`
`International Bureau
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(51) 1|1t°|'l|afi0l1al Patent Classification 5 1
`
`‘
`
`(11) International Publication Number:
`
`W0 94/02202
`
`A61N 1/373
`
`(43) International Publication Date:
`
`3 February 1994 (0102.94)
`
`(21) International Application Number:
`
`PCT/US93/06950
`
`(22) International Filing Date:
`
`16 July 1993 (l6.07.93)
`
`(74) Agents: KEOUGH, Steven, J. et al.; Patterson & Keough,
`1200 Rand Tower, 527 Marquette Avenue South, Min-
`neapolis, MN 55402 (US).
`
`(30) Priority data:
`07/913,626
`
`16 July 1992 (16.07.92)
`
`US
`
`(81) Designated States: CA, JP, European patent (AT, BE, CH,
`DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT,
`SE).
`
`(71) Applicant: ANGEMED, INC. [US/US]; 3650 Annapolis
`Lane, Minneapolis, MN 55447-5434 (US).
`
`; 4202 Sunnyside Road,
`(72) Inventors: ADAMS, Theodore, P.
`Edina, MN 55424 (US). BRUMWELL, Dennis, A.
`;
`8424 Irwin Road, Bloomington, MN 55437 (US). PERT-
`TU, Joseph, S.
`; 790 Santa Vera Drive, Chanhassen, MN
`55317 (US). SUPINO, Charles, G.
`; 1292 Karth Lake
`Circle, Arden Hills, MN 55112 (US).
`
`Published
`Wllh international search report.
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
`
`(54) Title: DUAL BATTERY SYSTEM FOR IMPLANTABLE CARDIOVERTER DEFIBRILLATOR
`
`76
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`CHARGER:
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`CIRCUIT
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`Q
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`7
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`0
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`A
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`74
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`C
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`‘RECHARGE
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`CIRCUIT
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`INVERTERI
`V
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`°”T'°‘”
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`°'RCU'T
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`27
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`(57) Abstract
`
`An improved dual battery power system uses two separate battery power sources for an implantable cardioverter defibrilla-
`tor, 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 pair of lithium iodide batteries, which is optimized for long life at very low current levels. The output energy deliv-
`ery 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.
`
`1
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`LIFECOR454-1008
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`
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`FOR THE PURPOSES OF INF0lMrlAT1ON ONLY
`
`Codes used to identify States party to the PCI‘ on the front pages of pamphlets publishing international
`applications under the PCT.
`
`France
`Gabon
`United Kingdom
`Guinea
`Greece
`Hungary
`Ireland
`Italy
`Japan
`Democratic People's Republic
`of Korea
`Republic of Korea
`Kazakhstan
`Liechtenstein
`Sri lanka
`Luxembourg
`Latvia
`Monaco
`Madagascar
`Mali
`Mongolia
`
`Mauritania
`Malawi
`NigerNetherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Slovenia
`Slovak Republic
`Senegal
`Chad
`Togo
`Ukraine
`United States of America
`Uzbekistan
`Viul. Nam
`
`Austria
`Australia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Bratil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Cote d'lvoire
`Cameroon
`China
`Czechoslovakia
`Czech Republic
`Germany
`Denmark
`Spain
`Finland
`
`AT
`AU
`BB
`BE
`BF
`BC
`R
`BY
`CA
`CF
`CG
`CH
`CI
`CM
`CN
`C5
`CZ
`DE
`DK
`ES
`FI
`
`MB
`
`2
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`W0 94/02202
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`PCI‘/US93/06950
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`DUAL BATTERY SYSTEM FOR IMPLANTABLE CARDIOVERTER
`
`._...
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`DEFIBRILLATOR
`
`‘
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`A’
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`"
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`EACKGROUND OF THE INVENTION
`
`1.
`
`Field gf 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.
`
`I
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`2.
`
`Background gf 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
`
`exclusivity, making it difficult to optimize the battery or 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 uA,
`
`while in its defibrillation mode, the same battery must deliver currents in
`
`the range of one to two amps, some five orders of magnitude greater than
`
`the current required for the monitoring mode.
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`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. Asthe device ages, its ability to deliver an adequate number
`aof defibrillating shocks‘ declines as the battery is depleted by the
`;:monitoring electronics. Similarly, if a patient receives a large number of
`eshocks 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 Vv
`SOL11‘C€
`
`. A
`
`t 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.
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`In the
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`V Medtronic Model 2315, lithium thionyl chloride batteries were employed
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`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.]., ”Implantable Cardioverters and
`
`Defibrillators”, Current Problems in Cardiology, Vol. XIV, No. 12, (Dec.
