the digital electrode housing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0081] In one embodiment of the present invention an apparatus for
treating cardiovascular disease in a medical patient is provided.
The apparatus includes a sensor, an implantable housing, at least
one implantable lead, a signal processor, and a signaling device.
In one embodiment, the apparatus is a physiologically optimized
dosimeter (POD), such as the HeartPOD.TM. device. Cardiovascular
disease, as used herein, shall be given its ordinary meaning, and
shall also include conditions that create or are the result of
heart disease such as high blood pressure, coronary artery disease,
valvular heart disease, congenital heart disease, arrthymia,
myocarditis, pericarditis, cardiomyopathy including dilated,
hypertrophic, obliterative, and restrictive/infiltrative types,
cardiac transplant rejection, and CHF. Additionally, cardiovascular
disease shall also include disease states that affect the
circulatory system including but not limited to peripheral arterial
atherosclerosis, Berger's disease, cerebral vascular
atherosclerosis, aortic or other great vessel aneurysm, aortic or
other great vessel dissection, vasculitis, venous thrombophlebitis,
and their sequelae.
[0082] In one embodiment of the present invention, a method of
treating cardiovascular disease in a medical patient is provided.
The method includes the steps of generating a sensor signal
indicative of a fluid pressure within a left atrium of a heart,
delivering an electrical stimulus to the heart, generating a
processor output indicative of a treatment to a signaling device,
and providing at least two treatment signals to the medical
patient. The electrical stimulus is based at least in part on the
sensor signal. The processor output is based at least in part on
the sensor signal. Each treatment signal is distinguishable from
one another by the patient, and is indicative of a therapeutic
treatment. At least one signal is based at least in part on the
processor output. In one embodiment, the step of delivering an
electrical stimulus includes using a pacemaker or a
defibrillator.
[0083] In several embodiments of the current invention, the
apparatus and/or method for treating cardiovascular disease
includes a cardiac rhythm management (CRM) apparatus. In one
embodiment, the cardiac rhythm management apparatus includes a
pacemaker. The term pacemaker includes antibradycardia and
antitachycardia types. The term pacemaker also includes single
chamber, dual chamber, and cardiac resynchronization therapy (CRT)
types, the latter also called a biventricular pacemaker. In another
embodiment, the cardiac rhythm management apparatus includes a
defibrillator. The term defibrillator, as used herein, shall be
given its ordinary meaning and shall include atrial and ventricular
defibrillators with or without combination with any of the
pacemaker types listed above, or other devices. In another
embodiment, the cardiac rhythm management apparatus includes
related devices that do not electrically depolarize all or some
portion of the heart muscle to manage a cardiac rhythm or the
synchrony of depolarization, but are used to perform some other
function. For example, delivering electrical stimuli to cardiac
muscle during the refractory period after depolarization may
increase the strength of cardiac contraction, a phenomenon known as
an `ionotropic` effect. This may be helpful in generating more
cardiac output in CHF patients with low cardiac output. In another
example, many CHF patients have a condition known as sleep apnea
where they momentarily stop breathing during sleep. This condition
is potentially dangerous because lack of oxygen can induce fatal
cardiac arrhythmias or worsening heart failure due to ischemia. In
one embodiment of the current invention, the CRM is a rhythm
management system that paces the diaphragm muscle or the phrenic
nerves to benefit such patients.
[0084] In one embodiment of the invention, the apparatus and/or
method for treating cardiovascular disease includes one or more
sensors. In one embodiment, the sensor is designed to generate a
sensor signal that is indicative of a fluid pressure within the
left atrium of the patient's heart. As described herein, fluid
pressure within the left atrium of a patient's heart is an
excellent indicator for quantifying the severity of congestive
heart failure, and for assessing the efficacy of drug therapy for
treating congestive heart failure. A measurement of the fluid
pressure within the left atrium of a patient's heart can be used
for other clinical purposes as well, as described in greater detail
below.
[0085] In one embodiment, the pressure sensor and its associated
electronics are integrated within a sensor module attached to the
distal end of a lead implanted in the heart. The proximal end of
the lead is connected to a housing located outside the heart,
typically under the skin in the area of the patient's shoulder. One
advantage of this embodiment is that placing some or all of the
sensor electronics in the distal module allows the number of
conductors required in the lead between the sensor and the proximal
housing to be minimized, as described in more detail below. In one
embodiment, the distal sensor module comprises a miniature
hermetically sealed housing. In one embodiment, the housing is
cylindrical, with a diameter similar to the diameter of the lead.
In one embodiment, the pressure sensor lead may also be used for
pacing, with all or preferentially a portion of the outside of the
sensor housing of the present invention used as one of the
electrodes of the pacemaker. To even greater advantage, some of the
pacing electronics (for example, the output pulse and input (sense)
amplifier, filter, threshold detector & refractory circuit) may
also be integrated within the sensor housing implanted within the
heart. This embodiment has several potential advantages. One such
advantage is that the lead conductors are isolated from the pacing
electrode, providing immunity from induced currents when, for
example, the patient is placed in the rapidly changing strong
magnetic fields of a magnetic resonance imaging machine. Another
such advantage is that placing the pacing sense electronics in the
distal module eliminates noise originating in the lead conductors
of a conventional pacemaker, since the low voltage sense signal
need not be conducted through the lead. Yet another advantage is
that separate sensing and pacing electrodes can be provided at or
near the distal module without requiring separate sense and pacing
conductors within the lead.
[0086] In one embodiment of the invention, the apparatus and/or
method for treating cardiovascular disease includes one or more
housing units comprising electronic modules. In one embodiment, the
implantable apparatus includes a proximal housing comprising the
generator of a cardiac rhythm management (CRM) apparatus, such as,
for example, a pacemaker, or a defibrillator. A pacemaker generator
conventionally includes various subassemblies for control,
operation, processing, and communication. However, in some
embodiments of the present invention, any one or more of these
control, operation, processing, and communication functions may be
performed by an assembly, or module, that is not included with the
proximal generator housing.
[0087] In one embodiment, when implanted in the patient, the
implantable housing contains a coil antenna and electronics to
provide reflected impedance communications with an external device.
However, as the patient's medical condition changes and indications
for CRM develop, the implantable housing may be subsequently
accessed, and the coil antenna may be removed and replaced with a
CRM system. The implantable housing and electronics may include an
interface that permits such interchangeability of components within
the implantable housing without requiring explantation of the
remaining components of the implanted congestive heart failure
treatment apparatus. This feature of an embodiment of the invention
is herein included within the term "upgradeability," or
"upgradeable". These and additional embodiments of the implantable
housing, as well as the apparatus, are provided in greater detail
below.
[0088] In one embodiment, the lead couples the sensor to the
implantable housing, and provides an electrical conduit for the
transmission and/or communication of the sensor signal from the
sensor to the housing. In other embodiments, however, as described
in greater detail below, the lead provides an electrical stimulus,
such as, for example, an electrical pulse, to a location in the
heart, as determined by the CRM apparatus. In some embodiments, the
electrical stimulus and the sensor signal are transmitted through
the same lead. In a preferred embodiment, the electrical stimulus
and the sensor signal are transmitted through the same conductors.
This embodiment is particularly advantageous because the use of one
conductor pair allows for a lead that thinner, more flexible and/or
sturdier. In another embodiment, separate conductors are provided
within the lead for sensor signal communication and the CRM
therapy. In yet another embodiment, energy or power is transmitted
from the implantable housing through the lead to a distal module
that may contain portions of a CRM apparatus, sensors, and portions
of the signal processing necessary to control the cardiovascular
disease treatment. These and other embodiments are described in
greater detail below.
[0089] In one embodiment of the invention, the apparatus and/or
method for treating cardiovascular disease includes one or more
signal processors. In one embodiment, the signal processor
determines a processor output that is indicative of an appropriate
therapeutic treatment in response to the pressure-indicative signal
provided by the sensor. The processor output is provided to a
signaling device, which provides an appropriate treatment signal to
the medical patient. The term "processor output" as used herein
shall be given its ordinary meaning and shall also mean output from
a signal processor and/or input to a signaling device, and shall
include, but not be limited to, signals, including analog, digital,
and/or optical signals, data, code, and/or text. The treatment
signal may be provided by, for example, vibrating a signaling
device located within the implantable housing. Alternatively, the
treatment signal may be generated within the implantable housing
and transmitted to a signaling device located external to the
patient, such as a personal digital assistant (PDA). In another
embodiment, the sensor signal is transmitted to an external device,
such as, for example, a PDA, which includes a processor and
signaling device to generate a processor output and provide a
treatment signal to the patient. These and other embodiments are
described in greater detail below.
[0090] In one embodiment of the invention, the apparatus and/or
method for treating cardiovascular disease includes one or more
signaling devices. In one embodiment, the signaling device includes
a buzzer, an alarm, a display, a computer, a telephone, or a PDA,
such as a PALM PILOT.TM. (Palm Computing, Inc.), a HANDSPRING
VISOR.RTM. (Handspring, Inc.), or a combination cellular
telephone/PDA. The signaling device may be operable to generate at
least two treatment signals distinguishable from one another by the
patient. In one embodiment, each signal is indicative of a specific
therapeutic treatment. The treatment signal may be an electrical
pulse, a vibration, a noise, audio, or visual data, including, but
not limited to, instructions on a display screen or light emitting
diodes. In one embodiment, the at least two treatment signals may
include two numerical values or designations, a numerical value and
an electrical pulse or vibration, multiple vibrations of varying
amplitudes, durations, or frequencies, or any combination of two or
more of any of the treatment signals described herein. In one
embodiment, the signaling device is a PDA that displays an
instruction, such as "take medication," "rest," or "call Doctor".
These and other embodiments are described in greater detail
below.
I. The System
[0091] A. Stand-Alone System
[0092] FIG. 1 shows an apparatus for treating cardiovascular
disease, such as congestive heart failure, which includes an
implantable module 5 in accordance with one embodiment of the
invention. The implantable module 5 includes a housing 7 and a
flexible, electrically conductive lead 10. The lead 10 is
connectable to the housing 7 through a connector 12 that may be
located on the exterior of the housing. In one embodiment, the
housing 7 is outwardly similar to the housing of an implantable
electronic defibrillator and/or pacemaker system. Defibrillator and
pacemaker systems are implanted routinely in medical patients for
the detection and control of tachy- and bradyarrhythmias. The
flexible lead 10 is also generally similar to leads used in
defibrillator and pacemaker systems, except that a compact sensor
package 15 is disposed at or near the distal end 17 of the lead 10,
the opposite end from the connector 12 on the housing 7. The sensor
package 15 contains sensors to measure one or more physical
parameters. An electrical signal or another form of signal
indicative of these physical parameters is then communicated or
transmitted along the lead 10 through the connector 12 and to the
housing 7. The housing 7 may include a signal processor (not shown)
to process the signal received from the sensor package 15 via the
lead 10. In addition, the housing 7 may include telemetry or
signaling devices (not shown), to either communicate with an
external device, or signal the patient, or both. The elements
inside the housing 7 may be configured in various ways, as
described below, to communicate to the patient a signal, such as a
treatment signal, indicative of an appropriate therapy or treatment
based at least in part on one or more of the measured physical
parameters.
[0093] One skilled in the art will appreciate that the lead can be
of any length appropriate to connect the sensor package located at
a first location with the housing located at a second location. In
another embodiment, the lead length is zero, such that the sensor
package are configured to occupy substantially the same location.
Thus, in one embodiment, a leadless implantable system using
telemetry between the heart and an external device is provided. In
one embodiment, reflected impedance, rather than transmitted
energy, is used to communicate with the implanted device, as
described by U.S. Pat. No. 6,409,674 to Brockway et al., herein
incorporated by reference.
[0094] FIG. 2 shows another embodiment in which the sensor package
or module 15 has distal 68 and proximal 70 anchoring mechanisms
configured to anchor the sensor package 15 within the atrial septum
of a patient's heart. FIG. 2 shows one embodiment of the implanted
internal module 5, in which the implanted internal module 5
includes a physiologic sensor package or module 15. The physiologic
sensor package 15 includes one or more sensors 155 and their
accompanying electronics (not shown). The implanted module 5 also
includes a flexible lead 10. The flexible lead 10 has a distal end
17 that comprises the sensor module 15, the metallic housing of
which also functions as an electrode for sensing the intracardiac
electrogram (IEGM), and an indifferent electrode 14. A header or
connector 12 connects the flexible lead 10 and housing 7 of the
implanted module 5. The housing 7 contains electronics (not shown)
and other components (not shown) for communicating with an external
module (not shown). One embodiment showing the contents of the
housing 7 is illustrated in FIG. 3.
[0095] As shown in FIG. 3, in one embodiment housing 7 includes a
power supply 153, a CRM system 159, and a signal processing and
patient signaling modules 157. The CRM system 159 is configured to
provide an electrical stimulus, such as a pacing signal, to the
patient's heart, and receive a sensor signal from implanted sensors
(not shown). In one embodiment, the CRM system 159 is configured to
include a defibrillator. The signal processing module 157 is
coupled to at least one sensor that provides a signal indicative of
the fluid pressure within the left atrium of the heart. The signal
processing module 157 may also be configured to control distally
implanted CRM components, or a sensor package or module, as
described in greater detail herein.
[0096] In one embodiment of the invention, the apparatus for
treating cardiovascular disease comprises at least one housing that
has a flat and oval shape. In another embodiment, the housing shape
is cylindrical, rectangular, elliptical, or spherical. One of skill
in the art will understand that a variety of other shapes suitable
for implantation can also be used. In one embodiment, the housing
is about 20 mm by about 30 mm, about 10 mm by about 20 mm, or about
5 mm by about 10 mm. In one embodiment, the housing is about 5 mm
thick. In one embodiment, the housing is implanted in the medical
patient near the shoulder. In another embodiment, the housing has
dimensions suitable for containing at least some components for
controlling, powering and/or communicating with a sensor, and
suitable for implantation inside of the body, as is well known to
those of skill in the art. In another embodiment, the housing
includes: an antenna, or a coil; a power source, including but not
limited to a battery or a capacitor; a signal processor; a
telemetry apparatus; a data memory; or a signaling device. In one
embodiment, the apparatus is powered by an external power source
through inductive, acoustical, or radio frequency coupling. In one
embodiment, power is provided using electromagnetic emissions
emitted from an electrical coil located outside the body. In one
embodiment, power and data telemetry are provided by the same
energy signal. In another embodiment, an electrical coil is
implanted inside the body at a location under the skin near the
patient's collarbone. In another embodiment, an electrical coil is
implanted inside the patient's body at other locations. For
example, in one embodiment, the coil is implanted under the skin in
the lower abdomen, near the groin. One of skill in the art will
understand that the device can be implanted in a variety of other
suitable locations.
[0097] As described above and in other embodiments herein, a system
for treating cardiovascular disease in a medical patient may
include at least one physiological sensor used to generate a signal
indicative of a physiological parameter on or in the patient's
body. The system includes signal processing apparatus operable to
generate a signal, such as a processor output, indicative of an
appropriate therapeutic treatment, which in one embodiment is based
at least in part upon the signal generated by the physiological
sensor. In one embodiment, the system also includes a patient
signaling device, which is used to communicate the signal
indicative of the appropriate therapeutic treatment, such as a
treatment signal, to the patient.
[0098] In one embodiment, the physiological sensor is a pressure
transducer that is positioned to measure pressures within the
patient's left atrium. Signals from the pressure sensor are
monitored continuously or at appropriate intervals. Information is
then communicated to the patient corresponding to appropriate
physician-prescribed drug therapies. In one embodiment, the
information is the treatment signal. In many cases, the patient may
administer the drug therapies to him or herself without further
diagnostic intervention from a physician.
[0099] FIG. 4 shows one embodiment of a system for treating
cardiovascular disease 9. The system 9 includes a first component
comprising an implantable module 5, such as that described with
reference to FIG. 2, and a second component comprising an external
patient advisory module 6, such as that described below with
reference to FIG. 5. During system 9 operation, radio frequency
signals are carried by a lead 10 between a pressure sensor package
15 located near the distal end 17 of the lead 10, and a housing 7
of an implantable module 5. The lead 10 includes a sensing/pacing
electrode which is part of the sensor module 15 and an indifferent
electrode 14. The circuitry inside the housing 7 includes an
antenna coil (not shown). In this embodiment, signals are
communicated between the implantable module 5 and an external
device, such as a patient advisory module 6, via the antenna coil
of the housing 7 and a second external coil (not shown) coupled to
the external device 6.
[0100] In one embodiment, the housing 7 contains a battery (not
shown) that powers the implantable device 5. In another embodiment,
the implanted device 5 receives power and programming instructions
from the external device 6 via radio frequency transmission between
the external and internal coils. The external device 6 receives
signals indicative of one or more physiological parameters from the
implanted device 5 via the coils as well. One advantage of such
externally powered implantable device 5 is that the patient will
not require subsequent surgery to replace a battery. In one
embodiment of the present invention, power is required only when
the patient or the patient's caregiver initiates a reading. In
other situations, where it is desired to obtain physiological
information continuously, or where it is desired that the implanted
device 5 also perform functions with higher or more continuous
power requirements, the housing 7 may also contain one or more
batteries. As described below, the housing 7 may also contain
circuitry to perform additional functions that may be
desirable.
[0101] FIG. 5 shows one embodiment of the second component of the
system, a patient advisory module 6. In one embodiment, the patient
advisory module 6 includes a palm-type computer with added hardware
and software. Referring to FIG. 5, a patient advisory module 6
includes a radio frequency telemetry module 164 with an associated
coil antenna 162, which is coupled to a processing unit 166. In one
embodiment, the processing unit 166 includes a palm-type computer,
or personal digital assistant (PDA), as is well known to those of
skill in the art. In one embodiment, the patient advisory module 6
powers the implanted apparatus (not shown) with the telemetry
hardware module 164 and coil antenna 162. In another embodiment,
the patient advisory module 6 receives physiological signals from
the implanted first component of the system by wireless telemetry
through the patient's skin.
[0102] The patient advisory module 6 may include an RF unit 168 and
a barometer 112 for measuring the reference atmospheric pressure.
In one embodiment, the RF unit 168 and barometer are located within
the telemetry module 164, although they can be integrated with the
processing unit 166 as well. The signal processing unit can be used
to analyze physiologic signals and to determine physiologic
parameters. The patient advisory module 166 may also include data
storage, and a sub-module that contains the physician's
instructions to the patient for therapy and how to alter therapy
based on changes in physiologic parameters. The parameter-based
physician's instructions are referred to as "the dynamic
prescription," or DynamicRx.TM. (Savacor, Inc.). The instructions
are communicated to the patient via the signaling module 166, or
another module. The patient advisory module 166 is located
externally and used by the patient or his direct caregiver. It may
be part of system integrated with a personal digital assistant, a
cell phone, or a personal computer, or as a "Stand-Alone" device
(e.g., in one embodiment, the HeartPOD.TM. diagnostic and
therapeutic drug management system) without combination with CRM
apparatus. In one embodiment, the external patient advisory module
comprises an external telemetry device, a signal processing
apparatus, and a patient signaling device. In one embodiment, the
patient advisory module is operable to obtain the sensor signal
from the implantable sensor by telemetry through the patient's
skin; obtain the atmospheric pressure from the barometer; and
adjust the sensor signal indicative of a fluid pressure based at
least in part upon the atmospheric pressure obtained by the
barometer so that the adjusted sensor signal indicates the fluid
pressure within the left atrium of the heart relative to the
atmospheric pressure. In one embodiment the patient advisory module
communicates with a remote site such as a doctor's office, clinic,
hospital, pharmacy, or database. Revised patient instructions
including the parameter-based dynamic prescription can be
communicated back to the patient advisory module. This can be
performed remotely via hard-wired telephone or fiberoptic cable
networks or wirelessly using a host of communication technologies
currently available. Data may be communicated in either direction
and the Internet may be in part the conduit for such
communication.
[0103] In one embodiment, the physiologic signals are analyzed and
used to determine adjustable prescriptive treatment instructions
that have been placed in the patient advisory module 6 by the
patient's personal physician. Communication of the prescriptive
treatment instructions to the patient may appear as written or
graphic instructions on a display of the patient advisory module 6.
These treatment instructions may include what medications to take,
dosage of each medication, and reminders to take the medications at
the appropriate times. In one embodiment, the patient advisory
module 6 displays other physician-specified instructions, such as
"Call M.D." or "Call 911" if monitored values become critical.
[0104] In an alternative embodiment, the treatment signal may be
the numerical representation of the mean left atrial pressure in mm
Hg, or the numerical representation of some other parameter
indicative of fluid pressure in the left atrium. Physician
specified treatments would be supplied to the patient in the form
of a decoding reference providing different treatment instructions
for specified ranges of left atrial pressure. Such a decoding
reference could be written or printed instructions on a card that
the patient keeps for reference. For example, a mean left atrial
pressure (LAP) of 15 mm Hg would could indicate the same treatment
as a mean LAP of 16 mm Hg, both values being in a range indicating
that the patient's heart failure is well compensated. An LAP of 25
mm Hg however would indicated decompensated CHF and would decode as
different therapeutic instructions aimed at recompensating the
state of CHF.
[0105] A third component of this system embodiment is designed for
physician use. The third component is used to program the dynamic
prescription and communicate it or load it into the patient
advisory module 166. The third module may also contain stored data
about the patient, including historical records of the physiologic
signals and derived parameters transmitted from the patient implant
and signaling modules. The third component may also communicate
with external databases. In one embodiment, the third component is
a physician input device, and includes a personal computer, a PDA,
a telephone, or any other such device as is well known to those of
skill in the art also comprising specific third component software
or firmware programs.
[0106] In one embodiment, the second component (e.g., the patient
advisory module 166) is in the form of one or more implants.
[0107] In one embodiment of the present invention, the first
implant module (such as, for example, implantable module 5 of FIG.
1 and FIG. 2) may also contain an implant therapy unit, or ITU. The
ITU generates an automatic therapy regime based upon the programmed
dynamic prescription. The therapy may include, but is not limited
to, a system for releasing bioactive substances from one or more
implanted reservoirs, a system for controlling electrical pacing of
the heart, and controllers for ventricular or other types of
cardiac assist devices. For example, in one embodiment the sensor
package is placed across the intra-atrial septum and serves as the
atrial lead of a multichamber pacemaker. The physiologic sensor
information is used to adjust pacing therapy such that pacing is
performed only when needed to prevent worsening heart failure. One
skilled in the art will appreciate that many systems or devices
that control the function of the cardiovascular system may be used
in accordance with several embodiments of the current
invention.
[0108] In one embodiment of the invention, the advisory module 6 is
programmed to signal the patient when it is time to perform the
next cardiac status measurement and to take the next dose of
medication. It will be recognized by those skilled in managing CHF
patients that these signals may help the many patients who have
difficulty taking their medication on schedule. Although treatment
prescriptions may be complex, one embodiment of the current
invention simplifies them from the patient's perspective by
providing clear instructions. To assure that information regarding
the best treatment is available to physicians, professional
cardiology organizations such as the American Heart Association and
the American College of Cardiology periodically publish updated
guidelines for CHF therapy. These recommendations can serve as
templates for the treating physician to modify to suit individual
patient requirements. In one embodiment, the device routinely
uploads data to the physician or clinic, so that the efficacy of
the prescription and the response to parameter driven changes in
dose can be monitored. This enables the physician to optimize the
patient's medication dosage and other important treatments without
the physician's moment-to-moment intervention.
[0109] In various embodiment of the invention, a device and method
for dynamically diagnosing and treating cardiovascular illness in a
medical patient are provided. In one embodiment, at least one
physiological sensor is used to generate a signal indicative of a
physiological parameter. In another embodiment, signal processing
apparatus operable to generate a signal indicative of an
appropriate therapeutic treatment based, at least in part, upon the
signal generated by the physiological sensor, is also provided. In
another embodiment a patient signaling device used to communicate
the signal indicative of the appropriate therapeutic treatment to
the patient is provided as well.
