U.S. patent application number 09/990045 was filed with the patent office on 2002-06-27 for apparatus for detecting and treating ventricular arrhythmia.
Invention is credited to Brown, Ward, Heinrich, Stephen D..
Application Number | 20020082658 09/990045 |
Document ID | / |
Family ID | 22957649 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020082658 |
Kind Code |
A1 |
Heinrich, Stephen D. ; et
al. |
June 27, 2002 |
Apparatus for detecting and treating ventricular arrhythmia
Abstract
A system and method for long-term monitoring of cardiac
conditions such as arrhythmias is disclosed. The invention includes
a pulse generator including means for sensing an arrhythmia. The
pulse generator is coupled to at least one subcutaneous electrode
or electrode array for providing electrical stimulation such as
cardioversion/defibrillation shocks and/or pacing pulses. The
electrical stimulation may be provided between multiple
subcutaneous electrodes, or between one or more such electrodes and
the housing of the pulse generator. In one embodiment, the pulse
generator includes one or more electrodes that are isolated from
the can. These electrodes may be used to sense cardiac signals.
Inventors: |
Heinrich, Stephen D.;
(Rochester, MN) ; Brown, Ward; (Lacrosse,
WI) |
Correspondence
Address: |
Beth L. McMahon
Medtronic, Inc., MS 301
710 Medtronic Parkway
Mailstop LC340
Minneapolis
MN
55432
US
|
Family ID: |
22957649 |
Appl. No.: |
09/990045 |
Filed: |
November 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60252811 |
Nov 22, 2000 |
|
|
|
Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61N 1/3918 20130101;
A61N 1/39624 20170801; A61N 1/3987 20130101; A61N 1/3622 20130101;
A61N 1/0504 20130101; A61N 1/3629 20170801; A61N 1/3956 20130101;
A61N 1/39622 20170801; A61N 1/365 20130101; A61N 1/3962 20130101;
A61N 1/3621 20130101; A61N 1/36071 20130101; A61N 1/3925
20130101 |
Class at
Publication: |
607/9 |
International
Class: |
A61N 001/36 |
Claims
What is claimed is:
1. A system for providing arrhythmia therapy to a patient,
comprising: an implantable pulse generator; a sensing circuit
coupled to the implantable pulse generator; and a subcutaneous
electrode array coupled to the implantable pulse generator to
deliver electrical stimulation to the patient upon detection by the
sensing circuit of an arrhythmia.
2. The system of claim 1, wherein the subcutaneous electrode array
is a defibrillation electrode array to deliver relatively
high-voltage electrical stimulation to the patient.
3. The system of claim 1, wherein the sensing circuit includes a
circuit to sense a bradyarrhythmia event, and wherein the
subcutaneous electrode array is configured to deliver at least one
pacing pulse to the patient upon detection of the bradyarrhythmia
event.
4. The system of claim 1, wherein the system is housed within a
can, and wherein the sensing circuit includes at least two sensing
electrodes on at least a first surface of the can to sense cardiac
signals.
5. The system of claim 2, wherein the system is housed within a
can, and wherein the sensing circuit utilizes the defibrillation
electrode array and the can to sense for an arrhythmia.
6. The system of claim 1, wherein the can includes at least one
surface to deliver high-voltage shocks.
7. The system of claim 4, wherein the can includes at least one
surface to deliver high-voltage shocks, and wherein the surface to
deliver high-voltage shocks is different from the at least first
surface of the can.
8. A method for treating patient arrhythmias, including the methods
of: a.) providing a subcutaneous pulse generator; b.) providing a
monitoring circuit to monitor the patient's cardiac signals for
arrhythmias; and c.) providing a subcutaneous electrode array to
deliver electrical therapy to a patient.
9. A method of using a subcutaneously-placed pulse generator to
treat arrhythmias, including the methods of: a.) detecting an
arrhythmia; and b.) employing at least one subcutaneous electrode
to deliver therapy based on the detected arrhythmia.
10. The method of claim 9, wherein the detected arrhythmia is a
tachyarrythmia, wherein the at least one subcutaneous electrode
includes a defibrillation electrode, and wherein the therapy that
is delivered is a relatively high-voltage shock.
11. The method of claim 9, wherein the detected arrhythmia is a
bradyarrythmia, and wherein step b includes delivering a pacing
pulse in response to the detected bradyarrythmia.
12. A system for delivering electrical energy to the heart of a
patient, the system comprising: a subcutaneous pulse generator; at
least one sensing electrode disposed on a surface of the pulse
generator and positioned proximate to subcutaneous tissue; and at
least one electrode array coupled to the pulse generator and
positioned subcutaneously on the patient.
13. An apparatus for monitoring cardiac signals of a patient,
comprising; a hermetically-sealed housing; sensing means included
within the housing; and first and second electrode sets coupled to
the sensing means, the first electrode set including at least one
electrode adjacent to a surface of the housing positionable
proximate subcutaneous tissue at a first location in the patient's
body, and the second electrode set coupled to a connector on the
housing and forming an electrode array subcutaneously positionable
in the patient's body at a location different from the first
location.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method and apparatus for
treating ventricular arrhythmias; and more particularly, relates to
a method and apparatus for long-term monitoring of arrhythmias, and
for the delivery of acute tachyarrhythmia and bradyarrhythmia
therapy using a subcutaneous stimulation device.
