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`by the United States Code Title 35, Sections 122, 181 and 388. P session outside the U.S.
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`PATENT APPLICATION
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`APPROVED FOR LICENSE
`
`INITIALS
`
`_____
`
`08601617
`CONTENTS.
`
`Date
`Received
`orMailed
`
`Date
`Entered
`or
`Counted
`
`4 papers.
`'7?e&t ,4x~ar/ ,/KL
`Application
`~
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`____
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`____21.
`
`--
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`_____
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`____30.
`
`_____
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`____31.
`
`3
`
`

`

`___SEARCHED
`Class
`Sub.
`Date
`
`Exmr.
`
`607
`
`c:i
`
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`Staple IKsue Slipf * ae
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`POSITION
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`EXAMINER
`TYPIST
`VERIFIER
`CORPS CORR.
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`FILE MAINT.
`DRAFTING
`
`ID NO.
`
`DATE
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`_
`
`INDEX OF CLAIMS
`
`Claim
`
`Date
`
`Claim
`
`Date
`
`1
`
`1
`
`I2
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`05
`
`1
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`53
`54
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`100k
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`SYMBOLS
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`
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`
`APPLICANT'S NAME IPLEASE PRINT)
`
`IF REISSUE, ORIGINAL PATENT NUMBER
`
`INTERNATION'AL CUMISFICATION
`
`600
`
`CLAS
`-7l
`
`CLASS
`
`CROSS REFERENCE(S)
`SUBCLASS
`~~(ONE
`SUBCLASS PER BLOCK)
`-c574 _
`
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`
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`(RE. 1
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`
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`
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`
`DEPARTMENT OF COMMERCE
`PATENT AND TRADEMARK OFCE
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`
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`
`XAMIN q (PLEAsF STAMP 0 PRINT FL L M~E)
`
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`
`6
`
`

`

`United States Patent t19]
`Gliner et al.
`
`[54] ELECTROTHIERAPY METHOD
`
`[75]
`
`Inventors: Bradford E. Gliner, Bellevue; Thomas
`D. Lyster, Bothell; Clinton S. Cole,
`Kirkland; Daniel J. Powers, Bainbridge
`Island; Carlton B. Morgan, Bainbridge
`Island, all of Wash.
`
`173] Assignee: Heartstreamn, Inc., Seattle, Wash.
`
`(21] Appl. No.: 601,617
`Feb. 14, 1996
`
`122] Filed:
`
`Related U.S. Application Data
`
`[62] Division of Scr. No. 103,837, Aug. 6, 1993.
`
`Int. CL6 ................. . . . . . . . . . . . . . . . . . . . . . . A61N W)9
`[51]
`607n; 607/5; 607n24
`[52] U.S. CI.............................
`[58] Fleld of Search .........................
`607n7, 5, 6, 4,
`607n74
`
`[56]
`
`References Cited
`U-S. PATENT DOCUMENTS
`Becker et a..
`Caywood et al..
`Milani et al..
`Bell.
`Bell et a!..
`Bell ei al..
`Ukkestad et al.-
`Pantridge et al..-
`Charbonnier et al. .
`Heath .
`(List continued on next page.)
`
`3,211,154
`3,241,553
`3,706,31:3
`3,782,389)
`3,860,00)
`3,862,6365
`3,886,950
`4,023,573
`4,328,80B
`4,419,998
`
`FOREIGN PATENT DOCUMENTS
`European Pat. Off..
`0281219
`European Pat. Off..-
`03 15368
`Europent Pat. Off..
`0353341
`European Pat. Off..-
`0437104
`European Pat. Off..
`0507504
`United Kingdom .
`2070435
`2083363
`United Kingdom.
`91/16759
`WIPO-
`
`US005 59 3427 A
`[ii] Patent Number:
`[45] Date of Patent:
`
`51593 ,427
`jan. 14, 1997
`
`94/21327
`9/1994 WIPO
`94/22530 1011994 WIPO
`OTHER PUBLICATIONS
`Alfeness 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.
`Bilie et al., "Predicting and validating cardiothoracic cur-
`rent flow using finite element modeling." PACE, 15:563,
`abstract 219 (Apr. 1992).
`(List continued on next page.)
`
`Primary Examiner-William E. Kamm
`Assistant Examiner-Kennedy J. Schaetzle
`Attorney, Agent, or Finn-Morrison & Foerster
`
`ABSTRACT
`This invention provides an external defibrillator and defibril-
`lation method that automatically compensates for patient-
`to-patient impedance differences in the delivery of electro-
`therapeutic pulses for defibrillation and cardioversion. 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 inventiori, 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. This
`method and apparatus of altering the delivered biphasic
`pulse thereby compensates for patient impedance differ-
`ences by changing the nature of the delivered electrothera-
`peutic pulse, resulting in a smaller, more efficient and less
`expensive defibrillator.
`
`18 Claims, 7 Drawing Sheets
`
`a
`
`b
`
`*
`
`flTAOmr.
`
`* a
`
`*
`
`p
`
`I-n~Fl
`
`7
`
`