[0110] In one embodiment, a device and method for continuously or
routinely monitoring the condition of a patient suffering from
chronic cardiovascular disease are provided. As will be described
in detail below, a system incorporating various embodiments of the
invention monitors various physiologic parameters, such as the
patient's left atrial pressure. Depending upon the magnitude of or
changes in this pressure, for example, the system communicates a
signal to the patient indicative of a particular course of therapy
appropriate to manage or correct, as much as possible, the
patient's chronic condition. In some embodiments, physician
instructions and automated therapy are provided.
[0111] In one embodiment, the physiological sensor generates a
signal indicative of a physiological parameter on or in the
patient's body. In one embodiment, the signal processing apparatus
generates a signal indicative of an appropriate therapeutic
treatment based at least in part upon the signal generated by the
physiological sensor. The patient signaling device may generate
signals indicative of therapeutic treatments or courses of action
the patient can take to manage or correct, as much as possible, the
patient's condition.
[0112] In one embodiment, this method includes the steps of
implanting one or more physiological sensors substantially
permanently within the patient, operating the physiological sensor
to generate a signal indicative of a physiological parameter,
processing this physiological signal to generate a signal
indicative of an appropriate therapeutic treatment, and
communicating the appropriate therapeutic treatment to a user. In
one embodiment, the user includes, but is not limited to, the
patient, a caregiver, a medical practitioner or a data collection
center.
[0113] In another embodiment, the system is combined with or
incorporated into a CRM system, with or without physiologic rate
control, and with or without backup cardioversion/defibrillation
therapy capabilities.
[0114] In one embodiment, at least one indication of congestive
heart failure (CHF) is monitored. Elevated pressure within the left
atrium of the heart is the precursor of fluid accumulation in the
lungs, which results in signs and symptoms of acute CHF. Mean left
atrial pressure in healthy individuals is normally less than or
equal to twelve millimeters of mercury (mm Hg). Patients with CHF
that have been medically treated and clinically "well compensated"
may generally have mean left atrial pressures in the range from 12
to 20 mm Hg. Transudation of fluid into the pulmonary interstitial
spaces can be expected to occur when the left atrial pressure is
above about twenty-five mm Hg, or at somewhat more than about
thirty mm Hg in some patients with chronic CHF. Pulmonary edema has
been found to be very reliably predicted by reference to left
atrial pressures and less well correlated with conditions in any
other chamber of the heart. Thus, the methods and apparatus of
several embodiments of the invention may prove very useful in
treating and preventing pulmonary edema and other adverse
conditions associated with CHF. Pressure in the pulmonary veins,
pulmonary capillary wedge position, and left ventricular end
diastolic pressure (LVEDP) are generally indicative of left atrial
pressure and are commonly used as surrogates of LAP. There are,
however, specific conditions, that are well known to those skilled
in the art, including cardiologists and physiologists, where these
surrogates vary substantially from LAP and may be less predictive
of impending heart failure. One example of such a condition is
mitral valve stenosis where pulmonary edema develops despite a
normal LVEDP due to a significant pressure gradient across the
mitral valve. However, one of skill in the art will understand that
several embodiments of the current invention can be used in
conditions where the surrogates do not directly correlate with LAP.
[Agreed!]Other surrogate pressures that also, on specific occasion,
indicate LAP include, but are not limited to: the pulmonary artery
diastolic (PAD), mean pulmonary artery pressure or algorithms that
estimate PAD from the right ventricular waveform, the right
ventricular end diastolic, the right atrial pressure, and the
central venous pressure, or the response of arterial pressure
during forced expiration against a closed glottis or other
resistance (Valsalva maneuver). Also included are other pressures,
parameters or algorithms that are indicative of left atrial
pressure that may be known to those skilled in the art.
[0115] An embodiment of the invention includes a permanently
implanted device designed to define the presence of worsening CHF
hours to days before the onset of symptoms and to provide for early
preventative treatment according to the physician's individualized
prescription. As such, an embodiment of the invention includes an
integrated patient therapeutic system that determines therapeutic
dosages for an individual patient based at least in part on
internal physiologic signals. In another embodiment, the system
consists of a small implantable sensor device and an external
patient advisory module comprising a personal data assistant (PDA)
and a telemetry module. The sensor system may be implanted into the
patient's left atrial chamber by a transseptal catheterization
procedure. There are already several thousand physicians in the
U.S. and abroad with the experience and skills required for such
device implantation. The implantation procedure can be performed on
an outpatient basis in a hospital's cardiac catheterization
laboratory. The implant may alternatively be placed at the time of
open-heart or minimally invasive valve or bypass surgery where the
surgeon, under direct, laparoscopic, or thorascopic vision,
positions the device in the left atrium, left atrial appendage, or
an adjacent pulmonary vein.
[0116] In one embodiment, the sensor system measures a left atrial
pressure waveform, core body temperature and a cardiac electrogram,
such as the intra cardiac electrogram (IEGM). Elevated left atrial
pressure is the most accurate predictor of impending CHF, often
preceding clinical symptoms by hours to days. Other embodiments of
the left atrial pressure waveform may be used to diagnose a number
of conditions, as listed in FIGS. 6A-6C. Core temperature is often
depressed in acute CHF, but elevated prior to the development of
fever in response to an infection, making core temperature a useful
parameter for differentiating between these common conditions with
similar symptoms but which require different treatments. The
intracardiac electrogram may be useful in diagnosing arrhythmias
and precipitating causes of worsening CHF.
[0117] FIG. 7 shows how left and right atrial pressure measurements
may be combined with IEGM and core temperature measurement to
diagnose a number of cardiac and non-cardiac conditions. The list
of diagnostic states in FIG. 7 is exemplary, and by no means
exhaustive of all the potential diagnostic states definable by the
given parameters. Multiple states can exist simultaneously, for
example, moderate CHF and rapid atrial fibrillation. The measured
parameters can be used over large populations to define the
probability of any given diagnostic state. Each diagnostic state
may have a unique treatment. For example, mild CHF may be treated
by increasing diuretic therapy, whereas rapid atrial fibrillation
is treated with a drug that blocks AV node conduction. Many of the
states listed can contribute to worsening CHF. Therefore, one of
skill in the art will appreciate that several embodiments described
herein can be used to treat not only CHF, but to treat
cardiovascular disease in general.
[0118] The embodiments summarized above and described in greater
detail below are useful for the treatment of cardiovascular
disease, including congestive heart failure (CHF). CHF is an
important example of a medical ailment currently not treated with
timely, parameter-driven adjustments of therapy, but one that the
inventors believe could potentially benefit greatly from such a
strategy. Patients with chronic CHF are typically placed on fixed
doses of an average of six drugs to manage the disease. The drug
regimen commonly includes but is not limited to diuretics,
vasodilators such as ACE inhibitors or A2 receptor inhibitors,
beta-blockers such as Carvedilol, neurohormonal agents such as
spironolactone, and inotropic agents usually in the form of cardiac
glycosides such as, for example, digoxin. In addition, patients
typically are taking other cardiovascular drugs to limit disease
progression, symptoms or complications. Examples include `statins`
to lower cholesterol, nitrate to relieve chest pain, and aspirin or
warfarin to prevent clotting.
[0119] 1. Implantation and Anchoring
[0120] a. Placement and Anchoring in the Left Atrium
[0121] In one embodiment, such as that illustrated in FIG. 8, an
implantable device is implanted percutaneously in the patient by
approaching the left atrium 36 through the right atrium 30,
penetrating the patient's atrial septum 41 and positioning one or
more physiological sensors 15 in the atrial septum 41, on the
septal wall of the left atrium 36, or inside the patient's left
atrium 36. FIG. 8 shows an embodiment in which a sensor package 15
is deployed across the atrial septum 41. The sensor lead 10 is
coupled to a physiological sensor or sensors 15 and anchoring
apparatus at the lead 10 distal end 17. The anchoring apparatus
includes a distal foldable spring anchor 68 that expands in
diameter upon release and is located at or near the distal tip of
the sensor 15, and a proximal foldable spring anchor 70. The distal
and proximal anchors 68, 70 are sufficiently close together that
when deployed the two anchors 68, 70 sandwich the intra-atrial
septum 41 between them, thus fixing the sensor/lead system to the
septal wall. The intra-atrial septum 41 is typically between about
1 and about 10 mm thick. In one embodiment, the anchors 68, 70 are
made of a highly elastic biocompatible metal alloy such as
superelastic nitinol. The lead 10 may contain a lumen that exits
the lead 10 at its proximal end. A stiffening or bending stylet can
be insert in the lumen to aid in passage of the sensor(s) and lead
15, 10. After a transseptal catheterization has been performed (as
described below), a delivery sheath/dilator system of diameter
sufficient to allow passage of the sensor/lead system is placed
from a percutaneous insertion site over a guidewire until the
distal end of a sheath 67 is in the left atrium 36. Left atrial
position can be confirmed under fluoroscopy by contrast injection,
or by the pressure waveform obtained when the sheath 67 is
connected to an external pressure transducer. To aid the procedure,
the sheath 67 may include a proximal hemostasis valve to minimize
air entrainment during device insertion. A side port with a
stopcock is useful to aspirate any remaining air and to inject
radiographic contrast material. Additionally, later sheath 67
removal may be facilitated by using a "peel-away" type of sheath.
These features of vascular sheaths are commercially available and
well know to those familiar with the art. With the spring anchors
68, 70 folded and forming a system with minimal diameter, the
system is loaded into the sheath 67 and advanced until the distal
spring 68 just exits the sheath 67 in the left atrium 36 and is
thus deployed to its sprung diameter. The sheath 67 is carefully
withdrawn without deploying the proximal anchor 70 and the sheath
67 and sensor/lead system are withdrawn as a unit while contrast is
injected through the sheath 67 around the sensor lead until
contrast is visible in the right atrium 30. The proximal sheath 67
is further withdrawn, allowing the proximal anchor 70 to spring to
its unloaded larger diameter, thus fixing the distal portion of the
sensor lead to the septum 41.
[0122] It will also be apparent that, in several embodiments, a
similar sensor/lead system can be inserted through an open
thoracotomy or a minimally invasive thoracotomy, with the anchoring
system fixating the sensor/lead to a location such as the free wall
of the left atrium, the left atrial appendage, or a pulmonary vein,
all of which provide access to pressures indicative of left atrial
pressure.
[0123] In one alternative embodiment, a flexible lead 10 is
partially advanced into a pulmonary vein 50 connected to the left
atrium 36 such that one or more physiological sensors 15 disposed
on the flexible lead 10 a predetermined distance from its distal
end 17 are positioned within the left atrium 36 or the pulmonary
vein 50, as shown in FIG. 9. In another embodiment, the distal
portion 17 of the flexible lead 10 is partially advanced into the
left atrial appendage such that anchoring apparatus will be
occlusive of the appendage, for example as taught by Lesh et al. in
U.S. Pat. No. 6,152,144, incorporated by reference herein. The
physiologic sensors 15 are positioned on the lead 10 proximal to
the occlusive anchors so that they sense conditions in the left
atrium.
[0124] In other embodiments, such as those shown in FIG. 12 and
FIG. 14, a first lead component 53 includes an anchoring apparatus,
for example, a helical screw 57, which is advanced to the atrial
septum 41. The anchoring apparatus is deployed to anchor the first
lead component 53 into the patient's atrial septum 41. A second
lead component 60 includes a physiological sensor, for example, a
pressure transducer 62, which is advanced along the first lead
component 53 until the second lead component 60 is in a position
such that the physiological sensor is positioned within the
patient's left atrium 36.
[0125] b. Implantation in the Left Atrium
[0126] Referring to the embodiment depicted in FIG. 8, the system
is implanted through the left atrial septum 41 such that the
pressure sensor 15 is exposed to the pressure in the left atrial
chamber 36 of the heart. The left atrial septum 41 can be accessed
from the right atrium 30 through the inferior or superior vena cava
35, 28, as is well known to those skilled in the arts of, for
example, pacemaker lead placement, catheter ablation for control of
arrhythmias originating in the left atrium or pulmonary veins,
percutaneous repair of the mitral valve, and percutaneous closure
of an atrial septal defect. In one embodiment, the flexible lead 10
and pressure transducer 15 are anchored to the atrial septum 41.
This placement can be achieved using vascular access techniques
that are well-known to those familiar with the performance of
invasive cardiovascular procedures, in particular, interventional
cardiologists, electrocardiologists, and cardiovascular surgeons.
These procedures are commonly performed with the aid of
visualization techniques, including standard fluoroscopy, cardiac
ultrasound, or other appropriate visualization techniques used
alone or in combination.
[0127] Access to the central venous circulation may be achieved by
use of the standard Seldinger technique through the left or right
subclavian vein, the right or left internal jugular vein, or the
right or left cephalic vein. Alternatively, access may be made via
the Seldinger technique into the right femoral vein. In either
case, a Brockenbrough catheter and needle are used to pierce the
atrial septum 41 for access to the left atrium 36, as described
below.
[0128] i. Superior Venous Access (Subclavian or Internal Jugular
Vein)
[0129] FIG. 10 provides a schematic sectional view of the patient's
heart 33 and shows the apparatus used to access the left atrium 36.
FIG. 10 depicts an access assembly 18 comprising a Brockenbrough
catheter 20 inside a sheath 22, with a flexible guidewire 25
residing within the Brockenbrough catheter 20. As FIG. 10
indicates, the access assembly has been placed through the superior
vena cava 28 into the right atrium 30 of the heart 33. FIG. 10 also
shows the inferior vena cava 35, the left atrium 36, the right
ventricle 37, the left ventricle 40, the atrial septum 41 that
divides the two atria 30, 36, and the valves 42 between the right
atrium 30 and right ventricle 37, and the left atrium 36 and left
ventricle 40. The reader will appreciate that the view of FIG. 10
is simplified and somewhat schematic, but that nevertheless FIG. 10
and the other views included herein will suffice to illustrate
adequately the placement and operation of an embodiment of the
present invention.
[0130] ii. Placement of the Lead
[0131] With the access assembly 18 in place within the right atrium
30, the Brockenbrough catheter 20 is used to pierce the atrial
septum 41 by extending the Brockenbrough needle (not shown) through
the atrial septum 41 into the left atrium 36. In the figures, the
atrial septum 41 has been pierced by the needle, the catheter 20
has been advanced over the needle, and the needle has been
withdrawn from the catheter 20, leaving the catheter 20 in place
inside the left atrium 36. Optionally, a guidewire 25 may be
advanced through the needle into the left atrium 36 before or after
advancing the catheter 20, or it may be placed into the left atrium
36 through the catheter 20 alone after the needle has been
withdrawn.
[0132] As indicated by the arrows 45 in FIG. 10, the sheath 22 may
extend into the left atrium 36, or it may remain on the proximal
side of the atrial septum 41 within the right atrium 30. FIG. 10
shows the guidewire 25 extended from the end of the Brockenbrough
catheter 20 to secure continuous access into the left atrium 36. As
depicted therein, the guidewire 25 has a curled, "pig-tail" style
distal tip 48 to better secure the guidewire 25 within the left
atrium 36 and to safeguard against inadvertent withdrawal through
the atrial septum 41. Alternatively, a "floppy tip" guide wire may
be used, which can be safely advanced well into one of the
pulmonary veins, again to safeguard against inadvertent withdrawal
through the atrial septum 41. Once the guidewire 25 is securely in
place in the left atrium 35, the Brockenbrough catheter 20 may be
withdrawn so that the flexible lead 10 may be placed through the
peel-away sheath 22.
[0133] With the guidewire 25 securely in place with its distal tip
48 inside the left atrium 36, the flexible lead 10 may be advanced
into the left atrium 36. The flexible lead 10 might itself include
a central lumen configured to receive the proximal end of the
guidewire 25, thereby allowing the flexible lead 10 to be advanced
down the guidewire 25 toward the left atrium 36. More commonly, an
exchange catheter, which may be in the form of a peel-away sheath
22, will be advanced down the guidewire 25 and placed into the left
atrium 36, the guidewire 25 may then be withdrawn, after which the
flexible lead 10 will be advanced down the exchange catheter and
into position.
[0134] In one embodiment, a peel-away sheath 22 is used to allow
the sheath to be removed once the distal end of the lead 10 is
implanted. The peel-away feature is used if the proximal end of the
lead 10 is permanently attached to the coil housing assembly
(described above). Alternatively, a non-peel-away sheath with
proximal hemostasis valve and side port as described above can be
used, for example, if the lead is detachable from the coil assembly
and if the lead or a stiffening stylet fixed within the central
lumen of the lead is long enough to remove the sheath while
maintaining control over the proximal end of the lead. These
configurations of sheaths and methods of sheath removal are well
known to those skilled in the art.
[0135] iii. Anchoring the Sensor and Lead
[0136] Once the pressure transducer 15 of the flexible lead 10 is
positioned within the left atrium 36, the lead 10 should be
anchored in place to ensure that the pressure transducer 15 stays
reliably and permanently in the desired location.
[0137] One method for anchoring the flexible lead 10 in place is
depicted in FIG. 9, which is a somewhat schematic depiction of the
major structures of the heart. FIG. 9 shows the four pulmonary
veins 50 that connect to the left atrium 36. In the particular
apparatus depicted in FIG. 9, the flexible lead 10 includes a
pressure transducer 15 located on the body of the lead 10 a
predetermined distance proximal of the distal end 17 of the lead
10.
[0138] Referring back to FIG. 9, the distal end 17 of the flexible
lead 10 in this embodiment can be bent by the operator in much the
same way as a distal tip such as might be found on a steerable
angioplasty guidewire or another similar device. This feature
assists the operator in steering the flexible lead 10 into a
selected one of the pulmonary veins 50, with the pressure
transducer 15 disposed within the interior space of the left atrium
36, or even within the pulmonary vein itself. Placement of the
pressure transducer 15 within the pulmonary vein is effective
because pressures within the pulmonary vein are very close to
pressures within the left atrium. It will be appreciated by those
skilled in the art that visualization markers (not shown) may be
provided at appropriate locations on the flexible lead 10 to assist
the operator in placing the device as desired. With the flexible
lead 10 in place as shown, the body's own natural healing mechanism
may permanently anchor the flexible lead 10 in place both at the
penetration site through the atrial septum 41, and where the
flexible lead 10 contacts the interior surface of the pulmonary
vein 50 in which the tip of the lead 10 resides. The pressure
transducer 15 might also be placed at locations such as the left
atrial appendage (not shown in FIG. 9) where the pressure is nearly
the same as the left atrium 36, or the left ventricular cavity,
where at identifiable phases of the cardiac cycle the pressure is
momentarily nearly the same as that in the left atrium 36.
[0139] FIG. 11 and FIG. 12 show alternative methods and devices for
anchoring the pressure transducer 15 in a location appropriate for
measuring pressures within the left atrium 36. The lead in this
embodiment includes a helical screw 57 for anchoring the lead to
the atrial septum 41. Similar configurations are used in some leads
for pacemakers and thus may be familiar to those skilled in the
art.
[0140] iv. Two-component Lead with Optional Second Pressure
Transducer
[0141] Referring now specifically to FIG. 11, the guidewire 25 is
shown positioned across the atrial septum 41 between the left
atrium 36 and the right atrium 30. A first lead component 53 is
delivered over the guidewire through an appropriate guiding
catheter 55 or sheath. This first lead component 53 includes a
helical screw 57 on its exterior surface. The helical screw 57 is
advanced into the tissue of the atrial septum 41 by applying torque
to the shaft of the first lead component 53. The helical screw 57
could also be coupled to a hollow or solid cylindrical mandrel (not
shown), or to a spirally wound mandrel (also not shown) disposed
along substantially the entire length of the first lead component.
When the helical screw 57 has been turned and advanced sufficiently
into the atrial septum 41, the guidewire 25 and guiding catheter
may then be withdrawn leaving the first lead component 53 anchored
securely in place.
[0142] In one embodiment, a second lead component 60 is advanced as
shown in FIG. 12 through a central lumen in the first lead
component 53. The first and second lead components 53, 60 are sized
and configured so that when the second lead component 60 is fully
advanced with respect to the first lead component 53, a left atrial
pressure transducer 62 at the end of the second lead component 60
protrudes by an appropriate predetermined amount into the left
atrium 36. In one embodiment, the second lead component 60 is then
securely fixed with respect to the first lead component 53.
[0143] It should be noted that the embodiments depicted in FIG. 11
and FIG. 12 includes a second pressure transducer 65 on the
exterior of the first lead component 53 that may be exposed to
pressure within the right atrium 30. This illustrates, in a
simplified way, the general principle, in which a pressure
transducer is used to measure fluid pressure within the left
atrium, but in which one or more additional transducers or sensors
may also be used to detect a physiologic condition other than left
atrial pressure. These physiologic conditions may include pressures
in locations other than the left atrium 36, and physical parameters
other than pressure.
[0144] v. Alternative Anchoring Systems and Methods
[0145] FIG. 8 and FIG. 13 through FIG. 16 show embodiments of the
flexible lead 10, in which folding spring-like fins or anchors
deploy to anchor the lead in place in the atrial septum 41.
Referring specifically to FIG. 13, a first lead component 53 is
advanced through a sheath 67, the sheath 67 having been advanced
across the atrial septum 41. In this embodiment, the first lead
component 53 includes folding distal anchors 68 and proximal
anchors 70 that lie folded and are held in place inside the
interior lumen of the sheath 67. When the first lead component 53
and sheath 67 are properly positioned, which will generally involve
the use of fluoroscopy or an alternative technique for imaging, the
operator may carefully withdraw the sheath 67 from around the first
lead component 53. As the distal and proximal anchors exit the
sheath 67, they deploy themselves (as depicted in FIG. 8) on either
side of the atrial septum 41, thereby anchoring the first lead
component 53 securely in place. Similar anchors are sometimes used
with leads for pacemakers and other medical devices where permanent
anchoring is desired, and the operation of these anchors thus will
not be entirely unfamiliar to the knowledgeable reader.
[0146] Referring now to FIG. 14, a second lead component 60 is
advanced through a central lumen of the first lead component 53
after the guidewire 25 (see FIG. 15 and FIG. 16) and sheath 67 are
removed. As in the previous embodiment, a left atrial pressure
transducer 62 is carried at the distal end of the second lead
component 60. Again, the first and second lead components 53, 60
are sized and configured with respect to one another so that the
left atrial pressure transducer 62 protrudes from the first lead
component 53 an appropriate amount into the left atrium 36. In
addition, as in the previous embodiment, a second pressure
transducer 65 on the exterior of the first lead component 53 allows
for the measurement and transmittal of pressure within the right
atrium 37.
[0147] Other anchoring methods may be devised by those skilled in
the relevant arts. Moreover, approaches have been described by
which the lead is positioned between the left atrium and an exit
site from the patient's superior venous circulation. Alternate lead
routes and exit sites may find use as well.
[0148] vi. Surgical Methods of Device Implantation
[0149] As described above, percutaneous transvenous implantation
methods are used in accordance with several embodiments of the
current-invention. One skilled in the art will understand that
alternative lead routes and exit sites from the venous system may
also be used. One important class of alternative implantation
methods consists of surgical implantation through the wall of the
heart, either directly into the left atrium through the left atrial
free wall or left atrial appendage, into the left atrium via a
pulmonary vein, into the left atrium through the intra-atrial
septum via the right atrial free wall, or directly into a pulmonary
vein.
[0150] In one embodiment, the pressure transducer is implanted in
the atrial free wall or in the wall of the atrial appendage. As
described above, in one embodiment, at these locations the pressure
sensing surface of the transducer is exposed to left atrial
pressure, and the body of the transducer extends through the wall
of the atrium or atrial appendage. A flexible lead from the
implanted transducer provides signal connection to a telemetry
antenna coil that the surgeon implants near the surface of the
skin. In another embodiment, this coil may be connected directly to
the implanted pressure transducer on the outside surface of the
heart, without need for a flexible lead. In yet another embodiment,
the flexible lead provides signal connection to a CRM generator
housing located near the surface of the skin.
