U.S. patent number RE38,777 [Application Number 08/766,634] was granted by the patent office on 2005-08-16 for dual battery power system for an implantable cardioverter defibrillator with voltage booster.
This patent grant is currently assigned to Angeion Corp.. Invention is credited to Theodore P. Adams, Dennis A. Brumwell, Joseph S. Perttu, Charles G. Supino.
United States Patent |
RE38,777 |
Adams , et al. |
August 16, 2005 |
Dual battery power system for an implantable cardioverter
defibrillator with voltage booster
Abstract
An improved dual battery power system uses two separate battery
power sources for an implantable cardioverter defibrillator, each
having optimized characteristics for monitoring functions and for
output energy delivery functions, respectively. The monitoring
functions are supplied electrical power by a first battery source,
such as a conventional pacemaker power source in the form of a
lithium iodide battery which is optimized for long life at very low
current levels. The output energy delivery functions are supplied
by a separate second battery source, such as a pair of lithium
vanadium pentoxide batteries, which is optimized for high current
drain capability and low self-discharge for long shelf life. The
first battery source provides electrical power only to the
monitoring functions of the implantable cardioverter defibrillator,
and the second battery source provides all of the electrical power
for the output energy delivery functions.
Inventors: |
Adams; Theodore P. (Edina,
MN), Brumwell; Dennis A. (Bloomington, MN), Perttu;
Joseph S. (Chanhassen, MN), Supino; Charles G. (Arden
Hills, MN) |
Assignee: |
Angeion Corp. (Minneapolis,
MN)
|
Family
ID: |
25433456 |
Appl.
No.: |
08/766,634 |
Filed: |
December 13, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
108130 |
Aug 16, 1993 |
05372605 |
Dec 13, 1994 |
|
|
Current U.S.
Class: |
607/5; 607/29;
607/34 |
Current CPC
Class: |
H01M
16/00 (20130101); A61N 1/3787 (20130101); A61N
1/3956 (20130101); A61N 1/3975 (20130101); A61N
1/3931 (20130101); H01M 6/5016 (20130101); H01M
50/209 (20210101) |
Current International
Class: |
A61N
1/39 (20060101); A61N 001/39 () |
Field of
Search: |
;607/5,29,34,7,11
;363/15,101,131 ;323/220,304 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schaetzle; Kennedy J.
Attorney, Agent or Firm: Patterson, Thuente, Skaar &
Christensen, P.A.
Claims
We claim:
1. An .[.improved power system for an.]. implantable cardioverter
defibrillator that is a self-contained human implantable device
.[.having.]. .Iadd.comprising.Iaddend.: monitoring means for
detecting myocardial arrhythmias in a human patient.Iadd.;
.Iaddend..[.and.]. output means for selectively determining an
appropriate electrical pulse therapy to be delivered in response to
a myocardial arrhythmia detected by the monitoring means and
delivering the appropriate electrical pulse therapy to two or more
implanted electrodes.[., the improved power system comprising:.].
.Iadd.; .Iaddend. first battery means for providing electrical
power primarily to the monitoring means; second battery means for
providing substantially all of its electrical power to the output
means; and backup means for allowing the second battery means to
provide electrical power to the monitoring means in the event that
the first battery means can no longer provide electrical power to
the monitoring means.
2. The .[.improved power system.]. .Iadd.implantable cardioverter
defibrillator .Iaddend.of claim 1 wherein the implantable
.[.cardivoerter.]. .Iadd.cardioverter .Iaddend.defibrillator
includes a capacitor means for storing an electrical charge which
is charged from the second battery means and wherein the output
means selects the appropriate electrical pulse therapy from a set
that includes: one or more cardioversion/defibrillation pulses,
each cardioversion/defibrillation pulse being delivered by the
output means as a capacitive discharge pulse from the capacitor
means; and one or more pacing pulses, each pulse being delivered by
the output means as an electrical pulse directly powered from the
second battery means.
3. The .[.improved power system.]. .Iadd.implantable cardioverter
defibrillator .Iaddend.of claim 1 wherein the backup means
comprises: transistor means operably connected to outputs of the
first battery means and the second battery means to sense a current
drain on the output of the first battery means and switch on the
output of the second battery means to add to the output of the
first battery means in the event that the current drain exceeds a
maximum current drain of the first battery means.
