I
`
`'0000ot/
`
`5749904.
`
`A~N
`
`COMFIRCATE
`MA1IR 161999g
`OF CREfO
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`NOTE-DISCLAIMJER
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`LIFECOR904-1002
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`

`

`PATENT APPLICATIONI
`Hull I l~ 111
`lUllI
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`08690529
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`

`

`~~~1
`
`
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`
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`'-->¢WmmwQWNWVwfimw,,,.,
`
`SEARCH NOTES
`4A~4 Date
`
`SEARCHED
`-_-- -
`
`INTERE’rfiENCE_SEARCHED
`
`I-
`
`3
`
`

`

`Staple Issue Slip Here
`
`POSITION
`
`CLASSIFIER__
`
`EXAMINER
`
`ID NO.
`
`DATE
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`TYPIST
`VERIFIER
`CORPS CORR.
`SPEC._HAND
`FILE MAINT.
`DRAFTING
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`_
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`_I_
`
`_
`
`f
`
`-
`
`INDEX OF CLAIMS
`
`Claim
`
`c: 0)
`
`Date
`
`__
`
`..................
`
`1_1
`
`1_1
`
`1
`
`1
`
`H
`
`05
`
`1
`52_
`53
`,54,
`55
`56
`57
`1581
`59
`60
`61
`.62
`63
`64
`65
`66
`67
`68
`69
`1701
`71
`72
`73
`74
`1751
`76
`77
`78
`79
`1801
`81
`82
`83
`
`184__
`85
`861
`871
`881
`891
`1901
`911
`
`__
`
`__
`
`__
`
`931
`194
`195 1
`
`96
`
`99-+
`100
`
`SYMBOLS
`
`Rejected
`Allowed
`...................
`-(Through numberal) Canceled
`.+........ ;* . **...
`.RestrIcted
`N....................... Non-elected
`Interference
`.......................
`A....................... Appeal
`o .....................
`Objected
`
`Claim
`
`Date
`
`Li
`
`7- -3:~7EI
`
`p 1
`
`19
`
`/
`
`20
`121,
`22
`23
`24
`25.
`
`27
`28
`29
`130
`31
`321
`33
`34
`35
`136
`1371
`38
`39
`40
`141
`
`43
`44
`145
`1461
`471
`481
`49
`50
`
`4
`
`

