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`Patent & Trademark Office is restricted to authorized employees and contractors only.
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`Staple Issue-Slip Here
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`POSITION
`CLASSIFIER_
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`ID NO.
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`DATE
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`EXAMINER
`TYPIST
`VERIFIER
`CORPS CORR.
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`INDEX OF CLAIMS
`
`Claim
`
`,Date
`
`ii: C 6
`\
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`C,
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`-
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`s met
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`AMER
`
`'WANE
`
`Date IF
`
`lei
`
`Claim
`
`FL
`
`Date
`
`531
`54
`
`1
`
`55
`
`561
`
`66
`671
`68
`64
`
`673
`74
`
`70
`76
`77
`,78
`
`SYMBOLS
`I..........Rejected
`Allowed
`.. ..............
`(Through numuberal) Canceled
`-
`RestrIcted
`.+...................
`Non-elected
`.......................
`nerference
`l..........
`A....................... Appeel
`0....................... Objected
`
`817
`
`85
`86
`877
`788
`89
`980
`911
`
`1
`1
`
`........
`.
`
`........
`
`4
`
`

`

`I
`
`PATENT NUMBER
`
`APPLICATION SERIAL NUMBER
`
`APPLICANT'S NAME (PLEASE PRINT)
`
`______________________________
`
`IF REISSUEi ORIG INAL PATENT NUMBER
`
`INTERNATIONAL CLASSIFICATION
`
`(RIEV6. 5e)
`
`PTO o
`
`STAPLE
`
`ý,REA
`
`*U.S. GOVERNMENT PRINTING OFFICE: 1998-440-769
`
`t,
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`CLASS
`
`ORIGINAL CLASSIFICATION
`SUBCLASS
`0
`
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`CROSS REFERENCE(S)
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`
`(ONE SUBCLASS PER BLOCK)
`
`______CLASS_____
`
`Coo-7 oQ5 0-74- 6O0?__
`
`'GROUP
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`ASSISTANT EXAM)NER (PLEASE STAMP OR PRINT FULL NAME)
`737 I M A~ M INER(PL SE S T
`ISUE CASSIICATON SIPt
`ISSUE CLASSIFICATION SLIP
`
`fAMO P .SLL 4AM EK~
`
`U.S. DJEPARTMENT OF COMMERCE
`PATENT AND TRADEMARK OFFICE
`
`5
`
`

`

`United States Patent [19]
`Gliner et al.
`
`[54] EXTERNAL DEFIBRILLATOR CAPABLE OF
`DELIVERING PATIENT IMPEDANCE
`COMPENSATED BIIPHASIC WAVEFORMS
`
`[75]
`
`Inventors: Bradford E. Glitner, Beilevue; Thomas
`D. Lyster, Bothwell; Clinton S. Cole,
`Kirkland; Daniel J. Powers; Canlton B.
`Morgan, both of Bainbridge Isand, all
`of Wash.
`
`[73] Assignee: Heartstream, Inc., Seattle, Wash.
`
`[*]J Notice:
`
`Thbis patent issued on a continued pros-
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`term provisions of 35 U.S.C.
`patent
`154(aX2).
`
`[21]
`
`[2-2]
`
`Appl. No.: 08/946,M4
`Oct. 8, 1997
`
`Filed:
`
`Related U.S. Application Data
`
`[63] Continuation of application No. 08/803,094, Feb. 20, 1997,
`Pat. No. 5,735,879, which is a continuation of application
`No. 081103,837, Aug. 6, 1993, abandoned.
`. . . . . . . . . . . . . . . . . . . . . A61N 1/39
`Int. Cl ...................
`[51]
`[52] U.S. Cl ........ ............... 607/7; 607/5; 607f74;
`607/8
`607/4-8, 74
`
`[58] Field of Search ............................
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,211,154
`3,241,555
`3,706,313
`
`10/1965
`3/1966
`12/1972
`
`Becker et al,.
`Caywood et al..
`Milani et al..
`
`(List continued on next page.)
`
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`
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`0315368 Al
`0353341 Al
`
`9/1988
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`2/1990
`
`European Pat. Off. .
`European Pat. Off. .
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`
`II US006047212A
`
`[i1] Patent Number:
`[45] Date of Patent:
`
`6,047,212
`*Apr. 4, 2000
`
`OTHER PUBLICATIONS
`Alferness, et al "The influence of shock waveforms on
`defibrillation efficacy" IEEE Engineering in Medicine and
`Biology, pp. 25-27 (Jun. 1990).
`Anderson et al. "The efficacy of trapezoidal wave forms for
`ventricular defibrillation" Chest 70(2):298-300 (1976).
`Blillie 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" Circulation
`Improved efficacy with hiphasic
`76:312, 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).
`(List continued on next page.)
`Primary Examiner-Kennedy J. Schaetzle
`ABSTRACT
`
`[57]
`
`le;.5qTbis invention provides an external defibrillator and
`defibrillation method that automatically compensates for
`patient-to-patient impedance differences in the delivery of
`electrotherapeutic pulses for defibrillation and cardiover-
`the defibrillator has an
`sion. In a preferred embodiment,
`energy source that may be discharged through electrodes on
`the patient to provide a biphasic 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 fails 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 phase
`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. Thbis method and apparatus of altering the delivered
`biphasic pulse thereby compensates for patient impedance
`differences by changing the nature of the delivered electro-
`therapeutic pulse, resulting in a smaller, more efficient and
`less expensive defibrillator.
`
`(List continued on next page.)
`
`Claims, 7 Drawing Sheets
`(Lis cotinud o nex pae.)12
`
`6
`
`