4. The .[.improved power system.]. .Iadd.implantable cardioverter
defibrillator .Iaddend.of claim 1 further comprising: voltage
regulation means operably connected to an output of the first
battery means and to a reference voltage value for regulating the
output of the first battery means to a predetermined voltage
value.
5. The .[.improved power system.]. .Iadd.implantable cardioverter
defibrillator .Iaddend.of claim 1 wherein the first battery means
is a relatively low current source, and wherein the second battery
means is a relatively high current source.
6. The .[.improved power system.]. .Iadd.implantable cardioverter
defibrillator .Iaddend.of claim 5, wherein the relatively low
current source is a 1.5 to 3.0 volt battery and the relatively high
current source is a 6 to 18 volt battery.
7. The .[.improved power system.]. .Iadd.implantable cardioverter
defibrillator .Iaddend.of claim 1 wherein the first battery means
is one or more lithium iodide battery cells.
8. The .[.improved power system.]. .Iadd.implantable cardioverter
defibrillator .Iaddend.of claim 1 wherein said second battery means
is one or more battery cells selected from the group consisting of:
lithium silver vanadium oxides, thionyl chlorides or rechargeable
battery cells. .Iadd.
9. The implantable cardioverter defibrillator of claim 1, further
comprising: a voltage booster connected to said second battery
means to insure a minimum boosted voltage to said output means
during periods of high current draw. .Iaddend..Iadd.
10. The implantable cardioverter defibrillator of claim 1, further
comprising: a voltage booster connected to said second battery
means to prevent voltage ripple to said output means during periods
of high current draw. .Iaddend..Iadd.
11. An implantable cardioverter defibrillator that is a
self-contained human implantable device comprising: monitoring
means for detecting myocardial arrhythmias in a human patient;
output means for selectively determining an appropriate electrical
pulse therapy to be delivered in response to a myocardial
arrhythmia detected by the monitoring means and delivering the
appropriate electrical pulse therapy to two or more implanted
electrodes; at least one battery means for providing electrical
power to the output means; and a voltage booster connected to at
least one of said at least one battery means to insure a minimal
booster voltage output of said at least one of said at least one
battery means during periods of high current draw.
.Iaddend..Iadd.
12. The implantable cardioverter defibrillator of claim 11, further
comprising: a diode connected to said voltage booster to isolate
the boosted voltage output from a voltage output of said at least
one battery means. .Iaddend..Iadd.
13. The implantable cardioverter defibrillator of claim 11, further
comprising: a charge pump circuit connected to the boosted voltage
output to increase the boosted voltage output; and an inverter
circuit including a high voltage transformer connected to said
charge pump circuit to produce a high voltage output from the
increased boosted voltage output to charge the output means.
.Iaddend..Iadd.
14. The implantable cardioverter defibrillator of claim 13, further
comprising: a capacitor connected between said inverter circuit and
said at least one battery means to decouple said at least one
battery means from said inverter circuit. .Iaddend..Iadd.
15. An implantable cardioverter defibrillator that is a
self-contained human implantable device comprising: monitoring
means for detecting myocardial arrhythmias in a human patient;
output means for selectively determining an appropriate electrical
pulse therapy to be delivered in response to a myocardial
arrhythmia detected by the monitoring means and delivering the
appropriate electrical pulse therapy to two or more implanted
electrodes; at least one battery means connected to the output
means; an inverter circuit, including a high-voltage transformer,
connected to the output means to provide a high voltage pulse to
the output means; and a voltage booster connected to at least one
of said at least one battery, to insure a minimum boosted voltage
output of said at least one of said at least one battery during
periods of high current draw. .Iaddend..Iadd.
16. The implantable cardioverter defibrillator of claim 15, wherein
said at least one battery comprises a first battery and a second
battery, said first battery provided for supplying electrical power
primarily to the monitoring means and said second battery connected
to said voltage booster. .Iaddend..Iadd.
17. The implantable cardioverter defibrillator of claim 16, further
comprising a diode connected to said voltage booster to isolate a
boosted voltage output of said voltage booster from a voltage
output of said second battery during periods of high current draw.
.Iaddend..Iadd.
18. The implantable cardioverter defibrillator of claim 15, further
comprising a charge pump circuit connected to the minimum boosted
voltage output and to said inverter circuit. .Iaddend..Iadd.
19. The implantable cardioverter defibrillator of claim 15, wherein
said voltage booster comprises: at least one capacitor for storing
a boosted voltage; and a diode connected to said at least one
capacitor to regulate said boosted voltage on said at least one
capacitor, and to prevent said at least one capacitor from creating
ripple in the voltage supplied to the output means.