`

`United States Patent
`GMier et al.
`
`[19]
`
`(54] ELECTROTHERAPY METHOD UTIOLIZING
`PATIENT DEPENDENT ELECTRICAL
`PARAMETERS
`
`[75]
`
`Inventors: Bradford E. Gliner, Bellevue; Thomas
`D. Lyster, Bothell; Clinton S. Cole,
`Seattle; Daniel J1. Powers, Issaquah;
`Carlton B. Morgan, Bainbridge Island,
`all of Wash.
`
`[73] Assignee: Heartstream, Inc., Seattle, Wash.
`
`[]Notice:
`
`The term of this patent shall not extend
`beyond the expiration date of Pat. No.
`5.601,612.
`
`[2 1]
`
`AppL No.: 690,529
`
`[22]
`
`Ffled-.
`
`Jul. 31, 1996
`
`
`
`
`
`1111 1111 II 111 S00~O5749904A111111111
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,749,9904
`*M~ay 12, 1998
`
`FOREIGN PATENT DOCUMENTS
`9/1988 European Pat. Off..
`0281219
`5/1989 European Pat. Off.
`0315368
`(List continued on next page.)
`
`OTHER PUBLICATIONS
`
`Alferness, et al 'The influence of shock waveforns on
`defibrillation efficacy" IEEE Engineering in Medicine and
`Biology, pp. 25-27 (Jun. 1990).
`
`(List continued on next page.)
`
`Primary Exnamner-William E. Kamm
`Assistant Examiner-Kennedy J. Schnetzle
`Attorney, Agent, or Fimn-James R. Shay; Cecily Anne
`Snyder
`[57]
`
`ABSTRACT
`
`Related US. Application Data
`
`[63] Continuation-in-part of Ser. No. 103,837, Aug. 6, 1993,
`abandoned, and Ser No. 227,553, Sep. 14, 1994, Pat. No.
`5,607,454.
`
`The invention provides a method for delivering electro-
`therapy to a patient through electrodes connected to a
`plurality of capacitors, including the steps of discharging at
`least one of the capacitors across the electrodes to deliver
`electrical energy to the patient, monitoring a patient-
`dependent electrical parameter (such as voltage, current or
`.... ................................ A61N 1139
`charge) during the discharging step, and adjusting energy
`hitCL.
`U.S. Cl .... .....~............................
`delivered to the patient based on a value of the electrical
`60~717; 607114
`parameter. The adjusting step may include selecting a serial
`Fleld of Search.
`607/5-7, 74
`or paraUel arrangement for the capacitors based on a value
`of the electrical parameter.
`
`[51]
`[52]
`[58]
`
`[56]
`
`...........
`
`References Cited
`
`3,211,154
`3,241,555
`3,706,313
`3,782,239
`3,860,009
`3,862,636
`3,886,950
`4,023,573
`4,328,808
`4,419,998
`4,473,078
`4,494,552
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`U.S. PATENT DOCUUMENTS
`10/1965 Becker et al..
`3/1966 Caywood et al. .
`I129172 Mflani et,al. .
`1/19174 BeRl.
`1/1975 Bell et al..
`1/1975 BellIet al..
`6/1975 Ukkstad et al. .
`5/1977 Pantuidge et al. .
`5/1982 Charbomnier et al. .
`12/1983 Heath .
`9/1984 Angd .
`1/1985 Heath .
`
`(List continued on next page.)
`
`In another embodiment, the invention provides a method for
`delivering electrotherapy
`to a patient through electrodes
`connectable to a plurality of capacitors including the steps of
`discharging at least one of the capacitors across the elec-
`trodes to deliver electrical energy to the patient in a wave-
`form having at least a first phase and a second phase,
`monitoring a patient-dependent electrical parameter (such as
`voltage, current or charge) during the discharging step, and
`modifying second phase initial voltage based on a value of
`the electrical parameter. The adjusting step may include
`selecting a serial or a parallel arrangement for the capacitors
`based on a value of the electrical parameter.
`
`17 Claims, 10 Drawing Sheets
`
`ZL7
`
`to~
`
`5
`
`