[0151] c. Pulmonary Vascular Implant
[0152] Vascular stents are implants that are deployed in blood
vessels to support the size of the vascular channel and maintain
adequate blood flow. A stent may also be used to anchor another
type of device in a fixed location within the cardiovascular
system. U.S. Pat. No. 5,967,986, incorporated by reference herein,
describes a stent coupled to one or more pressure transducers for
the purpose of measuring blood flow in a vessel. In one embodiment
of the current invention, a stent is used to support and anchor the
sensor measuring a signal indicative of left atrial pressure. As
mentioned above, the pressure in the pulmonary veins is
substantially identical to that in the left atrium. Thus, in one
embodiment of this invention, the pressure sensor is anchored in a
pulmonary vein by means of a stent expanded within the vein.
[0153] In one embodiment of the current invention, a method and
apparatus for continuous ambulatory detection, diagnosis and
treatment of acute congestive heart failure is provided. It will be
understood that the current invention may be implemented using
digital signal processing methods in which various input signals
are sampled and the described procedures are performed on a set of
samples. Hence, a periodic determination of the physiological
parameter of interest is within the definition of the term
continuous. In one embodiment, a percutaneously implantable system
comprises a hermetically sealed pressure transducer/communications
module mounted on an unexpanded vascular stent-like member. In one
embodiment, the stent-like member is a cylindrical vascular stent
such as a balloon expandable or self-expanding metallic stent
similar to those used to treat vascular stenosis such as
atherosclerotic stenosis of a coronary or peripheral artery. The
pressure transducer/communications module is mechanically coupled
to the unexpanded stent and the stent/transducer module is mounted
on a delivery catheter constituting a stent/transducer delivery
system. The stent/transducer delivery system is percutaneously
inserted into a patient's body via the venous or arterial
system.
[0154] In one embodiment, the delivery system courses over a guide
wire that has been positioned from proximal to distal, starting
outside the patient, percutaneously entering into the venous system
and into the right atrium, through the right ventricle and into a
branch of the pulmonary artery. The stent/transducer module is then
advanced over the guide wire into the selected branch of the
pulmonary artery that is approximately the diameter of the expanded
stent/transducer module.
[0155] In another embodiment, a standard transseptal
catheterization procedure is performed to place a guide wire that
courses from proximal to distal starting outside the patient
percutaneously into the venous system into the right atrium, across
the intra-atrial septum, into the left atrium and finally into one
of the four pulmonary veins. The stent/transducer delivery system
is then advanced over the guide wire until the unexpanded
stent/transducer is positioned in the pulmonary vein that is
approximately the diameter of the expanded stent/transducer module.
The stent is then expanded such that the cylinder described by the
stent is coaxially in contact with the vessel wall confining the
transducer/communications module so that its outer surface contacts
the vessel wall.
[0156] 2. Pressure Transducer
[0157] a. Pressure Sensor Locations
[0158] In one embodiment of the invention, the apparatus and/or
method for treating cardiovascular disease includes one or more
sensors, such as pressure sensors. In one embodiment, the pressure
sensor is located in the atrial septum, the left atrial appendage,
the left atrial free wall, one of the pulmonary veins, or any other
location in pressure communication with the left atrium, for
example, but not limited to, the right atrium, the central veins,
or any location as known to those of skill in the art suitable for
measuring a pressure related to the pressure in the pulmonary
veins, the pulmonary capillary wedge pressure, the pulmonary artery
diastolic pressure, the left ventricular end diastolic pressure, or
the right ventricular end diastolic pressure. In one embodiment,
the pressure signal includes a pulmonary vein pressure, a pulmonary
capillary wedge pressure, a pulmonary artery diastolic pressure, a
left ventricular end diastolic pressure, a right ventricular end
diastolic pressure, right atrial pressure, or the pressure measured
in the intrathoracic space, or the central veins. In another
embodiment, the signal includes algorithms that estimate pulmonary
artery diastolic pressure from the right ventricular waveform, the
right ventricular end diastolic pressure, the right atrial
pressure, or the response of the arterial blood pressure to the
Valsalva maneuver. In yet another embodiment, signals indicative of
left atrial pressure include spatial parameters (e.g., dimension of
chambers), septal shape, position, motion, and acceleration.
[0159] b. Pressure Sensor Design
[0160] In one embodiment, the physiological sensor includes a
pressure transducer. In one embodiment, the pressure transducer is
contained within a hermetically sealed sensor package, or module.
The sensor package may be provided in a wide range of sizes and
shapes. In one embodiment, the sensor package is cylindrical, and
is between about 1 mm and 5 mm long, and 3 mm in diameter. In
another embodiment, the sensor package is between about 5 mm and
about 15 mm long. In another embodiment the package is about 8 mm
long, and about 3 mm in diameter. In one embodiment the package is
less than about 1 mm in diameter. In another embodiment, the
package is less than about 10 mm long. Micro electromechanical
system (MEMS) pressure sensor devices may also be used. In one
embodiment, the package may be rectangular, square, spherical,
oval, elliptical; or any other shape suitable for implantation. In
one embodiment, the sensor package is rigid, and in another
embodiment, the sensor package is flexible.
[0161] In one embodiment, the sensor package includes a titanium
cylindrical housing that is closed at one end by titanium foil
membrane. In one embodiment, the foil membrane is between about
0.001 to 0.003 inches, between about 0.003 inches and about 0.005
inches, or less than 0.001 inches thick. In another embodiment, the
foil membrane is between about 0.001 inches to about 0.002 inches
(about 25 microns to about 50 microns) thick, and about 0.08 to
0.10 inches (about 2.0 to 2.5 mm) in diameter. Foil diaphragms of
this type have relatively low compliance, meaning that they exhibit
relatively little strain, or displacement, in response to changes
in pressure. For example, in one embodiment, a 2.5 mm diameter by
50-micron thick titanium foil diaphragm has a displacement at its
center of only about 4.3 nanometers per mm Hg pressure change.
Higher compliance is a disadvantage for implantable pressure
sensors because tissue overgrowth can limit the relatively larger
motion of a high compliance diaphragm, causing errors in the sensed
pressure reading.
[0162] In one embodiment, resistive strain gauges are bonded to the
inside surface of the foil.
[0163] In one embodiment, the titanium cylindrical housing
comprises an application specific integrated circuit (ASIC or
"chip") or "measurement electronics." Measurement electronics are
contained within the housing, connected to the strain gauges by
fine gold wires. The other end of the housing is sealed by a
ceramic feed-through that is brazed to a titanium cylinder.
[0164] In one embodiment, the pressure of the gas sealed in the
cylinder is slightly lower than the lowest external pressure
anticipated, so that the net force on the foil will be inward under
normal conditions of operation, forming a concave membrane shape.
The advantage of maintaining a concave membrane shape throughout
the pressure range of operation is that it avoids potential
pressure measurement artifacts that are known to sometimes occur
when a pressure sensing membrane transitions between a concave and
a convex shape, a phenomenon known as "oil-canning." In one
embodiment, oil-canning is avoided by using a transducer diaphragm
that has low compliance, with low compliance as described above,
and that is nearly flat in the absence of a pressure differential.
In one embodiment, the diaphragm is about 2.0 to 2.5 mm in diameter
and is within about 25 microns of flat in the absence of a pressure
differential. In another embodiment, the diaphragm thickness is
maximized to maximize flatness and minimize compliance, consistent
with the sufficient compliance to derive a useable transducer
signal.
[0165] In one embodiment, the pressure sensor includes temperature
compensation so that pressure measurements will not be affected by
temperature change. This also provides the temperature at the site
of the sensor. In one embodiment, temperature compensation or
modulation is achieved by using multiple resistive strain gauges
arranged in a Wheatstone bridge, such that the electrical voltage
output of the bridge is proportional to the ratio of two or more
resistances, as is well known in the art of electrical
measurements. By selecting resistive strain gauges with
substantially identical temperature coefficients, the intrinsic
output of the bridge is made to be temperature independent.
However, the overall response of the pressure transducer may still
be temperature dependent because of imperfect matching of the
resistive strain gauges, or due to other factors, such as the ideal
gas law behavior of the gas sealed within the chamber, or different
thermal expansions of the various components and contents of the
device. Another embodiment of temperature compensation utilizes an
internal thermometer consisting of, for example, a resistor whose
resistance depends upon temperature in a reproducible way, and
which is placed in a location isolated from the transducer
diaphragm so that its resistance does not depend on pressure
variations. Prior to implanting the device, calibration data is
collected consisting of the output of the transducer versus
pressure as a function of the reading of the internal thermometer.
After implantation, the signal from the internal thermometer is
used together with the transducer output and the calibration data
to determine the temperature compensated pressure reading. In one
embodiment, a band gap voltage reference is used to create a
current proportional to absolute temperature that is then compared
to the temperature-independent voltage reference. Such methods are
well-known in the art of CMOS integrated circuit design.
[0166] In one embodiment, the devices described herein are
configured similarly to a cardiac pacemaker, with a hermetically
sealed housing implanted under the patient's skin and a flexible
lead with a pressure transducer at its distal end. The housing
contains a battery, microprocessor and other electronic components,
including a patient signaling device and transcutaneous telemetry
means for transmitting programming information into the device and
for transmitting physiological data out to an external
programmer/interrogator.
[0167] One skilled in the art will understand that alternative
distributions of the components may be constructed in accordance
with several embodiments of the present invention. In one
alternative, the pressure sensing circuitry is incorporated into
the pressure transducer unit implanted in the heart, reducing the
number of conductors needed in the lead to as low as two.
[0168] In another embodiment, the signal processing, prescription
algorithms, and patient signaling components are located in a
device external to the patient's body in communication with the
implanted subcutaneous housing via one of various forms of
telemetry well known in the art, such as two-way radio frequency
telemetry.
[0169] In another embodiment, the pressure sensor is fabricated by
micro electro-mechanical systems (MEMS) techniques, as taught by,
for example U.S. Pat. No. 6,331,163, herein incorporated by
reference.
[0170] c. Sensor-Tissue Interaction Issues
[0171] In one embodiment, within several weeks after implantation,
the entire device is covered with new tissue, including fibrous
tissue and endothelium. A covering of endothelium is desirable
because it prevents the formation of blood clots that, if formed,
could break loose and cause a blocked artery elsewhere in the body,
most dangerously in the brain. A covering of fibrous tissue is also
a common component of the body's healing response to injury and/or
foreign bodies. An excessive growth of fibrous tissue on the left
atrial surface of the pressure sensor may be undesirable because it
may interfere with accurate transmission of fluid pressure in the
left atrium to the pressure sensitive diaphragm. In addition,
contraction of fibrous tissue over time may cause progressive
changes in the pressure waveform or mean value, which could
confound interpretation of the data.
[0172] i. Low Compliance Sensor Membrane
[0173] In one embodiment, the pressure transducer membrane is
designed to have very low compliance. In one embodiment, a low
compliance pressure transducer is fabricated using titanium foil as
described above. In another embodiment, a low compliance pressure
transducer is fabricated from, for example, silicon, using micro
electromechanical systems (MEMS) techniques. In yet another
embodiment, a coating is provided on the left atrial surface of the
pressure sensor.
[0174] ii. Coatings, Polishing, and Drug Eluting Surfaces
[0175] In one embodiment, a coating inhibits or minimizes the
formation of undesirable fibrous tissue, while not preventing the
beneficial growth of an endothelial covering. Coatings with these
properties are well known in the art of implanting medical devices,
particularly intravascular stents, into the blood stream. Surface
coating materials include, but are not limited to, paralene, PVP,
phosphoryl choline, hydrogels, albumen affinity, and PEO.
[0176] In one embodiment, at least some areas of the sensor package
and diaphragm are electropolished. Electropolished surfaces are
known by those skilled in the art to reduce the formation of
thrombosis prior to endothelialization, which leads to a reduced
burden of fibrotic tissue upon healing. Metallic intracoronary
stents currently approved for clinical use are electropolished for
this purpose.
[0177] Release of antiproliferative substances including radiation
and certain drugs are also known to be effective in stenting. Such
drugs include, but are not limited to, Sirolimus and related
compounds, Taxol and other paclitaxel derivatives, steroids, other
anti-inflammatory agents such as CDA, antisense RNA, ribozymes, and
other cell cycle inhibitors, endothelial promoting agents including
estradiol, antiplatelet agents such as platelet glycoprotein
IIb/IIIa inhibitors (ReoPro), anti-thrombin compounds such as
heparin, hirudin, hirulog etc, thrombolytics such as tissue
plasminogen activator (tPA). These drugs may be released from
polymeric surface coating or from chemical linkages to the external
metal surface of the device. Alternatively, a plurality of small
indentations or holes can be made in the surfaces of the device or
its retention anchors that serve as depots for controlled release
of the above mentioned antiproliferative substances, as described
by Shanley et al. in U.S. Publication No. 2003/0068355, published
Apr. 10, 2003, incorporated by reference herein.
[0178] d. Pressure Signal Detection
[0179] In one embodiment, the implanted portion of the device is
comprised of a plurality of up to n physiologic signal detection
sensors S described by the set:
[0180] {S.sub.1, S.sub.2, . . . S.sub.n}.
[0181] In one embodiment, S.sub.1, the first sensor, detects a
parameter that is indicative of left atrial pressure or S.sub.iLAP,
thus
[0182] {S.sub.iLAP, S.sub.2, . . . S.sub.n}.
[0183] Signals indicative of left atrial pressure can be pressure
signals measured at a variety of sites and may be detected by a
variety of pressure transducer types. The signals may be obtained
from locations in the cardiovascular system or adjacent to the
cardiovascular system known to be similar to or highly correlated
with direct pressure readings from the left atrium. Such locations
for obtaining pressure signals similar to the left atrium are well
known to those skilled in the art, such as Cardiologists. Locations
for sensing pressure include, but are not limited to, the left
atrium and its contiguous structures, the pulmonary veins, the
pulmonary capillary wedge or occlusion pressure, the pulmonary
artery diastolic pressure, and the left ventricular end diastolic
pressures. Other pressures indicative of left atrial pressure
include differential pressures such as the difference between the
left atria and the right atria, or the difference between the
pulmonary capillary wedge and right atrial pressures, as shown by
the correlation in FIG. 17. The individual signals comprising the
differential signal correlate independently with left atrial
pressure.
[0184] 3. Non-Pressure Sensors
[0185] a. Left Atrial Dimension
[0186] In one embodiment, the system may include one or more
additional sensors. In one embodiment, a non-pressure sensor is
also provided to generate a signal indicative of pressure in the
left atrium. Hemmingsson (U.S. Pat. No. 6,421,565), incorporated by
reference herein, describes such an implantable cardiac monitoring
devices as an A-mode ultrasound probe which is adapted to be
positioned in the right ventricle of a heart, and which emits an
ultrasound signal which is reflected from one cardiac segment of
the left ventricle of the heart, and the ultrasound probe receives
the resulting echo signal. The delay between the emission of the
ultrasound signal and the reception of the resulting echo is
measured, and from this delay a position of the cardiac segment is
determined. In one embodiment, an A-mode ultrasound probe is
deployed in the right atrium of a heart so that an ultrasound
signal is reflected from one or more cardiac segments of the left
atrium, either the atrial septal segment, the lateral wall segment,
or both. Increased left atrial pressure is known to cause in
increase in the volume of the left atrium by displacing the walls
of the left atrium away from each other. Thus, measurement of the
positions of one or more left atrial walls provides a signal
indicative of left atrial pressure, as described below, that can be
used to guide therapy for CHF.
[0187] Kojima (U.S. Pat. No. 4,109,644), incorporated by reference
herein, describes another implantable ultrasound transducer that
could be used in the manner described above to determine left
atrial dimension and thus derive a signal indicative of left atrial
pressure.
[0188] In one embodiment, the sensor comprises one pressure sensor,
a pressure sensor package, or module, with pressure sensor and
electronics, or a sensor package containing electronics, a pressure
sensor, and at least one non-pressure sensor. In one embodiment,
the at least one non-pressure sensor provides a signal indicative
of: an internal electrocardiogram; a temperature; a physical
dimension; an electrical resistance, such as, but not limited to, a
thoracic electrical impedance; a respiratory tidal volume; a
respiratory rate; lung acoustics; oxygen saturation; oxygen partial
pressure, including oxygen partial pressure in the left chamber or
the right chamber; or cardiac output. In another embodiment of the
invention, the non-pressure sensor measures: left atrial dimension,
cross-sectional area, or volume; left ventricular dimension,
cross-sectional area or volume; atrial septum position; velocity,
or acceleration. In one embodiment, a non-implanted sensor is
provided. In one embodiment, the non-implanted sensor includes: an
arterial pressure cuff, including an automated arterial pressure
cuff; and a weight scale. In one embodiment, two sensors are
provided, a first sensor and a second sensor. In one embodiment,
the first sensor measure a pressure in the heart and the second
sensor measures a non-pressure parameter, including, but not
limited to the parameters listed above. In one embodiment, the
second sensor is also a pressure sensor. In one embodiment, the
first sensor is located internal to the patient and the second
sensor is located external to the patient. Located "external", as
used herein, shall be given its ordinary meaning and shall also
mean located on the patient, in contact with the patient, or
located completely independent of the patient.
[0189] b. Core Temperature
[0190] Other non-pressure physiologic parameters may be used in
other embodiments. Casscells III, et al. (U.S. Pat. No. 6,454,707),
incorporated by reference herein, describe a method and apparatus
for predicting mortality in congestive heart failure patients by
monitoring body temperature and determining whether a downward
trend in temperature fits any predetermined criteria. The apparatus
described by Casscells et al. determines when death is imminent and
generates an alarm. In one embodiment of the present invention, the
trend in body temperature is used daily to adjust the patient's
therapy at an earlier point before any downward trend in
temperature becomes critical. In one embodiment, core body
temperature is measured at the atrial septum. In another
embodiment, core body temperature is measured at the site of a
measurement module located anywhere within the heart, heart
chambers, great vessels, or other locations within the thorax known
in the medical arts to maintain a temperature related in a
predictable way to core body temperature.
[0191] Regional elevations in temperature are known to those
skilled in the art of temperature physiology to occur in the
presence of inflammation. Inflammation occurs in the heart in many
cardiovascular diseases. Examples of such diseases include
myocarditis due to infectious causes such as certain viruses, and
other infectious agents, pancarditis associated with acute
rheumatic fever, and the inflammation associated with immunological
rejection of a transplanted heart. A temperature sensor of
sufficient precision residing in proximity to the walls of the
heart may detect regional elevations in temperature due to local
tissue inflammation. Inflammatory cardiac conditions may also be
associated with a rise in left atrial pressure. In one embodiment
of the present invention, an implanted monitoring system that
measures both local tissue temperature with a precision of
approximately 0.1.degree. C. and a parameter indicative of left
atrial pressure can be used to diagnose active cardiac inflammation
and concomitant cardiac dysfunction.
[0192] 4. Signals
[0193] a. Left Atrial Pressure Signals
[0194] In one embodiment, one of the physiological sensors is a
pressure transducer that is used to generate a signal indicative of
pressure in the left atrial chamber of the patient's heart (the
"left atrial pressure," or LAP). In one embodiment, a LAP versus
time signal is processed to obtain one or more medically useful
parameters. These parameters include, but are not limited to, mean
LAP, temporally filtered LAP (including low-pass, high-pass, or
band-pass filtering), heart rate, respiratory variations of LAP,
respiration rate, and parameters related to specific features of
the LAP waveform such as the so-called a, v, and c waves, and the
x, x', and y descents. All these parameters are well known to those
skilled in the art. Examples of such features in normal cardiac
pressure tracings are illustrated in FIG. 18. Examples of
parameters derived from specific LAP waveform features include the
mechanical A-V delay interval, as defined below (as distinct from
the electrical A-V interval derived from the electrocardiogram);
the relative peak pressures of the a and v waves, normal values of
which are given in the table in FIG. 19; and the pressure values at
specific times in the LAP waveform, as are understood by those
skilled in the art.
[0195] In another embodiment, the parameter is determined based
upon at least one wave selected from the group including, but not
limited to, one or more of the following: an a wave, a v wave, and
a c wave. In yet another embodiment, the parameter is determined
based upon a parameter signal selected from the group including,
but not limited to one or more of the following: a wave amplitude,
a waveform rate of ascent, a waveform rate of descent, timing of a
wave feature with respect to a cardiac cycle, timing of a wave
feature with respect to another wave feature, time difference
between an a wave and a c wave, time difference between an a wave
and a v wave, and time difference between a v wave and a c wave. In
one embodiment, the parameter is determined based upon at least one
descent selected from the group including, but not limited to one
or more of the following: an x descent, an x' descent, and a y
descent. In another embodiment, the parameter is determined based
upon a parameter signal selected from the group including, but not
limited to one or more of the following: a descent amplitude, a
descent rate of ascent, a descent rate of descent, timing of a
descent feature with respect to a cardiac cycle, timing of a
descent feature with respect to another wave feature, time
difference between an x descent and an x' descent, time difference
between an x descent and a y descent, and time difference between
an x' descent and a y descent. In another embodiment, the parameter
is determined based upon the width of a wave feature, such as the
width of the a wave or the v wave. In yet another embodiment, the
parameter is determined based upon the difference between the mean
pressure and the minimum of the respiratory component of the
pressure. It is well known to the skilled artisan that several of
these parameters are independent of ambient atmospheric pressure
and independent of pressure transducer calibration.
[0196] In one embodiment, signals indicative of left atrial
pressure are periodic signals that repeat with a period the length
of which is equal to the period in between heartbeats. Any portion
of the signal or a summary statistic of that periodic signal may be
indicative of left atrial pressure and provide diagnostic
information about the state of the heart. For example, the a, c, v
waves and the x, x', and y descents, described above, correlate
with mechanical events such as heart valves closing and opening.
Any one of these elements can yield useful information about the
heart's condition. Each discrete element represents an individual
signal indicative of left atrial pressure. A summary statistic such
as the arithmetic mean left atrial pressure also represents a
signal indicative of left atrial pressure. One skilled in the art
will appreciate that there are additional discrete elements and
summary statistics that are valuable indicators of left atrial
pressure. Advantageously these components of left atrial pressure
are relative to each other and therefore do not have to be
compensated for atmospheric pressure and are not subject to offset
drift inherent in most pressure transducers.
[0197] In one embodiment, the relative heights and/or shapes of the
left atrial a, v, and v waves are monitored to detect and diagnose
changes in severity of cardiovascular disease. This information
permits differentiation between worsening symptoms of CHF due to
volume overload versus impaired left ventricular pump function
(such as decrease left ventricular compliance, or acute mitral
regurgitation), allowing medical therapy to be appropriately
targeted. For example, pure volume overload is usually manifest
with a progressive elevation of the mean left atrial pressure and
generally responds to fluid removal by taking a diuretic
medication, natriuretic peptide, or and invasive technique known as
ultrafiltration of the blood. Decreased left ventricular compliance
is the diagnosis when the a wave increases without shortening of
the atrioventricular (AV) delay or in the presence of mitral
stenosis. Acutely decreased compliance may be indicative of left
ventricular (LV) ischemia, while chronically decreased compliance
may be indicative of LV wall thickening know as hypertrophy. The
former may respond to nitrates or coronary artery interventions,
while the latter may respond to beta or calcium antagonist drugs,
or chemical septal ablation. Increases in the v wave amplitude and
merging with the c wave to produce a cv wave is usually indicative
of acute mitral valve regurgitation. This may be due to a sudden
mechanical failure of the valve or its supporting apparatus, or it
may be due to acute ischemia of the supporting papillary muscles as
part of an acute coronary artery syndrome. Sudden mechanical
failure requires surgical repair or replacement, while ischemia may
require anti-ischemic medications such as nitroglycerin or coronary
artery interventions such as angioplasty or bypass surgery. FIGS.
6A-6C list these and other parameters derivable from cardiac
pressure tracings that may be interpreted to facilitate diagnosis
of cardiovascular disease states.
[0198] In another embodiment, atrial fibrillation and atrial
flutter are detected by analysis of the LAP waveform. In another
embodiment, spectral analysis of the LAP versus time signal is
performed.
[0199] i. Measurement of Absolute Pressure
[0200] In one embodiment, an apparatus for measuring absolute
pressure at a location within the body is provided. In one
embodiment, the apparatus includes a transducer/communications
module for making measurements, and communicating the measurement
to another device, as described above. The
transducer/communications module can include transducers or sensors
suitable for measuring pressure, as are well known to those of
skill in the art, temperature, or other physiological parameters.