DESCRIPTION OF THE PRIOR ART
[0002] It has long been known to use implantable systems to protect
patients that are at risk for life-threatening arrhythmias. For
example, rapid heart rhythms commonly referred to as
tachyarrhythmias are generally treated using implantable devices
such as the Medtronic Model 7273 GEM II DR or the 7229 GEM II SR,
both commercially available from the Medtronic Corporation. These
systems detect the presence of tachyarrhythmia conditions by
monitoring the electrical and mechanical heart activity (such as
intra-myocardial pressure, blood pressure, impedance, stroke volume
or heart movement) and/or the rate of the electrocardiogram. These
devices require that one or more defibrillation electrodes be
positioned within the atrium and/or ventricle of a patient's heart
using current endocardial lead placement techniques. The use of
such systems provides consistent long-term monitoring capabilities,
and relatively good protection against life-threatening
tachyarrhythmias.
[0003] Similarly, bradyarrhythmias, which are heart rhythms that
are too slow, are generally treated using implantable pulse
generators. Such devices are described in commonly-assigned U.S.
Pat. Nos. 5,158,078, 4,958,632, and 5,318,593, for example. As with
devices to treat tachyarrhythmias, most implantable pulse
generators that treat these types of conditions generally require
leads that are implanted within one or more cardiac chambers.
[0004] Although the use of endocardial leads placed within the
cardiac chambers of a patient's heart provides the capability to
deliver a relatively reliable, long-term arrhythmia therapy, there
are disadvantages associated with such treatments. The placement of
these leads requires a relatively time-consuming, costly procedure
that is not without risks to the patient including infection, the
possibility of vascular perforation, and tamponade. Moreover, some
people are not candidates for endocardial leads. For example,
patients with artificial mechanical tricuspid valves are generally
not candidates for leads that extend from the right atrium, through
this valve, to the right ventricle, as is the case with most right
ventricular endocardial leads. This is because the use of such
leads interfere with the proper mechanical functioning of the
valves. Other patients that are not candidates for endocardial lead
placement include those with occluded venous access, or patients
with congenital heart defects.
[0005] Patients that are contraindicated for endocardial lead
placement must often undergo a procedure to attach the lead to the
external surface of the heart. This type of epicardial lead
placement involves a more invasive procedure that requires a longer
recovery time, makes follow-up procedures very difficult, and is
also associated with increased patient risk, including an increased
chance of contracting an infection.
[0006] Another problem associated with both endocardial and
epicardial leads involves patient growth. More specifically, a lead
placed within a child's cardiac vasculature will likely need to be
re-positioned or replaced as the child matures. Such lead
replacement procedures can be dangerous, especially when
previously-placed leads are extracted rather than left in position
within the body.
[0007] One alternative to endocardial and epicardial leads involves
subcutaneously-placed electrode systems. For example, in U.S. Pat.
No. Re27,652 by Mirowski, et al., a defibrillation system employs a
ventricular endocardial electrode and a plate electrode mounted to
the heart directly, subcutaneously, or to the skin to deliver
high-voltage therapy to the patient. A similar lead system
disclosed in U.S. Patent No. in commonly-assigned U.S. Pat. No.
5,314,430 to Bardy includes a coronary sinus/great vein electrode
and a subcutaneous plate electrode located in the left pectoral
region which may optionally take the form of a surface of the
defibrillator housing.
[0008] What is needed, therefore, is a system and method that can
provide long-term monitoring for various types of arrhythmias,
provide patient therapy when needed, and also overcome the problems
associated with both endocardial and epicardial lead placement.
SUMMARY OF THE INVENTION
[0009] The current invention provides a system and method for
long-term monitoring for arrhythmias. The invention includes a
pulse generator including means for sensing an arrhythmia. The
pulse generator is coupled to at least one electrode or electrode
array for providing electrical stimulation to a patient. The
stimulation may include cardioversion/defibrillation shocks and/or
pacing pulses. The electrical stimulation may be provided between
multiple electrodes, or between one or more electrodes and the
housing of the pulse generator. In one embodiment, the pulse
generator includes one or more electrodes that are isolated from
the can. These electrodes may be used to sense cardiac signals.
[0010] According to one embodiment of the invention, an apparatus
is provided for monitoring cardiac signals of a patient. The
apparatus includes a hermetically-sealed housing, sensing means
included within the housing, and first and second electrode sets
coupled to the sensing means. The first electrode set includes at
least one electrode adjacent to a surface of the housing
positionable proximate subcutaneous tissue at a first location in
the patient's body. The second electrode set is coupled to a
connector on the housing and forms an electrode array
subcutaneously-positionable in the patient's body at a location
different from the first location.
[0011] According to another embodiment of the invention, a method
of therapy is provided. This method includes monitoring the
patient's cardiac signals for a condition such as an arrhythmia,
and thereafter delivering a electrical therapy to a patient via a
subcutaneous electrode array is the condition is detected. Other
aspects of the invention will become apparent from the drawings and
the accompanying description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates an exemplary subcutaneous electrode and
pulse generator as may be used in accordance with the current
invention.
[0013] FIG. 2 is a block functional diagram of an illustrative
embodiment of a pulse generator that may be employed according to
the present invention.