`

`5,749,904
`Page 2
`
`U.S. PATEMr DOCUMENTS
`3/1985
`Suzuki et al.
`4,504,773
`Ltsman.
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`Winstrom .
`4,745,923
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`Zenldch.
`4,850,357
`7/1989
`Bach, JL .
`4,953,551
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`4,998,531
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`1/1992
`5,078,134
`Hei1man et al..
`5,083,562
`1/1992
`de Coriolis et al..
`3/1992
`5,097,833
`Campos.
`5,107,834
`4/1992
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`5,111,813
`5/1992
`Charbonnier et al..
`5,111,816
`5/1992
`Pless et al. .
`5,199,429
`4/1993
`KroUl et al. .
`5/1993
`5,207,219
`Adams et al.
`5,215,081
`6/1993
`Ostroff .
`5,22,480
`6t1993
`Coudie et al.
`6/1993
`5,22,492
`Morgan et al. .
`5,230,336
`7/1993
`Fain et At..
`8/1993
`5,237,989
`Morgan et al..
`5,249,573 10/1993
`Fincke et al..
`5,275,157
`1/1994
`Morgan et al. .
`5,306,291
`4/1994
`Kroll et al..
`5,334,219
`98/1994
`Krull.
`5,334,430
`8/1994
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`5,352,239 10/1994
`Pleass.
`5,370,664 12/1994
`Morgan et al..
`5,372,606 12/1994
`Lang et al. .
`5,385,575
`1/1995
`Adams.
`5,411,525
`5/1995
`Swanson et al. .
`5,411,526
`5/1995
`Kroulet al. .
`5,431,686
`7/1995
`KroUl et at. .
`2/1996
`5,489,293
`Pless et al. .
`
`FOREIGN PATENT DOCUAMEMT
`0353341
`2/1990
`European Pat.Off.
`7/1991
`European Pat. Off.
`0437104
`611992
`0491649 A
`European Pat. Off.
`0507504
`10/1992
`European Pat. Off.
`2070435
`9/1981
`United Kingdom .
`2083363
`3/1982
`United Kingdom.
`wrPo.
`9/1993
`93/16759
`wIo.WIPO.
`9/1994
`94/21327
`9Vi22530
`10/1994
`OMHER PUBLICATIONS
`
`Anderson et al.'The efficacy of trapezoidal wave forms for
`ventricular defibrillation"' Chest 70(2):298-300 (1976).
`BMle et al. "Predicting and validating cardiothoracic current
`flow using finite element modeling" PACE 15:563, Abstract
`219 (Apr. 1992).
`Chapman et al.
`'"Non-thoracotomy internal defibrillation:
`shocks" Circulaftion
`hWpoved efficacy with biphasic
`76:3 12, Abstract No. 1239 (1987).
`Cooper et al. 'Temporal separation of the two pulses of
`single capacitor biphasic and dual monophasic waveforms"
`Circulation 84(4):612: Abstract No. 2433 (1991).
`Cooper et al.
`'The effect of phase separation on biphasic
`waveform defibrillationi" PACE 16:471-482 (Mar. 1993).
`
`Cooper et aL '"M'e effect of temporal separation of phases on
`biphasic waveform. defibrillation. efficacy" Thse Annual Inter-
`national Conference of the IEEE Engineering in Medicine
`and Biology 13(2):0766-0767 (1991).
`Crampton et al. "Low energy ventricular defibrillation and
`miniature defibrillators" JAMA 235(21):2284 (1976).
`Dahlback et al. "Ventricular defibrillation with square
`waves!' The Lancet (Jul. 2. 1966).
`Echt et al. "Biphasic waveform is more efficacious than
`monophasic waveform. for transthoracic cardioversion"
`PACE 16:914. Abstract No. 256 (Apr. 1993).
`Feeser et al. "Strengthd"uration and probability of success
`curves for defibrillation with biphasic waveforms" Circula-
`tion 82(6):2128-2141 (1990).
`Guse et al. "Defiburillation with low voltage using a left
`ventricular catheter and four cutaneous patch electrodes in
`dogs" PACE 14:443-451 (Mar. 1991).
`Jones et al. "Decreased defibrillator-induced dysfunction
`with biphasic rectangular waveforms" Am. J. Physiol.
`247:H792-796 (1984).
`Jones et al. "Defibrillator waveshape optimization" Devices
`and Tech Meeting NIH (1982).
`Jones et aL "Impoved defibrillator waveform. safety factor
`with biphasic waveforms" Am. J. Physiol. 245:H6M-5
`(1983).
`Jones et al. "Reduced excitation threshold in potassium
`depolarized myocardial cells with symmetrical biphasic
`waveforms" J. Mol. Cell. Cardiol. 17(39):MCVTJ, Abstract
`No. 39 (1985).
`Jude et aL. "Fundamentals of cardiopulmonary resuscitation"
`F.A.. Davis & Company, Philadelphia, PA, pp. 98-104
`(1965).
`Kerber et al. "¶Energy, current and success in defibrillation
`and cardioversion: clinical studies using an automated
`impedance-based method of energy adjustment" Circula-
`tion 77(5):1038 (May 1988).
`Knickerbocker et al. "'A portable defibrillator" IEEE Trans
`on Power a;d Apparatus Systems 69:1089-1093 (1963).
`Kuowenhoven
`"The development of the defibril.lator"
`Annals of Internal Medicine 71(3):449-458 (1969).
`Langer et aL. "Considerations in the development of the
`automatic implantable defibrillator" Medical Instrumenta-
`tion 10(3):163-167 (1976).
`Lerman et al. "Current-based versus energy-based ventricu-
`defibrilltion: A prospective
`JACC
`lar
`study"
`12(5):1259-1264 (1988).
`Lindsay et aL 'Prospective evaluation of a sequential pacing
`and high energy bi-directional shock algorithm for trans-
`venous cardioversion in patients with ventricular tachycar-
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`(1987).
`Mirowskd et al. "Clinical treatment of life threatening ven-
`tricular tachyarrhythmias with the automatic implantable
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`Mirowski et al. 'Temination of malignant ventricular
`arrhythmias with an implanted automatic defibrillator in
`human beings" New Engl J. Med. 303(6):322-324 (1980).
`Podolsky "Keeping the beat alive" U.S. News & World
`Report (Jul. 22, 1991).
`Product Brochure First Medic Semi-Automatic Defibrilla-
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`Street, P.O. Box 97013, Redmond. Washington.
`Product Brochure for the Shock Advisory System (1987),
`Physio-Control, 11811 Willow Road Northeast, P.O. Box
`97006, Redmond WA 98073.9706.
`
`6
`
`

