U.S. patent application number 10/913037 was filed with the patent office on 2005-01-27 for switched capacitor defibrillation circuit.
This patent application is currently assigned to Cameron Health, Inc.. Invention is credited to Mezack, Gary P., Ostroff, Alan H..
Application Number | 20050021094 10/913037 |
Document ID | / |
Family ID | 46280153 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050021094 |
Kind Code |
A1 |
Ostroff, Alan H. ; et
al. |
January 27, 2005 |
Switched capacitor defibrillation circuit
Abstract
A defibrillator circuit for generating a rectangular waveform
across a patient from capacitively stored energy and employing a
plurality of capacitors initially chargeable to a common voltage
and thereafter sequentially switchable into parallel relation with
one another so as to raise the voltage supplied to an H-bridge
circuit from a point of decay back to said common voltage.
Inventors: |
Ostroff, Alan H.; (San
Clemente, CA) ; Mezack, Gary P.; (Norco, CA) |
Correspondence
Address: |
CROMPTON, SEAGER & TUFTE, LLC
Suite 800
1221 Nicollet Avenue
Minneapolis
MN
55403-2420
US
|
Assignee: |
Cameron Health, Inc.
|
Family ID: |
46280153 |
Appl. No.: |
10/913037 |
Filed: |
August 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10913037 |
Aug 6, 2004 |
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10011952 |
Nov 5, 2001 |
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6778860 |
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Current U.S.
Class: |
607/5 |
Current CPC
Class: |
A61N 1/3912 20130101;
A61N 1/3956 20130101; A61N 1/3906 20130101 |
Class at
Publication: |
607/005 |
International
Class: |
A61N 001/39 |
Claims
What is claimed is:
1. A device for providing electrical cardiac treatment, the device
comprising: first capacitor means for storing and discharging
electrical energy; second capacitor means for storing and
discharging electrical energy; and a first switch coupled to the
first capacitor means and second capacitor means such that: when
the first switch is in a first state, the second capacitor means is
isolated from the first capacitor means; and when the first switch
is in a second state, the second capacitor means is connected in
parallel to the first capacitor means.
2. The device of claim 1, further comprising an H-bridge output
circuit for delivering energy from the capacitor means to a
receiver for receiving the proximal end of a lead electrode
assembly.
3. The device of claim 2, further comprising a control circuit
coupled to the switch and the H-bridge, the control circuit adapted
to provide control signals causing the H-bridge to send a biphasic
waveform to the lead, the control circuit further adapted to cause
the switch to be: in the first state for a first portion of the
first phase of the biphasic waveform; and in the second state for a
second portion of the first phase of the biphasic waveform.
4. The device of claim 3, wherein the control circuit is also
adapted to cause the switch to be in the second state during the
second phase of the biphasic waveform.
5. The device of claim 1, wherein the capacitor means are housed in
a canister and the device is adapted to provide the electric signal
between an electrode disposed on the canister and a receiver for
receiving the proximal end of a lead electrode assembly.
6. The device of claim 1, wherein the capacitor means are housed in
a canister and the device is adapted to provide the electric signal
between two electrodes disposed on a lead electrode assembly
secured to the canister.
7. A device for providing electrical cardiac treatment, the device
comprising: a plurality of separate energy storage devices each
characterized by a degrading discharge curve; at least one switch
coupled to the plurality of energy storage devices such that: when
a switch is in a first state it causes a first energy storage
device to be isolated from a second energy storage device; and when
the switch is in a second state it causes the first energy storage
device to be connected in parallel to the second energy storage
device; and a control circuit coupled to the at least one switch
and adapted to enable the first energy storage device to be
sequentially coupled in parallel to additional energy storage
devices.
8. The device of claim 7, wherein the at least one energy storage
device includes at least one capacitor.
9. The device of claim 7, further comprising an H-bridge output
circuit for delivering energy from the at least one energy storage
device to a receiver for receiving the proximal end of a lead
electrode assembly.
10. The device of claim 9, wherein the control circuit is coupled
to the H-bridge and is adapted to provide control signals causing
the H-bridge to send a biphasic waveform to receiver for the lead
electrode assembly.
11. The device of claim 10, wherein the control circuit is also
adapted to cause the at least one switch to sequentially place each
of the plurality of energy storage devices in parallel during the
second phase of the biphasic waveform.
