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`USOOS749904A
`
`United States Patent
`5,749,904
`[11] Patent Number:
`Gliner et al.
`[45] Date of Patent: *May 12, 1998
`
`
`
`[191
`
`[54]
`
`[75]
`
`[73]
`
`[* ]
`
`ELECTROTHERAPY METHOD UTILIZING
`PATIENT DEPENDENT ELECTRICAL
`PARAMETERS
`
`Inventors: Bradford E. Gliner, Bellevue; Thomas
`D. Lyster. Bothell; Clinton S. Cole.
`Seattle; Daniel J. Powers, Issaquah;
`Carlton B. Morgan. Bainbridge Island,
`all of Wash.
`
`Assignee: Heartstream, Inc., Seattle. Wash.
`
`Notice:
`
`The term of this patent shall not extend
`beyond the expiration date of Pat. No.
`5 601.612.
`
`[21]
`
`[22]
`
`Appl. No.: 690,529
`Filed:
`Jul. 31, 1996
`
`[63]
`
`[5 l]
`[52]
`[5 8]
`
`[56]
`
`Related US. Application Data
`
`Continuation-impart of Ser. No. 103,837, Aug. 6, 1993,
`abandoned, and Ser. No. 227,553, Sep. 14, 1994, Pat. No,
`5,607,454.
`Int. Cl.6 ....................................................... A61N 1/39
`
`US. Cl. ....................
`607/7; 607/74
`
`Field of Search ............ 607/5—7, 74
`
`References Cited
`
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`
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`
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`
`.
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`511989 European Pat. Off. .
`
`(List continued on next page.)
`OTHER PUBLICATIONS
`
`Alferness, et al "The influence of shock waveforms on
`defibrfllation efficacy” IEEE Engineering in Medicine and
`Biology, pp. 25—27 (Jun. 1990).
`
`(List continued on next page.)
`
`Primary Examiner—William E. Kamm
`Assistant Examiner—Kennedy J. Schnetzle
`Attorney, Agent, or Finn-James R. Shay; Cecily Anne
`Snyder
`[57]
`
`ABSTRACT
`
`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
`charge) during the discharging step. and adjusting energy
`delivered to the patient based on a value of the electrical
`parameter. The adjusting step may include selecting a serial
`or parallel arrangement 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.
`
`(List continued on next page.)
`
`17 Claims, 10 Drawing Sheets
`
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`MC." Deanne:
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`
`