.Iaddend..Iadd.
20. The implantable cardioverter defibrillator of claim 19, wherein
said voltage booster further comprises: an activity monitor
connected to said inverter circuit to time a charging operation of
said at least one capacitor in accordance with activity by said
inverter circuit. .Iaddend.
Description
RELATED APPLICATIONS
.[.This application is a continuation-in-part application of an
application filed in the United States Patent and Trademark Office
on Jul. 16, 1992, entitled DUAL BATTERY SYSTEM FOR IMPLANTABLE
DEFIBRILLATOR, Ser. No. 07/913,626, now U.S. Pat. No. 5,235,979
which is a file-wrapper continuation of an application by the same
title filed on Mar. 3, 1991, both of which are assigned to the
assignee of the present invention, and the disclosure of which is
incorporated by reference in the present application..]. This
application is related to .[.a co-pending application filed in the
United States Patent and Trademark Office on Mar. 15, 1993,
entitled IMPLANTABLE CARDIOVERTER DEFIBRILLATOR HAVING A SMALLER
DISPLACEMENT VOLUME, Ser. No. 08/033,632,.]. .Iadd.U.S. Pat. No.
5,405,363, which issued on Apr. 11, 1995, and .Iaddend.which is
assigned to the assignee of the present invention and the
disclosure of which is hereby incorporated in the present
application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a cardioverter defibrillator, and
more particularly, to an improved dual battery power system for use
with an implantable cardioverter defibrillator.
2. Background of the Invention
Implantable cardioverter defibrillators have several unique battery
requirements, as compared to other implantable products. An
implantable cardioverter defibrillator demands a battery with the
following general characteristics: very high reliability, highest
possible energy density (i.e., small size), extremely low
self-discharge rating (i.e., long shelf life), very high current
capability, high operating voltage, and high sealability (i.e., no
gas or liquid venting).
Some of these parameters have some measure of mutual exclusively,
making it difficult to optimize the battery of electronics without
making compromises to the design of the implantable device. In its
monitoring mode, the implantable cardioverter defibrillator
requires the battery to deliver continuous currents in the range of
only 10-30 .mu.A, while in its defibrillation mode, the same
battery must delivery currents in the range of one to two amps,
some five orders of magnitude greater than the current required for
the monitoring mode.
Presently, all manufactured implantable cardioverter defibrillators
use a single battery system to power the implantable device. The
longevity of an implanted cardioverter defibrillator with a single
battery configuration and the number of shocks the defibrillator is
capable of delivering are strictly dependant on the remaining
battery capacity at any given time. As the device ages, its ability
to deliver an adequate number of defibrillating shocks declines as
the battery is depleted by the monitoring electronics. Similarly,
if a patient receives a large number of shocks soon after implant,
the remaining monitoring life is reduced. Thus, it is difficult to
assess the condition of the battery and its remaining useful life
after it has been in use for a period of time.
A further disadvantage of the single battery configuration is that
the ideal voltage requirements for the monitoring and output
functions are opposite. For the monitoring function, it is
desirable to use the lowest possible voltage that the circuits can
operate reliably with in order to conserve energy. This is
typically in the order of 1.5-3.0 V. On the other hand, the output
circuit works most efficiently with the highest possible battery
voltage in order to produce firing voltages of up to about 750
V.
All existing manufactured implantable cardioverter defibrillators
have compromised between these two demands by using a single
battery system or configuration which is typically comprised of two
lithium silver vanadium pentoxide cells electrically connected in
series to produce an output battery voltage of about 6 V. The
battery voltage must be elevated via an inverter circuit to the
firing voltage of about 750 V. The net result is that power is
wasted in both the monitoring and output circuits because the
monitoring circuit which requires only 2-3 V must operate from a
relatively high 6 V source, and the output circuit whose efficiency
is a function of the supply voltage must operate from the
relatively low 6 V source.
At least two previous development attempts have been made to avoid
some of the problems inherent in using a single battery system
configuration for an implantable cardioverter defibrillator. In the
Medtronic Model 2315, lithium thionyl chloride batteries were
employed for the high-voltage charging circuit and lithium
manganese dioxide batteries were used for the remaining low voltage
circuitry. Similarly, the Telectronics Model 4201 initially tried
to employ separate batteries for the low voltage circuits (lithium
iodine) and high-voltage circuits (lithium silver vanadium
pentoxide). Troop, P. J., "Implantable Cardioverters and
Defibrillators", Current Problems in Cardiology, Vol. XIV, No. 12,
(December 1989), pp. 703-04. Unfortunately, neither of these
devices resulted in practical, manufactured implantable
cardioverter defibrillators and the dual battery approach was
abandoned in both cases.