`

`5,749,9904
`Page 3
`
`Product iniformuation for Model H MSA Portable Defibrilla-
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`Product information for MSA Portable Defibrillator (Bulle-
`-
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`improve survival" Medlines pp. 1-2
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`increase
`(Jun.-Jul. 1984).
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`current pathways for transvenous cardioversion in rapid
`ventricular tachycardia"' PACE 10:1130-1141 (Sep.-Oct.
`1987).
`Saksena et al. "Development for future implantable cardio-
`verters and defibrillators" PACE 10:1342-1358 (Nov.-Dec.
`1987).
`Schuder 'Ihe role of an engineering oriented medical
`research group in developing iprWoved methods and devices
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`Schuder et
`of
`of
`AL.
`"Comparison
`effectiveness
`relay-switched, one-cycle quasisinusoidal wayeform with
`critically damped sinusoid waveform
`in
`transthoracic
`defibrill.ation of 100-kilogram. calves" Medical Instrumen-
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`Schuder et al. "Defibrillation of 100 kg calves with asym-
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`18:419-426 (1984).
`implanted
`Schuder et al. "Development of automatic
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`shocks for open chest defibrillation in the calf" Abs. Am. Soc.
`Arfif. Intern. Organs 9:16.
`Schuder et al. 'Transthoracic ventricular defibrillation in the
`100 kg calf with symmetrical one-cycle bidirectional rect-
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`Schuder et al. 'Mtansthoracic ventricular defibrillation with
`Square-wave
`stiulih;
`one-half
`cycle" Cir. Res.
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`
`Schuder et al. "Ultrahigh-energy hydrogen thyratron/SCR
`bidirectional waveform defibrillator" Med. & Bio. Eng. &
`Comput. 20:419-424 (1982).
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`Schuder et al. "Waveform dependency in defibrillation"
`Devices & Tech Meeting NIH (1981).
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`and upper limit of vulnerablity in humans" PACE 15:563,
`Abstract 221 (Apr. 1992).
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`lation using biphasic: waveforms" PACE, 10: Abstract No. 49
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`Tang et al. "Ventricular defibrillation using biphasic wave-
`forms of different phasic duration" PACE 10:Abstract No. 47
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`Tang et al. "Ventricular defibrillation using biphasic wave-
`importance of phasic duration" JACC
`forms: The
`13(l):207-214 (1989).
`Walcott et al. "Comparison. of monophasic, biphasic, and the
`edmark waveform for external defibrillation" PACE 15:563,
`Abstract 218 (Apr. 1992).
`Wathen et al. "Improved defibrillation efficacy using four
`nonthoracotomy leads for sequential pulse defibrillation"
`PACE 15:563, Abstract 220 (Apr. 1992).
`Wetherbee et al. "Subcutaneous patch electrode-A means
`to obviate thoracotomy for implantation of the automatic
`cardiovcrter defibrillation system?" Circ. 72:384, Abstract
`No. 1536 (1985).
`Winkle et al.'The implantable defibrillator in ventricular
`arrhytlumias" Hospital Practice, pp. 149-165 (Mar. 1983).
`Winkle et al., "Improved low energy defibrillation efficacy
`in man using a bjphasic truncated exponential waveform"
`JACC 9(2):142A (1987).
`Zipes "Sudden cardiac death" Circulation 85(l):160-166
`(1992).
`
`7
`
`

