U.S. patent application number 14/867804 was filed with the patent office on 2016-03-24 for adaptive medium voltage therapy for cardiac arrhythmias.
The applicant listed for this patent is Galvani, Ltd.. Invention is credited to James E. Brewer, Byron L. Gilman, Mark W. Kroll.
Application Number | 20160082275 14/867804 |
Document ID | / |
Family ID | 48701474 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160082275 |
Kind Code |
A1 |
Gilman; Byron L. ; et
al. |
March 24, 2016 |
ADAPTIVE MEDIUM VOLTAGE THERAPY FOR CARDIAC ARRHYTHMIAS
Abstract
Aspects of the invention are directed to advanced monitoring and
control of medium voltage therapy (MVT) in implantable and external
devices. Apparatus and methods are disclosed that facilitate
dynamic adjustment of MVT parameter values in response to new and
changing circumstances such as the patient's condition before,
during, and after administration of MVT. Administration of MVT is
automatically and dynamically adjusted to achieve specific
treatment or life-support objectives, such as prolongation of the
body's ability to endure and respond to MVT, specifically
addressing the type of arrhythmia or other pathologic state of the
patient with targeted treatment, a tiered-intensity MVT treatment
strategy, and supporting patients in non life-critical conditions
where the heart may nevertheless benefit from a certain level of
assistance.
Inventors: |
Gilman; Byron L.; (Edina,
MN) ; Kroll; Mark W.; (Crystal Bay, MN) ;
Brewer; James E.; (Sebeka, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Galvani, Ltd. |
Edina |
MN |
US |
|
|
Family ID: |
48701474 |
Appl. No.: |
14/867804 |
Filed: |
September 28, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14337700 |
Jul 22, 2014 |
9144684 |
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14867804 |
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13921290 |
Jun 19, 2013 |
8805495 |
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14337700 |
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12830251 |
Jul 2, 2010 |
8483822 |
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13921290 |
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61270124 |
Jul 2, 2009 |
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Current U.S.
Class: |
607/7 |
Current CPC
Class: |
A61N 1/3993 20130101;
A61N 1/39044 20170801; A61N 1/3925 20130101; A61N 1/3621 20130101;
A61N 1/36564 20130101; A61N 1/3956 20130101; A61N 1/3904 20170801;
A61N 1/3605 20130101; A61N 1/3968 20130101; A61N 1/362
20130101 |
International
Class: |
A61N 1/39 20060101
A61N001/39 |
Claims
1. A device for administrating medium voltage therapy substantially
as shown and described herein, and its equivalents.
2. A method for administrating medium voltage therapy substantially
as shown and described herein, and its equivalents.
Description
PRIOR APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/270,124, filed Jul. 2, 2009, entitled "Method
and Apparatus for Providing Perfusion During VF, PEA and Asystole
in External and Implantable Cardiac Devices," and further
identified in its Application Data Sheet as "Medium Voltage Therapy
for the Treatment of Cardiac Arrhythmias Including Pulseless
Electrical Activity, Asystole and Ventricular Fibrillation," and
which is incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates generally to treatments for
individuals experiencing cardiac arrest and, more particularly, to
implantable or external treatment apparatus and associated methods
of operation thereof, for improving the applicability and
effectiveness of medium voltage therapy (MVT) for a variety of
patient conditions.
BACKGROUND OF THE INVENTION
[0003] Cardiac arrest is a significant public health problem
cutting across age, race, and gender. A positive impact on cardiac
arrest survival has been demonstrated with the substantial
reduction in time to defibrillation provided by the widespread
deployment of automated external defibrillators (AEDs), and the use
of implantable cardioverter defibrillators (ICDs) and implantable
pulse generators (IPGs). Examples of AEDs are described in U.S.
Pat. Nos. 5,607,454, 5,700,281 and 6,577,102; examples of ICDs are
described in U.S. Pat. Nos. 5,391,186, 7,383,085, and 4,407,288,
and examples of IPGs are described in U.S. Pat. Nos. 4,463,760,
3,978,865, and 4,301,804, the disclosures of which are incorporated
by reference herein.
[0004] Optimal resuscitation therapy for out of hospital (OOH)
cardiac arrest is the subject of substantial ongoing research.
Research has been clear in demonstrating that the timing of
resuscitation is of critical importance. For example, there is less
than a 10% chance of recovery just ten minutes after the onset of
ventricular fibrillation (VF). This knowledge led to the recent
widespread deployment of AEDs, primarily in public areas with a
high population concentration such as airports and shopping malls.
A positive impact on cardiac arrest survival has been demonstrated
due to the substantial reduction in time to defibrillation as a
result of more available access to AEDs. In addition, for those
patients identified as being at particularly high risk, an
implantable cardioverter-defibrillator is often implanted in order
to address episodes of cardiac arrest without the involvement of a
rescuer.
[0005] In the case of VF, performing CPR-type chest compressions
before defibrillation and minimizing the time to defibrillation
shock following the cessation of the CPR chest compressions is
important in facilitating effective recovery especially in cases of
long duration VF. It is generally believed that perfusion of the
myocardium achieved during CPR preconditions the heart for the
defibrillating shock. Despite the importance of CPR, it is often
not performed in the field for a variety of reasons.
[0006] Cardiac electrotherapy stimuli having an amplitude that is
greater than that of pacing-type stimuli, but less than the
amplitude and energy level associated with defibrillation-type
stimuli, are known in the art as medium voltage therapy (MVT). For
example, U.S. Pat. No. 5,314,448 describes delivering low-energy
pre-treatment pulses followed by high-energy defibrillation pulses,
utilizing a common set of electrodes for both types of stimuli.
According to one therapeutic mechanism of this pre-treatment, the
MVT pulses re-organize the electrical activity within the cardiac
cells of the patient to facilitate a greater probability of
successful defibrillation with a follow-on defibrillation pulse.