12. The device of claim 7, wherein the at least one energy storage
device is housed in a canister and the electric signal is provided
between the canister and a receiver for receiving the proximal end
of a lead electrode assembly.
13. The device of claim 7, wherein the device is adapted to provide
the electric signal between two electrodes disposed on a lead
electrode assembly.
14. A device for providing electrical cardiac treatment, the device
comprising: a first capacitor; means for selectively coupling the
first capacitor to a lead electrode assembly; a second capacitor;
and a first switch coupled to the first and second capacitors such
that, when the means for selectively coupling the first capacitor
to the lead is enabled to couple the first capacitor to the lead:
when the switch is in a first state, the second capacitor is
isolated from the first capacitor; and when the switch is in a
second state, the second capacitor is connected in parallel to the
first capacitor.
15. The device of claim 14, wherein the means for selectively
coupling includes an H-bridge circuit.
16. The device of claim 14, further comprising a control circuit
coupled to the switch and the means for selectively coupling, the
control circuit adapted to provide control signals causing the
means for selectively coupling to provide a biphasic waveform to
the lead, the control circuit further adapted to cause the switch
to be: in the first state for a first portion of the first phase of
the biphasic waveform; and in the second state for a second portion
of the first phase of the biphasic waveform.
17. The device of claim 16, wherein the control circuit is also
adapted to cause the switch to be in the second state during the
second phase of the biphasic waveform.
18. The device of claim 14, further comprising a canister.
19. The device of claim 18, wherein the capacitors are housed in
the canister and the device is adapted to selectively provide an
electric stimulus between the lead electrode assembly and an
electrode disposed on the canister.
20. The device of claim 18, wherein the device is adapted to
provide the electric signal between two electrodes disposed on the
lead electrode assembly.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S.
application Ser. No. 10/011,952, filed Nov. 5, 2001, the disclosure
of which is incorporated herein by reference.
[0002] The present invention may find application in systems such
as are disclosed in the U.S. patent application entitled
"SUBCUTANEOUS ONLY IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR AND
OPTIONAL PACER," having Ser. No. 09/663,607, filed Sep. 18, 2000,
now U.S. Pat. No. 6,721,597, and U.S. patent application entitled
"UNITARY SUBCUTANEOUS ONLY IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR
AND OPTIONAL PACER," having Ser. No. 09/663,606, filed Sep. 18,
2000, now U.S. Pat. No. 6,647,292, of which both applications are
assigned to the assignee of the present application, and the
disclosures of both applications are hereby incorporated by
reference.
[0003] Applications related to the foregoing applications include
U.S. application Ser. No. 09/940,283 entitled "DUCKBILL-SHAPED
IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR CANISTER AND METHOD OF USE,"
U.S. application Ser. No. 09/940,371 entitled "CERAMICS AND/OR
OTHER MATERIAL INSULATED SHELL FOR ACTIVE AND NON-ACTIVE S-ICD
CAN," U.S. application Ser. No. 09/940,468 entitled "SUBCUTANEOUS
ELECTRODE FOR TRANSTHORACIC CONDUCTION WITH IMPROVED INSTALLATION
CHARACTERISTICS," U.S. application Ser. No. 09/941,814 entitled
"SUBCUTANEOUS ELECTRODE WITH IMPROVED CONTACT SHAPE FOR
TRANSTHORACIC CONDUCTION," U.S. application Ser. No. 09/940,356
entitled "SUBCUTANEOUS ELECTRODE FOR TRANSTHORACIC CONDUCTION WITH
HIGHLY MANEUVERABLE INSERTION TOOL," U.S. application Ser. No.
09/940,340 entitled "SUBCUTANEOUS ELECTRODE FOR TRANSTHORACIC
CONDUCTION WITH LOW-PROFILE INSTALLATION APPENDAGE AND METHOD OF
DOING SAME," U.S. application Ser. No. 09/940,287 entitled
"SUBCUTANEOUS ELECTRODE FOR TRANSTHORACIC CONDUCTION WITH INSERTION
TOOL," U.S. application Ser. No. 09/940,377 entitled "METHOD OF
INSERTION AND IMPLANTATION OF IMPLANTABLE
CARDIOVERTER-DEFIBRILLATOR CANISTERS," U.S. application Ser. No.
09/940,599 entitled "CANISTER DESIGNS FOR IMPLANTABLE
CARDIOVERTER-DEFIBRILLATORS," U.S. application Ser. No. 09/940,373
entitled "RADIAN CURVE SHAPED IMPLANTABLE
CARDIOVERTER-DEFIBRILLATOR CANISTER," U.S. application Ser. No.