[0014] FIG. 3 is a top view of an electrode array 300 as may be
used with the current invention.
[0015] FIG. 4A is a side view of a pulse generator illustrating the
orientation of electrodes A, B and C disposed on the device
housing.
[0016] FIG. 4B is a side view of a pulse generator wherein at least
one of the electrodes extends away from the pulse generator via a
lead extension.
[0017] FIG. 4C is a side view of a pulse generator wherein at least
one of the electrodes is located at a proximal end of a lead.
[0018] FIG. 4D is a side view of a pulse generator wherein multiple
electrodes are located on an edge of a device housing.
[0019] FIG. 4E is a side view of yet another embodiment of a device
housing including an array of electrodes.
[0020] FIG. 4F is a side view of a device having a first
alternative shape.
[0021] FIG. 4G is a side view of a device having a second
alternative shape.
[0022] FIG. 5 is a timing diagram illustrating one embodiment of a
detection method used during bradyarrhythmia monitoring.
[0023] FIG. 6 is a block diagram illustrating an electrode array
positioned around a patient's side, with electrode coils extending
to the patient's back.
[0024] FIG. 7 is a block diagram illustrating an electrode array
positioned on patient's back in a more superior position.
[0025] FIG. 8 is a block diagram illustrating an electrode array
positioned around a patient's side, with coil electrodes extending
to the patient's back in a more posterior position.
[0026] FIG. 9 is a block diagram illustrating an electrode array
positioned on a patient's back, and a second subcutaneous disk
electrode positioned on a patient's chest.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The current invention provides a system and method for
long-term monitoring for arrhythmias. The invention also provides
acute therapy delivery in the event an arrhythmia episode is
detected. According to one embodiment of the invention, a
subcutaneous pulse generator is provided. This pulse generator may
be a transthoracic Implantable Cardioversion/Defibrillator (ICD)
such as the GemDR.TM. Model 7271 or the GEM II VR Model 7229, both
commercially available from the Medtronic Corporation. The pulse
generator is coupled to at least one subcutaneously-placed
electrode or electrode array. Cardioversion/defibrillation pulses
and/or pacing pulses may be delivered between the electrode and the
can of the device, or between two subcutaneously-placed
electrodes.
[0028] FIG. 1 illustrates an implantable pulse generator 10 and an
exemplary associated lead system according to the current
invention. Pulse generator 10 includes a device housing 12, and is
further coupled to a lead 14 which may be implanted subcutaneously
in the left chest or on the back as discussed below. Lead 14 may
include a subcutaneous plate electrode 16, which may be any of the
various known subcutaneous plate electrodes. This type of
subcutaneous electrode may be located proximal the left ventricular
cavity on the patient's chest, on the patient's side or back, or
any other portion of the body appropriate for providing electrical
stimulation to the heart. Similar electrodes are disclosed in
commonly-assigned U.S. Pat. Nos. 4,392,407, 5,261,400, and
5,292,338, all incorporated herein by reference. During use,
electrical stimulation may be delivered to heart 18 between
electrode 16 and device housing 12.
[0029] FIG. 2 is a block functional diagram of an illustrative
embodiment of a pulse generator that may be employed according to
the present invention. As illustrated, the device is embodied as a
microprocessor-based stimulator. However, other digital circuitry
embodiments and analog circuitry embodiments are also believed to
be within the scope of the invention. For example, devices having
general structures as illustrated in U.S. Pat. No. 5,251,624 issued
to Bocek et al., U.S. Pat. No. 5,209,229 issued to Gilli, U.S. Pat.
No. 4,407,288, issued to Langer et al, U.S. Pat. No. 5,662,688,
issued to Haefner et al., U.S. Pat. No. 5,855,893, issued to Olson
et al., U.S. Pat. No. 4,821,723, issued to Baker et al. or U.S.
Pat. No. 4,967,747, issued to Carroll et al., all incorporated
herein by reference in their entireties, may also be usefully
employed in conjunction with the present invention. FIG. 1 should
thus be considered illustrative, rather than limiting with regard
to the scope of the invention.
[0030] The primary elements of the apparatus illustrated in FIG. 2
are a microprocessor 100, read-only memory (ROM) 102, random-access
memory (RAM) 104, a digital controller 106, an input amplifier
circuit 110, two output circuits 108 and 109, and a
telemetry/programming unit 120. Read-only memory stores software
and/or firmware for the device, including the primary instruction
set defining the computations performed to derive the various
timing intervals employed by the device. RAM 104 generally serves
to store variable control parameters, such as programmed pacing
rate, programmed cardioversion/defibrillation intervals, pulse
widths, pulse amplitudes, and so forth which are programmed into
the device by the physician. Random-access memory 104 also stores
derived values, such as the stored time intervals separating
tachyarrhythmia pulses and the corresponding high-rate pacing
interval.
[0031] Controller 106 performs all of the basic control and timing
functions of the device. Controller 106 includes at least one
programmable timing counter, which is used to measure timing
intervals within the context of the current invention. On timeout
of the pacing escape interval or in response to a determination
that a cardioversion, defibrillation, or pacing pulse is to be
delivered, controller 106 triggers the appropriate output pulse
from high-voltage output stage 108, as discussed below. In one
embodiment, controller may also control the amplitude of pacing
pulses, as well as the energy associated with defibrillation and
cardioversion shocks.