`

`U.S., Patent
`
`May 12, 1998
`
`Sheet I of 10
`
`5,749,904
`
`FIG, 1
`
`TIME
`
`fI
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`B
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`
`FIG. 2
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`U.S. Patent
`US. Patent
`
`10 ~\
`10-
`
`5,749,904
`5,749,904
`
`Sheet 2 of 10
`May 12, 1998
`May 12, 1998
`Sheet 2 of 10
`
`
`
`INITIATE DISCHARGE
`
`IN FIRST POLARITY
`
`STOP DISCHARGE
`IN FIRST PHASE
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`FIG. 3
`FIG. 3
`
`
`
`
`
`9
`
`

`

`U.S. Patent
`
`May 12, 1998
`
`Sheet 3 of 10
`
`59749,904
`
`VOLTAGE
`
`t
`
`VTHRESHI --
`
`T I
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`10
`
`

`

`U.S. Patent
`
`May 12, 1998
`My1,19
`
`-Sheet 4 of 10
`he
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`597499904
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`
`FIG. 6
`
`11
`
`

`

`U.S. Patent
`
`May 12, 1998
`
`Sheet 5 of 10
`
`5,749,904
`
`INITIATE DISCHARGE
`IN FIRST POLARITY
`
`90
`
`NO.
`
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`
`93
`
`STOP DISCHARGE
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`
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`

`

`U.S. Patent
`
`May 12, 1998
`
`Sheet 6 of 10
`
`59749,904
`
`n
`
`o1
`
`I.
`L---------------------------------------------------------------_
`
`FIGs 10
`
`13
`
`

`

`U.S. Patent
`US. Patent
`
`May 12, 1998
`May 12, 1998
`
`Sheet 7 of 10
`.Sheet 7 of 10
`
`5,749,904
`5,749,904
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`U.S. Patent
`
`May 12, 1998
`
`Sheet 8 of 10
`
`59749,904
`
`96
`
`97
`
`- 96
`
`FIG. 12
`
`A
`
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`15
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`

`

`U.S. Patent
`
`May 12, 1998
`
`Sheet 9 of 10
`
`5,749,904
`
`142
`
`145
`
`134
`
`132
`
`-
`
`VOLTAGE
`
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`
`FIG. 14
`
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`
`16
`
`

`

`U.S. Patent
`
`May 12, 1998
`
`Sheet 10 of 10
`
`5,749,904
`
`134
`
`134
`
`160
`
`to charger
`
`164
`
`FIG. 16
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`
`17
`
`