09/940,273 entitled "CARDIOVERTER-DEFIBRILLATOR HAVING A FOCUSED
SHOCKING AREA AND ORIENTATION THEREOF," U.S. application Ser. No.
09/940,378 entitled "BIPHASIC WAVEFORM FOR ANTI-BRADYCARDIA PACING
FOR A SUBCUTANEOUS IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR," and
U.S. application Ser. No. 09/940,266 entitled "BIPHASIC WAVEFORM
FOR ANTI-TACHYCARDIA PACING FOR A SUBCUTANEOUS IMPLANTABLE
CARDIOVERTER-DEFIBRILLATOR," the disclosures of which applications
are hereby incorporated by reference.
FIELD OF THE INVENTION
[0004] The subject invention relates to electronic circuitry and
particularly to circuitry having applications in defibrillating
apparatus.
BACKGROUND OF THE INVENTION
[0005] Defibrillation/cardioversion is a technique employed to
counter arrhythmic heart conditions including some tachycardias in
the atria and/or ventricles. Typically, electrodes are employed to
stimulate the heart with electrical impulses or shocks, of a
magnitude substantially greater than pulses used in cardiac pacing.
Because current density is a key factor in both defibrillation and
pacing, implantable devices may improve what is capable with the
standard waveform where the current and voltage decay over the time
of pulse deliver. Consequently, a waveform that maintains a
constant current over the duration of delivery to the myocardium
may improve defibrillation as well as pacing.
[0006] Defibrillation/cardioversion systems include body
implantable electrodes that are connected to a hermetically sealed
container housing the electronics, battery supply and capacitors.
The entire system is referred to as an implantable
cardioverter/defibrillator (ICD). The electrodes used in ICDs can
be in the form of patches applied directly to epicardial tissue,
or, more commonly, are on the distal regions of small cylindrical
insulated catheters that typically enter the subclavian venous
system, pass through the superior vena cava and, into one or more
endocardial areas of the heart. Such electrode systems are called
intravascular or transvenous electrodes. U.S. Pat. Nos. 4,603,705,
4,693,253; 4,944,300; and 5,105,810, the disclosures of which are
all incorporated herein by reference, disclose intravascular or
transvenous electrodes, employed either alone, in combination with
other intravascular or transvenous electrodes, or in combination
with an epicardial patch or subcutaneous electrodes. Compliant
epicardial defibrillator electrodes are disclosed in U.S. Pat. Nos.
4,567,900 and 5,618,287, the disclosures of which are incorporated
herein by reference. A sensing epicardial electrode configuration
is disclosed in U.S. Pat No. 5,476,503, the disclosure of which is
incorporated herein by reference.
[0007] In addition to epicardial and transvenous electrodes,
subcutaneous electrode systems have also been developed. For
example, U.S. Pat. Nos. 5,342,407 and 5,603,732, the disclosures of
which are incorporated herein by reference, teach the use of a
pulse monitor/generator surgically implanted into the abdomen and
subcutaneous electrodes implanted in the thorax. This system is far
more complicated to use than current ICD systems using transvenous
lead systems together with an active can electrode, and therefore,
it has no practical use. It has, in fact, never been used because
of the surgical difficulty of applying such a device (3 incisions),
the impractical abdominal location of the generator and the
electrically poor sensing and defibrillation aspects of such a
system.
[0008] Recent efforts to improve the efficiency of ICDs have led
manufacturers to produce ICDs which are small enough to be
implanted in the pectoral region. In addition, advances in circuit
design have enabled the housing of the ICD to form a subcutaneous
electrode. Some examples of ICDs in which the housing of the ICD
serves as an optional additional electrode are described in U.S.
Pat. Nos. 5,133,353; 5,261,400; 5,620,477; and 5,658,321, the
disclosures of which are incorporated herein by reference.
[0009] ICDs are now an established therapy for the management of
life threatening cardiac rhythm disorders, primarily ventricular
fibrillation (V-Fib). ICDs are very effective at treating V-Fib,
but are therapies that still require significant surgery.