`

`6,047,212
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`OTHER PUBLICATIONS
`
`3,782,389
`3,860,009
`3,862,636
`3,886,950
`4,023,573
`4,328,808
`4,399,818
`4,419,998
`4,473,078
`4,494,552
`4,504,773
`4,574,810
`4,S95,009
`4,610,254
`4,619,265
`4,637,397
`4,745,923
`4,800,883
`4,821,723
`4,840,177
`4,848,345
`4,850,357
`4,953,551
`4,998,531
`5,0Y78,134
`5,083,562
`5,097,833
`5,107,834
`5,111,813
`5,111,816
`5,207,219
`5,215,081
`5,222,480
`5,222,492
`5,230,336
`5,237,989
`5,249,573
`5,275,157
`5,306,291
`5,334,219
`5,334,430
`5,352,239
`5,370,664
`5,372,606
`5,385,575
`5,411,525
`5,411,526
`5,413,591
`5,431,686
`5,441,518
`S,489,293
`5,507,781
`5,634,938
`
`1/1974 Bell.
`1/197S Bell et al.,
`1/1975 Bell et al..
`6/1975 Ukkcstad et at..
`5/1977 Pantridge et al.
`5/1982 Charbonnier et al.
`8/1983 Money .
`12/1983 Heath .
`9/1984 Angel .
`1/1985 Heath .
`3/1985 Suzuki et at..
`3/1986 Lenman .
`6/1986 Leinders.
`9/1986 Morgan et at..
`10/1986 Morgan et at..
`1/1987 Jones et at..
`5/1988 Winstrom.
`1/1989 Winstrom n
`4/1989 Baker, Jr. et at.
`6/1989 Charbonnier et at.
`7/1989 Zenkich .
`7/1989 Bach, Jr. .
`9/1990 Mehra et at..
`3/1991 Bocchi et at..
`1/1992 Heilman et al..
`1/1992 de Coriolis et al..
`3/1992 Campos .
`Ike-der et at,..
`4/1992
`5/1992 Charbonnier et at,.
`5/1992 Pleas et at. .
`5/1993 Adams et at..
`6/1993 Ostroff .
`6/1993 Couche et al..
`6/1993 Morgan et al..
`7/1993 Fain et at.,
`8/1993 Morgan et at. .
`10/1993 Fincke et at,.
`1/1994 Morgan et at. .
`4/1994 Kroll et at..
`8/1994 Kroll .
`Isbikawa et at. .
`8/1994
`10/1994 Pleas .
`12/1994 Morgan et at. .
`12/1994 Lang et at. .
`1/1995 Adams.
`5/1995 Swanson et at. .
`5/1995 Krolt et at.
`5/1995 Knott
`7/1995 Krott ei al.
`8/1995 Adams et at.
`2/1996 Pleas et at..
`4/199% Krotl et al ....................
`....607/7
`607/7
`6/1997 Swanson et at...... I .........
`
`0437104 Al
`0457604
`0 491 649 A2
`0507504 Al
`2070435
`2083363
`WO 93/16759
`WO 94/21327
`WO 94/22530
`WO 95/05215
`WO 95/09673
`WO 95/32020
`
`FOREIGN PATENT DOCUMENTS
`7/1991
`11/1991
`12/1991
`10/1992
`9/1981
`3/1982
`9/1993
`9/1994
`10/1994
`2/1995
`4/1995
`11/1995
`
`European Pat. Off..
`European Pat. Off. .
`European Pat, Off. .
`European Pat. Off. .
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`United Kingdom.
`WIPO.
`WIPO.
`WIPO.
`WIPO.
`WIPO.
`WIPO.
`
`Cooper et at. "The effect of phase separation on biphasic
`waveform defibrillation" PACE 16:471-482 (Mar. 1993).
`Cooper et at. "The effect of temporal separation of phases on