In one embodiment, the transducer/communications module measures an
absolute pressure. In another embodiment, the
transducer/communications module measures the pressure difference
between a location in the body and a reference pressure within the
implanted transducer/communications module.
[0201] ii. Measurement of Relative Pressure (Gauge Pressure)
[0202] In one embodiment, the system contains the necessary
components to obtain a signal indicative of pressure relative to
atmospheric pressure. An implanted apparatus for measuring absolute
pressure at a location within the body is provided as above, which
further communicates this information, as either an analog or
digital signal, to an external signal analyzer/communications
device. The external signal analyzer/communications device further
contains a second pressure transducer configured to measure the
atmospheric (barometric) pressure. The analyzer/communications
device performs a calculation using the absolute pressure from the
implanted module and the atmospheric pressure to obtain the
internal pressure relative to atmospheric pressure, that is,
difference between the absolute pressure at the location within the
body and the absolute barometric pressure outside the body. This
pressure, also known as the gauge pressure, is known to those
skilled in the art to be the most physiologically relevant pressure
measure.
[0203] In one embodiment, gauge pressure measurements are performed
only when the implanted apparatus is queried by the external
analyzer/communications device, advantageously assuring that the
atmospheric pressure at the time and patient's location is
available and correctly matched with the absolute internal pressure
reading. It will be clear to those skilled in the art that
unmatched internal and barometric pressure readings would render
the gauge pressure measurement inaccurate or useless. In this
embodiment, internal absolute measurements are made only when the
external analyzer/communications device is physically present. In
one embodiment, this is accomplished by having the external device
supply operating power to the implant module to make the
measurement. In another embodiment, such as when the implanted
module contains an internal power source such as a battery, this is
accomplished by requiring a proximity RF link to be present between
the external and implantable modules, either immediately before
and/or after and/or during the measurement.
[0204] iii. Measurement of Differential Pressure
[0205] In another embodiment, an apparatus for measuring
differential pressure is provided. In one embodiment, the apparatus
includes a transducer/communications module for making
measurements, and communicating the measurement to another device,
such as a processor, or patient advisory module. The
transducer/communications module can include transducers or sensors
(these terms are used synonymously herein), suitable for measuring
pressure as are well known to those of skill in the art,
temperature, or other physiological parameters. In one embodiment,
the transducer/communications module measures a differential
pressure that includes the pressure difference between two
locations inside of the body. For example, the
transducer/communications module measures the difference between
the fluid pressure of the blood in an artery, and the intrathoracic
pressure, detected through the artery's wall. In another example,
the transducer/communications module measures the difference
between the fluid pressure in the left atrium and the right atrium
of the heart, detected by a module.
[0206] In one embodiment, the transducer/communications module
includes a plurality of pressure sensing membranes, each with an
outer surface and an inner surface. In one embodiment, there are
two pressure sensing membranes in the module so that when the
device is implanted, for example in the atrial septum, one pressure
sensing membrane's outer surface is in contact with the blood of
the left atrium and the other pressure sensing membrane's surface
is in contact with the blood of the right atrium. The inner
surfaces of both pressure-sensing membranes are exposed to the same
internal space within the device. Each membrane has an associated
strain gauge, each strain gauge creating a signal indicative of the
pressure difference between the outer and the inner surfaces of the
respective membrane. Since the two membranes share the internal
space, the pressures on their inner surfaces are equal. Thus, the
differential pressure, determined by subtracting the pressure of
one transducer from the other, is proportional to the left atrial
pressure in reference to the right atrial pressure. The
baseline-offset calibration of the differential transducer can be
determined by having the patient perform a Valsalva maneuver, which
is known by those skilled in physiology to equalize the pressure
within the chambers of the heart.
[0207] In one embodiment, the module contains the necessary
components to obtain from the transducers a signal indicative of
differential pressure, and to communicate this information either
as an analog or digital signal, indicative of the severity of a
condition, such as congestive heart failure, to an external signal
analyzer/communications device. The implanted module may contain an
internal power source such as a battery, or it can be powered
transcutaneously by induction of radio frequency current in an
implanted wire coil connected to the module to charge an internal
power storage device such as a capacitor.
[0208] b. Other Measures Indicative of Left Atrial Pressure
[0209] In one embodiment, pulmonary artery diastolic pressure
(PADP) is estimated from an analysis of the right ventricular
pressure waveform, as taught by Carney in U.S. Pat. No. 5,368,040,
incorporated by reference in its entirety herein. In one
embodiment, the pressure module is placed in the right ventricle.
In other embodiments, the pressure module is placed in the right
atrium or a pulmonary artery. It is known to those skilled in the
art that under many circumstances, PADP approximates the pulmonary
capillary wedge pressure (PCWP), which is a clinically useful
measure of mean left atrial pressure. In this case, the right
ventricular pressure waveform provides a signal indicative of left
atrial pressure. Right ventricular end diastolic pressure, right
atrial pressure, and central venous pressure have been shown to
linearly correlate with LAP or PCWP but do so with a slope less
than 1.0, that is, they generally underestimate LAP/PCWP. An
inverse linear transformation of any of these right-sided cardiac
pressures will therefore yield a pressure that is indicative of
LAP. Similarly, the arterial blood pressure response to forced
exhalation against a blocked airway outflow, known as the Valsalva
maneuver, is linearly correlated with PCWP (as described by
Finkelstein in U.S. Pat. No. 4,899,758, incorporated by reference
in its entirety herein) and is therefore also indicative of
LAP.
[0210] In several embodiments, non-pressure physiologic signals are
used to indicate left atrial pressure. In most cases, these
non-pressure physiologic signals correlate to left atrial pressure
through straightforward mathematical relationships. For example,
for periodic signals of left atrial pressure and volume, a periodic
pressure-volume relationship may be used. One well-known example of
a pressure-volume relationship occurs during atrial diastole, when
the ratio .DELTA.V/.DELTA.P, known as the diastolic compliance, is
generally stable. Thus, a given left atrial volume, cross-sectional
area or any dimension indicative of that volume is also a signal
indicative of left atrial pressure, and a sensor capable of
measuring a left atrial dimension or area may be used to determine
left atrial pressure. Thus, in one embodiment of the invention, one
or more physiological sensors are provided to directly or
indirectly sense one or more of the following physiological
parameters: left atrial dimension, cross-sectional area, and/or
volume; left ventricular dimension, cross-sectional area or volume;
atrial septum position; heart chamber wall velocity, and/or
acceleration.
[0211] Examples of sensors capable of measuring such dimensions or
areas include, but are not limited to an intracardiac ultrasonic
imaging system operating in M-mode, 2-dimensional, or 3-dimensional
modes, as well as paired ultrasonic crystals. It is well known in
the art that heart chamber dimensions or cross-sectional areas may
be measured and volumes estimated by the use of ultrasound, as
described, for example, by Kojima (U.S. Pat. No. 4,109,644) and by
Hemmingsson (U.S. Pat. No. 6,421,565), both incorporated by
reference herein. Such ultrasonic systems may have additional
diagnostic value in that Doppler analysis can detect changes in
atrial flow patterns due, for example, to mitral regurgitation.
[0212] It is also known in the art that electrical impedance
changes may be indicative of changes in heart chamber dimensions.
An example of a physiological sensor suitable for use in one
embodiment of the current invention is described by Alt (U.S. Pat.
No. 5,003,976), incorporated by reference herein. Alt describes how
analyzing the impedance between two intracardiac electrodes may be
used to determine changes in cardiac chamber volumes, which under
certain circumstances as described above are indicative of changes
in chamber pressures, and thus may be used to detect worsening
heart failure and guide therapy according to the present
invention.
[0213] In accordance with the above description, an embodiment of
the present invention comprises a physiologic signal detection
sensors set which may be alternately described as:
[0214] {S.sub.iLAV, S.sub.2, . . . S.sub.n}, where S.sub.iLAV is a
sensor indicative of left atrial volume;
[0215] {S.sub.iLAA, S.sub.2, . . . S.sub.n}, where S.sub.iLAA is a
sensor indicative of left atrial cross-sectional area; or
[0216] {S.sub.iLAD, S.sub.2, . . . S.sub.n}, where S.sub.iLAD is a
sensor indicative of left atrial dimension;
[0217] where the first sensor in all sets detects a signal that is
indicative of left atrial pressure. Additional sensors in the
implanted portion of the device may include detectors for any other
physiologic signal. For example:
[0218] {S.sub.iLAP, S.sub.iLAD, S.sub.iECG, S.sub.iCT, S.sub.iO2, .
. . S.sub.n},
[0219] where sensors denoted by subscripts iECG, iCT, iO.sub.2 are
detectors or signals indicative of the electrogram, core
temperature, and oxygen saturation, respectively. One skilled in
the art will appreciate that there are numerous sensor
configurations and sensor types that may be used in accordance with
various embodiment of the present invention.
[0220] In one embodiment of the invention, multiple physiologic
sensors are contained in a single package. In another embodiment, a
plurality of packages is spatially distributed. Some of the
packaging may place a particular sensor outside of the body. For
example, in one embodiment, signal detection sensor packages
P.sub.1, P.sub.2, and P.sub.3 may be located internally or external
to the body and consist of the following sets:
[0221] P.sub.1={S.sub.iLAP, S.sub.iCT}, located in the intra-atrial
septum;
[0222] P.sub.2={S.sub.iECG}, located in the superior vena cava;
and
[0223] P.sub.3={S.sub.iABP}, where iABP is a signal indicative of
arterial blood pressure.
[0224] One skilled in the art will appreciate that several
embodiments of the current invention include the detection of
various signals indicative of left atrial pressure. Such signals
include, but are not limited to: a, c, v, x, x', and y of LAP, mean
LAP, the respiratory portion of LAP, the total cardiac portion of
LAP, and filtered LAP between frequencies. In several embodiments,
non-LAP signals are used. These non-LAP signals include, but are
not limited to, the detection of left atrial dimension, left atrial
cross-sectional area, left atrial volume, left ventricular volume,
atrial fibrillation, atrial flutter, respiratory tidal volume,
respiratory rate, weight change, blood pressure or change in blood
pressure, core temperature, oxygen saturation, oxygen partial
pressure, cardiac output, LA to RA temperature differential, lung
acoustic signal, and EEG.
[0225] One skilled in the art will understand that numerous
configurations of sensors and sensor packaging and locations may be
used in accordance with various embodiments of the current
invention.
[0226] c. Other Blood Pressure Signals
[0227] In another embodiment, one or more physiological sensors
measure central venous blood pressure.
[0228] In one embodiment of the invention, one or more of the
physiological sensors measure peripheral arterial blood pressure.
Analysis of peripheral artery blood pressure to obtain a parameter
indicative of congestive heart failure status has been described,
by Finkelstein (U.S. Pat. No. 4,899,758), incorporated by reference
herein. In one such embodiment, the peripheral artery blood
pressure sensor may be a cuff sphygmomanometer, and the patient's
systolic and diastolic blood pressures are entered into the signal
processing apparatus by the user. In a further embodiment, the
blood pressures may be sent by direct signal communication to the
signal processor.
[0229] Other arrangements of pressure transducers will be apparent
to one skilled in the art. The transducer/communications module may
contain other types of sensing apparatus. In one embodiment, in
addition to the implanted pressure sensor, electrocardiographic and
temperature sensors are provided.
[0230] d. Other Physiological Parameters
[0231] In one embodiment, the internal electrocardiogram (known as
the IEGM) is sensed at one or more locations. In a further
embodiment, the IEGM is processed to obtain one or more medically
useful parameters. These parameters include, but are not limited
to, heart rate, the timing of atrial and ventricular
depolarization, the time interval between atrial and ventricular
depolarization (known in the art as the A-V interval), the duration
of ventricular depolarization (known in the art as the Q-T
interval), ST segment changes to detect acute ischemia, and
spectral analysis to detect t-wave alternans (a known harbinger of
life threatening arrhythmias), all of which are familiar to those
skilled in the art.
[0232] In one embodiment, one of the physiological sensors is a
thermometer measuring core body temperature, as described
above.
[0233] In one embodiment of the present invention, Doppler
ultrasound provides a signal that is proportional to the relative
velocity of the ultrasound probe and a structure, such as a heart
chamber wall, producing an ultrasound echo. A velocity signal can
be differentiated to obtain acceleration, as is well known to those
skilled in the art. Conversely, implantable accelerometers are
sensors known in the art that provide a signal that is proportional
to the acceleration of the implanted sensor. An acceleration signal
can be integrated to obtain a velocity plus an arbitrary constant
velocity. Because it is known that the average velocity of any
structure in the body, relative to the body, is necessarily zero,
the arbitrary constant velocity is determined, and the relative
velocity signal can be uniquely recovered from the acceleration
signal. Thus, velocity and acceleration measurements of structures
in the heart are essentially equivalent, the one being derivable
from the other. As is well known in the art, a velocity signal may
be integrated to obtain a position or displacement signal plus an
arbitrary constant displacement. Thus, the motion and displacement
of a structure in the heart, or the range of variation of the
dimension of a chamber of the heart, may be recovered from the
velocity or acceleration signal of the structure or of the chamber
walls, respectively.
[0234] Vallana and Garberoclio (U.S. Pat. No. 5,454,838,
incorporated by reference herein) teach that components of the
velocity or acceleration signal are indicative of aspects of
cardiac activity, such as opening of the mitral valve, closure of
the mitral valve, opening of the aortic valve, closure of the
aortic valve, an amount of ventricular ejection, rapid ventricular
filling, delayed ventricular filling during atrial systole, and
cardiac flow rate. As these aspects of cardiac activity may be
indicative of changes in the patient's condition, and may be
responsive to changes in the patient's prescription, they are
within the scope of parameters contemplated to be used with
embodiments of the present invention.
[0235] In another embodiment of the present invention, a
physiological sensor measures respiratory tidal volume, respiratory
rate, lung acoustic signal, and/or thoracic electrical
impedance.
[0236] In one embodiment of the invention, one of the physiological
sensors measures total body weight. In one embodiment, the sensor
is a scale. In another embodiment, the patient's weight is entered
into the signal processing apparatus by the user. In another
embodiment, the weight sensor is a scale that communicates a signal
indicative of the patient's weight to the signal processing
apparatus without requiring a user to enter the value. Lloyd et al.
(U.S. Pat. No. 6,080,106), incorporated by reference herein,
describe a digital scale suitable for use in one embodiment of this
invention.
[0237] In yet another embodiment of the invention, one or more
sensors measure: oxygen saturation; oxygen partial pressure in the
left, right, both left and right-sided cardiac chambers, or
adjacent great blood vessels; or cardiac output.
[0238] 5. Signal Processing Apparatus
[0239] In one embodiment, the signal processing apparatus of the
present invention receives signals from the one or more sensors,
and processes them together with stored parameters relevant to the
patient's medical management. In one embodiment, the result of this
processing is a signal indicative of the appropriate therapeutic
treatment or course of action the patient or an immediate personal
care giver can take to manage or correct, as much as possible, the
patient's condition. In one embodiment, the signal processing
apparatus is located outside the patient's body. In one embodiment,
signals from one or more permanently implanted physiological
sensors are received by the external signal processing apparatus by
wireless telemetry. In one embodiment, certain signal processing is
performed within the one or more individual sensor devices prior to
the signal being sent to the signal processing apparatus. In one
embodiment one signal received by the signal processing apparatus
is the LAP versus time waveform sampled at over 20 Hz for a
duration of several respiratory cycles (for example, but not
limited to, 10 to 30 seconds). In one embodiment, the signal
processing apparatus also receives a signal from a temperature
sensor located at substantially the same position as the LAP sensor
and uses this temperature to apply a temperature compensation
correction to the LAP signal using calibration data stored in the
signal processing apparatus. In one embodiment, the processor also
receives ambient temperature and atmospheric pressure, performs
temperature compensation, and subtracts the atmospheric pressure
from the LAP to obtain the relative or "gauge" LAP. In one
embodiment, the signal processing apparatus then computes the mean
LAP from the relative LAP versus time waveform. In one embodiment
the signal processing apparatus then compares the mean LAP with
patient-specific treatment ranges for mean LAP that have been
programmed into the signal processing apparatus by the patient's
physician. In one embodiment, for each patient-specific programmed
treatment range the patient's physician stores in the signal
processing apparatus an indication of the appropriate therapeutic
treatment or action the patient should take to manage or correct,
as much as possible, the patient's condition. A signal indicative
of the physician-prescribed therapeutic action corresponding to the
patient-specific range into which the measured physiologic
parameter falls is then sent to a patient signaling device.
[0240] In another embodiment of the invention, the signal
processing apparatus is essentially permanently implanted within
the body, in either the same or a different location as the one or
more physiological sensors. In one embodiment, the sensors may be
in signal communication with the signal processing apparatus by
means of one or more connective leads that may carry electrical,
optical, hydraulic, ultrasonic or other forms of signaling energy.
The conductive lead(s) may vary in length up to and exceeding about
100 cm. In another embodiment, the sensors may be in wireless
communication with the signal processing apparatus. The lead can be
coupled to an antenna for wireless transmission or to additional
implanted signal processing or storage apparatus.
[0241] 6. Interpretation of Signals
[0242] In one embodiment of the present invention, patients are
diagnosed based upon the interpretation of signals generated by one
or more sensors. For example, a signal indicating low mean right
atrial pressure may suggest hypovolemia or improper zeroing of the
transducer. FIGS. 6A-6C provide other examples by which signals may
be interpreted to facilitate diagnosis, prevention and treatment of
cardiovascular disease according to various embodiments of the
present invention.
[0243] One skilled in the art will understand that other
interpretations may be used in accordance with various embodiments
of the current invention. Further, one skilled in the art will
understand that normal ranges of the various physiologic parameters
measured in several embodiments of the current invention can be
found in cardiology textbooks or reference books. Additionally, it
may be useful to compare patient parameters within the same patient
by ascertaining initial baseline values and comparing these
baseline numbers to values generated at some later desired time.
This may be particularly useful in determining progression of
disease and response to treatment.
[0244] In several embodiments, sensors in addition to the left
atrial pressure sensor are used. Additional sensors provide further
refined diagnostic modes capable of distinguishing between
different potential causes of worsening cardiovascular illness, and
then of signaling an appropriate therapeutic treatment depending
upon the particular cause for any particular occurrence.
[0245] For example, increased left atrial pressure is commonly
caused by improper administration of medication, patient
non-compliance, or dietary indiscretion, e.g., salt binging. These
causes will be generally well-handled by changes in the patient's
drug regimen like those described above. However, there are other
causes of increased left atrial pressure that are less common, but
by no means rare, and which require different therapies for
adequate treatment. For example, one such potential cause is
cardiac arrhythmia, and especially atrial fibrillation with a rapid
ventricular response. Other arrhythmias may contribute as well to
worsening heart failure. A system including an ECG electrode in
addition to the left atrial pressure sensor would allow the system
to diagnose arrhythmias and determine whether the arrhythmia
preceded or came after the increase in left atrial pressure.
Depending on the unit's programming, as specified by the patient's
physician, specific therapies could be signaled tailored to treat
the specific causes and conditions associated with particular
adverse events.
[0246] In another example of the usefulness of additional
physiological signals is to distinguish between pulmonary
congestion caused by worsening CHF and that caused by a respiratory
infection. In a further embodiment, core body temperature is used
together with left atrial pressure to allow the early detection of
fever associated with infection. It is well known that core body
temperature often becomes elevated hours to days prior to
symptomatic fever associated with infection-related pulmonary
congestion. In one embodiment, increased core temperature in the
presence of stable left atrial pressure would trigger a message to
the patient not to increase the dosage of oral diuretic despite
symptoms of increasing congestion, and to consult with the
physician.
[0247] 7. Patient Signaling Devices
[0248] In one embodiment, the signal processing apparatus and the
patient signaling device are permanently implanted, and the patient
is signaled using at least two distinguishable stimuli, such as
distinguishable sequences of vibrations, acoustic signals, or mild
electrical shocks, perceptible by the patient.
[0249] According to one embodiment of the invention, one or more
physiological sensors is implanted within the body, the signal
processing apparatus and the patient signaling device are located
outside the body, and the signal indicative of a physiological
parameter is communicated by wireless telemetry through the
patient's skin. In one embodiment, an external telemetry system is
combined with the signal processing apparatus and the patient
signaling device. In one embodiment, a hand-held personal data
assistant (PDA) such as the PALM PILOT.TM. (Palm Computing, Inc.)
and/or HANDSPRING VISOR.RTM. (Handspring, Inc.) is used for the
signal processing and patient signaling apparatus. In one
embodiment, patient signaling is accomplished using sound, text,
and/or images.
[0250] B. Combination with Other Devices
[0251] It will be clear to those skilled in the art that many
patients who would benefit from several embodiments of the present
invention would also benefit from an implantable CRM apparatus such
as a cardiac pacemaker. In one embodiment, the present invention is
combined with an implantable CRM apparatus generator. In one
embodiment, the flexible lead on which the physiological sensor is
disposed also serves as the sensing or pacing lead of an
implantable rhythm management apparatus. In this case, conductors
within the lead provide for EKG sensing, powering of the
physiological sensor, data communication for the physiological
sensor, and pacing stimulus.
[0252] In another embodiment, the present invention is functionally
integrated with another implantable device, such as, for example, a
pacemaker or a defibrillator. In one embodiment of this invention,
one or more parameters indicative of a physiological condition
produced by the present invention are used by the integrated device
to control its therapeutic function, as described below.
[0253] In yet another embodiment, the sensor and lead of the
Stand-Alone device may be connected without modification either to
a subcutaneous coil antenna as described above, or to a combination
CRM generator housing containing a battery power supply and other
components as described below. In one embodiment, the device may be
upgraded after permanent implantation by replacing the coil antenna
assembly with an implantable CRM apparatus.
[0254] 1. Combination with Cardiac Rhythm Management (CRM)
Apparatus
[0255] Many patients who might benefit from several embodiments of
the present invention described above would also be likely to
benefit from an implantable CRM apparatus for therapy of brady- or
tachy-arrhythmia in the setting of CHF. Examples of such CRM
devices include single or multichamber cardiac pacemakers;
automatic implanted cardiac defibrillators; combined
pacemaker/defibrillators; biventricular pacemakers; and
three-chamber pacemakers, all well known to those skilled in the
art. In these patients, it would be beneficial to combine several
embodiments of the present invention with such a CRM device. This
combination would have the advantage that certain components of
both systems could be shared, reducing cost, simplifying
implantation, minimizing the number of implanted devices or leads.
As described in detail below, in some embodiments a combination
with a CRM apparatus includes adding pacing and/or defibrillation
to the therapeutic actions included in the dynamic prescription of
several embodiments of the present invention.
[0256] In one embodiment, a flexible lead serves also as an atrial
septal pacing lead. It will be recognized by those skilled in the
art, such as cardiologists, that pacing the atrial septum provides
certain advantages for patients with congestive heart failure.
These advantages may include more direct control over left
atrial/left ventricular synchrony, inhibition of atrial
fibrillation, and it requires one less lead to be inserted in
patients that are in need of a rhythm management device that
includes atrial pacing and a hemodynamic monitoring/therapy device,
etc.
[0257] It will also be known to those skilled in the art that
pacing multichamber sites in appropriate sequence in addition to
the atria, such as the right ventricle and the lateral wall of the
left ventricle in combination, or the lateral wall of the left
ventricle alone, has specific advantages for some patients with
congestive heart failure due to enhanced synchrony of left
ventriclar contraction. FIG. 20 illustrates one embodiment of the
present invention in which a sensor package 15 at the end of
flexible lead 10 is implanted across the atrial septum 41 of a
patient's heart 33. The sensor package 15 measures the left atrial
pressure and also serves as the atrial septal pacing electrode 215
of a CRM device, which may be located within an implanted housing
7. A second flexible lead 160 is placed via the right atrium 30
into the right ventricle 37. Each lead is shown with an indifferent
electrode 14 proximal to its respective distal electrode 215,
although those skilled in the art will recognize one of these could
be eliminated. The housing 7 contains the CRM device (not shown),
which in one embodiment includes a battery and electrical circuitry
for pacing the heart 33, and components of a physiological
monitoring system. It will be clear to the skilled artisan that a
variety of configurations may be used to combine the CRM and
physiological monitoring functions of such a combined device,
examples of which are described below.