[0010] As ICD therapy becomes more prophylactic in nature and used
in progressively less ill individuals, especially children at risk
of cardiac arrest, the requirement of ICD therapy to use
intravenous catheters and transvenous leads is an impediment to
very long term management as most individuals will begin to develop
complications related to lead system malfunction sometime in the 5-
to 10-year time frame, often earlier. In addition, chronic
transvenous lead systems, their reimplantation and removals, can
damage major cardiovascular venous systems and the tricuspid valve,
as well as result in life threatening perforations of the great
vessels and heart. Consequently, use of transvenous lead systems,
despite their many advantages, are not without their chronic
patient management limitations in those with life expectancies of
.ltoreq.5 years. The problem of lead complications is even greater
in children where body growth can substantially alter transvenous
lead function and lead to additional cardiovascular problems and
revisions. Moreover, transvenous ICD systems also increase cost and
require specialized interventional rooms and equipment as well as
special skill for insertion. These systems are typically implanted
by cardiac electrophysiologists who have had a great deal of extra
training.
[0011] In addition to the background related to ICD therapy, the
present invention requires a brief understanding of a related
therapy, the automatic external defibrillator (AED). AEDs employ
the use of cutaneous patch electrodes, rather than implantable lead
systems, to effect defibrillation under the direction of a
bystander user who treats the patient suffering from V-Fib with a
portable device containing the necessary electronics and power
supply that allows defibrillation. AEDs can be nearly as effective
as an ICD for defibrillation if applied to the victim of
ventricular fibrillation promptly, i.e., within 2 to 3 minutes of
the onset of the ventricular fibrillation.
[0012] AED therapy has great appeal as a tool for diminishing the
risk of death in public venues such as in air flight. However, an
AED must be used by another individual, not the person suffering
from the potential fatal rhythm. It is more of a public health tool
than a patient-specific tool like an ICD. Because >75% of
cardiac arrests occur in the home, and over half occur in the
bedroom, patients at risk of cardiac arrest are often alone or
asleep and cannot be helped in time with an AED. Moreover, its
success depends to a reasonable degree on an acceptable level of
skill and calm by the bystander user.
[0013] What is needed therefore, especially for children and for
prophylactic long term use for those at risk of cardiac arrest, is
a combination of the two forms of therapy which would provide
prompt and near-certain defibrillation, like an ICD, but without
the long-term adverse sequelae of a transvenous lead system while
simultaneously using most of the simpler and lower cost technology
of an AED. What is also needed is a cardioverter/defibrillator that
is of simple design and can be comfortably implanted in a patient
for many years.
[0014] Moreover, it has appeared advantageous to the inventor to
provide the capability in such improved circuitry to produce a
defibrillating waveform which includes a defibrillating pulse
approximating a rectangular pulse. Such a pulse is advantageous,
for example, because it can approximate a constant current density
across the heart.
SUMMARY
[0015] According to the invention, circuitry is provided for
enabling the generation of an approximation of a rectangular
waveform from energy stored in energy storage devices such as a
capacitor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] For a better understanding of the invention, reference is
now made to the drawings where like numerals represent similar
objects throughout the figures and wherein:
[0017] FIG. 1 is an electrical circuit schematic of an illustrative
embodiment of the invention;
[0018] FIG. 2 is a waveform diagram illustrative of operation of
the circuit of FIG. 1; and
[0019] FIG. 3 is a waveform diagram illustrative of operation of
the circuit of FIG. 1.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0020] An illustrative embodiment is shown in FIG. 1. The
illustrative embodiment includes an H bridge circuit 13 and a drive
circuit 15 for supplying voltage or energy to the H bridge circuit
13.
[0021] The H bridge circuit 13 may be of conventional form,
including first and second high side switches H.sub.1, H.sub.2 and
first and second low side switches L.sub.1, L.sub.2. The switches
H.sub.1, H.sub.2; L.sub.1, L.sub.2 may be manipulated to
appropriately and selectively apply a voltage present at junction
17 across a patient indicated by a patient resistance R.sub.PAT.
The H bridge circuit 13 may also include features disclosed in
co-pending application Ser. Nos. 10/011,955 and 10/011,957, filed
herewith on behalf of inventor Alan H. Ostroff and entitled
Defibrillation Pacing Circuitry and Simplified Defibrillator Output
Circuit.
[0022] The drive circuit 15 of FIG. 1 includes a plurality of
energy storage devices in the illustrative form of four capacitors
C.sub.1, C.sub.2, C.sub.3, C.sub.4. Across each capacitor Cl,
C.sub.2, C.sub.3, C.sub.4 is connected a respective secondary
l.sub.1, l.sub.2, l.sub.3, l.sub.4 of a transformer T.sub.1. The
primary of the transformer T.sub.1 is switchable via a switch
SW.sub.1 to connect to a source of D.C. voltage V.sub.S, e.g., a
battery.