`biphasic waveform defibrillation efficacy" TheAnnual 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" JAAMA 235(21):2284 (1976).
`DaWlback et at. "Ventricular defibrillation with square
`waves" The Lancet (Jul. 2, 1966).
`Echt et al. "Biphasic waveform is more efficacious than
`tratnsthoracic cardioversion"
`for
`monophasic waveform
`PACE 16:914, Abstract No. 256 (Apr. 1993).
`Feeser et al. "Strength-duration and probability of success
`curves for defibrillation with biphasic waveforms" Circula-
`tion 82(6):2128-2141 (1990).
`Guse et at. "Defibrillation 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
`rectangular waveforms" Am. J. Physiol,
`with biphasic
`247:H792-796 (1984).
`Jones et al. "Defibrillator waveshape optimization" Devices
`and Tech Meeting NIH (1982).
`Jones et at. "Improved defibrillator waveform safety factor
`with biphasic waveforms" Am. J. Physiol. 245:H-60-65
`(1983).
`Jones et at. "Reduced excitation threshold in potassium
`depolarized myocardial cells with symmetrical biphasic
`waveforms" J. Mol. Cell. Cardiol. 17(39):XXVII, Abstract
`No. 39 (1985).
`Jude et at. "Fundamentals of cardiopulmonary resuscitation"
`F.A. Davis & Company, Philadelphia, PA, pp. 98-104
`(1965).
`Kerber et at. "Energy, Current, and success in defibrillation
`and cardioversion: clinical studies using an automated
`impcdance-based method of energy adjustment," Circ.
`77(5):1038-1046 (1988).
`Knickerbocker et al. "A portable defibrillator" IEEE Trans
`on Power and Apparatus Systems 69:1089-1093 (1963).
`"The development of the defibrillator"
`Kuowenhoven
`Annals of Internal Medicine 71(3):449-458 (1969).
`in the development of the
`Langer et al. "Considerations
`automatic implantable defibrillator" Medical Instrumenta-
`tion 10(3):163-167 (1976).
`Lerman et al. "Current-based versus energy-based ventricu-
`defibrillation: A
`study"
`JACC
`prospective
`lar
`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-
`dia" Circulation 76(3):601-609 (1987).
`Mirowski et at. "Clinical treatment of life threatening ven-
`tricular tachyarrhytbmias with the automatic implantable
`defibrillator" American Heart J, 102(2):265-270 (1981).
`Mirowskci et at. "Termination of malignant ventricular
`arrhythmias with an implanted automatic defibrillator in
`human beings" New Engl J. Med. 303(6):322-324 (1980).
`the beat alive" U.S. News & World
`Podolsky "Keeping
`Report (Jul. 22, 1991).
`for First Medical Semi-Automatic
`Product Brochure
`Defibrillator (1994), Spacelabs.
`
`7
`
`