U.S. Pat. No. 6,760,621 describes the use of MVT as pretreatment to
defibrillation that is directed to reducing the likelihood of
pulseless electrical activity and electromechanical dissociation
conditions as a result of the defibrillation treatment. The
mechanism by which these results are achieved by MVT has been
described as a form of sympathetic stimulation of the heart. These
approaches are directed to influencing the electrochemical dynamics
or responsiveness of the heart tissues.
[0007] MVT has also been recognized as a way of forcing some amount
of cardiac output by electrically stimulating the heart directly
with stimuli that cause the heart and skeletal muscles to expand
and contract in a controlled manner. See U.S. Pat. Nos. 5,735,876,
5,782,883 and 5,871,510. These patents describe implantable devices
having combined defibrillation, and MVT capability for forcing
cardiac output. U.S. Pat. No. 6,314,319 describes internal and
external systems and associated methods of utilizing MVT to achieve
a hemodynamic effect in the heart as part of an implantable
cardioverter defibrillator (ICD) for purposes of achieving a
smaller prophylactic device. The approach described in the '319
patent uses the MVT therapy to provide a smaller and less expensive
implantable device that can maintain some cardiac output without
necessarily providing defibrillation therapy.
[0008] Unlike a conventional defibrillator or an IPG, which
operates with the primary purpose of restoring a normal cardiac
rhythm, MVT stimulation can be used to provide cardiac output,
which in turn causes perfusion to the heart and brain, as well as
other critical body tissues. By providing perfusion to the heart
and other vital organs, MVT prolongs the life of the patient even
while the patient continues experiencing the arrhythmia.
Additionally, MVT improves the likelihood of successful
defibrillation or of a spontaneous return of circulation. In
another application, MVT may be utilized to place a heart into a
distended state by continuing venous return in the absence of
cardiac output, thus making it more likely to return to a
spontaneous pulsatile rhythm. An AED equipped with MVT can provide
consistent high quality chest compressions. In the case of an
implanted ICD or IPG, back up chest compressions provided by MVT
can, in one sense, be even more important than in an external,
since in the case of the implantable device there may be no rescuer
available to perform CPR when needed.
[0009] Recent studies have identified an increasing incidence of
patients whose initial rhythm is not VF, but may be (PEA), or
asystole. In addition in many cases an unsuccessful defibrillation
shock (whether from an AED or an ICD) results in PEA, asystole or
persistent VF. In all these cases the indicated therapy is CPR type
chest compressions. Conventional ICD, IPG, and AED devices, even
those enabled with MVT, work very well to treat VF, but provide
little or no therapy for other common arrhythmias of cardiac
arrest, namely, pulseless electrical activity (PEA) and
asystole.
[0010] While developments in defibrillator technology, both
automatic external defibrillators (AEDs) and implantable
cardioverter defibrillators (ICDs) have made great strides in
aiding the electrical cardiac resuscitation of individuals
experiencing cardiac arrest, a need exists for a solution that can
effectively treat the increasing number of victims that either
present with non-VF cardiac arrest or are shocked into a non-VF
non-pulsatile rhythm such as PEA or asystole.
[0011] U.S. Patent Application Publication No. 2006/0142809
describes a technique and associated apparatus that combines
defibrillation therapy with MVT into an external device having a
capability to perform electrical CPR. Externally-applied MVT is
proposed for stimulating skeletal and sympathetic muscles in
addition to myocardial muscle tissue to effect chest compression
and even ventilation in the patient. The '809 publication reflects
the knowledge in the art that due to the inclusion of differing
time constant components in an MVT waveform, the waveform can
stimulate contraction of a variety of different types of muscles,
e.g., myocardial, skeletal, sympathetic muscles, and the phrenic
nerve. Varying and controlling the MVT waveform parameters,
including variation of the musculature targeted by the waveform, is
described as a way to maximize coronary perfusion pressure
generated by application of MVT.
[0012] Notwithstanding the advancements in MVT for cardiac output
forcing made to-date, known MVT techniques have been shown to be
effective for only a limited time due to muscle fatigue resulting
from application of the MVT. Particularly, after repeated
application of the MVT electrical pulses, the muscles being
stimulated become unresponsive to further MVT stimulation,
resulting in a drop-off in coronary perfusion. A solution is
therefore needed for enabling longer duration and more productive
MVT sessions.
SUMMARY OF THE INVENTION
[0013] One aspect of the invention is directed to advanced
monitoring and control of medium voltage therapy (MVT) in
implantable and external devices. Apparatus and methods are
disclosed that facilitate dynamic adjustment of MVT parameter
values in response to new and changing circumstances such as the
patient's condition before, during, and after administration of
MVT. MVT is selectively targeted to specific muscles using
variation of waveform characteristics, and/or using specific
location-based targeting. The MVT is applied and adjusted based on
monitored patient condition information, including monitored
hemodynamic information. Administration of MVT is automatically and
dynamically adjusted to achieve specific treatment or life-support
objectives. One such objective is prolongation of the body's
ability to endure and respond to MVT. Other objectives are specific
to the type of arrhythmia or other pathologic state of the
patient.
[0014] In another aspect, advanced monitoring techniques are
applied to detect and treat specific conditions, such as pulseless
electrical activity (PEA), for example. In one type of embodiment,
MVT treatment electrodes are utilized to make hemodynamic
measurements. In one particular example, hemodynamic measurements
are made concurrently with the administration of the MVT. In
another type of embodiment, the administration of MVT is controlled
such that the MVT is synchronized with the ECG of a PEA
condition.
[0015] In another aspect, methods and apparatus are described for
administering a multi-tier MVT treatment algorithm, to be carried
out by an implantable or external MVT-enabled device. The device
according to one embodiment is configured to apply a higher
intensity MVT at certain stages of rescue or life support, and to
apply a lower intensity MVT at other stages. The intensity of MVT
is varied by adjusting certain MVT parameters in response to a
monitored condition of the patient. Higher-intensity and
lower-intensity MVT may be selectively applied differently between
MVT targeting the heart and MVT targeting the skeletal muscles,
depending on the treatment objective, which in turn depends on the
detected patient condition obtained using the patient monitoring
facilities of the device.