`
`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 pair of lithium iodide battery cells, 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
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`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 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
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`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 is required to maintain 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
`
`irrvention 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.
`
`Still other advantages include a greater longevity provided for by lower
`
`energy drain by the monitoring circuitry, the simplified circuit design that
`
`_-'.,3Sul’tS 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;
`3 illustrates a block diagram of the dual battery system of the
`
`30
`
`present invention using a rechargeable inserter/output battery;
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`FIGS. 34a, 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.
`
`4
`
`FIG. 6 is a detailed schematic diagram of the backup 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 size 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
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`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. A coil 72 connects with the external charger circuit 68 and transmits RF
`
`energy from the coil 72 through the epidennis 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 optionally sized electrically and physically to provide for the
`
`I
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`In this. configuration, the device has a finite and
`7' ‘most efficient operation.
`predictable monitoring life based upon the capacity .:-f 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 inducutive 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
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`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 timer 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/defibrillation 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
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`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 is 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 cardioverter defibrillator was powered
`from a low voltage battery. As a result, both the monitoring function
`
`(which typically operate on 3 V levels), as well as the pacing therapy
`
`output functions (which typically operate on 6 V levels), were designed to
`
`derive their 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 V
`monitoring circuitry were unsuccessful and did not
`result
`in
`
`manufacturedpimplantable cardioverter defibrillators.
`
`Referring now to FIGS. 4a-4e, a comparison between the electrical
`
`pulse therapy outputs and the longevity of the implantable cardioverter
`
`defibrillator is shown under various assumptions for a single battery
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`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 PCT/US93 /03249.
`I
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`In FIG. 4a, the graph shows a comparison of the devices under an
`
`assumption that the device will deliver five maxmimum 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
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`dual battery system 102 of the present invention provides a longer life
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`span with more average remaining shocks available over that life span.
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`This graph“ also shows how the energy of the output battery remains
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`relatively the same (i.e., same number of remaining shocks) when no
`output therapies are deliveredr
`In FIG. 4d, the graph shows a comparison of the devices under an
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`assumption that the device will deliver one defibrillation countershock
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`pulse per month and that pacing is enabled and will be utilized 50% of the
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`time. Again, the dual battery system 102 of the present invention has a
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`longer life span and more average remaining shocks over that life span.
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`It
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`is interesting to note that this situation, the previous dual battery systems
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`described in the background art section would encounter a severe
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`problem. After a period of 50% pacing, all of the energy from the low
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`voltage battery would have been drained, and the device would abruptly
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`stops working, even though there were plenty of shocks remaining in the
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`high voltage battery.
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`It is speculated that this is one of the major reasons
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`why implantable cardioverter defibrillators using the previous dual
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`battery systems were never manufactured.
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`In FIG. 4e,
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`the graph shows a comparison of the devices under an
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`assumption that the device will deliver no defibrillation countershock
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`pulses and that pacing is enabled and will be utilized 50% of the time.
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`Once again the dual battery system 102 of the present invention has a
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`longer life span and more average remaining shocks over that life span.
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`As with the problem of the previous dual battery systems described with
`respect to FIG. 4d, such an end-of—monitoring life problem is even more
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`pronounced in this situation as essentially all of the initial energy of the
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`high voltage battery remains unused in the previous dual battery systems,
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`but the device is ”dead” because the low voltage battery is drained of its
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`energy due to the energy requirements of the pacing therapy outputs.
`Referring now to FIGS. 5a and $b, a more detailed explanation of a
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`preferred embodiment of the dual battery power system of the present
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`invention will be described.
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`A pair of Lil monitoring battery cells 111, 112 provide a low current,
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`low voltage output of about 2.0 - 2.8 V with a maximum current draw on
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`the order of 10 p.Amps. The output of the monitoring battery cells 111, 112
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`is capacitively decoupled by a capacitor 114. Schottky diodes 118 and 120
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`enable the power system to run the 3
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`bus from the battery cells 111, 112
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`during battery startup sequencing such that the device can be successfully
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`initiated by first inserting the pair of battery cells 111, 112 before the output
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`batteries are inserted.