`

`5,749,904
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`Cooper et al. “The efiect of temporal separation of phases on
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`national Conference of the IEEE Engineering in Medicine
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`Crampton et 211. “Low energy ventricular defibrillation and
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`Dahlback et
`a1. “Ventricular defibrillation with square
`waves” The Lancet (Jul. 2. 1966).
`Echt et al. “Biphasic waveform is more efficacious than
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`PACE 16:914. Abstract No. 256 (Apr. 1993).
`Feeser et a1. “Strength—duration and probability of success
`curves for defibrillation with biphasic waveforms” Circula-
`tion 82(6):2128—2141 (1990).
`Guse et al. “Defibrillation with low voltage using a left
`ventricular catheter and four cutaneous patch electrodes in
`dogs” PACE 14:443451 (Mar. 1991).
`Jones et al. “Decreased defibrillator—induced dysfunction
`with biphasic rectangular waveforms” Am. J. Physiol.
`247 :H792—796 (1984).
`Jones et a1. “Defibrillator waveshape optimization” Devices
`and Tech Meeting N111 (1982).
`Jones et a1. “Improved defibrillator waveform safety factor
`with biphasic waveforms” Am. J. Physiol. 2452H60—65
`(1983).
`Jones et a1. “Reduced excitation threshold in potassium
`depolarized myocardial cells with symmetrical biphasic
`waveforms” J. Mol. Cell. CardioL 17(39):XXVI[, Abstract
`No. 39 (1985).
`Jude et a1. “Fundamentals of cardiopulmonary resuscitation”
`EA. Davis & Company, Philadelphia, PA, pp. 98—104
`(1965).
`Kerber et a1. “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 and Apparatus Systems 69:1089—1093 (1963).
`Kuowenhoven “The development of the defibrillator”
`Annals of Internal Medicine 71(3):449—458 (1969).
`Langer et a1. “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-
`lar
`defibrillation:
`A prospective
`study”
`JACC
`12(5):1259—1264 (1938).
`Lindsay et a1. “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 al. “Clinical treatment of life threatening ven—
`tricular tachyarrhythrnias with the automatic implantable
`defibrillator” American Heart J. 102(2):265—270 (1981).
`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” US. News & World
`Report (Jul. 22, 1991).
`Product Brochure First Medic Semi—Automatic Defibrilla—
`tors (1994), Spacelabs Medical Products, 15220 NE. 40th
`Street, PO. Box 97013, Redmond, Washington.
`Product Brochure for the Shock Advisory System (1987),
`Physio—Control, 11811 Willow Road Northeast, PO. Box
`97006, Redmond WA 98073.9706.
`
`.
`.
`
`.
`
`.
`
`.
`
`311935 Suzuki et a1..
`4,504,773
`3/1986 Lemma.
`4,574,810
`6/1986 Leinders.
`4,595,009
`9/1986 Morgan et a1.
`4,610,254
`4,619,265 10/1986 Morgan et a1.
`4,637,397
`1/1987 Jones et a1.
`.
`4,745,923
`5/1988 Winstrom.
`4,800,883
`1/1989 Winstrom.
`.
`4,821,723
`4/1989 Baker, Jr. et a1.
`4,840,177
`6/1989 Charbormier et a1.
`4,848,345
`7/1989 Zenkich .
`4,850,357
`7/1989 Bach, Jr. .
`.
`4,953,551
`9/1990 Mehta et a1.
`4,998,531
`3/1991 Bocchi et a]. .
`5,078,134
`1/1992 Heilman et a]. .
`5,083,562
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`.
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`5/1992 Pless et a1.
`.
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`4/1993 Kroll et a1.
`.
`5,207,219
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`.
`5,230,336
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`.
`5,237,989
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`.
`5,275,157
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`5,306,291
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`.
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`.
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`.
`5,489,293
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`
`.
`
`.
`
`.
`
`.
`
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`
`2/1990 European Pat. 01f. .
`0353341
`7/1991 European Pat. 01f. .
`0437104
`0491649 A 6/1992 European Pat. OE. .
`0507504 1011992 European Pat. Ofi‘.
`.
`2070435
`9/1981 United Kingdom .
`2083363
`3/1982 United Kingdom .
`93/16759
`9/1993 WIPO .
`94/21327
`9/1994 WIPO .
`94/22530 10/1994 WIPO.
`
`OTHER PUBLICATIONS
`
`Anderson et al. “The efficacy of trapezoidal wave forms for
`ventricular defibrillation” Chest 70(2):298—300 (1976).
`Blilie et al. “Predicting and validating cardiothoracic current
`flow using finite element modeling” PACE 15 :5 63, Abstract
`219 (Apr. 1992).
`Chapman et a1. “Non—thoracotomy internal defibrillation:
`Improved efficacy with biphasic shoc
`” Circulation
`762312, Abstract No. 1239 (1987).
`Cooper et a1. “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 eifect of phase separation on biphasic
`waveform defibrillation” PACE 16:471—482 (Mar. 1993).
`
`2
`
`

`

`5,749,904
`Page 3
`
`Product information for Model H MSA Portable Defibrilla-
`tor (Bulletin No. 1108—2).
`Product information for MSA Portable Defibrillator (Bulle—
`tin No. 1108—1).
`Redd (editor). “Defibrillation with biphasic waveform may
`increase safety.
`improve survival” Medlz'nes pp.
`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).
`Saksena et 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 venticular defibrillator: The University of
`Missouri experience” PACE 16:95—124 (Ian. 1993).
`Schuder et al. “A multielectrode—lime sequential laboratory
`defibrillator for the study of implanted electrode systems"
`Amer. Soc. Artif. Int. Organs XVIII:514—-5 19 (1972).
`of
`Schuder
`et
`al.
`“Comparison
`of
`effectiveness
`relay—switched, one—cycle quasisinusoidal waveform with
`critically damped sinusoid waveform in transthoracic
`defibrillation of loo-kilogram calves” Medical Instrumen-
`tation 22(6):281—285.
`Schuder et al. “Defibrillation of 100 kg calves with asym-
`metrical, bi—directional, rectangular pulses” Card. Res.
`18:419—426 (1934).
`Schuder et al. “Development of automatic implanted
`defibrillator” Devices & Tech Meeting Nil-I (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.
`Schuder et al. "I‘ransthoracic ventricular defibrillation in the
`100 kg calf with symmetrical one—cycle bidirectional rect-
`angular wave stimuli” IEEE Trans. BME 30(7):415—422
`(1983).
`Schuder et a1. ‘Transthoracic ventricular defibrillation with
`Square—wave
`stimuli;
`one—half
`cycle”
`Cir. Res.
`XV2258—264 (1964).
`
`Schuder et al. “Lfltrahigh—energy hydrogen thyratrorflSCR
`bidirectional waveform defibrillator” Med. & Bio. Eng. &
`Comput. 20:419—424 (1982).
`Schuder et al. “Waveform dependency in defibrillatiug 100
`kg calves” Devices & Tech. Meeting NIH (1981).
`Schuder et a1. “Waveform dependency in defibrillating 100
`kg calves” Devices & Tech Meeting NIH (1982).
`Schuder et al. “Waveform dependency in defibrillafion”
`Devices & Tech Meeting NIH (1931).
`Stanton et al. “Relationship between defibrillation threshold
`and upper limit of vulnerablilty 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 10:Abstract No. 47
`(1987).
`Tang et a1. “Ventricular defibrillation using biphasic wave-
`forms: The
`importance of phasic
`duration”
`JACC
`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 eflicacy 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
`cardioverter defibrillation system?” Circ. 722384. 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 eflicacy
`in man using a biphasic truncated exponential waveform”
`JACC 9(2):142A (1987).
`Zipes “Sudden cardiac death” Circulation 85(1):160—166
`(1992).
`
`3
`
`