`

`6,047,212
`Page 3
`
`Product Brochure for the Shock Advisory System (1987),
`Physio-Control, 11811 Willow Road Northeast, P.O. Box
`97006, Redmond WA 98073.9706.
`Redd (editor), "Defibrillation with biphasic waveform may
`improve survival" Medlines pp. 1-2
`increase safety,
`(Jun..-Jul. 1984).
`Saksena et al. "A prospective evaluation of single and dual
`current pathways for transvenous cardioversion in rapid
`ventricular tachycardia" PACE 10:1130-1141 (Sep.-Oct.
`1987).
`Saksena ct al. "Development for future implantable cardio-
`verters and defibrillators" PACE 10:1342-1358 (Nov.-Dec.
`1987).
`Schuder "The role of an engineering oriented medical
`research group in developing improved methods and devices
`for achieving ventricular defibrillator: The University of
`Missouri experience" PACE 16:95-124 (Jan. 1993).
`Schuder et al. "A multielectrode-time sequential laboratory
`defibrillator for the study of implanted electrode systems"
`Amer Soc. Artif Int. Organs XVIII:514-519 (1972).
`Schuder et al. "Comparison of effectiveness of relay-
`switched, one-cycle quasisinusoidal waveform with criti-
`cally damped sinusoid waveform in transthoracic defibril-
`lation of 100-kilogram calves" Medical Instrumentation
`22(6):281-285 (1988).
`Schuder et al. "Defibrillation of 100 kg calves with asym-
`metrical, bi-directional, rectangular pulses" Card, Res.
`18:419-426 (1984).
`implanted
`Schuder et al. "Development of automatic
`defibrillator" Devices & Tech Meeting NIH (1981).
`Schuder et al. "One-cycle bidirectional rectangular wave
`shocks for open chest defibrillation in the calf" Abs. Am. Soc.
`Artif. Intern. Organs 9:16 (1981).
`Schuder et al. "Transthoracic ventricular defibrillation in the
`100 kg calf with symmetrical one-cycle bidirectional rect-
`angular wave stimuli" IEEE Trans. BIME 30(7):415-422
`(1983).
`Schuder et al. "Transthoracic ventricular defibrillation with
`Square-wave
`stimuli;
`one-half
`cycle" Cir Res.
`XV.258-264 (1964).
`
`Schuder et al. "Ultrahigh-energy hydrogen thyratron/SCR
`bidirectional waveform defibrillator" Med. & Bio. Eng. &
`Comput. 20:419-424 (1982).
`Schuder et al. "Waveform dependency in defibrillating 100
`kg calves" Devices & Tech. Meeting NIH (1981).
`Schuder et al. "Waveform. dependency in defibrillation"
`Devices & Tech Meeting NIH (1981).
`Stanton et al. "Relationship between defibrillation threshold
`and upper limit of vulnerability in humans " PACE 15:563,
`Abstract 221 (Apr. 1992).
`Tang et al, "Strength duration curve for ventricular defibril-
`lation using biphasic waveforms" PACE, 10: Abstract No. 49
`(1987).
`Tang et al. "Ventricular defibrillation using biphasic wave-
`forms of different phasic duration" PACE 1 0:Abstract No. 47
`(1987).
`Tang et al. "Ventricular defibrillation using biphasic wave-
`importance of phasic duration" JACC
`forms: The
`13(1):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 thoracotomny for implantation of the automatic
`cardioverter defibrillation
`system?" Circ. 72:111-384,
`Abstract No. 1536 (1985).
`Winkle et al. "The implantable defibrillator in ventricular
`arrhythmias" Hospital Practice, pp. 149-165 (Mar. 1983).
`Winkle et al., "Improved low energy defibrillation efficacy
`in man using a biphasic truncated exponential waveform"
`JACC 9(2):142A (1987).
`Zipes "Sudden cardiac death" Circulation 85(1):160-166
`(1992).
`
`8
`
`

`

`U.S. Patent
`
`Apr. 4,2000
`
`Sheet 1 of 7
`
`69047,212
`
`FIG. 1
`
`fB
`
`VOLTAGEI-
`
`BI
`
`I
`
`r-G-H
`
`B
`
`i
`
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`
`TIME
`
`TIME
`
`FIG. 2
`
`FIG. 4
`
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`
`IAI
`
`-
`
`VTHRESHJ
`
`tTHTIME
`
`TIME
`
`9
`
`

`

`U.S. Patent
`US. Patent
`
`Apr. 4, 2000
`Apr. 4, 2000
`
`Sheet 2 of 7
`Sheet 2 of 7
`
`6,047,212
`6,047,212
`
`1O
`10
`
`INITIATE DISCHARGE
`
`IN FIFIST POLARITY
`
`
`
`16
`16
`
`14
`
`NO
`
`IS
`
`VOLTAGE < VTHRESH
`?
`
`YES
`
`STOP DISCHARGE
`IN FIRST PHASE
`
`
`
`
`
`
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`”W
`
`
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`1B
`18
`
`20
`20
`
`22
`22
`
`24
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`
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`
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`
`WAIT FOFI
`INTERIM TIME G
`
`CHANGE
`POLARITY
`
`RESUME DISCHARGE
`FOFI SECOND PHASE
`DURATION F
`
`STOP DISCHARGE
`
`FIG. 3
`FIG. 3
`
`10
`
`10
`
`