`

`5,593,427
`Page 2
`
`4,473,078
`4,494,552
`4,504,77:1
`4,574,810
`4,595,009
`4,610,254
`4,619,265
`4,637,397?
`4,745,9231
`4,800,88:5
`4,821,723
`4,840,177?
`4,848,345
`4,850,35-1
`4,953,551
`4,998,531
`5,078,134
`5,083,562
`5,097,833
`5,107,834
`5,111,813
`5,111,815
`5,207,219
`5,215,081
`5,222,48D
`5,222,492
`5,230,336
`5,237,989
`5,249,573
`5,272,157
`5,306,291
`5,334,219
`5,334,430
`5,352,239
`5,370,664
`5,12,606
`5,411,526
`
`U.S. PATENT DOCUMENTS
`Angel-
`Heath.
`Suzuki et al. .
`Lemn.
`Leinders .
`Morgan et al. .
`Morgan et a..
`Jones et al. .
`Winstrom .
`Winstromn,
`Baker et al..
`Chaibonnier et a..
`Zonkdch .
`Bach, Jr. .
`Mehra et a..
`Bomcii et a..
`Heilman et a..
`de Coriolis et al..
`Camnpos .
`Ideker et al.t
`Charbonmier et a.
`Pleas cE a..
`Adams et al..
`Ostroff.
`Couche et a..
`Morgan et a..
`Pain et al. .
`Morgan et al. .
`Fincke et al.t
`Morgan etal..
`Kroll et al..
`Kroll
`Berg etial. .
`Pless -
`Morgan et al. .
`Lang et al..
`Kroll eta]. .
`OTHER PUBLICATIONS
`
`Chapman el, al., "Non-thoracotomy internal defibrillation:
`Improved efficacy with biphasic shocks", Circulation,
`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):61Z2 abstract no. 2433 (1991).
`Cooper et al., "The effect of phase separation on bipbasic
`waveform dlefibrillation," PACE, 16:471-482 (Mar. 1993).
`Cooper et al., "The effect of temporal separation of phases
`on biphasic waveform defibrillation efficacy," The Annual
`International Conference of the IEEE Engineering in Medi-
`cine and Biology Society 13(2):0766-0767 (1991).
`Crampton etal., 'ow-energy ventricular defibrillation and
`miniature defibrillators," JAMA4, 23S(21):2284 (1976).
`defibrillation with
`et
`al.,
`"Ventricular
`DahbAek
`square-waxes," Thet Lancet (Jul. 2, 1966).
`than
`Echt et al., "Biphasic waveformn is more efficacious
`monophasic waveform for transthoracic cardioversion,"
`PACE, 16:914, abstract no. 256 (Apr. 1993).
`Feeser et al., "Strength-duration and probability of success
`curves for defibrillation with biphasic waveforms," Circu-
`lation, 8206):2129-2141 (1990).
`Guse et al., "Defibrillation with low voltage using a left
`ventricular catheter and four cutaneous patch electrodes in
`dogs," PACE, 14:443-451 (Mar. 1991).
`"Defibrillator waveshape optimization:'
`Jones et al.,
`Devices and Tech. Meeting, NIH (1982).
`
`Jones et at., "Reduced excitation threshold in potassium
`depolarized myocardial cells with symmetrical biphasic
`waveforms," J. Mo!. Cell. Cardiol., 17(39):XXVUI, abstract
`no. 39 (1985).
`Jones, et al., "Decreased defibrillator-induced dysfunction
`with bipbasic retangular waveforms," Am. J. Physiol.
`247:H792-796 (1984).
`Jones, et at., "Improved defibrillator waveform safety factor
`with biphasic waveforms," Am. 3. Physiot., 245:H460-65
`(1983).
`Jude et al., "Fundamientals of Cardiopulmonary Resuscita-
`tion," R. A. Davis Company, Philadelphia PA, pp. 98-I104
`(1965).
`Kerber, et al., "Energy, current, and success in defibrillation
`and cardioiversion: clinical studies using an automated
`impedance-based method of energy adjustment." Circula-
`tion, 77(5) : 1038-1046 (1988).
`Knickerbocker et al., "A portable defibrillator," IEEE Trams.
`on Power and Apparatus Systems, 69:1089-1093 (1963).
`Kouwenhoven, "The development of the defibrillator,"
`Annals of Internal Medicine, 7](3):449-458 (1969).
`Langer et al., "Considerations in the development of the
`automatic implantable defibrillator," Medical Instruienta-
`tion, 10(3):163-167 (1976).
`Lerman, et at., "Currency-Based Versus Energy-Based Ven-
`tricular Defibrillation: A Prospective Study," JACC
`12(5):1259-1264 (1988).
`Lindsay et al., "Prospective evaluation of a sequential pac-
`ing and high-energy bi-directional shock algorithm for
`transvenous cardioversion in patients with ventricular tachy-
`cardia," Circulation, 76(3):601-609 (1981).
`Mirowski et al., "Clinical treatment of life threatening
`ventricular tachyarrhythmias with the automatic implantable
`defibrillator," American Heart Journal, 102(2):265-270
`(1981).
`Mirowski et al., "rermination of malignant ventricular
`arrhythnmias with an implanted automatic defibrillator in
`human beings," The New England Journal of Medicine,
`303(6):322-324 (1980).
`Podolsky, "Keeping the beat alive," U.S. News & World
`Report (Jul. 22, 1991).
`Product Brochure for Eirst Medic Semi-Automatic Defibril-
`lators (1994), Spacelabs Medical Products, 15220 N.E. 40th
`Street, P.O. Box 97013, Redmond, WA 98073-9713.
`Product Brochure for the Shock Advisory System (1987),
`Physio-Control, 11811 Willows Road Northeast, P0O. Box
`97006, Redmond, WA 98073-9706.
`Redd (editor), "Defibrillation with biphasic waveform, may
`survival," Medlines, pp.
`increase
`safety,
`improve
`1-2(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).
`'Developments for future implantable car-
`Saksena et al.,
`dioverters and deffibrillators," PACE, 10:1342-1358 (Noy-
`.-Dec. 1987).
`Schuder 'The role of an engineering oriented medical
`research group in developing improved methods and devices
`for achieving ventricular defibrillation: The University of
`Missouri experience," PACE, 16:95-124 (Jan. 1993).
`
`8
`
`