While single battery systems have proved workable for implantable
cardioverter defibrillators, the use of a single battery system
necessarily involves a compromise between the ideal power supplies
which would otherwise be used for the various types of circuitry
within the implantable cardioverter defibrillator. Accordingly, it
would be desirable to provide for an improved dual battery power
system for an implantable cardioverter defibrillator which avoids
the need for the compromises required of single battery systems,
and which overcomes the problems of earlier attempts at dual
battery systems.
SUMMARY OF THE INVENTION
An improved dual battery power system in accordance with the
present invention involves the use of two separate battery power
sources for an implantable cardioverter defibrillator, each having
optimized characteristics for monitoring functions and for output
energy delivery functions, respectively. The monitoring functions
are supplied electrical power by a first battery source, such as a
conventional pacemaker power source in the form of a lithium iodide
battery cell which is optimized for long life at very low current
levels. The output energy delivery functions are supplied by a
separate second battery source, such as a pair of lithium vanadium
pentoxide battery cells, which is optimized for high current drain
capability and low self-discharge for long shelf life. The first
battery source provides electrical power only to the monitoring
functions of the implantable cardioverter defibrillator, and the
second battery source provides all of the electrical power for the
output energy delivery functions.
With the improved dual battery system configuration of the present
invention, the minimum expected monitoring life of an implantable
cardioverter defibrillator is independent of the amount of
electrical pulse therapy delivered by the device, such as the
number of cardioversion/defibrillation countershocks or the amount
of pacing. As a result, the end of the minimum useable lifespan of
the first battery source is highly predictable based on steady
state current drain calculations. The lifespan of the second source
battery source is also amenable to calculation based upon the
number and amount of energy levels of previously delivered
electrical pulse therapies.
The major advantage of the present invention is that each battery
source voltage can be optimized for the particular circuit wherein
it is used. The first battery source is preferably a relatively low
current, low voltage source, from 1.5 to 3.0 V typically; whereas
the second battery source is preferably comprised of as high of a
current and voltage as battery chemistry and battery packaging
efficiencies allow, typically ranging from 6 to 18 V.
Unlike existing implantable cardioverter defibrillators, a
preferred embodiment of the present invention utilizes a separate
hardware-based, low-power monitoring circuitry to monitor for
certain wake-up conditions which will then activate the output
delivery circuitry which includes a microprocessor that performs
further detection and, if necessary, selects an appropriate
cardioversion/defibrillation therapy to be delivered. The output
delivery circuitry includes additional hardware circuitry that,
when enabled, can .[.delivery.]. .Iadd.deliver .Iaddend.pacing
therapy pulses with energy supplied from the output power source
battery without the need to wake the microprocessor.
Because the two batteries of the present invention can be optimized
for their particular functions, different assumptions about the
total energy requirements of the implantable cardioverter
defibrillator can be made. For example, all existing manufactured
implantable cardioverter defibrillators provide power systems which
are designed to supply an initial number of defibrillation
countershocks of at least 250 shocks. In a single battery system,
even when no shocks are delivered, the number of remaining shocks
in the device decreases with age due to the fact that the energy
for the monitoring functions are drawn from this battery. In the
present invention, assuming good charge retention of the output
battery, essentially no energy is drawn from the output battery
until an electrical pulse therapy is delivered. Consequentially,
one advantage of the dual battery system of the present invention
is that a smaller initial number of defibrillation countershocks
can be specified for an implanted device, while maintaining the
same minimum expected life span for the device, thereby allowing a
reduction in the overall size of the implanted device.