[0258] Referring to FIG. 20, in one embodiment the housing 7
includes a coil antenna 161 for communicating the one or more
physiological signals from sensor package 15 to an external patient
advisory module 6. In one embodiment, the external patient advisory
module 6 includes a telemetry module 164 and antenna 162, a
barometer 165 for measuring atmospheric pressure, and a signal
processing/patient signaling device 166, such as described above
with reference to FIG. 5.
[0259] In one embodiment, components are housed within the
implantable housing of an implantable CRM apparatus, including but
not limited to the power source, signal processing apparatus,
telemetry apparatus, or patient alarm. Alternatively, in another
embodiment, components of a CRM may be shared with other
implantable devices, such as the apparatus for treating congestive
heart failure described in greater detail above. Components that
may be shared include, but are not limited to, a power source,
telemetry module, data memory, etc. For example, the flexible
physiological sensing lead of any of the apparatus for treating
congestive heart failure described above may be use as a pacing
and/or sensing lead of a CRM. In other embodiments, separate
pacemaker and sensing leads are provided.
[0260] In one embodiment of the present invention, components of
the apparatus for treating congestive heart failure are shared with
the components of a CRM apparatus in such a way that, while sharing
components, the two systems function essentially independently. In
one embodiment, the implantable CRM apparatus generator has a
housing that also serves as the housing for at least some
components of the apparatus described in greater detail above. In a
further embodiment, the power supply of the CRM apparatus,
typically comprising a long lifetime battery and power management
circuitry, also supplies power for one or more components of the
apparatus for treating congestive heart failure. In yet another
embodiment, the flexible lead or leads connecting the sensors of
the apparatus of FIG. 1, FIG. 2, and FIG. 4, to a shared
housing/generator are also coupled to sensing and/or pacing
electrodes of the CRM apparatus.
[0261] In one embodiment, one or more separate leads coupled to the
physiological sensor described above, such as a pressure
transducer, is also coupled to the CRM apparatus. In this
embodiment, the CRM apparatus shares its generator housing with
components of the implantable heart monitor apparatus described
above, but the CRM apparatus leads are separate from the
physiological sensor leads. In another embodiment, the pressure
sensing lead may be combined with a pacing lead, as described for
example by Pohndorf (U.S. Pat. No. 4,967,755) or Lubin (U.S. Pat.
No. 5,324,326), herein incorporated by reference.
[0262] a. Integration of Sensor and Pacing Lead
[0263] In one embodiment of the present invention, a system and
method is provided for combining a CRM apparatus, implantable heart
monitor, and patient communication device. The system provides the
following functionality via a single pacing/sensing lead which in
one embodiment includes only two conductors: (1) provides power to
the physiological measurement module(s); (2) provides signaling for
atrial pacing and sensing; (3) provides for programming of the
physiological sensor package(s); and (4) provides measurement data
from the physiological sensor package(s) to the
monitor/defibrillator housing for immediate or delayed use by the
patient, doctor or other caregiver via the patient signaling
module. Additional pacing and/or sensing leads may be added.
[0264] In one embodiment, an external telemetry device (such as
described above with reference to FIG. 4 and FIG. 5) is used to
communicate with and query a CRM/heart monitor system. The external
device analyzes the data with respect to the doctor's prescription,
and then indicates to the patient which and what dose of
medications or other actions he or she should take. In one
embodiment, the data is also provided to the logic within the CRM
system for improving pacing or defibrillation therapy.
[0265] For example, in one embodiment, the pressure waveform from
the left atrial chamber contains information pertinent to adjusting
atrioventricular dual chamber or atrio-biventricular triple chamber
pacing for optimizing the synchrony between left atrial and left
ventricular mechanical contraction. FIG. 21 shows why it is
difficult for pacemakers to automatically control the optimal delay
between the left atrium (LA) and left ventricle (LV). The
electrical atrioventricular delay (AV delay), which a conventional
CRM system can sense, may be substantially different that the
mechanical AV delay, which the conventional CRM cannot sense, but
which is the relevant interval for optimizing cardiac function. The
relationship between the electrical AV delay and the mechanical AV
delay is dependent on several, difficult to measure variables,
including intra-atrial conduction time, sub-AV node/HIS bundle
conduction delays, volume/pressure preloading of the atria and
ventricles and ventricular contractility, among other things, as is
known to cardiologists and electrophysiologists. The mechanical AV
delay is clinically important because if the delay is too long,
usually greater than about 250 msec, then atrial contraction does
not have an effective pressure boosting/volume priming effect on
the left ventricle, thus adversely effecting LV contractility,
stroke volume, and cardiac output. If the mechanical AV delay is
too short, usually less than about 120 msec, atrial contraction
occurs against a closed or closing mitral valve, again adversely
affecting atrial emptying, and pressure/volume boosting of the LV
pump. Both a too long and a too short LA-LV mechanical delay can
potentially worsen heart failure by further raising the LA
pressure. These conditions are potentially extractable from an LA
pressure tracing in the following ways. Too long an LA-LV
mechanical delay will manifest as an increase in the amplitude of
the LA pressure "v" wave relative to the "a" wave and an
exaggeration of the "x" descent. Too short an LA-LV mechanical
delay will manifest as an increase in the LA pressure "a" wave
relative to the "v" wave and a reduction in the "x" descent. As
illustrated in FIG. 21, the actual mechanical LA-LV delay can be
directly measured from the LA pressure waveform as the interval
from the onset of LA contraction represent by the LA pressure "a"
wave, to mitral valve closure represented by the "c" wave. In one
embodiment, the measured mechanical AV delay is used to adjust the
electrical AV delay by a feedback control system or an algorithm to
achieve a preset ideal AV delay, or alternatively by minimizing LA
mean pressure. In another embodiment, the frequency response of the
left atrial pressure transducer is sufficiently high to detect the
acoustic energy or sound of mitral valve closure or of other
cardiovascular acoustic energy generating phenomena. These
frequencies are well known to those skilled in the art of
phonocardiography. In one embodiment, this allows for even more
precise timing of the AV mechanical interval or other mechanical
intervals that are useful in regulating pacing and/or other
therapeutic measures. In another embodiment, a sensor is provided
that includes an intracardiac microphone. For example, the sensor
is operated with a sampling rate sufficient to capture the desired
acoustic waveforms, including but not limited to about 200 Hz, or
about 2000 Hz, etc., to capture acoustic waveforms with relevant
frequency components below about 100 Hz or about 1 kHz,
respectively. It is well known in the art of digital signal
processing to sample at a rate at least twice the highest frequency
component of interest within the signal. It is further well known
to limit aliasing artifacts by low pass filtering a signal to a
maximum frequency of half the sampling rate prior to sampling.
[0266] There are other features in the LA pressure waveform that
can be used to modify pacing parameters such as backup atrial
pacing rate and rate-responsive algorithms that will be apparent to
one skilled in the art. For example, to increase cardiac output,
and potentially lower the left atrial pressure, the resting heart
rate may be raised from the typical backup atrial pacing rate in
the range of 60 to 70 beats per minute when the patient is in
compensated heart failure (mean LAP<16-20 mm Hg), to a faster
backup atrial rate when the patient is decompensated with an
elevation of LAP. Similarly, the mean left atrial pressure can be
used to modify rate response algorithms, normally based on
activity, minute ventilation, or other physiologic parameters, so
that the rate response is also specific to the state of congestive
heart failure.
[0267] In another embodiment, the signal processor, dynamic
prescription, and patient signaling device are completely contained
within the implanted CRM apparatus housing. Several methods of
patient signaling from an implanted device are well known in the
art, including the use of mild electrical stimulation (e.g., U.S.
Pat. Nos. 4,140,131, 4,619,653 and 5,076,272), or audible sounds
(e.g., U.S. Pat. Nos. 4,345,603 and 4,488,555), including
intelligible speech (e.g., U.S. Pat. No. 6,247,474), all herein
incorporated by reference.
[0268] In another embodiment, the measurement of pressure or other
physiological parameters may be multiplexed with the pacing signal
(as described in greater detail below) so that pressure sensing and
telemetry would occur between pacing signals, for example as taught
by Barcel (U.S. Pat. No. 5,275,171) or Weijand et al. (U.S. Pat.
No. 5,843,135), both incorporated by reference herein.
[0269] In one embodiment, pressure sensor electronics are
integrated within a miniature hermetically sealed sensor package
implanted in the heart, minimizing the number of conductors
required in the lead between the sensor and the CRM apparatus
generator housing. In this embodiment, the pressure sensor lead may
also be used for pacing, with the sensor package, or portion
thereof, used to include one of the electrodes of the CRM
apparatus. In addition, in one embodiment, some of the pacing
electronics are integrated within the sensor package that is
implanted within the heart. This has the advantage that the lead
conductors are isolated from the pacing electrode, providing
immunity from induced currents when, for example, the patient is
placed in the rapidly changing strong magnetic fields of a magnetic
resonance imaging machine.
[0270] In clinical use, conventional cardiac pacemakers use analog
voltages on the lead between the pacemaker generator and the heart
for pacing, sensing and physiological measurements. As such, the
sensing signals in particular are subject to noise due to muscular
activity, radio frequency (RF) interference, and potential
cross-talk between physiological and electrical sensing signals.
Lead conductors carrying analog signals act as antennas for RF
noise and for induced voltages due to RF energy used in magnetic
resonance imaging (MRI) scanners. RF noise on a sense conductor may
cause erroneous pacing, even with sophisticated filtering
algorithms that are commonly used in pacemaker sensing systems.
Voltages induced by RF and changing magnetic fields are a primary
reason why MRI scanning is contraindicated for patients with
implantable cardiac pacemakers.
[0271] In one embodiment, a pacemaker is provided in which the
electronics for producing the pacing pulse output and for sensing
the ECG are integrated within a sensor package at the site of the
pacing electrode, which is generally implanted within the heart.
This allows the lead conductors to be substantially isolated from
the pacing electrode, thereby providing increased immunity from
induced currents when, for example, the patient is placed in the
rapidly changing, strong magnetic fields of a magnetic resonance
imaging machine. The lead may incorporate one or more sensors
without requiring additional lead conductors.
[0272] In one embodiment, the electronics in the proximal housing,
for example, a housing implanted near the shoulder, operate at
lower voltage than voltages required for pacing, and as a result
are fabricated using smaller feature size CMOS technology. This
allows for a smaller package and lower power consumption. The
distal pacemaker components, for example, those located in the
heart, are fabricated using larger feature size CMOS technology to
handle the higher pacing voltage.
[0273] In one embodiment, the system allows sensing signals to be
processed within the heart, thereby eliminating the risk of picking
up noise with lead conductors. Separate sensing and pacing
electrodes may be provided, with no additional lead conductors.
This allows the sensing and pacing electrodes to be individually
optimized. Pacing electrodes are optimally small in area to
minimize required voltage for pacing, while sensing electrodes are
optimally of large area to minimize impedance.
[0274] Referring now to FIG. 22 and FIG. 23, two embodiments of a
sensor package 200 are shown in which separate electrodes for
sensing 202 and pacing 204 are included. In the embodiment of FIG.
22, the sensing electrode 202 is located at the proximal portion or
segment 208 of the sensor package 200, while the pacing electrode
204 is located at the package distal portion or segment 210. The
sensing and pacing electrodes 202, 204 are electrically separated
by an insulating segment or ring 206. In one embodiment, the
insulating ring 206 is a cylindrical ceramic segment to which
metallic proximal and distal segments 208, 210 of the sensor
package 200 are hermetically fastened. Hermetic fastening may be
achieved by using methods that are well known to those skilled in
the art, such as, for example, braising.
[0275] In one embodiment, the surface area of the pacing electrode
204 is reduced by coating selected areas of the metallic distal
segment 210 with an insulating material. In one embodiment, the
insulating material is a tenacious thin coating such as, for
example, parylene. One or more selected small areas may be masked
off prior to coating to provide for one or more electrically
conducting pacing electrodes 204. Referring now to FIG. 23, in one
embodiment, the pacing electrode 204 includes an insulated band
222. In another embodiment, the pacing electrodes 204 include areas
on the distal anchor members 214 such that the pacing current is
applied preferentially to the left atrial wall of the septum. In
one embodiment, the pacing electrodes 204 include metallic
electrodes fastened to tips of one or more of the distal anchor
members 214. In one embodiment, the metallic tip electrodes are
made of tantalum, which has the desirable property that it can be
made as a porous, high surface area material. It will be familiar
to the skilled artisan that such materials reduce contact impedance
with tissue. Other materials known in the art to make effective
pacing electrodes include titanium nitride and a coating of finely
divided platinum called "platinum black." Tantalum has the
additional property of high x-ray density, which allows the anchor
tips to be visualized under fluoroscopy for verifying the
positioning and deployment of the anchor 214.
[0276] Referring now to FIG. 23, in another embodiment, two
insulating ceramic segments 216, 218 are provided, which divide the
sensor package housing 200 into distal, middle, and proximal
metallic segments 220, 222, and 224. In one embodiment, the distal
and proximal metal segments 220, 224 are substantially uncoated and
serve as a sensing electrode 202, while the middle metallic segment
222 includes the pacing electrode 204. In a further embodiment,
portions of the middle segment 204 are coated with a material such
as, for example, parylene, to produce one or more smaller area
pacing electrodes.
[0277] In one embodiment, the pacing and sensing electrodes 202,
204 of FIG. 22 and FIG. 23 are electrically coupled to pacing
electronics located within the sensor package 200. In another
embodiment, the sensor package pacing electronics are configured to
detect a specific electrical event within the heart, such as the
p-wave of the internal electrogram, as is well known to those
skilled in the art of electrophysiology, cardiology and cardiac
pacing. In one embodiment, the sensor package pacing electronics
are further configured to send a digital signal indicating a sensed
event, such as detection of the p-wave, to the pacing electronics
in the proximal housing, as described further below.
[0278] In one embodiment of the present invention, a defibrillator
and an implantable heart monitor (such as described above with
reference to FIG. 1 through FIG. 5) are combined to provide the
following functionality via an essentially standard
pacing/defibrillator lead with only two conductors: (1) provide
power to a physiologically optimized dosimeter (POD) measurement
module(s); (2) provide signaling for atrial and/or ventricular
pacing and sensing, (3) provide for atrial and/or ventricular
defibrillation through a third lead attached to a defibrillation
electrode; (4) provide for programming of the physiological sensor
package; and (5) provide measurement data from the physiological
sensor package(s) to the monitor/defibrillator housing for storage
and recovery by, e.g., a doctor or the patient via the patient
signaling module.
[0279] In one embodiment, digital signaling is used to provide for
power, two-way data communication, and pacing over a two-wire lead.
In one embodiment, digital signaling consists of dividing a "frame"
of a defined duration into a number of distinct sub-frame
intervals, each with a defined function, as shown in the pulse
timing diagram in FIG. 24. In one interval, a power pulse may be
provided to charge the power supply of the sensor/pacing module. In
one embodiment, the power pulse is provided during the first
interval of every frame, so that the power pulse defines the end of
one frame and the beginning of the next frame. In one embodiment,
power pulses are generated at a precisely timed frequency within
the generator module and this timing is used within the
sensor/pacing module(s) to adjust an internal RC or current source
clock for better synchronization between the distal sensor/pacing
module and the generator module at the proximal end of the lead.
Between one power pulse interval and the next, other intervals may
be defined as needed for the transmission of data and signals over
the lead. In one embodiment, the amplitude or magnitude of the
power pulse is the same as the amplitude or magnitude of the data
pulses, such as shown in FIG. 24. However, in other embodiments,
the amplitude or magnitude of the power pulse is greater than, or
less than the amplitude or magnitude of the data pulses. In one
embodiment, the amplitude of the power pulse does not vary between
pulses, and in another embodiment, the amplitude of the power pulse
varies between pulses, or within pulses.
[0280] In the embodiment described in FIG. 24, the next two
intervals are provided for signaling from the CRM module to the
sensor/pacing module(s). In one embodiment, these two intervals are
called the "download interval." The first interval is asserted by
the CRM module to command that a pacing stimulation pulse be
applied (e.g., A-pulse Trigger). The second interval is asserted by
the CRM module to indicate that commands producing a change in the
mode of operation of the sensor/pacing module are to follow (e.g.,
Programming Bit set). Following the download interval, an "upload
interval" may be provided for communication of information from the
sensor/pacing module back to the generator module. As shown in FIG.
24, this information may include a bit that, if asserted, indicates
an atrial and/or ventricular sensed event, and/or measurement data,
and/or status information about the current mode of operation of
the sensor/pacing module.
[0281] In one embodiment, the type of data following the A-sense
upload interval may be either upload or download data depending,
for example, on whether a programming or pacing command had been
asserted. In the embodiment of FIG. 24, if neither of the two
download bits has been asserted in the current or the previous
frame, the time intervals following the A-sense interval are used
by the sensor/pacing module to upload measured data, such as
pressure, temperature and electrogram (IEGM) waveform data. In
order to conserve power, the pressure, temperature and IEGM data
could be measured and output at a low duty cycle. If the
Programming Bit is asserted in the current frame, the sensor/pacing
module is set to listen for programming command bits sent by the
CRM module. If either the A-pulse trigger or the Programming Bit
was set in the previous frame, the sensor/pacer module provides
status information indicating whether the command was
successful.
[0282] In one embodiment, the download and upload intervals are
subdivided into data words, each containing a predefined number of
bits, so that multiple pieces of information are communicated. For
example, the download interval may consist of a pacing command
pulse followed by one or more programming bits. The upload interval
may consist of a sensing bit (set if P- or R-wave of internal
electrocardiogram is sensed by the measurement module), followed by
a predetermined number of bits of pressure data, followed by a
second predetermined number of bits of temperature data. All
signals, including pressure, IEGM, and temperature, may be
"alternated` in some fashion rather than being included in any
single frame, to allow for shorter frames and therefore more
frequent power supply support and synchronization. It will be clear
to one skilled in the art that data from additional sensors may be
appended in the same way. In one embodiment, additional checksum
bit(s) are added to guard against data transmission errors.
[0283] In one embodiment, the power and signaling pulses described
above are carried between the CRM module and the measurement
module(s) via a two-conductor lead. Each conductor is internally
connected within both modules. The first conductor may also be
attached to the "indifferent" electrode (as shown, for example, in
FIG. 31), which defines the baseline potential for sensing and
pacing. In one embodiment, a low impedance common conductor such as
drawn-filled-titanium (DFT) wire extends between the indifferent
electrode and the measurement module in order to prevent the
signaling pulses from affecting the sensing of the electrogram.
[0284] In another embodiment, the indifferent electrode 494 is
connected to the internal circuitry of the sensing/pacing module
476 by a third conductor 475 (as shown, for example, in FIG. 32).
The first conductor 490 is electrically isolated from the body.
Advantageously, this conductor 490 is physically contained by the
outer coaxial second conductor 492 and the housings 472, 476 at
each end. To ensure electrical isolation at the CRM package 472, a
spring contact (without a setscrew and seal) is provided on the
first, inner conductor 490 rather than on the outer conductor 492.
By providing a set screw to the outer conductor 492 only,
electrical isolation of the inner conductor 490 is preserved along
the entire lead length, from the proximal housing 472 to the distal
housing 476. In one embodiment, the outer conductor 492 extends all
the way from the proximal housing 472 to the distal housing 476,
thereby shielding the inner conductor 490 over its entire length,
including the portion or lead segment that extends between the
indifferent electrode 494 to the distal housing 476.
[0285] The measurement module stores electrical energy from one or
more power pulses and applies an appropriate pacing pulse to a
pacing electrode when a pacing command is received from the CRM
module during the download interval. Importantly, the distance
between the pacing electrode and the indifferent is substantially
reduced, thereby greatly reducing any induced voltages during
magnetic resonance imaging (MRI) or electrocautery procedures. In
one embodiment, the sensor/pacing module stores electrical energy
from one or more power pulses and applies an appropriate pacing
pulse to the pacing electrode when a pacing command is received
from the CRM module, for example, during the download interval. In
an alternative embodiment, pacemaker voltage and/or timing are
provided by circuitry within the sensor/pacing module, autonomous
from the CRM module. In both embodiments, the sensor/pacing module
may generate or store electrical energy for application of an
appropriate pacing pulse to the pacing electrode at intervals
defined by either the CRM module or the circuitry within the
sensor/pacing/measurement module itself. In another embodiment, the
pacing interval is modified or synchronized with a second digital
electrode in another location by the generator module by
downloading the appropriate command to the
sensor/pacing/measurement module.
[0286] In one embodiment, the circuitry includes current and
voltage limiting features known to those skilled in the art to
provide protection from defibrillator discharges, either from an
external or implantable defibrillator. In one embodiment,
series-connected oppositely oriented zener diodes are provided for
defibrillation protection as described, for example, by Langer
(U.S. Pat. No. 4,440,172, incorporated by reference herein).
[0287] Referring to FIG. 25, three embodiments are described to
implement a hybrid approach for performing pacing and physiological
sensing using the same lead.
[0288] In the first embodiment, the output voltage during the pacer
pulse is provided by a CRM device 306. Alternatively, in another
embodiment, an output voltage storage capacitor and a charge pump
are provided by a device contained within the intracardiac module
320.
[0289] Sensing may be performed according to at least two different
embodiments. In one embodiment, the circuitry is located in the
intracardiac module 320, and a digital signal is provided back to
the CRM 306 when a p-wave is detected. In the second embodiment, an
IEGM signal detected at the sense/pace electrode 328 is amplified
by an amplifier 333 and applied via switch 322 to the lead 323. For
both of these options, IEGM sampling is time-multiplexed in the
frame sequence.
[0290] Either on-chip or back-to-back Zener diodes 332 are provided
in the device 320, thereby keeping the RF path (during MRI) small
in order to improve immunity.
[0291] 2. Upgrade from Stand-Alone to Combination System
[0292] Referring now to FIG. 26A, in one embodiment, the same
sensor and lead 318 can be used either as part of a Stand-Alone
system (such as a heart monitoring system, pressure monitoring and
feedback system, HeartPOD.TM., POD, or apparatus for treating
congestive heart failure, as described above) or as part of a
combination system that includes a CRM or automated therapy system.
This flexibility allows for the implantation of a Stand-Alone
intracardiac module 320 that can be "upgraded" to include pacing
and/or defibrillation therapy if the need arises without having to
implant an additional lead. The combination system also allows the
communication coil module 302 of the apparatus for treating
congestive heart failure (such as that described above with
reference to FIG. 4) to be removed and replaced with a CRM 306.
Furthermore, in one embodiment, the sensor electronics (which in
one embodiment are located in a distal sensor package 320 implanted
within the patient's heart, as schematically illustrated in FIG.
26B) include the pace/sense circuitry that allows it to be used as
a smart "digital" electrode in conjunction with a CRM device, as
described below.
[0293] In an alternate embodiment, an additional lead conductor is
included to allow operation with pacing and sensing electronics
located within the CRM housing 306 of a CRM device. In one
embodiment, a sensor or sensor module 320 is coupled to the distal
end of a lead 318, which has a proximal IS1 connector 316, as is
familiar to those of skill in the art. In one embodiment, an
upgrade is performed by surgically opening the subcutaneous pocket,
unplugging the IS1 connector 316 from the RF coil antenna 302, or
pressure monitoring and feedback implanted module, and plugging the
lead 318 into an IS1 port 317 of a CRM housing 306, as described in
greater detail below.