[0016] In another aspect of the invention, adaptive MVT is applied
to support patients in non life-critical conditions but where the
heart may benefit from a certain level of assistance, such as
orthostatic hypotension, for example. Hemodynamic monitoring and
ECG measurements are used to identify such conditions, and to
control proper administration of the MVT.
[0017] A number of advantages will become apparent from the
following Detailed Description of the Preferred Embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0019] FIG. 1 is a diagram illustrating the sub-systems of an
implantable device enabled with medium voltage therapy (MVT)
facilities, according to one embodiment.
[0020] FIGS. 2A-2C illustrate various examples of electrode
arrangements for implantable MVT devices such as the device of FIG.
1 according to various embodiments.
[0021] FIG. 3A is a diagram illustrating the sub-systems of an
external device enabled with medium voltage therapy facilities,
according to one embodiment.
[0022] FIG. 3B is a diagram illustrating an exemplary operator
interface of the device of FIG. 3A.
[0023] FIG. 3C is a diagram illustrating various examples of
electrodes and sensors of the patient interface of the device of
FIG. 3A.
[0024] FIGS. 4A-4B are time-domain waveform diagrams illustrating
variable parameters of the MVT according to various embodiments of
the invention.
[0025] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] FIG. 1 is a block diagram illustrating an implantable MVT
device 10 constructed in accordance with one aspect of the
invention. The device circuitry is electrically coupled with
regions of the patient's upper body 40 via a series of
leads--output lead 32, pressure sense lead 34, and ECG sense lead
36. The electronic circuit includes a conventional ECG amplifier 30
for amplifying cardiac signals. The amplified cardiac signals are
analyzed by a conventional arrhythmia detector 20 which determines
if an arrhythmia is present. The arrhythmia detector 20 may be one
of several types well known to those skilled in the art and is
preferably able to distinguish between different types of
arrhythmias. For example; fibrillation, tachycardia, asystole.
[0027] The exemplary circuit also contains a hemodynamic sensing
section 28 which amplifies and conditions a signal from a one or
more hemodynamic sensors such as, for example, a pressure sensor
within the heart or artery, such as the pressure sensor described
in U.S. Pat. No. 6,171,252, the disclosure of which is incorporated
by reference herein. Another type of hemodynamic sensor that can be
used in an implantable embodiment is a microphone and associated
processing device for monitoring audible body sounds (much like an
indwelling stethoscope) indicative of blood flow as described in
U.S. Pat. No. 7,035,684, the disclosure of which is incorporated by
reference herein. Yet another suitable hemodynamic sensing
technique is one featuring an ultrasonic blood flow sensor, such as
he Doppler pulse sensor described in U.S. Pat. No. 4,823,800, the
disclosure of which is incorporated by reference herein. Still
another hemodynamic sensing technique that may be employed is
impedance plethysmography (tomography) in which a series of
electrodes are placed to measure changing impedance in localized
regions indicative of blood flow, a pulse, or movement of the
cardiac wall such as described in U.S. Pat. No. 5,824,029, the
disclosure of which is incorporated by reference herein. A further
technique of measuring the hemodynamic output of the patient is
with the use of a pulse oximeter such as the implantable one
described in U.S. Pat. No. 4,623,248, the disclosure of which is
incorporated by reference herein.
[0028] The output of the hemodynamic sense circuit 28 is fed to a
cardiac output detection circuit 18 which analyzes the data and
determines an estimate of the cardiac output. Data from the
arrhythmia detector circuit 20 and the cardiac output detection
circuit 18 is fed to the microprocessor 16. The microprocessor 16
determines if MVT is appropriate, and what MVT parameters to apply
at the present time. If MVT is indicated, the microprocessor 16
prompts the output control 22 to charge a capacitor within the
output circuit 26 via the capacitor charger 24. The output control
22 directs the output circuitry 26 to deliver the pulses to the
patient's upper body regions 40 via the output leads 32. The
microprocessor 16 may communicate with external sources via a
telemetry circuit 14 within the device 10. The power for the device
10 is supplied by an internal battery 12.
[0029] FIG. 2A is a diagram showing the connection of an
implantable device 10' according to one embodiment to the heart as
one of the regions in the patient's upper body 40 in an epicardial
patch configuration. In this thoracotomy configuration, current
passes through an output lead pair 32 to electrode patches 42 which
direct the current through the heart. A pressure sense lead 34
passes the signal from an optional pressure transducer 46 which
lies in the heart. The ECG is monitored by sense electrodes 44 and
passed to the device 10' by a lead 36. The area of the electrodes
42 is at least 0.5 cm.sup.2. The size of the electrode is greater
than that of a pacing lead and no more than that of a
defibrillation electrode or between approximately 0.5 cm.sup.2 and
20 cm.sup.2 each.
[0030] FIG. 2B illustrates an example of a non-thoracotomy
arrangement according to one embodiment. In this system, the
current passes from a coil electrode 52 in the heart to the housing
of the MVT device 10''. An endocardial lead 50 combines the ECG
sensing lead and the pulse output lead. The ECG is monitored by
sense electrodes 44 in the heart and passes through the endocardial
lead 50. There is an optional pressure transducer 46 in the heart
which passes a signal to the device 10'' via optional lead 34.
[0031] FIG. 2C illustrates an implantable MVT device 10''' that
supports a set of diverse electrode arrangements for selectively
applying MVT to different areas of the patient. In addition to
electrodes 42 and 52 discussed above in the thoracotomy and
non-thoracotomy arrangements for directing the MVT through the
myocardium, device 10''' further includes additional electrodes 58a
and 58b for placement at specific locations in the patient's upper
body, 60a and 60b, to direct MVT through non-cardiac muscles.
Examples of locations 60a and 60b include (without limitation)
locations for activating the pectorial muscles, intercostals
muscles, the diaphragm (e.g., via stimulation of the phrenic
nerve), and the abdominal muscles. The additional electrodes 58a
and 58b, in various embodiments, have a variety of constructions
and locations, including, for example, subcutaneous patch
electrodes, one or more additional electronics/battery housings,
intra-vascular leads, and the like. Placements include any suitable
location such as, for example, subcutaneously at the base of the
neck, in the azygos vein, in the cephalic vein, subcutaneously in
the lower torso, and subcutaneously on one or both sides of the
upper torso.