`

`US. Patent
`
`May 12, 1993
`
`Sheet 1 of 10
`
`5,749,904
`
`VOLTAGE
`
`
`
`VOLTAGE
`
`
`
`VOLTAG E
`
`1A
`
`VTHRESH[ ——~———-+~~~
`
`_
`
`D TIME
`
` E
`
`
`
`
`PM
`
`4
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 2 of 10
`
`5,749,904
`
` 10 »-\
`
`INITIATE DISCHARGE
`
`IN FIRST POLARITY r
`
`//
`
`//VOLTAGE
`
`< VTHRESH
`
`16 A\
`
`STOP DISCHARGE
`
`IN FIRST PHASE
`
`INTERIM TIME G
`
`20\
`
` CHANGE
`POLARITY
`
`
`
`
`
` WAIT FOR
`
` 22\
`
`
`
`
`RESUME DISCHARGE
`FOR SECOND PHASE
`DURATION F
`
`24
`
`STOP DISCHARGE
`
`FIG. 3
`
`5
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 3 of 10
`
`5,749,904
`
` VOLTAGE
`
`
`
`VOLTAGE
`
`IA
`
`VTHRESHJ
`
`L43+|
`tTHRESH
`
`VOLTAGE
`
`A
`VTHRESHi
`
`V
`
`6
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 4 of 10
`
`5,749,904
`
`50 \- INITIATE DISCHARGE
`IN FIRST POLARITY
`
`52 \
`
`NO
`
`
`
`,
`
`\
`
`r
`d4
`
`IS
`‘\»~”
`\\
`
`(/VOLTAGE < VIIIIRESII\
`---v— ”—0
`
`55 .\
`“ STOP DISCHARGE
`IN FIRST PHASE
`
`58 \
`
`WAIT FOR
`
`INTERIM TIME G
`
`60 \
`
` CHANGE
`POLARITY
`
`
`
`
`
`
`
`
`
`62 \\ RESUME DISCHARGE
`FOR SECOND PHASE
`
`DURATION F
`
`64
`
`STOP DISCHARGE
`
`FIG. 6
`
`7
`
`

`

`US. Patent
`
`May 12, 1998 ,
`
`Sheet 5 of 10
`
`5,749,904
`
`INITIATE DISCHARGE
`
`
`
`
`
`
`IN FIRST POLARITY
`
`
`
`
`TIME < ITHRESH
`
`IS
`
`
`VOLTAGE < v] HRESII
`
`
`
`
`
`// 94
`
`
`STOP DISCHARGE
`OF FIRST PHASE
`
`
`
`
`I
`
`
`INTERIMTIME G
`
`
`
`WAIT FOR
`
`95
`
`FIG. 9
`
`CHANGE
`
`
`POLARITY
`
`
` /96
` RESUME DISCHARGE
`
`
` /98
`STOP DISCHARGE
`
`FOR SECOND PHASE
`DURATION F
`
`97
`
`8
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 6 of 10
`
`795
`
`409,9
`
`40
`
`
`
`.Illllllllllllll'lll'l'lllllllll]
`
`FIG. 10
`
`9
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 7 of 10
`
`5,749,904
`
`mm<xgm
`
`Iobgm
`
`EEC.
`
`mHE2.EE.my0JV0I
`
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`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 8 of 10
`
`5,749,904
`
`98
`
` Ene rgy
`
`Source
`
`
`92
`
`94
`
`Coniroller I
`Mech.
`
`
`
`
`Connect.
`
`96
`
`Q7
`
`96
`
`FIG. 12
`
`
`
`Controller
`
`98
`
`
`
`FiG. 13
`
`11
`
`11
`
`