`

`U.S. PatentAp.4200
`Apr. 4, 2000
`
`Set3o76,721
`Sheet 3 of 7
`
`690479212
`
`FIG. 5
`
`-
`
`--
`
`-
`
`-
`
`-F
`
`-
`
`-
`
`-
`
`TIME
`
`tT6
`
`FIG. 7
`
`TIME
`
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`
`-
`
`FIG. 8
`
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`
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`
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`
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`E
`
`'
`
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`
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`
`TIME
`
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`
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`
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`
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`
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`
`t A
`
`VTHRESH-
`
`11
`
`

`

`U.S. PatentAp.4200
`Apr. 4,2000
`
`Set4o76,721
`Sheet 4 of 7
`
`690479212
`
`FIG. 6
`
`12
`
`

`

`U. S. Patent
`
`Apr. 4,2000
`
`Sheet 5 of 7
`
`6,047,212
`
`INITIATE DISCHARGE
`IN FIRST POLARITY
`
`90
`
`NO
`
`92
`
`93
`
`STOP DISCHARGE
`OF FIRST PHASE
`
`94
`
`95
`
`FIG. 9
`
`RESUME DISCHARGE
`FOR SECOND PHASE
`DURATION F
`
`'97
`
`13
`
`

`

`U.S. Patent
`
`Apr. 4, 2000
`
`Sheet 6 of 7
`
`6,047,212
`
`I,--------------------------------------------------------------------
`
`ENERGY
`SOURCE
`32
`
`'ODE
`
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`
`FIG. 10
`
`30
`
`14
`
`

`

`U.S. Patent
`US. Patent
`
`Apr. 4, 2000
`Apr. 4, 2000
`
`Sheet 7 of 7
`Sheet 7 of 7
`
`6,047,212
`6,047,212
`
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`
`1055
`
`$2:
`
`5
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`
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`