[0032] In a related embodiment, the additional one or more of
electrodes 58a and 58b are used for hemodynamic measurements such
as, for example, electrical impedance plethysmography or
tomography. In one such embodiment, one of the additional
electrodes 58a, for instance, is implanted high in the upper chest
region or at the base of the neck, while another one of the
additional electrodes, 59a, for instance, is implanted lower in the
abdominal region. Even though electrode 58a and electrode 59a may
not used as a cathode/anode pair for application of MVT (this would
be the case where, for example, electrode 58a has a complementary
electrode 58a placed elsewhere for applying MVT to region 60a, and
where electrode 59a has a complementary electrode 59a placed
elsewhere for applying MVT to region 60b), one of electrodes 58a
and one of electrodes 59a can be operated as an anode/cathode pair
with each other for purposes of impedance measurement to determine
blood flow, using a suitable switching arrangement in the
implantable MVT device 10'.
[0033] In a related embodiment, an electrical impedance measurement
is performed using frequency division or code division multiplexing
relative to applied MVT therapy. Thus, the impedance measurement
may be carried out while rejecting the interference caused by
application of the MVT signals. This approach permits a hemodynamic
impedance measurement to be performed without having to interrupt
application of the MVT and without having to time the measurement
to coincide with time periods between MVT pulse packets.
Accordingly, in one embodiment, a real-time, continuous hemodynamic
monitoring is performed while MVT is administered. The blood flow
can thus be plotted as a function of time, and correlated to the
parameters of the MVT being applied. This information can be
displayed to an operator as a chart recording or displayed trace,
and can be automatically stored and analyzed to ascertain MVT
performance.
[0034] FIG. 3A is a diagram illustrating an example AED 100 that
utilizes MVT according to one embodiment. AED 100 is can be a
hand-portable instrument that is self-powered from an
optionally-rechargeable battery 102. Battery 102 provides an energy
source that can be converted and conditioned for powering the
various circuitry of AED 100. A low voltage power supply 104
converts the battery power into one or more stabilized power supply
outputs 105 for supplying the power to the subsystems of AED 100.
The subsystems include a controller 106, for example a
microprocessor that is programmed and interfaced with other
subsystems to control most of the functionality of AED 100.
[0035] In the embodiments in which the controller 106 is
implemented as a microprocessor or microcontroller, the
microprocessor interface includes data and address busses, optional
analog and/or digital inputs, and optional control inputs/outputs,
collectively indicated at microprocessor interface 107. In one
example embodiment, the microprocessor is programmed to control the
sequence of the electrotherapy, as well as the output waveform
parameters. The user input to the system can be in the form of
simple pushbutton commands, or voice commands.
[0036] Example AED 100 includes a discharge circuit 108 for
administering therapeutic stimuli to the patient. Discharge circuit
108 controls the release of therapeutic energy to achieve a desired
stimulus having a particular waveform and energy. Charge circuit
110 energizes discharge circuit 108 to achieve the desired output
stimulus. High voltage power supply 112 provides a sufficient
energy source 113 to charge circuit 110 to enable charge circuit
110 and discharge circuit 108 to ultimately deliver one or more
defibrillation pulses to an exterior surface of the patient.
Typically, a voltage sufficient to achieve a therapeutic
defibrillation stimulus from the exterior of a patient is in the
range of 1 kV-3 kV.
[0037] In accordance with this embodiment, AED 100 also includes a
medium voltage power supply 114. Medium voltage power supply 114
provides a medium voltage source 115 that enables charge circuit
110 and discharge circuit 108 to ultimately deliver one or more MVT
signals to the exterior of the patient. In one embodiment, the
medium voltage power supply is adapted to provide a regulated
voltage in the range from 20-1000 V.
[0038] The defibrillation and MVT stimuli are administered to the
patient via patient interface 116. In one embodiment, patient
interface 116 includes electrodes 118a and 118b that are adhesively
applied to the patient's chest area, typically with an
electrically-conductive gel. Electrodes 118a and 118b are
electrically coupled, such as by insulated copper wire leads 120,
to discharge circuit 108. In one example embodiment, electrodes
118a and 118b can deliver the defibrillation stimuli and the MVT
stimuli as well as obtain information about the patient's
condition. For example, electrodes 118 can be used to monitor the
patient's cardiac rhythm. Signals originating in the patient that
are measured by electrodes 118 are fed to monitoring circuitry
122.
[0039] In one embodiment, electrodes 118a and 118b are part of
compound electrode patches in which each patch (having a common
substrate) has a plurality of individually-selectable electrodes.
In this arrangement, device 100 is programmed to select certain
ones of the individual electrodes on each compound patch to achieve
a therapeutic purpose. One such purpose is to activate an
individual electrode that is most optimally placed on the patient's
body for the desired MVT or defibrillation therapy. This approach
can be used to correct for the variability in placement of the
electrode patches by unskilled rescuers or even skilled rescuers
working under difficult circumstances in the field. Device 100 in
this embodiment may include a switching arrangement, either
electromechanical or electronic, or may communicate control
information to an external switching arrangement, which may be
incorporated into the compound patch. In a related embodiment, the
ECG signal strength, as measured using various pairs of the
individual electrodes of the compound patches, is used to determine
the electrodes to be used for MVT and/or defibrillation
administration. In another related embodiment, the hemodynamic
measurement of the MVT effectiveness, as recorded for different
electrode pairs, is used as a basis for switchably selecting the
electrodes to be used for defibrillation. In yet another
embodiment, certain electrodes are selected from among the
plurality of electrodes on each compound patch to target specific
regions to which MVT is to be applied.