[0294] In one embodiment, the intracardiac module (ICM) containing
the sensor is powered either by a pair of tuned coils, 302 and 303,
(Stand-Alone configuration) at 125 kHz (although any other suitable
frequency could be used) or "power" pulses from the implanted CRM
at a frame frequency (CRM configuration). In the Stand-Alone
configuration, data from the sensor is telemetered to a patient
advisory module (not shown) using reflected impedance. Other
telemetry schemes may also be employed, such as disclosed, for
example, in U.S. Pat. Nos. 4,681,111 and 5,058,581 to Silvian, both
incorporated herein by reference. Electronics provided within the
intracardiac module comprises circuitry that detects whether an
incoming signal is a 125 kHz signal (as may be provided by the
external patient advisory module, in one embodiment) or a frame
power pulse at a frequency between about 50 Hz and 20 kHz. (as may
be provided from a CRM device, in one embodiment). In one
embodiment, a frame rate between about 600 and 800 Hz is used. This
autosensing functionality allows the pressure monitoring and
feedback system described herein to be "upgraded," whereby the
additional functionality of a CRM system, such as a pacemaker or
defibrillator or other such device, is able to be provided by
merely changing, or swapping one implanted component, or module,
with another. At least two methods are provided for determining
which configuration (Stand-Alone or combination) is operable, as
described below with reference to FIGS. 26A-D. One method is based
on frequency discrimination and the other is based amplitude
discrimination. In both cases, the signals are half-wave rectified
by rectifier 300 to provide power for the sensor (and pace/sense)
electronics. As is recognized by the skilled artisan, full-wave
rectification could be employed as an alternative. Two embodiments
of rectifier 300 are provided in FIGS. 26C-D.
[0295] Referring now to FIG. 25 and FIG. 26B, in one embodiment, in
the Stand-Alone configuration (e.g., when a CRM 306 is not
present), the 125 kHz signal is output from a tuned coil 302 that
resides in a subcutaneous pocket. The 125 kHz signal is rectified
to provide DC power for the sensor electronics of the sensor module
320 and a 125 kHz clock for operation and timing. A shorting FET,
which in one embodiment is located within communications module
304, is placed across the 125 kHz input to provide a reflected
impedance signal that can be detected by the external device for
telemetry of the sensor(s) output. The FET is disabled after power
up until the POD has determined that the Stand-Alone configuration
is operable. Although full wave rectification could be used, in one
embodiment, half wave rectification is employed. Detection of the
unused half cycle is one of the methods used to differentiate
between the two modes of operation. In one embodiment, power is
turned off to the pacing and sensing electronics in the Stand-Alone
configuration to conserve power.
[0296] In one embodiment, in the CRM configuration, the sensor lead
is attached or coupled to a CRM device 306 that provides a power
pulse at a fixed frame rate, a pace trigger signal, and apparatus
for changing memory registers in the intracardiac module (ICM). The
power pulse is rectified to provide DC power for the ICM
electronics. The reflected impedance shorting FET used in the
Stand-Alone configuration is disabled at power up and in CRM mode.
As shown in FIG. 26B, a frame clock detector 308 is employed to
obtain the frame clock that is input to a DPLL 310 (digital phase
lock loop). The DPLL 310, by way of example, includes or is coupled
to an oscillator 311 with electronic frequency adjustment with its
output used for operation and timing for the ICM electronics. This
clock is fed into a divide by N counter, or bit counter, 312
through a clock select switch 314. The output of the bit counter
312 is coupled to the other input the DPLL 310 whose output is
connected to the frequency adjustment of the oscillator 311. This
provides for an internal clock, which is N times the frame clock
and is synchronized to the frame clock. In the Stand-Alone
configuration, the divide by N counter 312 receives its clock
signal from the 125 kHz clock divider 313. In another embodiment,
an analog PLL is used instead of a digital PLL. The DPLL 310 also
provides a signal to indicate the mode of operation (the frequency
discrimination method). If the DPLL 310 is locked at its limit (no
sync), then Stand-Alone operation is indicated. In the CRM mode,
the CRM device 306 goes to high impedance between power pulses
during the upload period, thereby allowing the ICM to send sensor
output(s) and a sense-detect signal to the CRM device 306. In one
embodiment, the output of the frame clock detector 308 is also used
to reset oscillator 311 and divide by N counter 312.
[0297] Since the physical connection is different between the two
modes of operation, the detection mechanisms for mode determination
can be optionally latched at power up and then disabled to conserve
power.
[0298] One embodiment of the present invention provides for a novel
variation of a standard IS1 header. In conventional IS1 headers,
typically a spring connector is employed for the outer conductor
and a setscrew is used for the inner conductor. Both the 125 kHz
for the Stand-Alone device and the digital power/signaling signals
of the combination device are isolated from the body, and
especially the heart, for patient safety. Advantageously, in one
embodiment of the present invention, the active conductor is the
inner conductor of a coaxial lead and a spring connector is used
for the inner conductor in the IS1 header, while the setscrew is
used to secure the outer conductor. This assures that, even in a
damaged lead or leaking setscrew seal, all leakage paths to the
body are completely surrounded by the common coax outer conductor,
and therefore isolated from the body.
[0299] In one embodiment, the system is designed to operate in at
least two different configurations, and in at least two modes of
operation. A first mode is the "Stand-Alone Configuration." A
second mode is "the CRM Combination" (or "Combination
Configuration"). One advantage of a multi-configuration system is
that it allows the device to be implanted as a Stand-Alone system
for CHF therapy and later to be upgraded for use with a CRM device
if the patient's condition changes. In the Combination
Configuration, in one embodiment, the sensor module 320 acts as a
pace/sense electrode for the CRM device.
[0300] In one embodiment, there are three modes of operation based
on the configuration: (1) A "Power-Up Mode" which is used to
automatically detect whether the Stand-Alone Configuration or the
Combination Configuration is present. This mode is entered into
when the power is applied to the sensor module 320. As described
below by way of example, at least two alternative methods are
described for detecting the configuration. Alternative methods will
be apparent to one skilled in the art; (2) A Stand-Alone
Configuration; and (3) A Combination configuration.
[0301] In one embodiment, the CRM module logic includes logic to
detect any problems with the sensor module 320. Should any
unrecoverable problem be detected, the CRM module stops the power
pulses to the sensor module 320 and restarts, thus allowing for a
new power-up sequence. In another embodiment, restart can be
limited to be under physician supervision.
[0302] The following paragraphs describe the functional components
of one embodiment of the upgradeable intracardiac module 320, with
reference to FIG. 26B:
[0303] Communication block: In one embodiment, a communication
block 304 is provided. In one embodiment, the communication block
304 is responsible for the bidirectional communication. The Mode
and PwrUp inputs define how the device operates. Incoming
communication in a preferred embodiment is by FSK on the 125 kHz
carrier for the Stand-Alone Configuration and by digital command
signals between power pulses for the Combination Configuration.
Outgoing communication in one embodiment is by reflected impedance
for the Stand-Alone Configuration and by digital signals between
power pulses for the Combination Configuration. During the power-up
mode, all outgoing communication is suppressed. The figure for
Combination Configuration signals depicts a RZ code. One skilled in
the art will understand that other encoding methods, such as NRZ,
Manchester, etc., can also be used in accordance with several
embodiments of the current invention.
[0304] Voltage Detector Block: In one embodiment, a voltage
detector block 322 is provided. In one embodiment, the voltage
detector block 322 detects the operating configuration after power
is applied (during the power-up mode). In one embodiment, it only
needs to be powered during this brief time and can be disabled to
conserve power. In one embodiment, the voltage detector block 322
detects whether or not there are 125 kHz excursions above Vdd,
which will occur in the Stand-Alone Configuration, but not in the
Combination Configuration.
[0305] Clock Detector Block: In one embodiment, a clock detector
block 308 is provided. In one embodiment, this block 308 is a
comparator with two thresholds that outputs a digital clock signal
from the signal on the lead. In the Stand-Alone Configuration, the
threshold is set to Vdd and the output is a 125 kHz square wave. In
both the Combination Configuration and Power-Up Mode, the threshold
is set to approximately 0.5 V below Vdd (although other thresholds
may be used) and the output is used to recover the frame sync which
are the power pulses in the combination mode and 125 kHz during the
power-up mode in the Stand-Alone Configuration. One reason for the
0.5 V threshold is to allow signaling pulses to have lower
amplitude than the power pulses and will not be erroneously
detected as clock pulses (and will also dissipate less power).
Alternatively, the midpoint supply voltage may be used as a
threshold, with equal amplitude power and signaling pulses,
provided that the DPLL 310 and related timing provides for a
defined gap between the last signaling pulse and the next power
pulse.
[0306] Clock Divider Block: In one embodiment, a clock divider
block 314 is provided. In one embodiment, this block 314 divides
down the 125 kHz to provide a bit clock in the Stand-Alone
configuration. It is disabled in the CRM configuration.
[0307] Oscillator block: In one embodiment, an oscillator block 311
is provided. In one embodiment, this block 311 contains a capacitor
that is charged up from Vss to a settable threshold voltage. A
short reset pulse is provided to fully discharge the capacitor
after the threshold reached and if a reset pulse is provided. The
threshold is determined by the oscillator control lines that
specify to either to increase or to decrease the threshold by a
small delta V. In an alternative embodiment, the capacitor is
arranged in a binary array and the DPLL 310 is an up/down
counter.
[0308] Clock Select Block: In one embodiment, a clock select block
314 is provided. In one embodiment, this block 314 switches the bit
clock to the sensor module's internal oscillator output for the CRM
Combination Configuration and during the power-up mode. For the
Stand-Alone Configuration, the bit clock 314 is switched to the
output of the 125 kHz clock divider.
[0309] Bit Counter Block: In one embodiment, a bit counter block
312 is provided. In one embodiment, this block 312 is a divide by N
counter that is reset by the Frame sync in the CRM configuration
and during power-up. It provides the bit timing sequence for each
frame. During power-up, in the Stand-Alone Configuration, it is
substantially held reset by the 125 kHz "frame sync" pulses.
[0310] DPLL Block: In one embodiment, a DPLL block 310 is provided.
In one embodiment, the DPLL 310 provides the feedback to control
the internal oscillator frequency to be N times the frame sync. In
one embodiment, it also determines the configuration during
power-up mode by detecting that the Bit counter 312 is stuck
reset.
[0311] Rectifier Block: In one embodiment, a rectifier block 300 is
provided. Two alternative embodiments are shown in greater detail
in FIGS. 26C-D. In the embodiment of FIG. 26C, Vdd is tied to the
outer lead winding which is tied to the Indifferent Electrode. A
schottky diode is provided to protect the CMOS from the positive
swing on the inner "Lead" winding in the Stand-Alone configuration.
Alternatively, a full wave rectifier could be used. A separate
charge pump and pacing output voltage storage cap is provided to
generate and store the pace voltage. In the second rectifier
embodiment, which is illustrated in FIG. 26D, the charge pump and
storage cap are omitted from the sensor module. Instead, a MOS
switch is provided between Vdd and the Indifferent. This switch is
normally ON but is switched OFF during a pacer pulse so that the
pace voltage is stored in the CRM device and switched out to the
distal electrode. Additional circuitry is provided to handle
start-up and well switching issues.
[0312] Control Circuit Block: Referring back to FIG. 26B, in one
embodiment, a control circuit block 324 is provided. In one
embodiment, this block 324 provides substantially all the memory
storage, logic and timing required for operation.
[0313] Measurement Circuit Block: In one embodiment, a measurement
circuit block 326 is provided. In one embodiment, this block 326
provides substantially all the measurement circuitry to measure
pressure, temperature, etc.
[0314] Input Amp & Filter Block: In one embodiment, an input
amp & filter block 328 is provided. In one embodiment, this
block 328 contains an AC coupled amplifier, filter and window
comparator for the detection of heart depolarization signals
(P-wave and/or R-wave). The circuits for this function are well
known in the art. This block 328 is shown connected to a separate
sensing electrode. Normally the pacing and sensing electrode are
the same, which is still possible in this invention by merely
shorting these points together. Advantageously, one embodiment
provides for the possibility of separate pacing and sensing
electrodes without having to have a separate lead conductor and
extra connector pin. This allows each electrode to be optimized
independently for each electrode. In addition, the recovery
discharge voltage is eliminated on the sensing electrode, allowing
for sensing of the induced P or R-wave for capture verification
and/or threshold tracking. This advantage is due to the inclusion
of the pacing & sensing electronics remotely in the sensor
module. If two distinct electrodes are employed, additional
defibrillator protection may be needed for the sense amplifier.
This protection is relatively easy because the impedances can be
much higher and the induced currents are easily handled.
[0315] Defibrillation Protection Block: In one embodiment, a
defibrillation protection block 330 is provided. In one embodiment,
this block 330 is composed of two back-to-back zener diodes or
other method as is known in the art.
[0316] One embodiment of an upgradeable system is illustrated in
FIG. 28 and FIG. 29. The system of FIG. 28 illustrates a
"Stand-Alone" embodiment, and includes an implantable housing 400
coupled to an implantable lead 402 with a connector 404. In one
embodiment, the housing 400 is the housing 7 as described above. In
another embodiment, the lead 402 is the lead 318 or lead 10 as
described above. In one embodiment, connector 404 is the IS1 header
316, IS1 port 317, or connector 10, as described above. The
connector 404 may be any connector known to those of skill in the
art used to couple an implantable lead to an implantable
housing.
[0317] The lead 402 is connected to a sensor module (not shown) as
described in greater detail above. The lead 402 also has an
indifferent electrode 406, which provides a non-stimulatory
electrical return path from the patient, as is well known to those
of skill in the art. The implantable housing 400 of the Stand-Alone
embodiment includes an antenna 408. In one embodiment, the antenna
408 is the antenna 162 or coil 302 as described in greater detail
above. The antenna 408 may be any coil of wire as is known to those
of skill in the art, which may be used for telemetry communications
with an external device, such as a patient advisory module (not
shown), as described in greater detail above with reference to
FIGS. 4 and 5. In one embodiment, the antenna 408 is coupled to the
lead 402 via the connector 404, and functions as described
above.
[0318] One embodiment of a "combination" unit is described with
reference to FIG. 29. As described above, in one embodiment, when
the Stand-Alone unit is upgraded to provide CRM functionality in
addition to left atrial pressure sensing and patient feedback, the
housing of the Stand-Alone system may be exchanged with the housing
of a combination system without having to provide an additional
lead for cardiac rhythm management.
[0319] As illustrated in FIG. 29, in one embodiment, the housing
400 of the combination unit is coupled to a lead 402 via a
connector 404 as described above. In one embodiment, the lead is
coupled to an indifferent electrode 406, also as described above.
In one embodiment, the housing 400 of the combination unit is the
same as the housing 400 of a Stand-Alone unit, or CRM housing 306,
as described in greater detail above.
[0320] The housing 400 of the combination unit includes an antenna
408, battery 410, telemetry module 412, communication and power
pulses module 414, programming module 416, and pacing circuitry
418. The battery 410 provides power to the components within the
housing 410, as well as those within the sensor module (not shown),
as describe above. The telemetry module 412 provides communication
between the combination unit and the patient advisory module (not
shown). The communication and power pulses module 414 control
communication between the sensor module (not shown) and the housing
400 components as well as power distribution to the sensor module
from the battery 410. Programming module 416 provides programming
control over the system, including the pacing module 418, which
controls the transmission of electrical pulses or stimuli as
required by the CRM device.
[0321] FIG. 29 illustrates one embodiment of a CRM Combination
configuration. In this configuration, the housing 400 contains a
battery 410 that powers both the CRM device and the sensor module
(not shown). The communication and power pulse circuit 414 provides
power to and communicates with the sensor module via the lead
conductor 402 using, in one embodiment, for example, the coding
scheme described with respect to FIG. 24. The communication circuit
414 also decodes physiological sensor signals, such as pressure
signals, a-wave and/or p-wave sense signals received from the
sensor module via the lead 402. Sense signals received by the
communication circuitry 414 are passed to the pacing circuitry 418
where they are used to determine if and when to provide a pacing
stimulus.
[0322] In one embodiment, the pacing circuitry 418 triggers a
pacing stimulus by sending a signal to the communication circuitry
414, which sets the appropriate pulse trigger bit to the sensor
module as described above with respect to FIG. 24. In one
embodiment, the pacing circuitry 418 delivers the pacing stimulus
to the lead 402 a predetermined interval after setting the pulse
trigger bit, and commanding the sensor module to allow the pacing
stimulus to pass from the lead 402 through the sensor module
electronics to the pacing electrode. In another embodiment, the
pacing stimulus is applied to the pacing electrode from a storage
capacitor within the sensor module when a pulse trigger bit is
received by the sensor module from the communication circuitry
414.
[0323] In one embodiment, various operational modes and parameters
are programmed using an external programming device (not shown)
that communicates with the implanted pacemaker transcutaneously
using telemetry system 412, which decodes programming commands from
a programmer and passes them to the programming circuitry 416. In
one embodiment, physiological sensor signals, such as but not
limited to pressure, temperature, or internal electrocardiogram
signals, are passed from the communication circuitry 414 to the
telemetry circuitry 412 for telemetry to the external patient
advisory module, such as the patient advisory module illustrated
and described above with reference to FIG. 4. In one embodiment,
physiological sensor signals are also communicated from the
communication circuitry 414 to the programming circuitry 416, where
they are used to at least partially to control the operation of the
pacemaker in response to the patient's condition.
[0324] 3. Automated Therapy
[0325] According to one embodiment of the current invention, a
method for treating cardiovascular disease in a medical patient
includes implanting a physiological sensor package and a therapy
delivery unit (e.g., the "treatment system") within the patient's
body, operating the physiological sensor package to generate a
signal indicative of a physiological parameter, communicating the
signals indicative of the physiological parameters to a signal
processing apparatus, operating the signal processing apparatus to
generate a signal indicative of an appropriate therapeutic
treatment, and communicating to the patient the signal indicative
of the appropriate therapeutic treatment. The patient may then
administer to him or herself the prescribed therapeutic treatment
indicated by the signal or instructions. In another embodiment, the
signal indicative of the appropriate therapeutic treatment is
communicated to an automated therapy unit to generate an automatic
therapy regime.
[0326] a. Dynamic Prescription
[0327] In one embodiment, the automatic therapy regime is based
upon a programmed dynamic prescription. "Dynamic prescription," as
used herein, shall mean the information that is provided to the
patient for therapy, including instructions on how to alter therapy
based on changes in the patient's physiologic parameters. The
instructions may be provided by a physician, practitioner,
pharmacist, caregiver, automated server, database, etc. The
information communicated to the patient includes authorizing new
prescriptions for the patient and modifying the patient's medicinal
dosage and schedule. The "dynamic prescription" information also
includes communicating information which is not "prescribed" in its
traditional sense, such as instructions to the patient to take bed
rest, modify fluid intake, modify physical activity, modify
nutrient intake, modify alcohol intake, perform a "pill count,"
measure additional physiological parameters, make a doctor's
appointment, rush to the emergency room, call the paramedics, etc.
One skilled in the art will understand that numerous other
instructions may be beneficially provided to the patient predicated
at least in part upon measurement of one or more physiological
parameters in accordance with various embodiments of the present
invention.
[0328] b. Therapy Delivery Units
[0329] According to another embodiment, a therapy delivery unit is
provided, including but not limited to a system for releasing
bioactive substances from implanted reservoir(s), a system for
controlling electrical pacing of the heart, and cardiac assist
devices including pumps, oxygenators, artificial hearts, cardiac
restraining devices, ultrafiltration devices, intravascular and
external counterpulsation devices, continuous positive airway
pressure devices, and a host of related devices for treating
cardiovascular conditions where knowledge of the left atrial
pressure would be beneficial for optimal therapy delivery. Cardiac
electrical pacing may be controlled in response to changes in
physiological parameters in accordance with the present invention
by, for example, AV delay optimization or any number of other
methods, as are well known to one skilled in the art of
cardiology.
[0330] According to one embodiment of the invention, the therapy
delivery unit is implanted according to the methods described
herein for the pressure transducer.
[0331] i. Drug Infusion
[0332] In one embodiment of the invention, a drug delivery unit is
provided. In this embodiment, intravenous or subcutaneous, bolus or
continuous infusion of drug from an implantable drug delivery unit
can be triggered or regulated by the signal processing apparatus
when certain predefined conditions are met. In one embodiment,
automatic drug delivery or other therapeutic measure is used as a
last resort "rescue mode" when the monitored physiological
parameters indicate the patient's condition requires urgent
therapeutic response. Typically, in "rescue mode", the patient's
condition is not amenable to a change in oral medication dose (see
"Dynamic Prescription"). Thus, in one embodiment, this invention
includes both the dynamic prescription with patient signaling, and
automated therapy via electrical stimulation, drug infusion, or
other therapy delivery unit. Drugs that may be so administered
include but are not limited to natriuretic peptides (e.g.,
Natricor), diuretics (e.g., furosimide), and inotropes (e.g.,
epinephrine, norepinephrine, dopamine, dobutamine, milrinone). In
one embodiment, rescue mode emergency drug infusion,
defibrillation, or other therapy is performed automatically based
at least in part on signals indicative of the patient's condition
derived from the one or more sensors of the invention. In another
embodiment, rescue mode therapy is initiated by the present
invention only after receiving doctor authorization to deliver the
therapy. In one embodiment, doctor authorization is given by
entering a password into the external patient
signaling/communication module. This permits potentially dangerous
emergency therapy to be delivered only after consultation with and
authorization by a qualified healthcare professional.
[0333] In one embodiment, dosimetry for multiple drugs or other
associated therapeutic devices is relayed based on parameter values
as input to a parameter-driven prescription. In one embodiment, the
system essentially replicates, in the home setting, the way
inpatients are managed based on their doctor's standing orders in
the Intensive Care Unit (ICU) of a hospital. In the ICU, nurses
periodically look at real-time physiologic values from diagnostic
catheters, and administer medications based on predetermined orders
by the patient's attending physician. One embodiment of the present
invention accomplishes the same thing. In one embodiment, wireless
communications technology is integrated with diagnostic and
treatment methods that are well established in cardiology. As such,
the system is designed to be convenient and time-efficient for both
the patient and his physician. The combination of monitoring key
physiologic parameters and the patient's own physician's
prescription drive a real-time feedback loop control system for
maintaining homeostasis. Thus, in one embodiment, the system
comprises an integrated patient management system tightly and
directly linking implantable sensor diagnostics with pharmacologic
and other therapies. As a result, this therapeutic approach enables
better, more cost effective care, improves out-of-hospital time,
and empowers patients to play a larger and more effective role in
their own healthcare.
[0334] In one embodiment, a portable system for continuously or
routinely monitoring one or more parameters indicative of the
condition of a patient is provided. Depending upon changes in the
indicated condition, the system determines, based on
parameter-driven instructions from the patient's physician, a
particular course of therapy. The course of therapy is designed to
manage or correct, as much as possible, the patient's chronic
condition. In one embodiment, the system communicates the course of
therapy directly to the patient or to someone who assists the
patient in the patient's daily care, such as, for example, but not
limited to, a spouse, an aid, a visiting nurse, etc.
[0335] C. Telemetry
[0336] In one embodiment of the invention, one or more signals are
communicated between the permanently implanted components of the
system and a component of the system external to the patient's
body. In one embodiment, signaling from the implanted to the
external components is achieved by reflected impedance using radio
frequency energy originating from the external device, and
signaling from the external components to the internal components
is achieved by frequency or amplitude shifting of radio frequency
energy originating from the external device. Thus, in this
embodiment, the current invention allows for telemetry of data from
within the heart without transmitting radio frequency energy from
the implanted device, advantageously resulting in significantly
reduced power consumption compared to implants that perform
telemetry by transmitting signals from within the body.
[0337] In another embodiment, signaling from the implanted to the
external components is achieved through the metal housing of the
implanted device using the method of Silvian (U.S. Pat. No.
6,301,504) incorporated by reference in its entirety herein.
[0338] In yet another embodiment, signaling from the implanted
housing containing components of a CRM device is achieved via an
antenna embedded within a dielectric around the periphery of the
housing, as taught, for example, by Amundson et al. in U.S. Pat.
No. 6,614,406, included herein by reference.