[0023] The first capacitor C.sub.1 has a first terminal connected
to ground and a second terminal in common with the junction 17. The
second terminal of the capacitor C.sub.1 is further connected to
the cathode of a diode D.sub.1, whose anode is connected to a first
terminal of the first secondary winding l.sub.1. The remaining
capacitors C.sub.2, C.sub.3, C.sub.4 have second terminals which
are switchable via respective switches SW.sub.2, SW.sub.3, SW.sub.4
to establish or remove electrical connection to the junction 17.
The respective first terminals of the capacitors C.sub.2, C.sub.3,
C.sub.4 are connected to respective switches SW.sub.5, SW.sub.6,
SW.sub.7 which can be selectively operated to connect those
respective first terminals to ground. The respective second
terminals of the capacitors C.sub.2, C.sub.3, C.sub.4 are connected
to the respective cathodes of respective diodes D.sub.2, D.sub.3,
D.sub.4. The respective anodes of the diodes D.sub.2, D.sub.3,
D.sub.4 are connected to respective first terminals of the
secondary windings l.sub.2, l.sub.3, l.sub.4, whose second
terminals are connected to ground.
[0024] In illustrative operation of the circuit of FIG. 1, the
capacitors C.sub.1, C.sub.2, C.sub.3, C.sub.4 are charged to a
common voltage level V. Next, the high side switch H.sub.1 and the
low side switch L.sub.2 are closed while H.sub.2 and L.sub.1 are
open, thereby connecting the voltage on the capacitor C.sub.1
across the patient resistance R.sub.PAT.
[0025] As shown in FIG. 2, the voltage across the patient is
initially V.sub.PAT and decays with a time constant RC.sub.1 for a
selected time period up to a point in time denoted t.sub.1 in FIG.
2. At time t.sub.1, a switching signal .PHI..sub.2 (FIG. 3) is
activated to close the switch SW.sub.2. The patient voltage
V.sub.PAT initially rises and then begins to decay with a time
constant equal to R(C.sub.1+C.sub.2). At a selected time t.sub.2, a
switching signal .PHI..sub.3 is activated, closing the switch
SW.sub.3 and connecting the voltage across the capacitor C.sub.3 to
the junction 17. As shown in FIG. 2, the patient voltage again
rises and thereafter begins to decay with a time constant equal to
R(C.sub.1+C.sub.2+C.sub.3). Then, at time t.sub.3, the switching
signal .PHI..sub.4 is activated, closing the switch SW.sub.4,
thereby applying the voltage across the capacitor C.sub.4 and to
the junction 17, again resulting in the voltage V.sub.PAT rising
and thereafter decaying with a time constant
R(C.sub.1+C.sub.2+C.sub.3+C.sub.4). Finally, at time t.sub.4, the
switches H.sub.1, L.sub.2 are opened, thereby terminating the first
phase of the waveform.
[0026] If desired, these switches H.sub.2, L.sub.1 may then be
closed to produce a conventional second phase 19 of a biphasic
waveform. This waveform drops to a voltage V.sub.PAT1 and then
decays with a time constant determined by the patient resistance
R.sub.PAT and the effective value of the parallel capacitors
C.sub.1, C.sub.2, C.sub.3, C.sub.4. An inverted biphasic waveform
may also be produced by first activating H.sub.2 and L.sub.1.
[0027] It will be observed that circuitry according to the
preferred embodiment produces an approximation to a square or
rectangular pulse. The times t.sub.1, t.sub.2, t.sub.3, t.sub.4 can
easily be adjusted to further control the shape of the waveform,
for example, such that .DELTA.V remains constant for each interval
of decay despite the change in time constants each time an
additional capacitor, e.g., C.sub.2, C.sub.3, C.sub.4, is switched
into the current. Additionally, the number of parallel capacitors,
e.g., C.sub.1, C.sub.2, C.sub.3, etc., may be more or less than the
number depicted in FIG. 1, a particularly useful range being two to
seven.
[0028] While the present invention has been described above in
terms of specific embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments. On the
contrary, the following claims are intended to cover various
modifications and equivalent methods and structures included within
the spirit and scope of the invention.
* * * * *