[0040] In one embodiment, patient interface 116 includes an MVT
effectiveness sensor 124 coupled to monitoring circuitry 122. MVT
effectiveness sensor 124 can measure observable patient
characteristics that are related to the patient's condition, in
like fashion to the hemodynamic monitoring and determining
arrangements described above for an implantable embodiment.
Additional details about the MVT effectiveness monitoring are
discussed below.
[0041] AED 100 also includes a rescuer interface 126 operatively
coupled with controller 106. In one embodiment, rescuer interface
126 includes at least one pushbutton, and a display device for
indicating at least the operational status of AED 100. In a related
embodiment, rescuer interface includes a system for providing
visual or audible prompting or instructions to the rescuer. In
another embodiment, rescuer interface 126 includes a plurality of
human-operable controls for adjusting the various AED operational
parameters, and a display device that indicates measurements made
by monitoring circuitry 122.
[0042] FIG. 3B is a diagram illustrating human interface portions
of example AED 100' according to one embodiment. AED 100' is a
physical implementation of AED 100 (FIG. 1A). AED 100' is housed in
a lightweight portable housing 130 having a base portion 132 and a
hinged lid 134 in an exemplary clam-shell arrangement as
illustrated, where opening and closing of the lid turns the device
on and off, as diagrammed at 136. Other embodiments do not have the
base-cover arrangement, and instead have a housing consisting of a
single enclosure, in which case the device has an on/off switch.
The device's relatively small size and weight, and carrying handle
138 facilitate hand-portability of the device. Display 126a' may
have a text only display 140 or may include a graphical display 142
that could, among other items, display an ECG waveform. The device
also has a speaker 126b for voice prompting of the proper rescue
sequence, a non-volatile readiness indicator 126d' that indicates
whether or not the device is in working order, an optional "shock"
button 126c' and receptacles for the patient electrodes 118a' and
118b' and an MVT effectiveness sensor 124'.
[0043] AED 100' includes two types of patient interface. First,
electrodes 118a' and 118b' are adapted to be adhesively coupled to
the patient's skin. In one embodiment, the adhesive consists of an
electrically conductive gel. Electrodes 118a' and 118b' can be used
to measure the patient's cardiac rhythm, and to apply MVT and
defibrillation therapy to the patient. Second, MVT effectiveness
sensor 124' includes a transducer adapted for measuring one or more
vital signs of the patient.
[0044] FIG. 3C is a diagram of several possible patient 160
connections to an AED 158 according to one embodiment including:
defibrillation/ECG electrodes 118a' and 118b', pulse oximeter
124a', ETCO2 sensor 124b', Doppler or ultrasound pulse sensor
124c', and blood pressure sensor 124d'. More generally, the MVT
Effectiveness sensor can be a variant of any of the monitoring
techniques discussed above, for instance, the pulse oximetry
measurement for an external embodiment may be achieved using a
fingertip pulse oximeter as the MVT effectiveness sensor 124. Other
suitable techniques for monitoring a hemodynamic state of the
patient may also be used. For instance, alternatively or in
conjunction: a pulse oximeter, a sonic arterial pulse sensor, a gas
sensor, or a blood pressure sensor. In another embodiment, the
O.sub.2 saturation sensor 124a', end tidal sensor 124b', and pulse
detection unit 124c', are battery-powered and are adapted to
communicate measurement data via wireless radio frequency link. For
example, Bluetooth technology could be utilized to accomplish
close-range wireless data communications.
[0045] In one example embodiment, arterial pulse activity measured
from an exterior of the patient by way of pressure sensing, or by
way of Doppler ultrasound technology. In one embodiment, the MVT
effectiveness sensor includes a transthoracic impedance measuring
arrangement that detects changes in the chest impedance with
cardiac output. Referring again to GIG. 3B, in one embodiment, MVT
effectiveness sensor 124' is integrated with an adhesive patch
adapted to be attached to the patient's skin. In a related
embodiment, the transducer portion of MVT effectiveness sensor 124'
is implemented in a thin-or-thick-film semiconductor technology.
Examples of suitable sites for arterial pulse sensing include the
patient's aorta, femoral arteries, carotid arteries, and brachial
arteries. Other accessible arteries may also be suitable. In one
example embodiment of AED 100', the measurement collected via MVT
effectiveness sensor 124' is displayed, substantially in real-time,
on display 126'. The displayed measurement can be numerical or
graphical, such as a bar-type or chart recorder-type display.
[0046] In a related embodiment, a plurality of different techniques
may be used together in a more advanced AED device enabled with
MVT. Such devices, with their multiple sensors to engage with the
patient, may be more suitable for use by trained rescuers, such as
paramedics, for example.
[0047] In operation, AED 100 is interfaced with the patient via
leads 118a/118b, and MVT effectiveness sensor. In one embodiment,
AED 100 provides guidance to a rescuer, via rescuer interface 126,
for properly interfacing with the patient. AED 100 measures the
patient's condition using monitoring circuitry 122 and at least a
portion of the patient interface 116. Next, AED 100 analyzes the
measured patient's condition to determine the existence of any
indications for treating the patient. If the patient exhibits a
condition treatable by AED 100, the device determines the type of
therapeutic signal to apply to the patient, and proceeds to apply
the treatment. The therapeutic signal can be an MVT signal, CPR
prompt, or a defibrillation signal, either of which is delivered
via discharge circuit 108 and leads 118a/118b. During a rescue
process, AED 100 provides prompting or instructions to a rescuer
for facilitating the therapy and for protecting the rescuer's
safety.
[0048] Speaking generally for both, implantable, and external
MVT-equipped electrotherapy devices, in various embodiments, a
plurality of different MVT waveforms adapted to force muscular
contractions are disclosed herein. The waveforms are each adapted
to repeatedly artificially force and maintain musculature of the
patient in a contracted state for a time sufficient to achieve
myocardial perfusion and to subsequently cause the musculature to
relax, thereby achieving a forced hemodynamic effect sufficient to
reduce a rate of degradation of the patient's physical condition
resulting from a cardiac arrhythmia.