[0032] Following generation of stimulus pulses, controller 106 may
be utilized to generate corresponding interrupts on control lines
132 to microprocessor 100, allowing it to perform any required
mathematical calculations, including all operations associated with
evaluation of return cycle times and selection of
anti-tachyarrhythmia therapies according to the present invention.
The timing/counter circuit in controller 106 also may control
timing intervals such as ventricular refractory periods, as is
known in the art. The time intervals may be determined by
programmable values stored in RAM 104, or values stored in ROM.
[0033] Controller 106 may also generate interrupts for
microprocessor 100 on the occurrence of sensed ventricular
depolarizations or beats. The timing and morphology of sensed
cardiac waveforms may also be used by microprocessor 100 to
determine whether an arrhythmia is occurring so that therapy may be
delivered as discussed further below.
[0034] Output stage 108 contains a high-output pulse generator
capable of generating cardioversion/defibrillation pulses.
According to the current invention, these pulses may be applied
between a subcutaneous electrode or electrode array coupled to
terminal 134 and the can of the pulse generator. Alternatively, the
pulses may be provided between an electrode coupled to terminal 134
and a second subcutaneous electrode or electrode array coupled to
terminal 136. Typically the high-output pulse generator includes
one or more high-voltage capacitors, a charging circuit, and a set
of switches to allow delivery of monophasic or biphasic
cardioversion or defibrillation pulses to the electrodes employed.
Output circuit 108 may further provide pacing pulses to the heart
under the control of controller 106. These pacing pulses, which may
be between 50 and 150 volts in amplitude, are provided via one or
more of the subcutaneously-located electrodes.
[0035] Sensing of ventricular depolarizations (beats) is
accomplished by input circuit 110, which is coupled to electrode
138 and one of electrodes 140 and 142. This circuitry may include
amplification, and noise detection and protection circuitry. In one
embodiment, signal sensing is disabled during periods of excessive
noise. Noise rejection filters and similar circuitry may also be
included, as is known in the art. Input circuit 110 provides
signals indicating both the occurrence of natural ventricular beats
and paced ventricular beats to the controller 106 via signal lines
128. Controller 106 provides signals indicative of the occurrence
of such ventricular beats to microprocessor 100 via signal lines
132, which may be in the form of interrupts. This allows the
microprocessor to perform any necessary calculations or to update
values stored in RAM 104.
[0036] Optionally included in the device may be one or more
subcutaneously or cutaneously-positioned physiologic sensors 148,
which may be any of the various known sensors for use in
conjunction with implantable stimulators. Any sensor of this type
known in the art may be employed within the context of the current
invention. Additionally, if desired, sensors positioned within the
cardiovascular system may be utilized. For example, sensor 148 may
be a hemodynamic sensor such as an impedance sensor as disclosed in
U.S. Pat. No. 4,865,036, issued to Chirife or a pressure sensor as
disclosed in U.S. Pat. No. 5,330,505, issued to Cohen, both of
which are incorporated herein by reference in their entireties.
Alternatively, sensor 148 may be a demand sensor for measuring
cardiac output parameters, such as an oxygen saturation sensor
disclosed in U.S. Pat. No. 5,176,137, issued to Erickson et al. or
a physical activity sensor as disclosed in U.S. Pat. No. 4,428,378,
issued to Anderson et al., both of which are incorporated herein by
reference in their entireties.
[0037] Sensor processing circuitry 146 transforms the sensor output
into digitized values for use in conjunction with detection and
treatment of arrhythmias. These digitized signals may be monitored
by controller 106 and microprocessor 100 and used alone or in
combination with sensed electrical cardiac signals to provide
diagnostic information used to determine the onset of an arrhythmia
or other cardiac conditions. These signals may also be used to
determine an optimal time for shock delivery. For example, an
impedance sensor may be used to determine when a patient has
exhaled so that shock delivery may occur when the lungs are
relatively deflated, since this may result in lower defibrillation
thresholds (DFTs). Sensor signals may also be stored in RAM 104 for
later diagnostic use.
[0038] External control of the implanted cardioverter/defibrillator
is accomplished via telemetry/control block 120 that controls
communication between the implanted cardioverter/pacemaker and an
external device 121. Any conventional programming/telemetry
circuitry is believed workable in the context of the present
invention. Information may be provided to the
cardioverter/pacemaker from the external device and passed to
controller 106 via control lines 130. Similarly, information from
the cardioverter/pacemaker may be provided to the telemetry block
120 via control lines 130 and thereafter transferred to the
external device.
[0039] In one embodiment, the external device 121 is a programmer
that may be utilized to diagnose patient conditions and to provide
any necessary re-programming functions. In another embodiment, the
external device may be a patient interface used to provide
information to, and/or receive commands from, the patient. For
example, the patient interface may be an externally-worn device
such as a wrist band that provides a warning to a patient
concerning an impending shock. The patient may be allowed to cancel
the shock if the patient believes the shock was prescribed
erroneously. This may be accomplished, for example, by pushing a
button, or issuing a voice command. The patient interface may
provide additional information, including a warning that medical
attention is required, and/or an indication concerning a low power
source. If desired, the patient interface could automatically place
an emergency telephone call via a wireless link, and/or could issue
patient positional information via a global positioning
system(GPS).