`

`5,749,904
`
`1
`ELECTROTHERAPY METHOD UTILIZING
`PATIENT DEPENDENT ELECTRICAL
`PARAMETERS
`
`This application is a continuation-in-part of U.S. patent
`application Ser. No. 08/103,837, "Electrotherapy Method
`and Apparatus," filed Aug. 6. 1993'. now abandoned, and a
`continuation-in-part of U.S. patent appilication Ser. No.
`08/227,553. "Electrotherapy Method and Apparatus," filed
`Apr. 14, 1994, now U.S. Pat. No. 5,607,454. the disclosures
`of which are incorporated herein by reference.
`BACKGROUND OF THE INVENTnON
`This invention relates generally to an electrotherapy
`method and apparatus for delivering a shock to a patient's
`heart. In particular, this invention relates to a method and
`apparatus for shaping the electrical waveform delivered by
`an external defibrillator based on an electrical parameter
`measured during delivery of the waveform.
`Sudden cardiac death is the leading cause of death in the
`United States. Most sudden cardiac death is caused by
`ventricular fibrillation, in which the heart's muscle fibers
`contract without coordination, thereby interrupting normal
`blood flow to the body. The only effective treatment for
`ventricular fibrillation is electrical defibrillation, which
`applies an electrical shock to the patient's heart.
`To be effective, the defibrillation shock must be delivered
`to the patient within minutes of the onset of ventricular
`fibrillation. Studies have shown that defibrillation shocks
`delivered within one minute after ventricular fibrillation
`begins achieve up to 100% survival rate. The survival rate
`falls to approximately 30% if 6 minutes elapse before the
`shock isadiitr. Beyond 12 minutes, the survival rate
`approaches zero.
`One way of delivering rapid defibrillation shocks is
`through the use of impatbe defibrillators. Implantable
`defibrill,ators, are surgically implanted in patients who have
`a high likelioo of needing electrotherapy in the future.
`Implanted defibrillators typically monitor the patient's heart
`activity and automatically supply electrotherapeutic: pulses
`directly to the patient's heart when indicated.. Thus,
`implanted defibrillators permit the patient to function in a
`somewhat normal fashion away from the watchful eye of
`medical personnel. Implantable defibrillators are expensive,
`however, and ar used on only a small fraction of the total
`population at risk for sudden cardiac death.
`External defibrillators send electrical 'pulses to the
`patient's heart through electrodes applied to the patient's
`torso. External defibrillators are useful in the emergency
`room, the operating room, emergency medical vehicles or
`other situations where there may be an unanticipated need to
`provide electrotherapy to a patient on short notice. The
`advantage of external defibrillators is that they may be used
`on a patient as needed, then subsequently moved to be used
`with another patient.
`However, because external defibrillators deliver their
`electrotherapeutic pulses to the patient' s heart indirectly (ie.,
`from the surface of the patients skin rather than directly to
`the heart), they must operate at higher energies, voltages
`and/or currents than implanted defibrMlators. These high
`energy, voltage and currentrequirements have made existing
`external defibrillators; large, heavy and expensive, particu-
`larly due to the large size of the cVapactors or other energy
`storage media required by these prior art devices. The size
`and weight of prior art external defibrillators have limited
`their utility for rapid response by emergency medical
`response teams.
`
`2
`DefibriMaor waveforms, ie., time plots of the delivered
`current or voltage pulses, are characterized according to the
`shape, polarity, duration and number of pulse phases. Most