[0049] The MVT waveforms discussed herein are administered at a
higher energy than a pacing pulse, but at a lower energy than a
defibrillation pulse. A pacing pulse is adapted to initiate a
myocardial cell activation process in the heart, wherein myocardial
tissue naturally contracts due to the heart's natural activation
wavefront propagation. Pacing merely adjusts natural cardiac
activity, such as electrically stimulating cardiac muscles such
that they contract synchronously across different regions of the
heart. Therefore, a pacing waveform is incapable of electrically
forcing and/or maintaining a heart contraction or inducing cardiac
perfusion during a cardiac event such as ventricular fibrillation.
A defibrillation pulse, on the other hand, involves the delivery of
energy sufficient to shock the heart into a "reset state", and is
intended to reset the natural electrical activity of the heart. In
contrast with pacing and defibrillation pulses, in one embodiment,
the MVT waveforms as discussed herein are delivered with sufficient
energy to electrically force a cardiac contraction, however without
delivering energy intended to perform a cardiac "reset" such as
would result from a defibrillation pulse. In various embodiments,
the MVT waveforms discussed herein adapted to artificially force
and maintain the heart in a contracted state for a time sufficient
to achieve cardiac perfusion.
[0050] FIG. 4A is a diagram illustrating some of the general
parameters of the MVT pulse waveforms The train rate TR can be
considered to be the forced "heart rate" in beats per minute, since
a pulse packet produces one chest constriction. The duration is the
length of time for during which a single session of MVT is applied.
FIG. 4B is a diagram detailing a single pulse packet, having
parameters of amplitude (AMP), pulse width PW, pulse period PP, and
train width TW.
[0051] Certain effective parameters have been reported in the
following published manuscripts, incorporated by reference herein:
"Transthoracic Application Of Electrical Cardiopulmonary
Resuscitation For Treatment Of Cardiac Arrest," Crit Care Med, vol.
36, no. 11, pp. s458-66, 2008 and "Coronary Blood Flow Produced by
Muscle Contractions Induced by Intracardiac Electrical CPR during
Ventricular Fibrillation," PACE vol. 32, pp. S223-7, 2009.
[0052] Table 1 below provides an exemplary range of parameter
values corresponding to empirically determined effectiveness.
TABLE-US-00001 TABLE 1 Exemplary Parameter Value Ranges for MVT
Value of Parameter Value of Parameter Parameter (Implanted Devices)
(External Devices) MVT Duration 20-120 sec. 20-120 sec. Train Rate
30-120 per min. 30-120 per min. Pulse Current 0.25-5 A 0.25-5 A
Amplitude Pulse Voltage 15-250 V? 60-300 V Amplitude Pulse Width
0.15-10 ms 0.15-10 ms Pulse Period 5-70 ms 5-70 ms
[0053] In a related aspect of the invention, the MVT waveform is
tuned to increase selectivity of muscle type in the application of
the MVT. Muscle type selectivity permits more precise targeted
treatment based on the patient's condition, and facilitates
management of muscle fatigue to prolong the MVT treatment
duration.
[0054] An MVT waveform that is optimized for skeletal muscle
capture (OSC) according to one embodiment is adapted to force
primarily skeletal muscle contractions. The OSC waveform is adapted
to force a contraction and subsequent release of skeletal muscles
in order to achieve perfusion of the heart and other vital organs,
and can force some amount of ventilation.
[0055] An MVT waveform that is optimized for myocardial capture
(OMC) according to a related embodiment is adapted to force cardiac
muscle contractions. The OMC waveform is adapted to force
contraction of primarily cardiac muscles in order to achieve some
level of perfusion for the heart and other vital organs. Tables 2
and 3 below provide exemplary ranges for OSC and OMC MVT parameter
values; whereas tables 4 and 5 below provide an exemplary optimal
set of values for OSC and OMC waveforms, respectively.
TABLE-US-00002 TABLE 2 Example Ranges of Optimal OSC Parameter
Values. Variable Parameter Optimal Range Pulsed Output 75-300 V
(external); Voltage 20-80 V (implantable) Pulsed Output 1-5 A
Current Pulse Width .10-.25 ms Pulse Period 10-20 ms Duration 10-30
seconds Packet Width 100-300 ms Train Rate 80-160 bpm
TABLE-US-00003 TABLE 3 Example Ranges of Optimal OMC Parameter
Values. Variable Parameter Optimal Range Pulsed Output 75-300 V
(external); Voltage 20-80 V (implantable) Pulsed Output 1-5 A
Current Pulse Width 5-10 ms Pulse Period 20-40 ms Duration 10-30
seconds Packet Width 100-300 ms Train Rate 80-160 bpm
TABLE-US-00004 TABLE 4 Exemplary Stimulation Waveform for OSC
Variable Parameter Optimal Value Pulsed Output 75-300 V (external);
Voltage 20-80 V (implantable) Pulsed Output 2 A Current Pulse Width
7.5 ms Pulse Period 30 ms Duration 20 seconds Packet Width 200 ms
Train Rate 120 bpm
TABLE-US-00005 TABLE 5 Exemplary Stimulation Waveform for OMC
Variable Parameter Optimal Value Pulsed Output 75-300 V (external);
Voltage 20-80 V (implantable) Pulsed Output 2 A Current Pulse Width
.15 ms Pulse Period 15 ms Duration 20 seconds Packet Width 200 ms
Train Rate 120 bpm
[0056] In one type of embodiment, the waveform parameters are
varied or modulated for different purposes. One such purpose is to
enhance or adjust the MVT effectiveness--that is, to vary the
hemodynamic and other electrostimulation effects to achieve one or
more treatment goals. One such treatment goal is management of
muscle fatigue. MVT stimulation can, in a matter of a few minutes,
fatigue the heart or other muscles to a point where they become
unresponsive to further stimulation. Accordingly, in this
embodiment, the MVT parameters are set or adjusted to minimize, or
simply reduce, MVT-induced muscle fatigue, thereby allowing the MVT
treatment to be prolonged.