[0040] Any other system and method used for the detection and
treatment of tachyarrhythmias may be incorporated within the
current invention. Such systems and methods are described in
commonly-assigned U.S. Pat. Nos. 5,849,031, 5,193,535, and
5,224,475. In one embodiment, the system may include "tiered
therapies" for delivering treatment based on the type of arrhythmia
detected by the device. According to this approach, arrhythmias are
differentiated by analyzing the rate and morphology of a sensed
cardiac signal. Those arrhythmias considered less dangerous such as
ventricular tachycardias (VTs) may be treated by delivering a
series of low-power, relatively high-rate, pacing pulses to the
heart. This therapy is often referred to as anti-tachyarrhythmia
pacing therapy (ATP). In contrast, more perilous arrhythmias such
as ventricular fibrillations (VFs) may be treated by immediately
delivering more aggressive shock therapy. This type of system is
described in commonly-assigned U.S. Pat. No. 5,193,536, issued to
Mehra, U.S. Pat. No. 5,458,619 to Olson, U.S. Pat. No. 6,167,308 to
DeGroot, and U.S. Pat. No. 6,178,350 to Olson, et al., all
incorporated herein by reference. Within the context of the current
invention, ATP therapy is delivered using one or more subcutaneous
electrodes in the manner discussed below. In one embodiment of the
invention, a separate electrode may be provided within a
subcutaneous electrode array for delivering the ATP therapy.
[0041] According to another aspect of the inventive system, the
device may include means for decreasing discomfort associated with
high-voltage shocks. It is well known that high-voltage shocks are
painful for the patient. This discomfort can be minimized by
decreasing the amount of energy associated with the shock. One
mechanism for accomplishing this involves delivering a pre-shock
pulse waveform, as described in U.S. Pat. No. 5,366,485 issued to
Kroll. In one embodiment, this type of waveform could be a
programmable feature that is controlled by controller 106 via
parameters stored in RAM 104.
[0042] In yet another embodiment of the invention, the implantable
device includes a drug pump 150 as shown in FIG. 2. This pump may
be used to deliver a biologically-active agent such as an analgesic
drug to the patient prior to shock delivery to reduce discomfort.
The drug delivery may be accomplished via a catheter 152 that is
implanted subcutaneously or within the patient's vascular system. A
similar system is described in commonly-assigned U.S. Pat. No.
5,893,881 to Elsberry, incorporated herein by reference.
Alternatively, or in addition, this pump may deliver an agent such
as D-salotol, Procainamide or Quinidine to reduce the
defibrillation threshold of the required shock, thereby serving to
reduce pain. In a more complex embodiment, two separate drug pumps
might be employed to allow delivery of the threshold reducing agent
alone or in conjunction with an analgesic.
[0043] Pain control may also be accomplished by providing spinal
cord stimulation (SCS). For example, the Medtronic Itrel II
implantable neurostimulation system is widely implanted for
treatment and alleviation of intractable pain. Clinical reports and
studies have shown that SCS can reduce the discomfort associated
with high-voltage shocks. This type of system may utilize a lead
system of the type described in commonly-assigned U.S. Pat. Nos.
5,119,832, 5,255,691 or 5,360,441. These leads, as well as the
Medtronic Model 3487A or 3888 leads, include a plurality of spaced
apart distal electrodes that are adapted to be placed in the
epidural space adjacent to spinal segments T1-T6 to provide SCS
stimulation for pain reduction. In this embodiment, initial
detection and verification of fibrillation is followed by epidural
neural stimulation to produce paraesthesia. Thereafter, a shock may
be delivered. Should the cardioversion shock prove unsuccessful,
the process is repeated until the cardioversion therapies prove
successful or are exhausted. When successful defibrillation is
confirmed, the epidural SCS stimulation is halted.
[0044] In addition to SCS therapy, other types of stimulation such
as Transcutaneous Neurological Stimulators (TENs) may be provided
via electrode patches placed on the surface of a patient's body.
Subcutaneously-placed electrodes may also be positioned in the
T1-T6 area or in other areas of the body to deliver subcutaneous
electrical stimulation to reduce pain. In the context of the
current invention, the subcutaneously-placed electrode arrays may
include specialized electrodes to deliver the subcutaneous
stimulation prior to shock delivery to reduce patient
discomfort.
[0045] Turning now to a more detailed discussion of the electrode
systems used with the current invention, the electrode may be of a
type shown in FIG. 1. Alternatively, this electrode array may be
similar to the Model 6996 SQ commercially-available from the
Medtronic Corporation.
[0046] FIG. 3A is a top view of an electrode array 300 as may be
used with the current invention. Electrode array 300 is coupled to
distal end of lead 302. The array includes multiple finger-like
structures 304A through 304E. More or fewer of these finger-like
structures may be provided. Each finger includes a defibrillation
coil electrode shown as 306A through 306E. When connector 308 is
coupled to a pulse generator, a cardioversion/defibrillation pulse
may be provided via one or more of the electrodes 306A through
306E. In one embodiment, the electrodes that are activated may be
selected via a switch provided by the lead.