[0339] D. Power
[0340] In one embodiment of the invention, the implanted apparatus
is powered by a battery located within an implanted housing,
similar to that of a cardiac pacemaker, as is well known in the art
of cardiac pacing. In another embodiment, the implanted apparatus
is powered by an external power source through inductive,
acoustical or RF coupling. In one embodiment, power is provided to
the implanted device using 125 kHz emissions emitted from an
electrical coil placed outside the body. In one embodiment power
and data telemetry are provided by the same energy signal. In one
embodiment of the system a second electrical coil is implanted
inside the body at a location under the skin near the patient's
collarbone, similar to the placement of the generator housing of an
implantable pacemaker. In one embodiment, the implanted module
includes an internal power source such as a battery, or it can be
powered transcutaneously by induction of radio frequency current in
an implanted wire coil connected to the module to charge an
internal power storage device such as a capacitor.
[0341] E. Physical Location of System Components
[0342] In one embodiment of the present invention, the apparatus
for diagnosing and treating cardiovascular disease is modular and
consists of a plurality of modules. Each module contains hardware,
and may contain one or more software programs. The component
modules can be physically located in different places and their
functions can differ dependent on the particular design of the
modules. FIG. 4 shows one embodiment of the current invention, in
which the first implantable module 5 of the apparatus is implanted
within the patient. A patient advisory module 6 is located external
to the patient's body and generally resides with the patient or his
direct caregivers. A third module (not shown in FIG. 4) may reside
with the physician. Each module performs multiple functions and
some of the functions may be performed on multiple modules. In one
embodiment, the modules consist of component sub-modules that
perform a particular function, such as described above.
[0343] 1. Leads
[0344] Although the pressure transducer in the embodiment produces
an electrical signal indicative of pressures in its vicinity and,
accordingly, an electrical lead is used to transmit the signals to
the electronic circuitry, other types of pressure transducers may
be used as well. For example, the pressure transducer and lead
might comprise a tube filled with an incompressible fluid leading
from the site in the body where the pressure is to be measured back
to a transducer in another location. Signals in the form of
pressures in the incompressible fluid indicate pressures at the
site of interest, and those pressures are sensed by the transducer
and utilized by the electronic circuitry in generating signals
indicative of appropriate therapeutic treatments. Signals in other
forms may be used as well and may be transmitted, for example, by
fiber optic means, or by any other suitable electrical,
electro-mechanical, mechanical, chemical, or other mode of signal
transmission.
[0345] Moreover, although the signal lead in one embodiment is of
an appropriate length so that the housing containing the electronic
circuitry can be implanted in the region of the patient's shoulder,
in alternative embodiments the lead may be of virtually any useful
length, including zero. In one embodiment, an integrated unit is
used in which the pressure transducer is disposed directly on the
housing and the entire device is implanted inside or very near to
the site at which pressure measurement is desired, for example the
left atrium of the patient's heart.
II. System Operation
[0346] A. Signal Processing
[0347] FIG. 27 is a schematic diagram of operational circuitry that
in one embodiment is located inside the housing 7 (not shown) and
is suitable for use in accordance with one embodiment of the
present invention. The apparatus depicted in FIG. 27 includes
digital processors, but the same concept could also be implemented
with analog circuitry, as is well known to those of skill in the
art.
[0348] As described above, in one embodiment, the system of the
invention includes a pressure transducer 73 permanently implanted
to monitor fluid pressure within the left atrium of the patient's
heart. Moreover, the system may include one or more additional
sensors 75 configured to monitor pressure at a location outside the
left atrium, or a different physical parameter inside the left
atrium or elsewhere. For each sensor 73, 75, a sensor lead 77, 80
conveys signals from the sensor 73, 75 to a monitoring unit 82
disposed inside the housing of the unit. Alternatively, several
sensors may be located in a compact sensor package or sensor module
as, for example, illustrated in FIGS. 1, 2, 4, 22 and 23. In this
case, the several sensors may share a single sensor lead for
conveying signals from the sensors to the monitoring unit or a
telemetry antenna. It should also be noted that the sensor lead
connecting the pressure transducer to the monitoring apparatus
might also be combined with or run parallel to another lead such as
an electrical EKG sensor lead or a cardiac pacing lead, either of
which might be placed in or near the left atrium.
[0349] In one embodiment, when the signal from the left atrial
pressure transducer 73 enters the monitoring unit 82, the signal is
first passed through a low-pass filter 85 to smooth the signal and
reduce noise. The signal is then transmitted to an
analog-to-digital converter 88, which transforms the signals into a
stream of digital data values, which are in turn stored in digital
memory 90. From the memory 90, the data values are transmitted to a
data bus 92, along which they are transmitted to other components
of the circuitry to be processed and archived. The stream of binary
digital values may be immediately transmitted to a telemetry device
external to the patient one bit at a time as they are generated
from the most significant bit to the least significant bit by a
successive approximation analog-to-digital converter. An additional
filter 95, analog-to-digital converter 97, and digital memory area
100 may be provided as shown for each optional sensor 75 whenever
such a sensor 75 is present. In another embodiment, several sensors
share one analog-to-digital converter.
[0350] In one embodiment, the digital data on the data bus 92, are
stored in a non-volatile data archive memory area 103. The archive
103 stores the data for later retrieval, for example, by a
physician at the patient's next regularly scheduled office visit.
The data may be retrieved, for example, by transcutaneous telemetry
through a transceiver 105 incorporated into the unit. The same
transceiver may serve as a route for transmission of signals into
the unit, for example, for reprogramming the unit without
explanting it from the patient. The physician may thereby develop,
adjust, or refine operation of the unit, for example, as new
therapies are developed or depending on the history and condition
of any individual patient. By way of an additional example,
reprogramming the implanted device could include changing the
sampling frequency for digitizing the pressure, IEGM or other
waveforms, or selecting which sensor data is to be monitored.
Devices for transcutaneous signal transmission are known in the art
in connection with pacemakers and implantable cardiac
defibrillators (collectively known as cardiac rhythm management
apparatus), and the transceiver used in the present invention may
be generally similar to such known apparatus.
[0351] In one embodiment of the present invention, the digital data
indicative of the pressure detected in the left atrium, as well as
data corresponding to the other conditions detected by other
sensors, where such are included, are transferred via the data bus
92 into a central processing unit 107, which processes the data
based in part on algorithms and other data stored in non-volatile
program memory 110. The central processing unit 107 then, based on
the data and the results of the processing, sends an appropriate
command to a patient signaling device 113, which sends a signal
understandable by the patient and based upon which the patient may
take appropriate action such as maintaining or changing the
patient's drug regimen or contacting his or her physician.
[0352] Circuits or software for extracting relevant components from
a pressure waveform are familiar to those skilled in the art. For
example, a low pass filter element may be used to extract the
long-term average, or "DC" component. In one embodiment, the
outputs of overlapping low pass filters, one designed to include
only frequencies lower than respiratory cycle frequencies, and the
other designed to include respiratory but not cardiac cycle
frequencies, are sampled at a fixed time in each cardiac cycle and
subtracted to derive the respiratory component. In general, the
respiratory contribution to the waveform is negative during
inspiration and positive during expiration, with a mean
contribution of zero. Thus, the long-term average of the pressure
waveform is equal to the average of the cardiac component. The term
of the long-term average is chosen to be long compared to the
respiration rate but short compared to the rate of mean pressure
change due to changes in a change in the patient's condition, so
that slowly changing physiological information relevant to managing
the patient's condition is not lost.
[0353] B. Signal Communication
[0354] In several embodiments of the invention, the patient
signaling device 113 comprises a mechanical vibrator housed inside
the housing of the system. In one embodiment, the vibrator delivers
a small, harmless, but readily noticeable electrical shock to the
patient. In some embodiments, a low power transmitter configured to
transmit information transcutaneously to a remote receiver, which
could include a display screen or other means for communicating
instructions to the patient. In one embodiment, the system includes
communication devices for communicating information back to a base
location. These telecommunication devices and methods include, but
are not limited to cellular or land-line telephone equipment or a
device connected to the Internet, for communicating information
back to a base location. In one embodiment, these telecommunication
devices and methods are used to transmit information concerning the
patient's condition back to a hospital or doctor's office, or to
transmit information concerning the patient's prescription usage
back to a pharmacy. In another embodiment, these telecommunication
devices and methods may be used bidirectionally such that the
physician, clinic, hospital, pharmacy, disease management service,
database, etc., may modify patient instructions and dynamic
prescriptions based on the information communicated from apparatus
coupled to the patient.
[0355] In one embodiment, the signal processing and patient
signaling components of the invention are combined into a patient
advisory module, external to the patient's body. The patient
advisory module further comprises a telemetry module to receive
pressure and other physiological data from the implanted sensor
system via wireless telemetry. This configuration has the advantage
that the external device may be based in part on a general purpose
computer such as a personal data assistant (PDA), allowing
increased flexibility and complexity in signal processing,
prescription algorithm processing, as well as providing
telecommunications or other wire-based or wireless communications
capability. Wireless communication platforms include, but are not
limited to devices supporting 802.11b Wireless Networking (Wi-Fi)
or the Bluetooth short range digital radio standard for wireless
personal area networking.
[0356] An additional advantage of this configuration is that it
provides essentially unlimited storage for digital physiological
data from the patient, as well as for information on medications
and other relevant information to help the patient and physician
manage congestive heart failure.
[0357] Yet a further advantage of the externalized patient
signaling device component is that a much richer and easier to use
interface with the patient is facilitated using a display screen
and/or audio communication with the patient. In one embodiment, a
reminder function is incorporated in the external device such that
the patient is prompted to initiate measurement just prior to
scheduled medications or other therapy. The patient is then advised
of the appropriate doses of medications and/or other therapies
based on the measurements and his physician's dynamic
prescription.
[0358] In one embodiment, the patient advisory module is external
and serves as a treatment and medications record. In this use, the
patient will be asked to verify which of the prescribed medications
were taken and which were, for whatever reason, were skipped, thus
creating a record of compliance with the dynamic management
program. This function will permit the physician to better manage
the patient and, additionally, will improve patient compliance. Yet
another advantage of the externalized patient advisory module is
that it can be easily integrated with a cellular telephone or
PDA/cell phone combination, allowing automated telemetry of alerts
and/or physiological data to a remote health care provider such as
the patient's physician, hospital, nursing clinic, or monitoring
service.
[0359] Apparatus as described herein may also be useful in helping
patients comply with their medication schedule. In that case, the
patient advisory module could be programmed to signal the patient
each time the patient is to take medication, e.g., four times
daily. This might be done via an audio or vibratory signal as
described above. In versions of the apparatus where the patient
signaling device includes apparatus for transmitting messages to a
hand held device, tabletop display, or another remote device,
written or visual instructions could be provided. In one
embodiment, apparatus generates spoken instructions, for example,
synthesized speech or the actual recorded voice of the physician,
to instruct the patient regarding exactly what medication is to be
taken and when.
[0360] Where the system includes apparatus for communicating
information back to a base location, e.g., the hospital, doctor's
office, or a pharmacy, the system in one embodiment, tracks the
doses remaining in each prescription and to reorder automatically
as the remaining supply of any particular drug becomes low.
[0361] In one embodiment of this invention, the external device
communicates with a personal computer (PC) in the doctor's office
either directly when the patient is present for an office visit, or
via electronic communications, including, but not limited to, a
telephone modem or the internet. During this communication, data is
uploaded from the external device to the PC, including the records
of physiological measurements, symptoms, and medication compliance,
as well as information regarding the operation and calibration of
the implanted device. Software on the PC displays the patient
information, and the doctor enters a new dynamic prescription or
edits the existing one. The PC then downloads the new or edited
dynamic prescription to the external device. Re-calibration of the
pressure transducer in the external device may be performed
relative to a reference manometer in the physician's office.
[0362] In one embodiment, the physician's PC maintains a database
of all the patients under medical management by the physician using
the device of this invention. The database includes the patients
identifying, demographic, and medical information, the implantable
device's unique identification number. For each patient, the
database maintains a record of all data uploaded from the external
device, device calibration records, patient dynamic prescription
records, and compliance records.
[0363] In one embodiment, data stored in the external patient
advisory module is uploaded to the physician's PC at the time of
the patient's regular office visit. The external device is placed
in a data interface cradle connected to the PC, and the data is
transferred. In one embodiment of the data transfer, the external
device is a modified personal data assistant such as a PALM
PILOT.TM. (Palm Computing, Inc.), and the data interface cradle is
the cradle used by such PDA devices for data synchronization with a
personal computer.
[0364] In another embodiment, the data from the external device is
uploaded to the physician PC via the Internet, telephone, or
cellular telephone network. In this case, the data may be uploaded
at regular intervals, or whenever the patient or physician
determines there is a need for physician review of the patient's
management.
[0365] The prescription editor is a software program on the
physician's PC that allows the physician to create, view, and
modify the dynamic prescription for each patient. The dynamic
prescription may consist of sets of prescribed treatments depending
on the values of one or more physiological measurements, and/or
patient symptoms, and/or changes and/or rates of change of
measurements or symptoms (collectively, input parameters). A
prescription editor allows the physician to define thresholds for
each input parameter and to define the combination of treatments to
be administered for each possible combination of input parameters.
In one embodiment, the prescription editor has a graphical user
interface that displays the possible combinations of input
parameter ranges and the corresponding treatments in a way that the
physician can clearly see that all possibilities have been defined
according to his intended management of the patient. In another
embodiment, the prescription editor provides for the entry and/or
editing by the physician of a set of rules relating data collected
from the patient and treatments to be administered or instructions
to be followed by the patient.
[0366] In one embodiment, the revised dynamic prescription and/or
calibration data is downloaded from the physician's PC to the
external device in the same way that data is uploaded from the
external device to the physician's PC. Such downloading and/or
uploading may occur, for example, by connecting the patient's
external device to the physician's PC by direct hardwire connection
(e.g. serial interface), by wireless connection, or via the
Internet. In one embodiment, a unique identification number from
the external device is used to verify the correct match between the
prescription and the patient. This unique identification number is
obtained by the external device from the implanted device, which
has a unique identification number programmed into its integrated
processor chip at the time of manufacture. In one embodiment, a
27-bit unique identification code is permanently programmed into
the implanted device at the time of manufacture. This
identification number is sent along with data communicated from the
implanted device to the external device to uniquely identify the
implanted device to the external device software.
[0367] C. Power Management
[0368] In one embodiment, the circuitry of the invention may also
include a power management module 115 configured to power down
certain components of the system between times when those
components are in use. Such components include, but are not limited
to, analog-to-digital converters 88, 97, digital memories 90, 100,
and central processing unit 107, as shown in FIG. 27. This helps to
conserve battery power and thereby extend the useful life of the
device so that it can remain operational inside the patient's body
for extended periods between maintenance or replacement. Other
circuitry and signaling modes may be devised by one skilled in the
art.
[0369] In one embodiment, the implanted pressure monitor operates
on transmitted power from outside the body, eliminating the need
for an implanted battery. This approach is particularly well suited
when periodic, as opposed to continuous, monitoring is required. In
one embodiment, 125-kHz radio-frequency energy is transmitted from
an external coil, through the patient's skin, and received by an
implanted antenna coil connected to the electronics package of the
implantable pressure monitor, as described above. The signal in the
antenna coil is rectified and used to charge a capacitor, which in
turn powers the measurement electronics. Low power telemetry of the
measured data is performed by varying the impedance of the antenna
coil circuit. In still another embodiment, the coil antenna is
incorporated into or immediately adjacent to the pressure sensor
within the heart.
III. Digital Pacemaker Lead and Electrode
[0370] A. Overview of Pacemaker Technology
[0371] As described above, in several embodiments a cardiac rhythm
management apparatus includes a pacemaker. In one embodiment, the
cardiac rhythm management apparatus includes a conventional "analog
electrode." A conventional pacemaker is a pacemaker where an
electrical stimulus is generated in a proximally located housing,
or generator unit (which in one embodiment is implanted
subcutaneously near the patient's shoulder), and travels through an
electrical conductor in a pacemaker lead to a distal electrode,
where it is delivered to a location within the patient's heart, as
described in greater detail above. In addition, in a conventional
pacemaker, sensed signals from the electrode are conducted in
analog form from the heart to the proximal housing, where they are
amplified and used to control pacing. FIG. 30, described in detail
below, illustrates one embodiment of an analog pacemaker.
[0372] Alternatively, in another embodiment, the cardiac rhythm
management apparatus includes a "digital electrode." In one
embodiment, as used herein, a digital pacemaker shall be given its
ordinary meaning and shall also mean a pacemaker in which digital
signals, including energy pulses, are communicated between the
proximal housing, or generator unit, and a distal module. In one
embodiment, the distal module comprises a digital electrode module,
as described below. In another embodiment, the distal module
comprises both a digital electrode and a sensor package or module
as described above with reference to FIG. 22 and FIG. 23. In one
digital pacemaker embodiment, the digital signals include control
signals to control the transfer of energy stored in the proximal
housing to an energy storage device in the distal module. Energy
pulses are transmitted from the proximal housing to the distal
module, where the energy is stored in the distal module until
delivery to the patient's heart. In another embodiment, the digital
signals include sensor signals that are transmitted from the distal
module to the proximal housing, from which they may be telemetered
to an external device, such as a patient signaling device, as
described in greater detail above. As described in greater detail
below with respect to FIG. 31, the distal module may comprise a
sensor housing that includes electrodes, sensors, and electronic
circuits. In other embodiments, as described in greater detail
below, the distal electrode may include only a single electrode and
electronic circuits.
[0373] B. Conventional Pacemaker Technology
[0374] FIG. 30 illustrates one embodiment of a conventional
pacemaker 450 (sometimes referred to herein as an analog pacemaker)
in accordance with one embodiment of the present invention. The
conventional pacemaker 450 includes a generator 452, lead 454,
first and second electrodes 456, 458. The first and second
electrodes 456, 458 are electrically coupled to the generator 452
with first and second conductors 460, 462, which travel at least
partially within the lead 454.
[0375] As described above, the generator 452 is generally implanted
subcutaneously near a patient's shoulder, and provides an
electrical stimulus across the electrodes 456, 458, which is in
contact with the medical patient's heart. The electrode in contact
with the heart, e.g., the first electrode 456, which provides such
stimulation, is also referred to as a pacing electrode 456. The
second electrode 458 may or may not be in contact with the
patient's heart, and is also referred to as the indifferent
electrode 458. In one embodiment, the indifferent electrode 458 is
not located within the patient's heart.
[0376] In one embodiment, a stimulating electrical pulse is
produced by the generator 452 and travels through a conductor 460
located within the electrically insulated lead 454, to the pacing
electrode 456, where the stimulating pulse is delivered to a
location within the patient's heart. In one embodiment, the pacing
electrode 456 is placed in the apex of the right ventricle of the
patient's heart.
[0377] In one embodiment, the lead 454 is a bipolar lead, such as
illustrated in FIG. 30. As shown in FIG. 30, the bipolar lead 454
includes two conductors 460, 462. One conductor is connected to a
pacing electrode 456 located at the lead's 454 distal end. The
other conductor 462 is connected to an indifferent electrode 458,
located proximal the distal end of the lead 454. In one embodiment,
the indifferent electrode 458 is a ring electrode, although other
types of electrodes may be used, as is well known to those of skill
in the art.
[0378] In another embodiment (not illustrated), the lead is a
unipolar lead, which includes only one electrode, that is located
at the lead's distal end. In such embodiment, the indifferent
electrode is provided at some other portion of the lead, as part of
the metallic housing of the generator, or coupled to a second lead.
In one embodiment, the unipolar lead has a single conductor which
couples the generator to a single pacing electrode located at the
lead's distal end.
[0379] a. Sensing Functionality
[0380] Referring again to FIG. 30, the pacemaker 450 is able to
measure or sense the natural electrical activity within the heart
through a sensing electrode. The sensing electrode is incorporated
with the lead 454. As illustrated, the pacing electrode 456 is also
able to operate as a sensing electrode 456. By sensing the
electrical activity within the heart, the pacemaker 450 is able to
adjust, withhold, or apply a stimulation in response to the sensed
electrophysiological condition.
[0381] There are limitations, however, to using the same electrode
for pacemaker sensing and pacing. For example, sensed electrical
signals are generally smaller in magnitude that pacing pulses, and
are generally amplified by an amplifier 330 before being processed
by the pacemaker generator. In addition, an ideal sensing electrode
should have a large surface area, while an ideal pacing electrode
should have a small surface area to minimize power requirements. In
addition, after pacing pulses are delivered, there is a time
interval, such as a delay interval, that occurs before sensing may
be performed with the single electrode. Such a time interval is
provided generally because the relatively high pacing pulse voltage
persists for some time on the lead and conductor due to lead
capacitance. Potentially important electrophysiological data may be
lost during this time interval. One example of such data is the
tissue's response to a pacing pulse, known as the "evoked
response." Detection of evoked responses can be used by the
pacemaker to determine whether capture has or has not occurred,
allowing the pacemaker to adjust to changing threshold levels.
[0382] The limitations and disadvantages of a single electrode
pacemaker may be overcome by providing a lead with separate sensing
and pacing electrodes. However, such lead would generally require
separate sensing and pacing conductors as well, which
disadvantageously increases lead diameter, and increases the number
of connectors required.
[0383] b. Multiple Conductor Leads
[0384] In one embodiment, the pacemaker lead also includes one or
more physiological sensors in addition to the electrode or
electrodes. In such embodiment, the lead provides the electrical
conductors and connections required to power the sensor(s), and to
conduct the sensor signal(s) to the pacemaker generator. However,
increasing the number of electrical conductors within the lead
disadvantageously increases the diameter and decreases the
flexibility of the lead, and/or requires the conductor diameters to
become smaller. Smaller conductors are generally weaker, break more
frequently over time, and are less reliable. Smaller diameter
conductors also generally have higher electrical resistance, which
results in an undesirable voltage drop between the generator and
pacing electrode(s). Increasing the number of conductors within the
lead also increases the complexity of the connector that couples
the lead to the pacemaker generator.
[0385] Multiplexing may be used to switch the function of
conductors between pacing and sensing, in order to reduce the
number of conductors within the pacemaker lead. Such techniques are
taught by Barcel in U.S. Pat. No. 5,275,171 and Weijand, et al. in
U.S. Pat. No. 5,843,135, both incorporated by reference herein.
Although such methods may reduce the number of connectors within a
pacemaker lead, they do so by sharing the remaining conductors
between several analog signals, including the pacing stimulus. Such
analog signals may contain electrical nose due to muscular
activity, radiofrequency (RF) interference, and potential
cross-talk between physiological and electrical sensing signals. In
addition, lead conductors that carry analog signals act as antennas
for RF noise and for induced voltages from RF energy sources, such
as magnetic resonance imaging (MRI) scanners. RF noise on the sense
conductor may cause erroneous pacing, even with sophisticated
digitally filtering algorithms as are commonly used by and known to
those of skill in the art. In addition, MRI scanning is
contra-indicated for patients with implantable cardiac pacemakers
because of the risks of inducing voltages from such procedures.
[0386] The digital electrode embodiments of the present invention
solve these and other problems, as described in greater detail
below.
[0387] C. Digital Electrode Technology
[0388] FIG. 31 illustrates a digital pacemaker in accordance with
one embodiment of the present invention. Digital pacemaker 470
includes a proximal housing 472, a lead 474, and a distal module
476. In one embodiment, the proximal housing 472 is approximately
the same size and shape of the analog pacemaker 450 generator 452,
as illustrated in FIG. 30. In another embodiment, the proximal
housing 472 is smaller than the generator 452.
[0389] In one embodiment, the proximal housing 472 includes an
antenna 478, telemetry module 480, and energy storage device 482,
charge pump 496 and pacing capacitor 327. In one embodiment, the
distal housing 476 includes an energy storage device 484, a control
module 486, and an electrode and sensor module 488. (In one
embodiment, the distal housing 476 is the sensor package or module
200 shown in FIG. 22 and FIG. 23.) A lead 474 couples the proximal
housing 472 to the distal housing 476, and includes first and
second conductors 490, 492 to facilitate communication
therebetween. In one embodiment, the lead 474 comprises an
indifferent electrode 494 in electrical communication with lead
conductor 492.