Another advantage of a preferred embodiment of the present
invention includes a backup protection feature whereby energy from
the output power source battery can be used to power the monitoring
circuitry in the event that the monitoring power source battery
ceases to function. A further advantage of a preferred embodiment
of the present invention includes a booster feature which regulates
the system supply voltage to prevent ripple in the supply voltage
during capacitor charging. Still .[.another.]. .Iadd.other
.Iaddend.advantages include a greater longevity provided for by
lowering energy drain by the monitoring circuitry, the simplified
circuit design that results in a decrease in the risk of high
internal currents causing interference to other parts of the low
current monitoring and control circuitry, and the ability to use
rechargeable batteries.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 illustrates a block diagram of a single battery system for
an implantable cardioverter defibrillator;
FIG. 2 illustrates a block diagram of the dual battery system of
the present invention for an implantable cardioverter
defibrillator;
FIG. 3 illustrates a block diagram of the dual battery system of
the present invention using a rechargeable inserter/output
battery;
FIGS. 4a, 4b, 4c, 4d and 4e are graphs comparing the predicted
lifespan of an implantable cardioverter defibrillator having a
single battery system and a dual battery power system; and
FIGS. 5a and 5b is a schematic diagram of a preferred embodiment of
the present invention.
FIG. 6 is a detailed schematic diagram of the backup feature of the
embodiment of the present invention shown in FIGS. 5a and 5b.
FIG. 7 is a detailed schematic diagram of the booster feature of
the embodiment of the present invention shown in FIGS. 5a and
5b.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates a single battery system for an implantable
defibrillator system 10 including a single battery 12, which
provides power both to a monitoring circuit 14 and an
inverter/output circuit 16 simultaneously. The monitoring circuit
14 and the inverter/output circuit 16 are interconnected to each
other, and to two or more implanted electrodes 18 located on, near
or in a heart 20. The implanted electrodes 18 include appropriate
leads and sensors to monitor the electrical activity of the heart
20 and to deliver an appropriate electrical therapy to the heart 20
in the event that the monitoring circuit detects a cardiac
arrhythmia. As discussed in the background of the invention, the
electrical capacity of the single battery 12 may be excessive in
relation to the circuit requirements of the monitoring circuit 14,
and marginal or even somewhat lacking in electrical size in
relation to the circuit requirements of the inverter/output circuit
16.
FIG. 2 illustrates a block diagram of the dual battery system 30
for an implantable defibrillator of a preferred embodiment of the
present invention. A battery 32 of appropriate voltage and physical
size connects to and powers a monitoring circuit 34 only. Another
battery 36 of appropriate voltage and physical size connects to and
powers the inverter/output circuit 38 only. The monitoring circuit
34 and the inverter/output circuit 38 each connect to two or more
implanted electrodes 40 on, near or in a heart 42. The monitoring
circuit 34 also connects to and triggers the inverter/output
circuit 38. The batteries 32 and 36 are optimally sized
electrically and physically to provide for the most efficient
operation for their respective circuitry.
FIG. 3 illustrates a dual battery system 50 for an implantable
defibrillator of an alternate embodiment of the present invention
where the batteries are rechargeable. A battery 52 of appropriate
voltage and physical size connects to and powers a monitoring
circuit 54 only. Another battery 60, which is rechargeable and of
appropriate voltage and physical size connects to and powers the
inverter/output circuit 62 only. Charging of the battery 60 occurs
by a radio frequency inductive link between an external charger
circuit 68 and an implanted recharge circuit 70 that includes a
rectifier. A coil 72 connects with the external charger circuit 68
and transmits RF energy from the coil 72 through the epidermis 76
where it is received by an implanted coil 74. The coil 74 supplies
RF energy to the recharge circuit 70 so that the battery 60 may be
charged.
In operation, as in FIG. 2, the monitoring circuit 54 and the
inverter/output circuit 62 each connect to two or more implanted
electrodes 64 on, in or near a heart 66. The monitoring circuit 54
also connects to and triggers the inverter/output circuit 62. The
batteries 52 and 60 are optimally sized electrically and physically
to provide for the most efficient operation. In this configuration,
the device has a finite and predictable monitoring life based upon
the capacity of the primary monitoring battery 52, and an infinite
life for the output power surface battery 60 based on a
theoretically perfect secondary rechargeable battery that only
needed to be recharged after a predetermined number of electrical
pulse therapies were delivered. Optionally, the battery 52 which
powers the monitoring circuit 54 can also be rechargeable and would
also include another similar RF inductive charging link as used for
the rechargeable batter 60.