[0047] Electrode array 300 may include one or more sensing
electrodes such as electrode 310 provided for sensing cardiac
signals. This electrode may be used in a unipolar mode wherein
signals are sensed between an electrode and the device housing.
Alternatively, sensing may be performed between electrode 310 and
one of the coil electrodes 306 or another sensing electrode.
[0048] In use, the fingers 304 of electrode array are positioned
under the skin on a patient's chest, side, back, or any other point
of the body as required. Insulative spacers may be located between
the fingers, if desired, to prevent the coil electrodes 306A-E from
shorting together. If desired, multiple such electrode arrays may
be used in conjunction with the current invention. For example, one
electrode array may be positioned on the chest over the left
ventricle, while another electrode array is positioned behind the
left ventricle on the back. Cardioversion/defibrill- ation shocks
or pacing pulses may be delivered between the two electrode arrays.
Alternatively, electrical stimulation may be provided between one
or more electrode arrays and the device housing. As noted above,
sensing of the patient's cardiac signals may be performed between a
subcutaneous electrode array and the device can.
[0049] FIG. 3B is a top view of an alternative embodiment of
electrode array, shown as array 300A. In this embodiment, fingers
320A through 320C have a serpentine shape. More or fewer such
fingers may be provided. This shaped array directs current provided
by coiled electrodes 322A through 322C through a larger tissue
area, thereby decreasing defibrillation thresholds in some
instances. This embodiment may also include one or more sensing
electrodes 322. Any other shape may be utilized for the electrode
array.
[0050] The electrodes used with the current invention may be any of
the electrode types now known or known in the future for
subcutaneous delivery of electrical stimulation. Such electrodes
may be coated with a biologically-active agent such as
glucocorticoids (e.g. dexamethasone, beclamethasone), heparin,
hirudin, tocopherol, angiopeptin, aspirin, ACE inhibitors, growth
factors, oligonucleotides, and, more generally, antiplatelet
agents, anticoagulant agents, antimitotic agents, antioxidants,
antimetabolite agents, and anti-inflammatory. Such coating may be
useful to prevent excessive tissue in-growth. Such electrodes may
further include a low-polarization coating such as TiN.
Alternatively, the electrodes may be coated with an antibiotic or
other biologically-active agent used to prevent infections and
inflammation.
[0051] In another embodiment, the can itself may include a
subcutaneous electrode array of the type described in
commonly-assigned U.S. Pat. No. 5,331,966, which is incorporated
herein by reference in its entirety. This type of array, which is
provided by the Medtronic Model 9526 Reveal Plus Implantable Loop
Recorder, includes at least two sensing electrodes on the can for
sensing of cardiac signals. In all such systems, it will be
understood that the electrodes A, B, C on the surface of the
housing are electrically isolated from one another and the
conductive surface of the pulse generator housing 10 through
suitable insulating bands and electrical feedthroughs as described
in U.S. Pat. No. 4,310,000, incorporated herein by reference.
Examples of possible electrode orientations and configurations of a
three electrode system comprising the electrodes are set forth in
FIGS. 4A through 4G.
[0052] FIG. 4A is a side view of a pulse generator illustrating the
orientation of orthogonally-disposed electrodes A, B and C with two
electrodes on the connector block 418 and one electrode on the
pulse generator case 410. The spacing of the electrodes A, B and C
on each of the illustrated orientations of FIGS. 4A through 4G may
be on the order of about one inch but can be larger or smaller
depending on the exact size of the device. Smaller devices and
closer spacing will require greater amplification.
[0053] FIG. 4B is a side view of a pulse generator wherein at least
one of the electrodes extends away from the pulse generator by a
lead extension member 420 to achieve a greater inter-electrode
spacing, if desirable.
[0054] FIG. 4C is a side view of a pulse generator wherein at least
one of the electrodes 230 is located at a proximal end of a lead
432, which may be a lead coupled at a distal end to a subcutaneous
electrode or electrode array.
[0055] FIG. 4D is a side view of a pulse generator wherein multiple
electrodes are located of an edge of a device housing. It will be
understood that the electrodes placed on the edge of the pulse
generator case could constitute insulated pins of feedthroughs
extending through the wall of the case. As illustrated in FIGS. 4C
and 4D, the relative orientation of the electrodes may vary
somewhat from the orthogonal orientation depicted in FIGS. 4A and
4B.
[0056] FIG. 4E is a side view of yet another embodiment of a device
housing including an array of electrodes.
[0057] FIG. 4F is a side view of a device having a first
alternative "T" shape. This shape allows at least two of the
electrodes A and C to be positioned at a maximum distance from one
another, optimizing signal reception between the two
electrodes.
[0058] FIG. 4G is a side view of a device having a second
alternative "boomerang" shape which may be used to optimize
electrode positioning so that better signal reception is
achieved.
[0059] It will be appreciated that the shapes, sizes, and electrode
configurations of the devices shown in FIGS. 4A through 4G are
exemplary only, and any other shape, size or electrode
configuration imaginable is within the scope of the current
invention. As will be appreciated by those skilled in the art,
those configurations allowing for greater inter-electrode distances
will generally provide better signal reception. As such, it is
usually desirable to provide electrodes on at least two quadrants
of the device.