[0057] In one example embodiment, the MVT-enabled implantable or
external electrotherapy device uses its hemodynamic monitoring
facilities to measure variables such as blood flow, blood pressure,
or blood oxygenation, or a combination thereof. Using this measured
information, the intensity and targeting of the MVT is adjusted. To
illustrate targeting, in one specific example, when the monitored
hemodynamic output from MVT stimulating the heart with an OMC
waveform begins to decrease, the MVT circuit responds to the
reduction by switching to a OSC waveform to stimulate the
non-cardiac muscles and give the heart the opportunity to rest and
either conserve or restore its ATP stores. To illustrate adjustment
of MVT intensity, the pulse amplitude, or pulse period (or both)
are adjusted to reduce the degree of stimulation being applied
while the hemodynamic condition is monitored. In one situation, the
MVT intensity is reduced to a minimum level where the hemodynamic
output is still adequate. This reduction in intensity reduces
muscle fatigue effects and preserves battery life of the device,
which also prolongs the MVT treatment duration that is
possible.
[0058] In a related example, for a device that performs
defibrillation therapy, the controller is programmed to adjust the
MVT parameters to improve the likelihood of successful
defibrillation. Accordingly, in this embodiment, as the time to
administer the defibrillation shock approaches, the MVT-enabled
defibrillator switches to the OSC waveform for stimulating
primarily non-cardiac muscles. This gives the heart more time to
rest, and to be in a "fresher" state for receiving the
defibrillation therapy, which improves the likelihood of successful
conversion of the arrhythmia with defibrillation.
[0059] In another embodiment, for either the OSC, or OMC waveforms,
or in another type of MVT waveform which may be non-targeted to
muscle groups, the pulse period is modulated during administration
of the MVT administration. The degree of modulation can be in the
neighborhoods of 5%, 10%, 15%, or more. In one variant of this
embodiment, the modulation is randomized, or noise-like. In another
embodiment, the modulation is applied with a certain pattern (i.e.,
with a predetermined modulating signal), or with a certain
combination of patterns, which can be alternated based on
randomization or based on one or more alternation functions.
Modulation of the pulse period in any of these fashions may help to
recruit more muscle fibers than a MVT signal with non-modulated
pulse period, and may reduce or delay the onset of muscle fatigue
caused by MVT. Additionally, the modulation of pulse period may
enhance the hemodynamic effect, which in turn permits a reduction
in pulse amplitude for an equivalent hemodynamic output or
sympathetic stimulation effect.
[0060] In a further aspect of the invention, the various electrodes
described above for MVT administration can be selectively switched
in and out of the pulse generating circuitry, enabling selective
application of MVT to specific regions of the body (corresponding
to specific muscles or muscle groups). Table 6 below lists various
exemplary muscles that are individually targeted in one type of
embodiment.
TABLE-US-00006 TABLE 6 Exemplary Muscles Targeted through Specific
MVT Electrode Placement Muscle ID Muscle Description A Heart B
Right Pectoral C Left Pectoral D Right Intercostals E Left
Intercostals F Right Abdominals G Left Abdominals
[0061] In one type of embodiment according to this aspect of the
invention, the targeting of muscles is automatically coordinated
and varied based on changing circumstances, by the MVT-enabled
device, to achieve a desired therapeutic effect based on the
monitored patient condition, including the type of arrhythmia, the
hemodynamic effect of applied MVT, and on the specific treatment or
rescue algorithm being administered. In a related embodiment, the
targeting of specific muscles is coordinated with the MVT waveform
to be applied to further enhance the specificity of the MVT
targeting.
[0062] One example of the desired therapeutic effect is management
of muscle fatigue. In a corresponding embodiment, certain muscles
are stimulated by MVT for longer or shorter durations based on that
muscle's endurance of MVT. In a related embodiment, muscle groups
having left and right sides, i.e., pectorals, intercostals,
abdominals, are stimulated such that only one side at a time is
activated by MVT, allowing the other side to rest and recuperate.
Variation of muscle selection can be predetermined according to a
programmed algorithm which is selected in response to the detected
type of arrhythmia. Alternatively, to account for variation among
patients, selection of muscles for stimulation is made in response
to hemodynamic monitoring.
[0063] In one embodiment, the controller of the MVT circuit
maintains a one or more data structures that relate the different
muscles for which the device is configured to stimulate via MVT, to
amplitude and waveform parameter information corresponding to that
muscle group. In a related embodiment, the data structure(s)
further include associations between treatment algorithms
corresponding to various arrhythmias or patient conditions, as
measured by the patient monitoring facilities of the device, and
MVT parameter values to use for those arrhythmias or
conditions.
[0064] In one example, the device is programmed to apply relatively
higher intensity MVT to one type of muscle group (or one side of
the body) than to another muscle group or side of the body as a
test of endurance of the patient's musculature to MVT. The other
side, which is less intensely stimulated, may then remain available
for longer-duration MVT therapy.
[0065] In another embodiment, the device is configured with an
algorithm to apply MVT as a test stimulus to assist in diagnosis of
the patient's condition or in adjustment of the MVT parameters in
order to provide better patient-specific treatment. In one example
of such an embodiment, the hemodynamic monitoring includes both,
blood flow information, and blood oxygenation information. MVT is
applied to force perfusion and ventilation, and the hemodynamic
condition is monitored. The presence of adequate blood flow being
generated by the MVT, as measured by the blood flow monitoring,
while the blood oxygenation reads lower than expected (based on
baseline data stored in the device corresponding to the duration of
the patient's arrhythmia and amount of flow measured), suggests
that the patient is not achieving sufficient respiration.
Accordingly, in this embodiment, the MVT is adapted to increase the
proportion of time or degree of stimulation targeting muscles that
provide a ventilation effect. Thus, for instance, the MVT may be
adapted to stimulate the phrenic nerve for a longer period (to
thereby cause the diaphragm to contract for a longer time, causing
a larger breath to be forced).