A preferred mode of operation of the implantable cardioverter
defibrillator shown in FIG. 2 is dependent upon the monitoring
circuit 34 and the inverter/output circuit 38. In the event that
the monitoring circuit 34 detects a wake-up condition, for example,
the monitoring circuit 34 wakes up a microprocessor-based circuit
in the inverter/output circuit 38 to respond to the wake-up
condition. In the event that the monitoring circuit 34 is
programmably enabled for pacing detection, and the monitoring
circuit 34 detects a pacing condition, the monitoring circuit
enables a hardware-based pacing circuit portion of the
inverter/output circuit 38 to deliver a pacing pulse using energy
from the battery 36. It will be noted that many different
variations in conditions detected by the monitoring circuit 34 and
types of responses provided by the inverter/output circuit 38 are
possible, and it is intended that such combinations are within the
scope of the present invention.
In one embodiment, a microprocessor with an RC gated oscillator
circuit that is controlled by the microprocessor within the
inverter/output circuit 38 implements a wake-up control that can
respond to the wake-up conditions. The wake-up conditions handled
by the microprocessor based circuit in the inverter/output circuit
38 include, for example, a tachycardia threshold determination, a
telemetry indication, or a time condition. In the case of the
tachycardia threshold determination, for example, threshold
determination circuitry in the monitoring circuit 34 detects the
occurrence of 3 consecutive R-waves at a rate faster than a
predetermined programmable rate. In response, the monitoring
circuit 34 wakes-up the microprocessor in the inverter/output
circuit 38, which verifies that a cardiac arrhythmia is occurring
and selects an appropriate electrical pulse therapy. If an
electrical pulse therapy is to be delivered, the battery 36 would
charge the inverter/output circuit 38 to deliver one or more high
voltage cardioversion/defibrillator countershocks. If the wake-up
condition was a telemetry indication, then the microprocessor
circuit of the inverter/output circuit 38 might "output" a
telemetry response, for example, rather than a electrical pulse
therapy response. Alternatively, if the microprocessor circuit of
the inverter/output circuit 38 determines that no action is
required in response to the wake-up condition, then no "output" may
be generated in response and the microprocessor would turn off the
RC gated oscillator circuit, thereby shutting off the clock to the
microprocessor.
One important feature which distinguishes the improved dual battery
system 30 from the previous attempts to implement dual battery
systems in that the division of labor between the battery 32 and
the battery 36 is not based on low voltage output vs. high voltage
output, but rather is based on monitoring functions vs. output
functions. In the two dual battery systems described in the
background art section, all of the low voltage circuitry of the
implantable cardiovascular defibrillator was powered from a low
voltage battery. As a result, both the monitoring function (which
typically .[.operate.]. .Iadd.operates .Iaddend.on 3 V levels), as
well as the pacing therapy output functions (which typically
operate on 6 V levels), were designed to derive the energy from the
low voltage battery. The end result of this type of arrangement is
that the life of the low voltage battery is totally dependant upon
the amount of pacing therapy which may be delivered by the device
and, thus, the minimum effective life of the device is effectively
unknown.
In contrast, the improved dual battery power system of the present
invention takes all of its "output" energy from the output battery
32. For example, the present invention does not take the energy for
pacing therapy from the monitoring battery 32, but rather from the
output battery 36. As a result, the monitoring lifespan of an
implantable defibrillator in accordance with the present invention
is known and calculable based on the specifications of the
monitoring battery 32. Without a known lifespan of the device, it
is simply not possible to provide a viable implantable
defibrillator, as evidenced by the fact that both of the previous
attempts at dual battery systems which did not have known lifespans
for the monitoring circuitry were unsuccessful and did not result
in manufactured implantable cardioverter defibrillators.
Referring now to FIGS. 4a-4e, a relative comparison between the
electrical pulse therapy outputs and the longevity of the
implantable cardioverter defibrillator is shown under various
assumptions for a single battery system 100 and the improved dual
battery system 102 of the present invention. One of the advantages
of the present invention is that a smaller initial number of
countershocks is required in order for the implantable cardioverter
defibrillator to have the same minimum effective life span as a
device with a single battery power system. This, in turn, decreases
the overall power requirements, and, hence, the total size of the
implantable cardioverter defibrillator. In the preferred
embodiment, an additional advantage of having a more optimum
discharge capacitor system in the implantable cardioverter
defibrillator of a preferred embodiment also reduces the overall
power requirements for the dual battery system of the present
invention. For a more detailed explanation of the relationship
between the therapies provided by the device and the power
requirements and size of the device in the preferred embodiment,
reference is made to the previously identified .[.copending
application entitled IMPLANTABLE CARDIOVERTER DEFIBRILLATOR HAVING
A SMALLER DISPLACEMENT VOLUME..]. .Iadd.U.S. Pat. No. 5,405,363.