[0060] As described above, in one embodiment, the current invention
provides a pulse generator coupled to one or more subcutaneous
electrodes or electrode arrays. The electrodes provide electrical
stimulation to a patient based on sensed cardiac signals. The
sensed signals may be obtained using a selected pair of sensing
electrodes, which may reside on one or more of the leads coupled to
pulse generator 10, or on the device housing itself, as indicated
by FIGS. 4A through 4G.
[0061] Although all of the foregoing examples illustrate a housing
including three electrodes, more than three electrodes may be
provided. In one embodiment, four or more electrodes may be coupled
or adjacent to the device, and the physician may select which of
the electrodes will be activated for a given patient. In one
embodiment, cardiac signals are sensed between a selected pair of
the electrodes based on a signal optimization method. One
embodiment of this type of method is disclosed in U.S. patent
application Ser. No. 09/721,275 filed Nov. 22, 2000 and
incorporated herein by reference in its entirety.
[0062] Regardless of which one or more electrodes or electrode
pairs are selected for monitoring purposes, the sensed cardiac
signals may be analyzed to detect the presence of an arrhythmia.
The arrhythmia detection system and method could be, for example,
that employed by the Medtronic Model 9526 Reveal Plus device
commercially available from Medtronic Corporation. Alternatively, a
detection method such as described in commonly-assigned U.S. Pat.
Nos. 5,354,316 or 5,730,142 could be employed. If an arrhythmia is
detected, appropriate therapy may be administered. As described
above, one embodiment of the invention includes at least one
subcutaneous defibrillation electrode array. If monitoring
indicates the presence of a tachyarrhythmia or ventricular
fibrillation, a high-voltage shock may be delivered between one or
more subcutaneous defibrillation electrode(s) and a shocking
surface of the can, or one or more electrodes on the can. The shock
may alternatively be delivered between multiple defibrillation
electrodes. The monitoring system would then determine whether the
arrhythmia or fibrillation has terminated. If not, another shock
will be administered. This therapy will continue until normal
rhythm has been restored. In one embodiment, signals indicative of
sensed cardiac waveforms may be stored in RAM 104 and later
transferred to an external device via a communication system such
as telemetry circuitry 120.
[0063] According to another aspect of the invention, the sensing
electrodes may be placed on a surface of the can that is different
from the shocking surface of the can. Preferably, the shocking
surface is adjacent to muscle tissue, whereas the sensing
electrodes are placed adjacent to subcutaneous tissue.
[0064] As described above, therapy for bradyarrhythmia may be
provided in addition to, or instead of, the tachyarrhythmia
therapy. In this embodiment, output circuit 108 includes the
capability to deliver lower-voltage pulses for transthoracic pacing
therapy for bradyarrhythmias, as described above in reference to
FIG. 1. These lower-voltage pulses could be on the order of between
50 and 150 volts, for example. In one embodiment, these pulses have
an amplitude of around 100 volts. Monitoring for a bradyarrhythmia
could be accomplished using the sensing electrodes discussed above.
For example, the device may be programmed to detect a period of
asystole that is greater than a predetermined period, such as three
seconds. When a period greater than this length is detected, the
output circuit of the device is charged to the pacing voltage. A
transthoracic, monophasic pacing pulse may then be delivered
between the shocking surface of the can and a subcutaneous
electrode or electrode array, or between two such electrode or
electrode arrays. The sensing electrodes monitor the cardiac
waveform to ensure that the pacing pulse is only delivered during
predetermined periods of the cardiac cycle. For example, delivery
of the pulse should not occur during the occurrence of a T
wave.
[0065] Following delivery of a pacing pulse, the output circuit
begins charging in preparation for delivery of another pulse while
monitoring of the cardiac signals continues. For example,
monitoring of the patient's heart rate may be performed to
determine whether it is less than some predetermined rate such as
forty beats per minute. If so, another transthoracic, monophasic
pacing pulse is delivered. This process of pulse delivery followed
by charging of the output circuit is repeated until an intrinsic
heart rate of greater than the predetermined minimum rate is
detected.
[0066] The transthoracic pacing provided by the current invention
will likely be uncomfortable for the patient. Thus, this function
is not intended to provide chronic therapy. Once therapy delivery
has occurred for a bradyarrhythmic episode, a more traditional
device should be implanted to provide long-term therapy. In one
embodiment, the device may record whether any ACC/AHA class I
pacing indications has been met by the detected bradyarrhythmic
event. For example, if asystole greater than three seconds and/or
an escape rate less than forty beats per minute has been detected,
these indications are recorded. This data may then be transferred
to an external device to generate a physician notification. Other
actions may be taken, such as sounding an alarm, for example.
[0067] FIG. 5 is a timing diagram illustrating one embodiment of a
detection method used during bradyarrhythmia monitoring. If
asystole is detected for greater than, or equal to, a first
predetermined time period 500 such as three seconds, charging of
output capacitors occurs to a predetermined voltage such as 100
volts. This charging occurs during time period 502. At time 504, a
first pacing pulse is delivered, and recharging of the capacitors
begins at time 506. Monitoring for an escape rate longer than a
predetermined rate occurs during time period 508, which in one
embodiment is 1500 milliseconds. Thereafter, a second pacing pulse
is delivered at time 510 if an intrinsic beat does not occur. At
time 512, recharging occurs, and monitoring for the escape rate
again proceeds. If such therapy is not discontinued because of the
re-occurrence of the patient's intrinsic normal heart beat, the
patient will be required to seek immediate emergency attention,
since such therapy will be uncomfortable for the patient. The times
utilized to provide therapy as shown in FIG. 5 may be
programmable.