`

`6,047,212
`
`1
`EXTERNAL DEFIBRILLATOR CAPABLE OF
`DELIVERING PATIENT IMPEDANCE
`COMPENSATED BIPHASIC WAVEFORMS
`
`This application is a continuation of application Scr. No.
`08/803,094 filed Feb. 20, 1997, now U.S. Pat. No. 5,735,
`879, which is a continuation of application Ser, No. 08/103,
`837 filed Aug. 6, 1993, now abandoned.
`
`BACKGROUND OF TIHIl INVENTION
`This invention relates generally
`to an electrotherapy
`method and apparatus for delivering a shack to a patient's
`beant. In particular, this invention relates to a method and
`apparatus for using an external defibrillator
`to deliver a
`biphasic defibrillation shock to a patient's heart through
`electrodes attached to the patient.
`Defibrillators apply pulses of electricity to a patient's
`heart to convert ventricular arrhythmias, such as ventricular
`fibrillation and ventricular
`tachycardia, to normal heart
`rhythms
`through
`the processes of defibrillation and
`cardioversion, respectively. There are two main classifica-
`tions of defibrillators: external and implanted. Implantable
`defibrillators are surgically implanted in patients who have
`a high likelihood 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.
`External defibrillators send electrical pulses to
`the
`patient's heart through electrodes applied to the patient's
`torso. External defibrillators are usefuil 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 defibrilla-
`tors deliver their electrotherapeutic pulses to the patient's
`beant indirectly (i.e., from the surface of the patient's skin
`rather than directly to the heart), they must operate at higher
`energies, voltages and/or currents than implanted defibril-
`lators. The high energy, voltage and current requirements
`have made current external defibrillators large, heavy and
`expensive, particularly due to the large size of the capacitors
`or other energy storage media required by these prior art
`devices.
`The time plot of the current or voltage pulse delivered by
`a defibrillator shows the defibrillator's characteristic wave-
`form. Waveforms are characterized according to the shape,
`polarity, duration and number of pulse phases. Most current
`external defibrillators deliver monophasic current or voltage
`electrotherapeutic pulses, although some deliver biphasic
`sinusoidal pulses. Some prior art implantable defibrillators,
`on the other hand, use truncated exponential, biphasic wave-
`forms. Examples of biphasic implantable defibrillators may
`be found in U.S. Pat. No. 4,821,723 to 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.;
`and U.S. Pat. No. 4,953,551 to Mehra et al.
`Because each implanted defibrillator
`is dedicated to a
`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
`defibrillator's effectiveness, Thus, for example, the initial
`
`5
`
`20
`
`35
`
`2
`voltage, first phase duration and total pulse duration may be
`set when the device is implanted to deliver the desired
`amount of energy or to achieve that desired start and end
`voltage differential (i.e, a constant tilt).
`In contrast, because external defibrillator electrodes are
`not 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
`10 and duration parameters
`that will be effective
`in most
`patients, no matter what
`the patient's physiology. For
`example, the impedance presented by the tissue between
`external defibrillator electrodes and the patient's beant varies
`from patient to patient, thereby varying the intensity and
`15 waveform 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.
`Prior art external defibrillators, have not fully addressed
`the patient variability problem. One prior art approach to this
`problem was to provide the external defibrillator with mul-
`tiple energy settings that could be selected by the user. A
`common protocol for using such a defibrillator was to
`25 attempt defibrillation at an initial energy setting suitable for
`defibrillating a patient of average impedance, then raise the
`energy setting for subsequent defibrillation attempts in the
`event that the initial setting failed. The repeated defibrilla-
`tion attempts require additional energy and add to patient
`30 risk. What is needed, therefore, is an external defibrillation
`method and apparatus that maximizes energy efficiency (to
`minimize the size of the required energy storage medium)
`and maximizes therapeutic efficacy across an entire popu-
`lation of patients.
`SUMMARY OF THE INVENTION
`Thbis invention provides an external defibrillator and
`defibrillation method that automatically compensates for
`patient-tn-patient impedance differences in the delivery of
`40 electrotberapeutic 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 biphasic voltage or current pulse. In
`one aspect of the invention, the first and second phase
`45 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 fails to fall to a threshold value
`by the end of the predetermined first phase duration, as
`50 might occur with a high impedance patient. In a third aspect
`of the invention, the first phase ends when the first phase
`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
`55 patient. This method and apparatus of altering the delivered
`biphasic pulse thereby compensates for patient impedance
`differences by changing the nature of the delivered electro-
`therapeutic pulse, resulting in a smaller, more efficient and
`less expensive defibrillator.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic representation of a low-tilt biphasic
`electrotherapeutic waveform according to a first aspect of
`this invention.
`FIG. 2 is a schematic representation of a high-tilt biphasic
`electrotherapeutic waveform according to the first aspect of
`this invention.
`
`60
`
`65
`
`16
`
`