`

`5,593,427
`
`of
`effectiveness
`"Comparison of
`al.,
`et
`Schuder
`relay-switched, one-cycle quasisinusoidal waveform with
`in transthoracic
`critically damped sinusoid waveform
`defibrillation of 100-kilogram calves," Medical Instrumen-
`tation, 22(6):281-285 (1988).
`Schuder et al., "A multielectrode-time sequential laboratory
`defibrillator for the study of implanted electrode systems,"
`Amer Soc. Artif. Int. Organs, XV111:514-519 (1972).
`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. AN.( Intern. Organs. 9: 16.
`Schuder, et al., "Tranthoracic Ventricular Defibrillation with
`Square-wave Stimuli: One half Cycle." Cirm. Res.,
`XV-.258-264 (1964).
`Schuder, et a., "Defibrillation of 100 kg calves with assy-
`retangular pulses," Can. Res.,
`metrical, bidirectional,
`18:419-426 (1984).
`Schuder, et Ed., "fransthoracic Ventricular Defibrillation in
`the 100 kg Calf with Synnetrical One-Cycle Bidirectional
`IEEE Trans. BME,
`Stimuli,"
`Rectangular Wave
`30(7):415-422 (1983).
`Schuder, et Ed., "Ultrahigh-energy hydrogen thyraton/SCR
`Biderectional waveform defibrillator," Med. & Biol. Eng. &
`Comput., 20:419-424 (1982).
`Schuder, et al., "Wave form 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., "Ventricular defibrillation using biphasic wave-
`forms: The
`importance of phasic duration," JACC,
`13(l):207-214 (1989).
`Tang, et al., "Strength Duration Curve for Ventricular
`Defibrillation Using Biphasic Waveforms," PA CE, abstract
`no. 49 (1987).
`IEng, et al., "Ventricular Defibrillation Using Biphasic
`Waveforms of Different Phasic Duration," PACE, abstract
`no. 47 (1987).
`Walcott et al., "Comparison of mnonophasic, 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
`Implantable cardioverter Defibrillation System?, " Cimr.
`72:111-384, abstract no. 1536 (1985).
`Winkle "The implantable defibrillator in ventricular arrbyth-
`mias," Hospital Practice, pp. 149-165 (Mar. 1983).
`Winkle et a]., "Improved Low Energy Defibrillation Efficacy
`in Man Using a Biphasic ThEuncated Exponential Wave-
`form," JACC, 9(2): 142A (1987).
`Zipes, "Sudden cardiac death," Circulation, 85(l):160-166
`(1992).
`
`9
`
`