[0068] It may be appreciated from the foregoing discussion that
providing repeated therapy, and in particular, repeated
high-voltage pacing stimulation, will deplete a system power source
such as a battery relatively quickly. Therefore, in one embodiment,
the power source is rechargeable. For example, the pulse generator
may include rechargeable nickel cadmium batteries. Such batteries
may be recharged over a period of several hours using a radio
frequency link. Alternatively, a rechargeable capacitive energy
source such as disclosed in U.S. Pat. No. 4,408,607 to Maurer may
be utilized. In yet another embodiment, the pulse generator may
include both an implanted radio frequency (RF) receiving unit
(receiver) incorporating a back-up rechargeable power supply and a
non-rechargeable battery, as described in U.S. Pat. No. 5,733,313
incorporated herein by reference. The rechargeable power supply is
charged by an external RF transmitting unit worn by the patient.
Any other type of rechargeable power supply known in the art for
use with implantable medical devices may be used in the
alternative.
[0069] In one embodiment, the power source selected for use in the
current invention is capable of delivering up to ten therapy
shocks, with additional power being available for threshold
testing. However, compromises will exist since the power source
capacity will determine device size. In yet another embodiment, the
device is a 75-joule device having a volume of no more than 75
cubic centimeters. Preferably, the device includes a power source
and associated charge circuitry that provides a charge time of no
more than three minutes during the useful life of the device. In
another embodiment, the device should be capable of delivering a
35-joule shock after a one-minute charge time over the useful life
of the device.
[0070] FIGS. 6 through 9 illustrate various exemplary electrode
configurations as may be used with the current invention.
[0071] FIG. 6 is a block diagram illustrating an electrode array
300 positioned around a patient's side, with fingers 304 extending
to the patient's back. Electrical stimulation is delivered between
the electrode array and the device can 10, which is positioned over
the left ventricle. In one embodiment, sensing electrodes 600 are
positioned substantially facing toward subcutaneous tissue.
[0072] FIG. 7 is a block diagram illustrating an electrode array
positioned on a patient's back in a more superior position than is
shown in FIG. 6. Electrical stimulation is delivered between the
electrode array and the device can 10, which is positioned in the
abdominal cavity.
[0073] FIG. 8 is a block diagram illustrating an electrode array
positioned around a patient's side, with fingers 304 extending to
the patient's back in a more posterior position than is shown in
FIG. 6 or 7. Electrical stimulation is delivered between the
electrode array and the device can, which is positioned proximal
the right side of the heart.
[0074] FIG. 9 is a block diagram illustrating an electrode array
with fingers 304 positioned on a patient's back, and a second
subcutaneous disk electrode 306 such as electrode 16 (FIG. 1)
positioned on a patient's chest. Electrical stimulation may be
delivered from one of electrodes 304 or 306 to the other electrode
and/or the device housing 10. Alternatively, stimulation may be
provided from both electrode assemblies to the device housing. In
yet another embodiment, one or more additional subcutaneous
electrode or electrode arrays may be coupled to the device for
providing high-voltage shocks, for sensing cardiac signals, and/or
for delivering SCS, TENs, or subcutaneous low-voltage stimulation
as discussed above. If desired, the device may include programmable
logic to selectably enable those electrode and/or electrode arrays
to be activated during a given therapy delivery session. For
example, switching networks may be incorporated into output
circuitry 108 and/or input circuitry 110 (FIG. 2) such that this
type of programmably selected therapy may be provided. In one
instance, it may be desirable to activate one electrode
configuration to optimize sensing of cardiac signals, while
utilizing another configuration to provide optimal therapy
delivery.
[0075] The above-described inventive system and method provides a
therapy that avoids the risks of transvenous lead delivery. Such a
system may be used for patients that are at-risk for arrhythmias,
but have not yet experienced a confirmed arrhythmic episode. The
device may therefore provide a needed long-term monitoring
function, as well as any interventional therapy that is required.
Preferably, after an episode is detected and therapy is delivered
for a first time, the current system would be replaced with a more
conventional implantable defibrillator.
[0076] As discussed above, the inventive system provides many
important benefits over other conventional systems for some
patients. The procedure is faster because there is no need for
venous or epicardial access, and therefore the procedure is less
invasive, and would not require procedures needing sophisticated
surgical facilities and devices. Additionally, the implant
procedure can be accomplished without exposing the patient to
potentially-harmful radiation that accompanies fluoroscopy. The
risk of infection is reduced, and the procedure may be provided to
patients that are contraindicated for a more traditional device.
Additionally, one hundred percent patient compliance is achieved,
and the system is more comfortable than externally-worn devices.
The system is well suited for pediatric use, since the placement of
the electrodes allows lead length to be easily extended as a
patient grows. The system may also be employed in parts of the
world where more long-term therapies and treatments are not
available, and where sophisticated surgical skills and equipment
cannot be readily obtained.
* * * * *