[0390] The antenna 478 and telemetry module 480 are used to
communicate with an external device, such as a programmer, or
patient advisory module, as described in greater detail above. In
addition, in another embodiment, the antenna 478 and telemetry
module 480 are used to receive energy from an external device and
store that energy within energy storage device 482. In another
embodiment, energy received from an external device is delivered
through the antenna 478 and telemetry module 480 directly to the
distal module 476, where it is stored in energy storage device 484.
Energy storage device 482, 484 may include a battery, capacitor, or
other electrical energy storage circuit or device as is well known
to those of skill in the art.
[0391] In one embodiment, the control module 486 includes a
microprocessor, microcontroller, or discrete digital and analog
control circuits, as are well known to those of skill in the art.
The control module 486 controls the transfer of stored energy from
the proximal energy storage device 482 to the distal energy storage
device 484, as well as the transfer of stored energy from the
distal energy storage device 484 to the patient's heart via the
electrodes of the electrode and sensor module 488. In one
embodiment, energy is transferred from the proximal housing 472 to
the distal module 476 according to the digital communications
protocol and timing diagram described above with respect to FIG.
24. In such embodiment, the proximal housing 472 includes a CRM
Module, and the distal module includes an LAP Module (as described
in FIG. 24). In another embodiment, the distal module 476 includes
the device 320, POD 320, or sensor module 320, as described in
greater detail above, with respect to FIG. 25.
[0392] In one embodiment, the electrode and sensor module 488
includes at least one electrode as described above. In one
embodiment, the electrode and sensor module 488 includes an
electrode for providing pacing stimuli to the heart, and a separate
sensing electrode (not shown) to measure and/or sense the
electrical activity of the heart. In another embodiment, the
electrode and sensor module 488 includes at least one physiological
sensor for measuring a physiological parameter of the heart. In one
embodiment, the physiological sensor is a pressure sensor,
thermometer, ultrasonic sound emitter, ultrasonic sound receiver,
IEGM sensor and/or any other sensor as described above, or as known
to those of skill in the art. In one embodiment, the physiological
parameter is a pressure indicative of the pressure within the left
atrium of the heart, a temperature indicative of the patient's core
temperature, an acoustic signal indicative of a volume of a chamber
of the heart, or an electrical signal indicative of the pulsing
and/or beating of the patient's heart.
[0393] In one embodiment, the electrode and sensor module 488
includes a full Wheatstone bridge strain gauge, coupled to four
conductors (not shown). In another embodiment, the electrode and
sensor module 488 includes a half-bridge strain gauge, coupled to
three conductors (not shown). Even in such embodiments, only two
conductors 490, 492 extend through the lead 474 to the proximal
housing 472.
[0394] FIG. 32 illustrates another configuration of a CRM device
with a digital electrode according to the present invention. This
embodiment is similar to that shown in FIG. 31, except that the
charge pump 496 and pacing capacitor 327 are now located within the
digital electrode housing 476 rather than the proximal housing
472.
[0395] In a conventional pacemaker, and in the embodiment of FIG.
31, the pacing pulse charge is first stored on a capacitor 327 in
the proximal housing, and is then applied to the pacing electrode
via the lead 474. In such embodiment, lead 474 resistance, which in
one embodiment is as high as 150 Ohms, reduces the voltage applied
to the tissue during pacing, requiring capacitor 327 to be charged
to a higher voltage to compensate. In the embodiment of FIG. 32,
the pacing capacitor 327 is located in the distal module 476, so
the pacing voltage is applied directly to the pacing electrode 488,
without passing through the lead resistance.
[0396] In one embodiment, the electrical components in the proximal
housing 472 operate at a voltage lower than that required for
pacing, and are fabricated with 0.12 .mu.m CMOS technology. In such
embodiment, the size and power consumption of the proximal housing
472 is reduced. In another embodiment, the electrical components
within the distal module 476 are fabricated with 0.5 .mu.m CMOS
technology in order to accommodate the greater pacing voltages not
found, generated or transmitted to or from the proximal housing
472. Other semiconductor manufacturing techniques and line-widths
may be utilized, as is well known to those of skill in the art.
[0397] In one embodiment, sensor signals are processed by the
control module 486 within the distal module 476, which is generally
implanted within the patient's heart. By sensing and processing
within the heart (and not communicating the sensed signal through a
lead to a proximal housing for processing), susceptibility to noise
is essentially eliminated.
[0398] In another embodiment, separate sensing and pacing
electrodes are provided. By providing separate sensing and pacing
electrodes, each can be optimized in shape, dimension, area,
contact area with tissue, and/or materials. For example, in one
embodiment, a pacing electrode has a small surface area to reduce
the voltage required for pacing, and the sensing electrode has a
large surface area to minimize impedance, or resistance. One
embodiment of separate, optimized sensing and pacing electrodes is
illustrated and described with reference to FIG. 22 and FIG. 23. In
another embodiment, additional sensors, sensing and pacing
electrodes are provided without increasing the number of conductors
traveling through the lead 474.
[0399] In one embodiment, the electrode and sensor module 488
includes a pressure sensor and a pressure sensor lead (not shown).
The pressure sensor lead extends from the distal module 476 to the
pressure sensor, which in one embodiment is implanted within a wall
of the heart. In such embodiment, the pressure sensor includes a
housing which may be used as as an electrode for pacing, sensing,
or for delivering defibrillation stimuli. In one embodiment, the
pressure sensor lead provides pacing or defibrillation stimuli to
the pressure sensor housing, which acts as an electrode for pacing
or defibrillation.
[0400] In several embodiments, the distal electrode module
comprises the defibrillation protection circuitry 330, as shown for
example in FIGS. 31, 32, and 33. Referring now to FIG. 33, a CRM
device is shown comprising a proximal housing 472, a lead 474, and
a distal electrode module 476, in which the defibrillation
protection is located in the distal electrode module. This has the
advantage that the conduction path from the pacing electrode 488 to
the indifferent electrode 494 (shown in bold lines) is very short,
and is almost entirely within the distal electrode housing. This
may be compared to the conduction path in the prior art CRM device
(shown in bold lines in FIG. 30), which runs the length of the lead
from the pacing electrode all the way back to the proximal housing.
This aspect of the present invention reduces the effect of induced
voltages due to magnetic resonance imaging. In another embodiment,
the housing of the distal module 476 acts an the indifferent
electrode 494, and the electrode 488 is attached to a conductor
that extends a distance from the distal module 476.
[0401] D. Digital Defibrillation
[0402] In another embodiment, a digital defibrillator includes an
implantable heart monitor and a defibrillator, as described in
greater detail above. In another embodiment, the implantable heart
monitor includes any of the implantable heart monitors described
above. The digital defibrillator provides power to the monitor, and
it provides signaling for atrial and/or ventricular defibrillation,
pacing, and sensing. In addition, the digital defibrillator
includes a physiological sensor module that provides measurement
data to a memory within a proximal housing. The digital
defibrillator also allows the physiological sensor module to be
programmed by an external device, such as a patient signaling
module, as described in greater detail above.
[0403] E. Digital Communication
[0404] Referring back to FIG. 24, there is provided one
illustration of a digital communication protocol over a
two-conductor lead between a proximal housing and a distal module.
In one embodiment the digital communication protocol is implemented
in a digital pacemaker, and in another embodiment, the digital
communication protocol is implemented in a digital defibrillator.
Each power pulse-to-power pulse interval illustrated in FIG. 24
defines a frame of information over a particular time span. Each
frame is further divided or segmented into a number of distinct
sub-frame intervals. In one embodiment, each sub-frame interval is
used to implement a defined function.
[0405] In one sub-frame interval a power pulse is delivered from a
proximal housing to a distal module to charge the energy storage
device, or power supply of the distal module. As described above,
the distal module is generally located at the distal end of a lead
which is coupled to a proximal housing at the lead's proximal end.
In one embodiment, the power pulse is provided in the first
interval of the frame, and it defines the end of one frame, and the
beginning of the next frame. In one embodiment, the power pulses
are generated at a particular frequency determined by a control
module (such as control module 486 of the digital pacemaker 470
illustrated in FIG. 31). The frequency is used by the control
module and a sensor module to adjust an internal RC or current
source clock to synchronize operation between the measurement
components and sensors of the distal module, and the defibrillator
and/or pacing components of the digital defibrillator and/or
pacemaker.
[0406] In one embodiment, data transmission intervals are defined
between power pulse intervals. In one embodiment, a data
transmission interval signals the defibrillator or pacemaker to
provide an electrical stimulus, such as an electrical pulse to the
electrode coupled to the patient's heart. In another embodiment,
the data transmission interval commands a change in operation mode
of a measurement or sensor module. In one embodiment, the data
transmission interval includes a download interval, where data,
including digitized data from a sensor is transmitted from the
distal module to components, such as a memory device, or telemetry
module, within the proximal housing.
[0407] In another embodiment, the data transmission interval
includes an upload interval, during which information, commands, or
data from the proximal housing is communicated to a distal module.
In one embodiment, the proximal housing includes a measurement
module, such as a POD or HeartPOD.TM. as described in greater
detail above, and the distal module includes a defibrillator. In
one embodiment, information communicated during the upload interval
includes measurement data and/or status information regarding the
current mode of operation of the measurement module, or a trigger
signal that indicates that a sensed signal has been detected. In
one embodiment, the type of data is conditional, depending, for
example, on whether a programming mode change was called for in the
previous download interval. In one embodiment, if a programming
mode change was called for in the previous download interval, the
upload interval data provides status information indicating whether
the mode change was successful.
[0408] In one embodiment, the download and upload intervals are
subdivided into data words, each containing a predefined number of
bits, so that multiple pieces of information are communicated in
each interval or word. For example, in one embodiment, the download
interval includes a pacing pulse trigger bit followed by one or
more programming bits. In another embodiment, the upload interval
includes a sensing bit which is set if an R-wave and/or a P-wave of
the internal electrocardiogram is sensed by the measurement module.
The upload interval also includes NP bits of pressure data and NT
bits of temperature data. In another embodiment, checksum bits are
provided as well to guard against data transmission errors.
IV. EXAMPLES OF SYSTEM APPLICATION
A. Example 1
[0409] Exemplary modes of operation for an embodiment of the system
of the invention are described as follows. The following Example
illustrates various embodiments of the present invention and is not
intended in any way to limit the invention.
[0410] In one embodiment, the system is programmed to power up once
per hour to measure the left atrial pressure and other conditions
as dictated by the configuration of the particular system and any
other sensors that might be present. Left atrial pressure
measurements are taken at a 20-Hertz sampling rate for sixty
seconds, yielding 1200 data values reflective of the fluid pressure
within the left atrium. The central processing unit then computes
the mean left atrial pressure based on the stored values. Then, if
the mean pressure is above a threshold value predetermined by the
patient's physician, the central processing unit causes an
appropriate communication to be sent to the patient via the patient
signaling device.
[0411] A set of coded communications to the patient can be devised
by the treating physician and encoded into the device either at the
time of implantation or after implantation by transcutaneous
programming using data transmission into the non-volatile program
memory 110 via the transceiver 105. For example, assume that the
physician has determined that a particular patient's mean left
atrial pressure can be controlled at between 15 and 20 mm Hg under
optimal drug therapy. This optimal drug therapy might have been
found to comprise a drug regimen including 5 milligrams (mg) of
Lisinopril, 40 mg of Lasix, 20 milliequivalents (mEq) of potassium
chloride, 0.25 mg of Digoxin, and 25 mg of Carvedilol, all taken
once per day.
[0412] The patient is implanted with the device and the device is
programmed as follows. The device includes a pressure transducer
implanted across the atrial septum such that the transducer
responds to the difference in pressure between the right and left
atria. This differential pressure is independent of changes in
atmospheric pressure, and in most circumstances is well correlated
with, and thus indicative of, the left atrial pressure. The
device's programming provides for four possible "alert levels" that
are specified according to mean differential atrial pressure
detected by the transducer and computed in the central processing
unit, and that the patient signaling device is a mechanical
vibrator capable of producing pulsed vibrations readily discernable
by the patient.
[0413] At predetermined intervals, for example, hourly, daily,
weekly, monthly, 3-4 times per day, or in response to a detected
event, in response to a symptom, or in response to an instruction,
the device measures the patient's mean left arterial pressure as
described above, and determines the appropriate alert level for
communication to the patient according to programming specified by
the physician. For example, a mean left atrial pressure of less
than 15 mm Hg could be indicative of some degree of over-medication
and would correspond to alert level one. A pressure between 15 and
20 mm Hg would indicate optimal therapy and correspond to alert
level two. A pressure between 20 and 30 mm Hg would indicate mild
under-treatment or mild worsening in the patient's condition, and
would correspond to alert level three. Finally, a mean left atrial
pressure above 30 mm Hg would indicate a severe worsening in the
patient's condition, and would correspond to alert level four.
[0414] When the proper alert level is determined, the device sends
a two-second vibrating pulse to notify the patient that the device
is about to communicate an alert level through a sequence of
further vibrations. A few seconds later, a sequence of one to four
relatively short (one second) vibratory pulses, the number
corresponding to the applicable alert level, are made by the device
and felt by the patient. The patient can easily count the pulses to
determine the alert level, then continue or modify his own therapy
with reference to a chart or other instructions prepared for him by
the physician.
[0415] For example, two pulses corresponds to alert level two, an
optimal or near optimal condition for that particular patient. In
that case, the doctor's instructions tell the patient to continue
his or her therapy exactly as before. The signal for alert level
two is given once every 24 hours, at a fixed time each day. This
serves mainly to reassure the patient that the device is working
and all is well with his therapy, and to encourage the patient to
keep taking the medication on a regular schedule.
[0416] One pulse, in contrast, corresponds to alert level one, and
most likely some degree of recent over-medication. The doctor's
orders then notify the patient to reduce or omit certain parts of
his therapy until the return of alert level two. For example, the
doctor's instructions might tell the patient temporarily to stop
taking Lasix, and to halve the dosage of Lisinopril to 2.5 mg per
day. The coded signal is given to the patient once every twelve
hours until the return of the alert level two condition.
[0417] Three pulses indicates alert level three, a condition of
mild worsening in the patient's condition. Accordingly, the
doctor's instructions notify the patient to increase the diuretic
components of his therapy until alert level two returned. For
example, the patient might be instructed to add to his to his
normal doses an additional 80 mg of Lasix, twice daily, and 30 mEq
of potassium chloride, also twice daily. The level three alert
signal would be given every four hours until the patient's
condition returned to alert level two.
[0418] Four pulses indicates alert level four, indicating a serious
deterioration in the patient's condition. In this case, the patient
is instructed to contact his physician and to increase his doses of
diuretics, add a vasodilator, and discontinue the beta-blocker. For
example, the patient might be instructed to add to his therapy an
additional 80 mg of Lasix, twice daily, an additional 30 mEq of
potassium chloride, twice daily, 60 mg of Imdur, twice daily, and
to stop taking the beta-blocker, Carvedilol. The signal
corresponding to alert level four would be given every two hours,
or until the physician was able to intervene directly.
B. Example 2
[0419] In one embodiment, the system is configured as an externally
powered implantable device with a sensor implanted in the
intra-atrial septum. The pressure transducer of the sensor is
exposed to the pressure in the left atrium. In one embodiment, the
sensor is anchored in the septum such that the pressure transducer
is substantially flush with the left atrial wall in fluid contact
with blood in the left atrium. In another embodiment, the anchor is
designed such that the pressure sensor extends a predetermined
distance into the left atrium. In both these embodiments, the
pressure sensor package is located in the septum with its proximal
end extending back into the right atrium. A flexible lead extends
from the proximal end of the sensor package back through the right
atrium, into the superior vena cava, up to a subclavian vein, and
out through the wall of the subclavian vein, terminating at an
antenna coil assembly located in a subcutaneous pocket near the
patient's clavicle, similar to a pacemaker generator housing.
[0420] The temperature at the site of the sensor and an internal
electrocardiogram (IEGM) are also detected by the sensor. A digital
signal is communicated to an external telemetry device via an
antenna coil implanted under the patient's skin and connected to
the sensor by a flexible lead. The sensor is powered by radio
frequency energy received by the implanted coil from an external
coil connected to the external telemetry device. The external
telemetry device forms part of an external patient advisory module,
that also includes a battery power source, a signal processor, and
a patient signaling device that consists of a personal data
assistant (PDA) with a display screen and software for
communicating with the patient.
[0421] The external patient advisory module is programmed to alert
the patient at times determined by the physician, preferably at the
times the patient is scheduled to take prescribed medications,
typically one to three times per day. In one embodiment, the alert
consists of an audible alarm and the appearance of a written
message on the graphical interface of the patient-signaling device.
The message instructs the patient to perform a "heart check," that
is to obtain physiological measurements from the implanted device.
Instructions to the patient may include instructions to establish
certain standard conditions, such as sitting quietly in a chair,
prior to beginning the measurements. The patient is instructed to
place the external telemetry/power coil over the implanted antenna
coil, then to press a button to initiate the measurement sequence.
Once the patient presses the button, the external device begins
emits energy via the external coil to power and communicate with
the implanted device. In one embodiment the external device emits
an audible signal while communication is being established, then
emits a second audible signal distinct from the first when
communication has been established and while the measurement is
taking place. Once the measurement is concluded, typically after 5
to 20 seconds, a third audible signal, distinct from the first two,
is emitted to signal the patient that the measurement is
complete.
[0422] In one embodiment, the external device will further instruct
the patient, using its graphical interface, to enter additional
information relevant to the patient's condition, such as weight,
peripheral blood pressure, and symptoms. The signal processing
apparatus of the external device then compares the measured
physiological parameters from the implanted device, together with
information entered by the patient, with ranges and limits
corresponding to different therapeutic actions as predetermined by
the physician and stored in the external device as a dynamic
prescription, or DynamicRx.TM.. The prescribed therapeutic action
will then be communicated to the patient on the graphic
display.
[0423] In one embodiment, the patient signaling apparatus will
prompt the patient to confirm that each prescribed therapy has been
performed. For example, if the therapy is taking a specific dose of
oral medication, the patient will be prompted to press a button on
the graphical interface when the medication has been taken. In one
embodiment of the invention, this information is used to keep track
of the number of pills remaining since the last time the patient's
prescription was filled, so that the patient or caregiver can be
reminded when it is time to refill the prescription.
[0424] As an example of a DynamicRx.TM. for a congestive heart
failure patient, the level and rate of change of left atrial blood
pressure (LAP) may be used by the physician to determine the dosage
of diuretic. If the LAP remains in the normal range for that
patient, the patient signaling device would display the normal
dosage of diuretic. As in Example 1 above, if the LAP falls below
the patient's normal range, the doctor may prescribe a reduction or
withholding of diuretic, and that instruction would appear on the
graphical interface. In another embodiment of a DynamicRx.TM. the
patient may be instructed to take some other kind of action, such
as calling the physician or caregiver, altering diet or fluid
intake, or getting additional rest. Thus, the apparatus and methods
of the present invention allow the physician to conditionally
prescribe therapy for the patient, and to communicate the
appropriate therapy to the patient in response to dynamic changes
in the patient's medical condition.
[0425] In one embodiment, the physician enters the therapeutic plan
for the patient, e.g., the DynamicRx.TM., on a personal computer
and the DynamicRx.TM. is then loaded from the PC into the patient
advisory module. In one embodiment, the patient advisory module is
a PDA using the PALM OS.RTM. (Palm Computing, Inc.), or like,
operating system and the DynamicRx.TM. is loaded from the
physician's PC via the HOTSYNC.RTM. (Palm Computing, Inc.), or
like, facility of PALM OS.RTM.. Loading of the DynamicRx.TM. from
the physician's PC could be performed in the physician's office, or
could be performed over a telephone modem or via a computer
network, such as the Internet.
[0426] In one embodiment, DynamicRx.TM. software running on the PC
contains treatment templates that assist the physician in creating
a complete DynamicRx.TM., such that appropriate therapies/actions
are provided for all possible values of the patient's physiological
parameters.
[0427] In one embodiment of the present invention, the
DynamicRx.TM. includes a patient instruction. In one embodiment,
the patient instruction may includes directions or instructions to
take medications, instructions to call 911, instructions to rest;
or instructions to call a physician or medical care provider. In
another embodiment of the present invention, one or more devices
are provided to enable a physician or medical care provider to
provide instruction to the patient. These devices include, but are
not limited to, workstations, templates, PC-to-Palm hotsync
operations, uploading processes, downloading processes, linking
devices, wireless connections, networking, data cards, memory
cards, and interface devices that permit the physician instruction
to be loaded onto a patient's signal processor. In another
embodiment, a user instruction is provided, where the user includes
a patient, a physician, or a third party.
C. Example 3
[0428] Heart failure patients implanted with the embodiments
described in the above two examples may at the time of such
implantation, or subsequently develop a medical indication for
concurrent implantation of a CRM device. For example, required
heart failure treatment with beta-blocking medication may slow the
heart rate sufficiently to induce symptoms such as fatigue, or may
prevent the heart rate from increasing appropriately with exertion,
a condition known as chronotropic incompetence. These conditions
are recognized indications for atrial pacing or atrial pacing with
a rate responsive type of pacemaker. Normally this involves the
placement of a pacemaker generator and an atrial pacing lead
usually positioned in the right atrial appendage. In many cases, a
dual chamber pacemaker is placed to synchronously pace the right
atrium via one lead and the right ventricle via a second pacing
lead. In other cases, such heart failure patients may have an
abnormality of electrical conduction within the heart such as is
known to occur with a condition called left-bundle branch block
that causes dysynchronous left ventricular contraction thereby
worsening heart failure. Implantation of a biventricular pacemaker
has been shown to improve many of these patients. Because severe
heart failure also carries an increased risk of sudden cardiac
death due to a ventricular cardiac tachyarrhythmia, many of these
patients are now being treated with implantable cardiac
defibrillators (ICD's). In some cases combination rhythm management
devices comprised of a biventricular pacemaker and an ICD are
implanted.
[0429] In such cases where a CRM device is needed, it would be
beneficial to the patient if the rhythm management device were
integrated with the heart failure management devices described by
Eigler, et al., in U.S. Pat. No. 6,328,699 and U.S. Patent
Application Publication Nos. 2003/0055344 and 2003/0055345, all of
which are incorporated by reference in their entireties, to utilize
the sensing lead yielding a pressure indicative of left atrial
pressure additionally as an atrial pacing lead. It would be further
beneficial if the LAP sensing lead system described in Example 2
could be upgraded to combination heart failure management/CRM
device by replacing the coil antenna with an appropriately
integrated CRM generator without removing or changing the LAP
sensing lead.
[0430] In one embodiment, the implanted heart failure device of
Example 2 above is modified by replacing the implanted
communications coil with an appropriately integrated CRM generator
and additional pacing/ICD leads. The LAP sensing lead is connected
as the atrial pacing lead to the generator. The generator has
appropriate circuitry to power the sensing circuitry of the atrial
lead. LAP is read out by telemetry between the external PDA and the
telemetry coil in the housing of the integrated rhythm management
generator. If clinically appropriate, right and left ventricular
pacing or defibrillation leads can be placed and connected to the
generator. There are many potential benefits from such a combined
rhythm and heart failure management system in addition to the
clinical benefits from each individual system. Fewer leads need to
be placed in the heart and a single venous insertion site can be
used with the combined system. Atrial pacing from the intra-atrial
septum has been show to inhibit paroxysmal atrial fibrillation, an
arrhythmia common in heart failure patients. Patients can be
titrated to higher or more appropriate beta-blocker dose levels
with potentially increased survival benefits. Additionally, the LAP
sensor can be used to control pacing parameters. As described
above, the LAP waveform may be helpful in adjusting mechanical
left-sided AV delay to optimize LV filling. Also, when LAP is
within the desired normal range and thus the patient is not in
acute heart failure, synchronous ventricular pacing can be
inhibited to prolong battery life. It is understood by those
skilled in the art, such as cardiologists and cardiac surgeons,
that there may be additional clinical benefits bestowed by the
combination of heart failure and rhythm management devices.
[0431] While this invention has been particularly shown and
described with references to embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the scope of
the invention. For all of the embodiments described above, the
steps of the methods need not be performed sequentially.
* * * * *