.Iaddend.
In FIG. 4a, the graph shows a comparison of the devices under an
assumption that the device will deliver five maximum defibrillation
countershock pulses per month and that pacing is not enabled. It
will be noted that in a preferred embodiment of the present
invention, the initial number of shocks is 150, as compared with
275 for the other device. It will also be noted, however, that the
expected minimum life span of both the single battery system 100
and the present invention 102 are equal at 30 months under these
assumptions.
In FIG. 4b, the graph shows a comparison of the devices under an
assumption that the device will deliver one defibrillation
countershock pulse per month and that pacing is not enabled. In
this example, the dual battery system 102 of the present invention
has more remaining shocks after 30 months than the single battery
system, even though it started with almost one-half the initial
number of shocks.
In FIG. 4c, the graph shows a comparison of the devices under an
assumption that the device will deliver no defibrillation
countershock pulses and that pacing is not enabled. Again, due to
the energy drain on the single battery system 100 associated with
its monitoring functions, the dual battery system 102 of the
present invention provides a longer life span with more average
remaining shocks available over that life span. This graph also
shows how the energy of the output battery remains relatively the
same (i.e., same number of remaining shocks) when no output
therapies are delivered.
In FIG. 4d, the graph shows a comparison of the devices under an
assumption that the device will deliver one defibrillation
countershock pulse per month and that pacing is enabled and will be
utilized 50% of the time. Again, the dual battery system 102 of the
present invention has a longer life span and more average remaining
shocks over that life span. It is interesting to note that .Iadd.in
.Iaddend.this situation, the previous dual battery systems
described in the background art section would encounter a severe
problem. After a period of 50% pacing, all of the energy from the
low voltage battery would have been drained, and the device would
abruptly stop working, even though there were plenty of shocks
remaining in the high voltage battery. It is speculated that this
is one of the major reasons why implantable cardioverter
defibrillators using the previous dual battery systems were never
manufactured.
In FIG. 4e, the graph shows a comparison of the devices under an
assumption that the device will deliver no defibrillation
countershock pulses and that pacing is enabled and will be utilized
50% of the time. Once again the dual battery system 102 of the
present invention has a longer life span and more average remaining
shocks over that life span. As with the problem of the previous
dual battery systems described with respect to FIG. 4d, such an
end-of-monitoring life problems is even more pronounced in this
situation as essentially all of the initial energy of the high
voltage battery remains unused in the previous dual battery
systems, but the device is "dead" because the low voltage battery
is drained of its energy due to the energy requirements of the
pacing therapy outputs.
Referring now to FIGS. 5a and 5b, a more detailed explanation of a
preferred embodiment of the dual battery power system of the
present invention will be described.
A LiI monitoring battery cell 111 provides a low current, low
voltage output of about 2.0-2.8 V with a maximum current draw on
the order of 30-80 .mu.A. The output of the monitoring battery cell
111 is capacitively decoupled by a capacitor 114. Schottky diodes
118 and 120 enable the power system to run the 3 V bus from the
battery cell 111 during battery startup sequencing such that the
device can be successfully initiated by first inserting the
monitoring battery cell 111 before the output batteries are
inserted.
A pair of LiAgV.sub.2 O.sub.5 output battery cells 121, 122 provide
a relatively high current, high voltage output of 4.0 to 6.5 V with
a maximum current draw of between about 2.0-4.0 A. The high current
output of the output battery cells 121, 122 is capacitively
decoupled by a capacitor 124. A center point ground 126 isolates
the high current portion of the circuitry from the low current
portion of the circuitry, thereby allowing for simpler circuit
design and greater reliability of the low current portion of the
circuitry. A voltage booster 130 insures a 6 V supply on the 6 Volt
Bus, even while the output battery cells 121, 122 are under heavy
load conditions, while the diodes 132 in the voltage booster 130
isolates the boosted voltage from the battery cell voltage during
periods of high current draw.
An inverter circuit 140 uses the high current output and an
Inverter Gate Drive Voltage of 12 to 18 volts provided by a 3X
charge pump circuit 142 from the 6 Volt Bus to drive a high-voltage
flyback transformer in the inverter circuit 140. The output of the
transformer charges a capacitor system (not shown) to produce the
high voltage (50-800 V) capacitive discharge output pulse which
forms either a cardioversion of defibrillation pulse countershock.