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`A pair of LiAgV2O5 output battery cells 121, 122 provide a relatively
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`high current, high voltage output of 4.0 to 6.5 V with a maximum current
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`draw of between about 2.0 - 4.0 A. The high current output of the output
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`battery cells 121, 122 is capacitively decoupled by a capacitor 124. A center
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`point ground 126 isolates the high current portion of the circuitry from the
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`low current portion of the circuitry, thereby allowing for simpler circuit
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`design and greater reliability of the low current portion of the circuitry. A
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`voltage booster 130 insures a 6 V supply on the 6 Volt Bus, while the diode
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`132 in the voltage booster 130 isolates the boosted voltage from the battery
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`cell voltage during periods of high current draw.
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`An. inverter circuit 140 uses the high current output and an
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`Inverter Gate Drive Voltage of 12 to 18 volts provided by a 3X charge
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`pump circuit 142 from the 6 Volt Bus to drive a high-voltage flyback
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`transformer in the inverter circuit 140. The output of the transformer
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`charges a capacitor system (not shown) to produce the high voltage (50-800
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`V) capacitive discharge output pulse which forms either a cardioversion
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`or defibrillation pulse countershock. The Inverter Gate Drive Voltage is
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`capacitively decoupled by capacitor 144.
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`The Main System Power is a regulated 3.0 V supplied primarily by
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`the monitoring battery cells 111, 112, unless the current draw on the Main A
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`System Power exceeds about 10 uA.
`In the event of a current overdraw
`situation, such as when the microprocessor in inverter/output circuitry 38
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`responds to a wake-up condition, the output of the output battery cells 121,
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`122 is added to the output of the monitoring battery cells 111, 112 to
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`generate the required current. The circuitry to accomplish this is shown
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`generally at 150 and is described in greater detail in connection with the
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`description of FIG. 6.
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`The unregulated 2.5 V output of the monitoring battery cells 111,
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`112 is supplied as an input to a 3/2 charge pump 136 which, like the 3X
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`charge pump circuit 142, is driven by a 1 KHz output of a 32 KHz oscillator
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`crystal 134. The charge pump circuit 136 raises the output of the
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`monitoring batteries to about 3.75 V which is capacitively decoupled by
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`capacitor 146. The 3.75 V output of the charge pump circuit 136 and the
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`unregulated 6.0 Volt Bus are fed as inputs to a dual input voltage regulator
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`152. A voltage/current reference circuit 146 provides a reference voltage of
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`1.28 V and a reference current of 100 nA to the voltage regulator 152. A p-
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`n-p transistor 154 controls whether the 6.0 Volt Bus input will be added to
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`the 3.75 V output of the charge pump circuit 136 if a current overdraw
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`condition exists with respect to the monitoring battery ct. was 111, 112. The
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`charge pump circuit 136 also provides a negative output of -2.0 to -2.5 V to
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`supply the Main Power System negative voltage requirements for op
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`amps, etc. H 4
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`Referring now to FIG. 6, a more detailed explanation of the
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`operation of the backup feature of a preferred embodiment of the present
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`invention is shown. A feedback amplifier circuit 156 compares the
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`reference voltage signal from the voltage / current reference circuit 146 to a
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`divided down value of the 3 Volt Bus signal. The divide down is
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`accomplished by resistors 158 and 160 and capacitor 162. A FET transistor
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`circuit 164 responds to an output of the feedback amplifier circuit 156 to
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`keep the voltage on the 3 Volt Bus at 3.0 V.
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`If the current drain through
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`the gate of the FET transistor circuit 164 is more than the maximum
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`current draw for the monitoring battery cells 111, 112, then the transistor
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`circuit 154 is turned on by feedback amplifier circuit 156 to supply the
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`necessary overdraw current from the output battery cells 121, 122 via the 6
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`Volt Bus.
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`I
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`WE CLAIM:
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`CLAIMS
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`An improved power system for an implantable cardioverter
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`defibrillator that is a self—contained human implantable device having
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`monitoring means for detecting myocardial arrhythmias in a human
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`patient and output means for selectively determining an appropriate
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`electrical pulse therapy to be delivered in response to a myocardial
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`arrhythmia detected by the monitoring means and delivering the
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`appropriate electrical pulse therapy to two or more implanted electrodes,
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`the improved power system comprising:
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`first battery means for providing electrical power primarily
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`only to the monitoring means; and
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`second battery means for providing substantially all of the
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`electrical power to the output means,
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`such that a minimum expected lifespan of the first battery
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`means is predictable regardless of the electrical pulse therapies
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`delivered by the implantable cardioverter defibrillator.
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`2.
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`The improved power system of claim 1 wherein the output means
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`selects the appropriate electrical pulse therapy from a set that includes:
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`one or more cardioversion/defibrillation pulses, each
`i cardioversion/defibrillation pulse being delivered by the output
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`means as a capacitive d