[0066] In another example, hemodynamic monitoring is configured to
distinguish between forced pulse output and return. In one
particular embodiment, the device is configured to first test for a
weak return, then test for a weak pulse. An indication of weak
return but adequately high pulse pressure suggests that the heart
is having difficulty expanding to fill with blood (e.g.,
tamponade). Accordingly, the MVT is automatically adapted to
enhance and prolong the targeting of muscles that tend to expand
the chest cavity, thereby lowering pressure around the heart to
help draw in more blood. In another example, a strong return but
weak pulse indicates that the heart is likely to have become
distended. In response, the MVT is adapted to optimize contraction
of the distended heart, such as, for instance, extending the
duration of the pulse packets to force the heart to stay contracted
for a longer period of time. Alternatively, or additionally, an OSC
waveform can be synchronized with an OMC waveform such that one
immediately follows the other. Thus, the heart can be compressed
for an extended period by first capturing myocardial cells to
contract, then by squeezing the heart using the skeletal
muscles.
[0067] In yet another specific example of this aspect of the
invention, hemodynamic monitoring is combined with ECG monitoring
and MVT to identify and treat PEA. In this example, PEA is detected
by the absence of hemodynamic output while the ECG measurement
indicates the presence of a heart rhythm. In this condition, MVT is
applied in synchronous fashion with the ECG. In one case, MVT is
applied such that the forced contraction and permitted relaxation
of the heart coincides with the QRS complex, thereby forcing the
heart to beat as if the ECG and the mechanical action were normal.
In another case, MVT is applied at a specific offset angle relative
to the normal QRS complex and mechanical action. In a related case,
the MVT is applied sequentially at a series of specific offset
angles for each ECG cycle.
[0068] Another aspect of the invention is directed to a multi-tier
MVT treatment algorithm, to be carried out by an implantable or
external MVT-enabled device. The device according to one embodiment
is configured to apply a higher intensity MVT at certain stages of
rescue or life support, and to apply a lower intensity MVT at other
stages. The intensity of MVT is varied by adjusting certain MVT
parameters. For MVT waveforms targeting skeletal muscle, the pulse
period is primarily varied to control the intensity of muscle
contraction. For MVT waveforms targeting primarily the myocardium,
the amplitude is the parameter primarily responsible for the MVT
intensity. To a lesser extent, the pulse period may also be
adjusted to control OMC intensity. Higher-intensity and
lower-intensity MVT may be selectively applied differently between
MVT targeting the heart and MVT targeting the skeletal muscles,
depending on the treatment objective, which in turn depends on the
detected patient condition obtained using the patient monitoring
facilities of the device. Thus, for example, in certain
circumstances, high-intensity MVT may be applied to skeletal
muscles while low-intensity MVT is applied to the myocardium, and
vice-versa.
[0069] In one embodiment, selection of high-intensity and
low-intensity MVT is based in part on the duration of the
arrhythmia, and on the current point in the treatment protocol. For
example, in the case of a patient condition treatable with
defibrillation or cardioversion, the MVT protocol requires
high-intensity MVT prior to the shocks for converting the
arrhythmia. More intensive MVT in this case places the heart in a
better condition to respond favorably to the defibrillation or
cardioversion. A refinement of this approach in a related
embodiment distinguishes between MVT targeting the myocardium and
MVT targeting skeletal muscles. In this refined approach, as
discussed above, the myocardium is progressively given
reducing-intensity MVT as the time to defibrillate approaches,
while the skeletal MVT remains at a high-intensity. This
improvement allows the heart to recover from the MVT. The
reduced-intensity MVT applied to the heart may also be adjusted to
optimize sympathetic stimulation (again, facilitating better
defibrillation success) while reducing the MVT energy applied to
force contraction, which fatigues the heart.
[0070] In a related embodiment, if defibrillation is unsuccessful
following the standard protocol of 4-6 shocks, the MVT for both,
the heart and the skeletal muscle, is automatically adjusted to
their respective low-intensity modes so that the patient's life
support can be prolonged with MVT. This becomes essentially a
muscle fatigue management (and device energy conservation)
strategy.
[0071] In another aspect of the invention, adaptive MVT is applied
to support patients in non life-critical conditions but where the
heart may benefit from a certain level of assistance. Hemodynamic
monitoring and ECG measurements are used to identify such
conditions, and to control proper administration of the MVT. In one
such condition, orthostatic hypotension, an omni-directional
accelerometer is included in the device, and is configured with the
measuring circuitry and decision logic to detect blood pressure
relative to movement and orientation of the patient. Thus, when the
patient is standing up from a seated or reclined position, and when
the patient's blood pressure fails to respond to accommodate such
movement, MVT may be applied to assist the heart to develop more
pressure. In one specific embodiment, the MVT for this application
targets the myocardium, with a specific OMC waveform to reduce the
discomfort the patient may experience due to inadvertent
stimulation of skeletal muscle.
[0072] The embodiments above are intended to be illustrative and
not limiting. Additional embodiments are within the claims. In
addition, although aspects of the present invention have been
described with reference to particular embodiments, those skilled
in the art will recognize that changes can be made in form and
detail without departing from the spirit and scope of the
invention, as defined by the claims.
[0073] Persons of ordinary skill in the relevant arts will
recognize that the invention may comprise fewer features than
illustrated in any individual embodiment described above. The
embodiments described herein are not meant to be an exhaustive
presentation of the ways in which the various features of the
invention may be combined. Accordingly, the embodiments are not
mutually exclusive combinations of features; rather, the invention
may comprise a combination of different individual features
selected from different individual embodiments, as understood by
persons of ordinary skill in the art.
[0074] Any incorporation by reference of documents above is limited
such that no subject matter is incorporated that is contrary to the
explicit disclosure herein. Any incorporation by reference of
documents above is further limited such that no claims included in
the documents are incorporated by reference herein. Any
incorporation by reference of documents above is yet further
limited such that any definitions provided in the documents are not
incorporated by reference herein unless expressly included
herein.
[0075] For purposes of interpreting the claims for the present
invention, it is expressly intended that the provisions of Section
112, sixth paragraph of 35 U.S.C. are not to be invoked unless the
specific terms "means for" or "step for" are recited in a
claim.
* * * * *