`

`6,047,212
`
`3
`FIG. 3 is a flow chart demonstrating part of an electro-
`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-
`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-
`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
`and 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-
`tion.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`FIGS. 1 and 2 illustrate the patient-to-patient differences
`that an external defibrillator design must take into account.
`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,
`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
`high-tilt waveform, where tilt H is defined as a percent as
`follows:
`
`H1
`
`Al- IDI
`-_xtQ00
`JAI
`
`As shown in FIGS. 1 and 2, A is the initial first phase voltage
`and D is the second phase terminal voltage. The first phase
`terminal voltage B results from the exponential decay over
`time of the initial voltage A through the patient, and the
`second phase terminal voltage D results from the exponen-
`tial decay of the second phase initial voltage C in the same
`manner. The starting voltages and first and second phase
`durations of the FIG. 1 and HIG. 2 waveforms are the same;
`the differences in end voltages B and D reflect differences in
`patient impedance.
`Prior art disclosures of the use of truncated exponeotial
`biphasic waveforms in implantable defibrillators have pro-
`vided little guidance for the design of an external defibril-
`lator that will achieve acceptable defibrillation or cardiover-
`sion rates across a wide population of patients. The
`defibrillator operating voltages and energy delivery require-
`ments affect the size, cost, weight and availability of com-
`ponents. In particular, operating voltage requirements affect
`the choice of switch and capacitor technologies. Total
`
`10
`
`4
`energy delivery requirements affect defibrillator battery and
`capacitor choices.
`We have determined that, for a given patient, externally-
`applied truncated exponential biphasic waveforms defibril-
`5 late at lower voltages and at lower total delivered energies
`than externally-applied monophasic waveforms. In addition,
`we have determined that there is a complex relationship
`between total pulse duration, first to second phase duration
`ratio, initial voltage, total energy and total tilt.
`Up to a point, the more energy delivered to a patient in an
`electrotherapeutic pulse, the more likely the defibrillation
`attempt will succeed. Low-tilt biphasic waveforms achieve
`effective defibrillation rates with less delivered energy than
`low-tilt waveforms are
`high-tilt waveforms. However,
`is energy inefficient, since much of the stored energy is not
`delivered to the patient. On the other hand, dcfibrillators
`delivering high-tilt biphasic waveforms deliver more of the
`stored energy to the patient than defibrillators delivering
`low-tilt waveforms while maintaining high efficacy up to a
`20 certain critical tilt value. Thus, for a given capacitor, a given
`initial voltage and fixed phase durations, high impedance
`patients receive a waveform with less total energy and lower
`peak currents but better conversion properties per unit of
`energy delivered, and low impedance patients receive a
`25 waveform with more delivered energy and higher peak
`currents. There appears to be an optimum tilt range in which
`high and low impedance patients will receive effective and
`efficient therapy. An optimum capacitor charged to a prede-
`tertmined voltage can be chosen to deliver an effective and
`30 efficient waveform across a population of patients having a
`variety of physiological differences.
`Thbis invention is a defibrillator and defibrillation method
`that takes advantage of this relationship between waveform
`tilt and total energy delivered in high and low impedance
`35 patients. In one aspect of the invention, the defibrillator
`operates in an open loop, i.e., without any feedback regard-
`ing patient impedance parameters and with preset pulse
`phase durations. The preset parameters of the waveforms
`shown in FIGS. 1 and 2 are therefore the initial voltage A of
`the first phase of the pulse, the duration E of the first phase,
`the interphase duration G, and the duration F of the second
`phase. The terminal voltage B of the first phase, the initial
`voltage C of the second phase, and the terminal voltage D of
`the second phase are dependent upon the physiological
`the physical connection
`45 parameters of the patient and
`between the electrodes and the patient.
`the total
`For example, if the patient impedance (i.e.,
`impedance between the two electrodes) is high, the amount
`of voltage drop (exponential decay) from the initial voltage
`s0 Ato the terminal voltage B during time E will be lower (FIG.
`1) than if the patient impedance is low (FIG. 2). The same
`is true for the initial and terminal voltages of the second
`phase during time E. The values of A, E, G and F are set to
`optimize defibrillation and/or cardioversion efficacy across a
`impedance patients
`55 population of patients. Thus, high
`receive a low-tilt waveform that is more effective per unit of
`delivered energy, and low impedance patients receive a
`high-tilt waveform that delivers more of the stored energy
`and is therefore more energy efficient.
`Another feature of biphasic waveforms is that waveforms
`with relatively longer first phases have better conversion
`properties than waveforms. with equal or shorter first phases,
`provided the total duration exceeds a critical minimum.
`Therefore, in the case of high impedance patients, it may be
`65 desirable to extend the first phase of the biphasic waveform
`is kept constant) to
`(while
`the second phase duration
`increase the overall efficacy of the electrotherapy by deliv-
`
`40
`
`60
`
`17
`
`

`

`6,047,212
`
`5
`ering a more efficacious waveformn and to increase the total
`amount of energy delivered. FIGS. 3-5 demonstrate a
`defibrillation method according to this second aspect of the
`invention in which information related to patient impedance
`is fed back to the defibrillator to change the parameters of
`the delivered electrotherapeutic pulse.
`FIG. 3 is a flow chart showing the method steps following
`the decision (by an operator or by the defibrillator itselo) to
`apply an electrotherapeutic shock to the patient through
`electrodes attached to the patient and charging of the energy
`source, e.g., the defibrillator's capacitor or capacitor bank, to
`the initial first phase voltage A. Block 10 represents initia-
`dion of the first phase of the pulse in a first polarity.
`Discharge may be initiated manually by the user or auto-
`matically in response to patient heart activity measurements
`(e.g., ECG signals) received by the defibrillator through the
`electrodes and analyzed by the defibrillator controller in a
`manner known in the art.
`Discharge of the first phase continues for at least a
`as shown by block 12 of FIG. 3. If,
`t