The Inverter Gate Drive Voltage is capacitively decoupled by
capacitor 144. The inverter circuit 140 may be of the type
described, for example, in U.S. Pat. No. 4,800,883.
The Main System Power is a regulated 3.0 V supplied primarily by
the monitoring battery cell 111 unless the current draw on the Main
System Power exceeds about 30-80 .mu.A. In the event of a current
overdraw situation, such as when the microprocessor in
inverter/output circuitry 38 responds to a wake-up condition, the
output of the output battery cells 121, 122 is added to the output
of the monitoring battery cell 111 to generate the required
current. The circuitry to accomplish this is shown generally at 150
and is described in greater detail in connection with the
description of FIG. 6.
The unregulated 2.5 V output of the monitoring battery cell 111 is
supplied as an input to a 3/2 charge pump 136 which, like the 3X
charge pump circuit 142, is driven by a 1 KHz divider output of a
32 KHz oscillator crystal 134. The charge pump circuit 136 raises
the output of the monitoring batteries to about 3.75 V which is
capacitively decoupled by .Iadd.a .Iaddend.capacitor .[.146.]. .
The 3.75 V output of the charge pump circuit 136 and the
unregulated 6.0 Volt Bus are fed as inputs to a dual input voltage
regulator 152. A voltage/current reference circuit 146 provides a
reference voltage of 1.28 V and a reference current of 100 nA to
the voltage regulator 152. A p-n-p transistor 154 controls whether
the 6.0 Volt Bus input will be added to the 3.75 V output of the
charge pump circuit 136 if a current overdraw condition exists with
respect to the monitoring battery cell 111. The charge pump circuit
136 also provides a negative output of -2.0 to -2.5 V to supply the
Main Power System negative voltage requirements of op amps,
etc.
Referring now to FIG. 6, a more detailed explanation of the
operation of the backup feature of a preferred embodiment of the
present invention is shown. A feedback amplifier circuit 156
compares the reference voltage signal from the voltage/current
reference circuit 146 to a divided down value of the 3 Volt Bus
signal. The divide down is accomplished by resistors 158 and 160
and capacitor 162. A FET transistor circuit 164 responds to an
output of the feedback amplifier circuit 156 to keep the voltage on
the 3 Volt Bus at 3.0 V. If the current drain through the gate of
the FET transistor circuit 164 is more than the maximum current
draw for the monitoring battery cell 111, then the transistor
circuit 154 is turned on by feedback amplifier circuit 156 to
supply the necessary overdraw current from the output battery cells
121, 122 via the 6 Volt Bus. In the preferred embodiment, a local
feedback loop is added to transistor circuit 154 to sin-relate a
quasi-complementary darlington circuit in order to achieve a low
drop voltage across transistor circuit 154.
Referring now to FIG. 7, a more detailed explanation of the
operation of the booster feature of a preferred embodiment of the
present invention is shown. Voltage supply ripple is caused by
changes in the battery impedance due to the high current draw
required by the flyback charging operation of inverter circuit 140.
If the drop out voltage of the voltage supply is too great, or if
the power supply rejection ratio of monitoring circuitry 34 and
output circuitry 38 is .[.exceeded. The result may.].
.Iadd.exceeded, the result may .Iaddend.be either local or
catostrophic circuit failure. To prevent voltage supply ripple from
affecting the voltage supply of the preferred embodiment of the
present invention, a voltage booster 130 is used.
The voltage booster 130 of the preferred embodiment as shown in
FIG. 7 runs the battery output current through an inductor 170 for
a period of time, and then switches the current through a zener
diode 172 to a capacitor 174 and to ground. Zener diode 172
regulates the voltage on capacitor 174 and also blocks capacitor
174 from creating ripple in the voltage supply (V.sub.DD). Voltage
booster 130 senses activity by inverter circuit 140 using a FET
transistor 176 and begins cycling inductor 170 in accordance with
the delays generated by diodes 178 in response to the value of the
voltage supply (V.sub.DD) and the switching of logic gate 180 and
FET transistor 182. In this way, voltage booster 130 may
efficiently adjust its cycle time to immediately match the various
levels of the voltage supply (V.sub.DD) that may be encountered
during the charging operation. In the preferred embodiment, voltage
booster 130 runs at a fixed frequency with a variable duty cycle
dependent upon the output voltage of the battery. When voltage
booster 130 is not active, current from the output of the battery
is routed through Schottky diode 184 and through a choke inductor
186 to the voltage supply (V.sub.DD).
* * * * *