`

`U.S. Patent
`
`jan. 14, 1997
`
`Sheet 1 of 7
`
`5,593,427
`
`VOLTAGE
`
`A
`
`VOL'TAGE
`
`I
`
`VOLTAGE
`
`VTHRESH
`
`FIG. 1
`
`~~- F
`
`FIG. 2
`
`FIG. 4
`
`-c-------F
`
`tTHRESH
`
`10
`
`

`

`U.S. Patent
`
`Jn 4 97
`jan.14,1997
`
`Set2o
`Sheet 2 of 7
`
`,9,2
`5 5939427
`
`FIG. 3
`
`11
`
`

`

`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 3 of 7
`
`5,593,427
`
`FIG. 5
`
`---------------
`
`------
`
`FIG.
`
`7
`
`--
`
`--
`
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`
`F
`
`FIG. 8
`
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`A
`
`V'THRESH
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`U.S. Patent
`
`jan.14,1997
`Jn 4 97
`
`Sheet 4 of 7
`Set4o
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`595939427
`,9,2
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`FIG. 6
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`13
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`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 5 of 7
`
`5,593,427
`
`INITIATE DISCHARGE
`IN FIRST POLARITY
`
`STOP DISCHARGE
`OF FIRST PHASE
`
`FIG. 9
`
`RESUME DISCHARGE
`FOR SECOND PHASE
`DURATION F
`
`14
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`U.S. Patent
`
`Jn 4 97
`jan.14,1997
`
`Sheet 6 of 7
`Set6o
`
`,9,2
`595939427
`
`36
`
`I 30
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`40
`
`FIG. 10
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`15
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`U.S. Patent
`
`Jan. 14, 1997
`
`Sheet 7 of 7
`
`5,5939427
`
`16
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`

`

`5,593,427
`
`1
`ELECT'ROTHERAPY MIETHOD
`
`This application is a divisional of application 5cr. No.
`08/103,837 filed Aug. 6. 1993.
`BACKGROUND OF THE INVENTION
`to an electrotherapy
`This invention relates generally
`method and apparatus for delivering a shock to a patient's
`heart. In particular, this invention relates to a method and
`apparatus for using an external defibrillator to deliver a
`biphasic defibrTillation 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
`to normal heart
`fibrillation end ventricular tachycardia,
`rhythms through the processes of defibrillation and cardio-
`version, respectively. There are two main classifications of
`defibrillators: external and implanted. Implantable defibril-
`lators are surrgically 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
`the
`to
`send electrical pulses
`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
`to a patient on short notice. The
`provide electrotherapy
`advantage oE 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
`heart indirectly (i.e., from the surface of the patient's skin
`rather tan 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. Wave forms 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 at.; 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
`voltage, first phase duration and total pulse duration may be
`set when Cue device is implanted to deliver the desired
`amount of crnergy or to achieve that desired start and end
`voltage differential (i.e, a constant tit).
`
`10
`
`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-
`5 nal defibrillators must operate according to pulse amplitude
`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 heart varies
`from patient to patient, thereby varying the intensity and
`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
`15 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
`20 common protocol for using such a defibrillator was to
`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-
`25 Lion attempts require additional energy and add to patient
`risk. What is needed, therefor, 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.
`
`30
`
`45
`
`35
`
`SUMMARY OF THE INVENTION
`This 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-
`sion. In a preferred embodiment, the defibrillator has an
`40 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
`50 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. This method and apparatus of altering the delivered
`biphasic pulse thereby compensates for patient impedance
`55 differences by changing the nature of the delivered electro-
`therapeutic pulse, resulting in a smaller, more efficient and
`less expensive defibrillator.
`
`60
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. I is a schematic representation of a low-tilt biphasic
`electrotherapeutic waveform according to at first aspect of
`this invention.
`PIG. 21is a schematic representation of a high-tilt biphasic
`electrotherapeutic waveform according to the first aspect of
`this invention.
`
`17
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`