`

`US. Patent
`
`May 12,1998
`
`Sheet 9 of 10
`
`5,749,904
`
`164 x
`
`142
`
`
`
`to switches
`
`'
`152
`
`to sensor
`
`to charger
`
`Controller
`140
`
`
`
`electrode
`1 56
`
`elecirode
`158
`
`HQ. 14
`
`VOLTAGE
`
`TIME
`
`FIG. 15
`
`12
`
`12
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 10 of 10
`
`5,749,904
`
`
`
`electrode
`1 56
`
`
`
`160
`
`1 32 "-——
`
`142
`
`226
`
`electrode
`
`
`158
`
`Io sensor
`
`
`to swilches
`
`152
`
`to charger
`
`
`
`FIG. 1 6
`
`228
`l
`
`
`
`eteclrode
`1 56
`
`1 34
`
`char—
`
`ger
`
`220
`\
`
`1 32 ";
`
`222
`
`
`
`
`
`1 60
`
`e1ectrode
`1 58
`
`
`
`
`152
`to sensor
`10 switches
`
`
`to charger
`
`Controller
`140
`
`FIG. 17
`
`13
`
`13
`
`

`

`5 ,749,904
`
`1
`ELECTROTHERAPY METHOD UTILIZING
`PATIENT DEPENDENT ELECTRICAL
`PARANIETERS
`
`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.
`08/227553. “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 INVENTION
`
`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 eifective treatment for
`ventricular fibrillation is electrical defibrillation, which
`applies an electrical shock to the patient’s heart.
`To be eifective, 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 is administered. Beyond 12 minutes. the survival rate
`approaches zero.
`One way of delivering rapid defibrillation shocks is
`through the use of implantable defibrillators. 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. Implantable defibrillators are expensive.
`however. and are 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 electrothcrapy 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’ 5 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 defibrillators. These high
`energy, voltage and currentrequirements have made existing
`external defibrillators large. heavy and expensive, particu-
`larly due to the large size of the capacitors 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
`Defibrillator 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
`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
`Baker. Jr.. et a1.; U.S. Pat. No. 5.033.562 to de Coriolis et al.;
`U.S. Pat No. 4.800.883 to Winstrom; U.S. Pat. No. 4.850,
`357 to Each. lr.; U.S. Pat. No. 495355 1 to Mehra et at; and
`U.S. Pat No. 5.230.336 to Fain et a1.
`Because each implanted defibrillator is dedicated to a
`single patient. its operating parameters. such as electrical
`pulse amplitudes and total energy delivered. may be eifec—
`tively titrated to the physiology of the patient to optimize the
`defibrillator’s efi’ectiveness. Thus. for example, the initial
`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 a desired start and end
`voltage difl’erential (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
`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
`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 djlferences, exter—
`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 elecn‘odes 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 efiective and
`energy eflicient treatments to high impedance patients.
`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-
`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
`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-
`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
`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
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`defibrillator 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 defibrillators is described
`in an article written by R. 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
`
`4
`FIG. 2 is a schematic representation of a high-tilt biphasic
`electrotherapeutie waveform according to the first aspect of
`this invention.
`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.
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`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
`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.
`the invention provides a
`In yet another embodiment.
`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 discharging step. and
`adjusting energy delivered to the patient based on a value of
`the electrical parameter. The adjusting step may include
`selecting a serial or parallel arrangement 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 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.
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`FIG. 8 is a schematic representation of a biphasic wave
`form delivered according to the third aspect of this inven—
`tion.
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`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. '
`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.
`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.
`
`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.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIJVIENT
`
`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 diifcrent
`patients from an external defibrillator according to the
`elecn-otherapy 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:
`
`IAI — IDI
`IAl
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`x100
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`As shown in FIGS. 1 and 2,Ais the initial first phase voltage
`and D is the second phase terminal voltage. The first phase
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`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 FIG. 2 waveforms are the same;
`the diiferences in end voltages B and D reflect difierences in
`patient impedance.
`Prior art disclosures of the use of truncated exponential
`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 afiect the size. cost. weight and availability of com—
`ponents. In particular. operating voltage requirements affect
`the choice of switch and capacitor technologies. Total
`energy delivery requirements afiect defibrillator battery and
`capacitor choices. We have determined that, for a given
`patient, externally-applied truncated exponential biphasic
`waveforms defibrillate 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
`efiective defibrillation rates with less delivered energy than
`high-tilt waveforms. However,
`low—tilt waveforms are
`energy inefficient, since much of the stored energy is not
`delivered to the patient. On the other hand, defibrillators
`delivering high-tilt biphasic waveforms deliver more of the
`stored energy to the patient than defibrillators delivering
`low-tilt waveforms while maintaining high eflicacy 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
`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
`eflicient therapy. An optimum capacitor charged to a prede-
`termined voltage can be chosen to deliver an effective and
`efiicient 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. 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
`parameters of the patient and the physical connection
`between the electrodes and the patient.
`For example. if the patient impedance (ie.. the total
`imped