`current external defibrillators deliver monophasic current or
`5 voltage electrotherapeutic pulses. although some deliver
`biphasic sinusoidal pulses. Some prior art implantable
`defibrillators, on the other hand.,-use truncated exponential.
`biphasic waveforms. Examples of biphasic implantable
`defibrillators may be found in U.S. Pat. No. 4,821,723 to
`io Baker, Jr., et al.; U.S. Pat. No. 5,083,562 to de Coriolis et al.;
`U.S. Pat No. 4,800.883 to Winstrom.; U.S. Pat. No. 4,850,
`357 to Bach, Jr.; U.S. Pat. No. 4,953,551 to Mehra et al.; and
`U.S. Pat No. 5..230,336 to Fain et al.
`'Because each implanted defibrillator is dedicated to a
`15 Single patient, its operating parameters. such as electrical
`pulse amplitudes and total energy delivered, may be effec-
`tively titrated to the physiology of the patient to optimize the
`defibillator's effectiveness. Thus, for example, the initial
`voltage, first phase duration and total pulse duration may be
`20 set when the device is implanted to deliver the desired
`amount of energy or to achieve a desired start and end
`voltage differential (i.e., a constant tilt). Even when an
`implanted defibrillator has the ability to change its operating
`parameters to compensate for changes in the impedance of
`25 the defibrillators leads and/or the patient's heart (as dis-
`cussed in the Fain patent), the range of potential impedance
`changes for a single implantation in a single patient is
`relatively small.
`In contrast, because external defibrillator electrodes are
`30not in direct contact with the patient's heart, and because
`external defibrillators must be able to be used on a variety of
`patients having a variety of physiological differences, exter-
`nal defibrillators must operate according to pulse amplitude
`that will be effective in most
`35and duration parameters
`patients, no matter what the patient's physiology. For
`example, the impedance presented by the tissue between
`external defibrillator electrodes and the patient's heart varies
`from patient to.patient, thereby varying the intensity and
`40waveform shape of the shock actually delivered to the
`patient's heart for a given initial pulse amplitude and dura-
`tion. Pulse amplitudes and durations effective to treat low
`impedance patients do not necessarily deliver effective and
`energy efficient treatments to high impedance patients.
`45 External.defibrillators may be subjected to extreme load
`conditions which could potentially damage the waveform
`generator circuits. For example, improperly applied defibril-
`lator electrodes may create a very low impedance current
`path during the shock delivery. which could result in exces-
`50 sively high current within the waveform circuit. Thus, an
`external defibrillator has an additional design requirement to
`limit the peak current to safe levels in the waveform circuit,
`which is not normally a concern for implanted defibrillators.
`Prior art defibrillators have not fully addressed the patient
`55 variability problem. One prior art approach to this problem
`was to provide an external defibrillator with multiple energy
`settings that could be selected by the user. A common
`protocol for using such a defibrillator was to attempt
`defibrillation at an initial energy setting suitable for defibril-
`60 lating a patient of average impedance, then raise the energy
`setting for subsequent defibrillation attempts in the event
`that the initial setting failed. The repeated defibrillation
`attempts require additional energy and add to patient risk.
`Some prior art defibrillators measure the patient
`65 impedance, or a parameter related to patient impedance and
`alter the Shape of a subsequent defibrillation shock based on
`the earlier measurement. For example,
`the implanted
`
`18
`
`