`5,593,427
`
`3
`FIG. 3 [s 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 bipliasic wave-
`form delivered according to the second aspect of this inven- 5
`tion.
`FIG. 5 is a schematic representation of a biphasic wave-
`fornm delivered according to the second aspect of this inven-
`tion.
`FIG. 6 is a flow chart demonstrating part of an electro- 1
`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-
`dion.
`FIG. 9 is a flow chart demonstrating part of an electro-
`therapy method according to a combination of the second 20
`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 2
`system according to a preterd embodiment of this inven-
`tion.
`
`15
`
`the choice of switch and capacitor technologies.
`'Ibtal
`energy delivery requirements affect defibrillator battery and
`capacitor choices.
`We have determined that, for a given patient externally-
`applied truncated exponential biphasic waveformns defibril-
`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-mit biphasic waveforms achieve
`effective defibrillation rates with less delivered energy than
`high-tilt waveforms. However,
`low-ilt waveforms are
`energy inefficient, since much of the stored energy is not
`delivered to the patient. On the other hand, defibrMlators
`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
`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
`waveformn 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-
`termined voltage can be chosen to deliver an effective and
`efficient waveform across a population of patients having a
`variety of physiological differences.
`This 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
`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 FIG. I 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 P 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
`parameters of the patient and the physical connection
`between the electrodes and the patient.
`For example, if the patient impedance (i.e., the total
`impedance between the two electrodes) is high, the amount
`of voltage drop (exponential decay) from the initial voltage
`A to 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 termninal voltages of the second
`phase during time F. The values of A, E, G and F are set to
`optimize defibrillation andfor cardioversion efficacy across a
`population of patients. Thus, high impedance patients
`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 mnore 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
`desirable to extend the first phase of the biphasic waveformi
`(while
`the second phase duration is kept constant) to
`
`3
`
`DETAILE 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 ame schematic representations of truncated
`exponential biphasic waveforms delivered to two different 35
`patients firom an external defibrillator according
`to the
`electrotheapy method of this invention for defibrillation or
`cardioiversion. 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 40
`versus time as well, however.
`The waveform shown in FIG. 1 is called a low-tilt
`waveform, and the waveformn shown in FIG. 2 is called a
`high-tilt waveformn, where tilt H is defined as a percent as
`follows:
`
`4
`
`W I- Un
`H1 - W,
`
`XI100
`
`As shown in FIGS. 1 and 2, A is the initial first phase voltage so
`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 saint 5
`manner. The starting voltages and first and second phase
`durations of the FIG. 1 and FIG. 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 exponential 60
`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- 65
`ments affect the size, cost, weight and availability of com-
`ponents. In particular, operating voltage requirements affect
`
`18
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`

`5,593,427
`
`5
`increase the overall efficacy of the electrotherapy by deliv-
`ering a more efficacious waveform 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 itself) to
`apply an electrotherapeutic shock to the patient through
`electrodes attached to the patient and charging of the energy
`source, e.g.. tlae 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-
`maticadly in response to patient heart activity measurements
`(e.g., BCG 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
`threshold time
`as shown by block 12 of FIG. 3. If,
`at the end of time t...~H the voltage measured across the
`energy source has not dropped below the minimum first
`phase terminal voltage threshold V,.
`first phase dis-
`charge continues, as shown in block 14 of FIG. 3. For high
`impedance patients, this situation results in an extension of
`the first phase duration beyond tr,~,as shown in FIG. 4,
`until
`the measured voltage drops below the threshold
`V ,,=,. Discharge then ends to complete the first phase, as
`represented by block 16 of FIG. 3. If, on the other hand, the
`patient has low impedance, the voltage will have dropped
`below V.Rs,, when the time threshold is reached, result-
`ing in a waveform like the one shown in FIG. 5.
`At the end of the first phase, and after a predetermined
`interim period G, the polarity of the energy source connec-
`tion to the electrodes is switched, as represented by blocks
`18 and 20 of FIG. 3. Discharge of the second phase of the
`biphasic Pulse then commences and continues for a prede-
`terrnined second phase duration F, as represented by block
`26 of HIG. 3, then ceases. This compensating electrotherapy
`method ensures that the energy is delivered by the defibril-
`lator in the most efficacious manner by providing for a
`mnmnum waveform tilt and by extending the first phase
`duration to meet the requirements of a particular patient.
`Because this method increases the waveform tilt for high
`impedance patients and delivers more of the energy from the
`energy source than a method without compensation, the
`defibrillator's energy source can be smaller than in prior art
`external deffirrillators, thereby minimizing defibrillator size,
`we