`

`5,749,904
`
`3
`defibrilator described in the Fain patent delivers a defibril-
`lation shock of predetermined'shape to the patient's heart in
`response to a detected arrhythmia. The Fain device measures
`the system impedance during delivery of that shock and uses
`the measured impedance to alter the shape of a subsequently
`delivered shock.
`Another example of the measurement and use of patient
`impedance information in prior art defibrMlators is described
`in an article written by IR.E. Kerber. et al., "Energy, current,
`and success in defibrillation and cardioversion,." Circulation
`(May 1988). The authors describe an external. defibrillator
`that administers a test pulse to the patient prior to adminis-
`tering the defibrillation shock. The test pulse is used to
`measure patient impedance; the defibrillator adjusts the
`amount of energy delivered by the shock in response to the
`measured patient impedance. The shape of the delivered
`waveform. is a damped sinusoid.
`SUMMARY OF THE INVENTION
`This invention provides an external defibriflator and
`defibrillation method that automatically compensates for
`patient-to-patient imnpedance differences in the delivery of
`electrotherapeutic pulses for defibrillation and cardiover-
`sion. In a preferred embodiment, the defibrillator has an
`energy.source that may be discharged through electrodes on
`the patient to provide a b1phasic voltage or current pulse. In
`one aspect of the invention, the first and second phase
`duration and initial first phase amplitude are predetermined
`values. In a second aspect of the invention, the duration of
`the first phase of the pulse may be extended if the amplitude
`of the first phase of the pulse falls to fall to a threshold value
`by the end of the predetermined first phase duration, as
`might occur with a high impedance patient. In a third aspect
`of the invention, the first phase ends when the first phae
`amplitude drops below a threshold value or when the first
`phase duration reaches a threshold time value, whichever
`comes first, as might occur with a low to average impedance
`patient.
`In yet another embodiment, the invention provides a
`method for delivering electrotherapy to a patient through
`electrodes connected to a plurality of capacitors, including
`the steps of discharging at least one of the capacitors across
`the electrodes to deliver electrical energy to the patient,
`monitoring a patient-dependent electrical parameter (such as
`voltage, current or charge) during the dischm&gig step, and
`adjusting energy delivered to the patient based on a value of
`the electrical. parameter. The adjusting step may indlude
`selecting a serial. or parallel arragement for the capacitors
`based on a value of the electrical parameter.
`In another embodiment, the invention provides a method
`for delivering electrotherapy to a patient through electrodes
`connectable to a plurality of capacitors including the steps of
`discharging at least one of the capacitors across the elec-
`trodes to deliver electrical energy to the patient in a wave-
`form having at least a first phase and a second phase,
`monitoring a patient-dependent electrical parameter (such as
`voltage, current or charge) during the discharging step, and
`modifying second phase initial voltage based on a value of
`the electrical parameter. The adjusting step may include
`selecting a serial or a parallel arrangement for the capacitors
`based on a value of the electrical parameter.
`The invention is described in more detail below with
`reference to the drawings.
`BRIEF DESCRUMTON OF THlE DRAWINGS
`FIG. 1 is a schematic representation of a low-tilt biphasic
`electrotherapeutic waveform. according to a first aspect of
`this invention.
`
`10
`
`4
`FIG. 2 is a schematic representation of a high-tilt biphasic
`electrotherapeutic waveform, according to the first aspect of
`this invention.
`FIG. 3 is a flow chart demonstrating part of an electro-
`5 therapy method according to a second aspect of this inven-
`tion.
`FIG. 4 is a schematic representation of a biphasic wave-
`form delivered according to the second aspect of this inven-
`tion.
`FIG. 5 is a schematic representation of a biphasic wave-
`form delivered according to the second aspect of this inven-
`tion.
`FIG. 6 is a flow chart demonstrating part of an electro-
`15 therapy method according to a third aspect of this invention.
`FIG. 7 is a schematic representation of a biphasic wave-
`form delivered according to the third aspect of this inven-
`tion.
`FIG. 8 is a schematic representation of a biphasic wave-
`20 form delivered according to the third aspect of this inven-
`tion.
`FIG. 9 is a flow chart demonstrating part of an electro-
`therapy method according to a combination of the second
`25and third aspects of this invention.
`FIG. 10 is a block diagram of a defibrillator system
`according to a preferred embodiment of this invention.
`FIG. 11 is a schematic circuit diagram of a defibrillator
`system according to a preferred embodiment of this inven-
`30 tion.
`FIG. 12 is a block diagram showing another embodiment
`of the external defibrillator system of this invention.
`FIG. 13 is a schematic diagram of a defibrillator system
`According to a preferred embodiment of this invention.
`35 FIG. 14 is a schematic diagram of yet another embodi-
`ment of this invention.
`FIG. 15 is a schematic representation of a biphasic
`waveform. delivered by the external defibrillator shown in
`FIG. 14.
`40 FIG. 16 is a schematic diagram of another, embodiment of
`-
`this invention.
`FIG. 17 is a schematic diagram of yet another embodi-
`ment of this invention.
`45DETAILED DESCRIMTON OF TME
`PREFERRED EMBODIMENT
`FIGS. 1 and 2 ilustrate the patient-to-patient differences
`that an external defibrillator design must take into account.
`50 These figures are schematic representations' of truncated
`exponential biphasic waveforms. delivered to 'two different
`patients from an external defibrillator according' to the
`electrotherapy method of this invention for defibrillation or
`cardioversion. In these drawings, the vertical axis is voltage,
`55 and the horizontal axis is time. The principles discussed here
`are applicable to waveforms described in terms of current
`versus time as well, however.
`The waveform. shown in FIG. 1 is called a low-tilt
`waveform, and the waveform shown in FIG. 2 is called a
`60 high-tilt wavefo