‘
`
`lllllllllllllllll||ll|||||||l|ltl|||l|||||llllll||||||||||l||||l||||||l||||
`USOOS749905A
`
`Unlted States Patent
`[19]
`[11] Patent Number:
`5,749,905
`
`Gliner et al.
`[45] Date of Patent:
`*May 12, 1998
`
`[54] ELECTROTIIERAPY METHOD UTILIZING
`PATIENT DEPENDENT ELECTRICAL
`PARAMETERS
`
`3/1932 United Kingdom 1
`2033363
`9/1993 WIPO .
`93/16759
`9/1994 WIPO.
`94/21327
`94/22530 10/1994 WIPO _
`
`[75]
`
`Inventors: Bradford E. Gliner. Bellevue; Thomas
`D. Lyster, Bothell; Clinton S. Cole.
`Kirkland; Daniel J. Powers; Carlton B.
`Morgan. both of Bainbridge Island. all
`of Wash.
`
`$3 3:832: Z133: $8 ‘
`W0 95,320” 11,1995 WIPO '
`‘
`OTHER PUBLICATIONS
`
`[73] Assignee: Heartstream, 11112.. Seattle, Wash.
`
`[*] Notice:
`
`The term of this patent shall not extend
`beyond the expiration date of Pat. No.
`5’601'612‘
`
`[21] APPL N04 691,755
`[22] Filed:
`Aug. 2, 1996
`
`Related U.S. Application Data
`
`[63] Continuation of Ser. No. 103,837,Aug.6, 1993, abandoned.
`5
`
`
`Int. Cl.
`[51]
`....................................................... A61N 1139
`
`[52] U.S. Cl. ............................ 607/7, 607/74
`[58] new 0f Search "
`607/4, 5' 69 7’
`507/87 21 39- 401 42’ 43—45, 48’ 50. 53~
`629 74
`
`[56]
`
`.
`REECNDCCS Clted
`U.S. PATENT DOCUMENTS
`
`3,211,154 10/1965 Beckeretal..
`3,241,555
`3/1966 Caywood etal..
`
`Winkle et al., “Improved low energy defibrillation efficacy
`in man using a biphasic truncated exponential waveform”
`JACC9(2):142A (1987).
`_
`.
`0‘1“ contmued on next page.)
`Primary Examiner—William E. Kamm
`Assistant Examiner—Kennedy J. Schactzle
`Attorney, Agent, or Finn—James R. Shay; Cecily Anne
`snyd“
`[57]
`
`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 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. This
`method and apparatus of altering the delivered biphasic
`pulse thereby compensates for patient impedance difier-
`ences by changing the nature of the delivered electrothera-
`peutic pulse, resulting in a smaller. more eflicient and less
`expensive defibrillator.
`
`5”
`
`I
`
`6.1..
`
`
`
`11mm DISCHAFEE
`in nasr POLAR!"
`
`7
`52-.
`/15 \\
`_ W (Wilma/x
`\\:/
`\ m
`/
`h,
`gvmaflvmfim \— _
`m
`\\\7//
`Sin? DlQWIRGE
`56 . __ _1_‘
`IHFFSTVHME
`
`i _l_ _wu- Fort
`lurzmW:a
`
`_ _L 7
`CHANGEmm
`
`
`,_-__
`n2 N 10quDISCHARGE
`firm sanctum:
`nth/mm F
`_.
`‘—
`N»,‘
`SIUP USCMRGE
`
`
`
`
`
`11 Claims, 7 Drawing Sheets
`
`L|FECOR905-1001
`
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`0281219
`9/1988
`0315368
`5/1989
`0353341
`2/1990
`0437104
`7/1991
`0457604 A 11/1991
`0491649 A 6/1992
`0507504 10/1992
`2070435
`9/1981
`
`European Pat.
`European Pat
`European Pati
`European Pat,
`European Pat,
`European Pat,
`2
`.
`European Pat,
`United Kingdom .
`
`page
`
`.
`
`1
`
`LIFECOR905-1001
`
`

`

`5,749,905
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`
`
`Schuder et al.“U1trah.igh—energy hydrogen thyratronlSCR
`bidirectional waveform defibrillator” Med. & Bio. Eng. &
`Comput. 20:419—424 (1982).
`Schuder et al. “Transthoracic ventricular defibrillation with
`Square—wave
`stimuli;
`one—half
`cycle"
`Cit:
`Res.
`XV1258—264 (1964).
`Schuder et a1. “Waveform dependency in defibrillating 100
`kg calves” Devices dz. Tech. Meeting NIH (1981).
`Tang et al. “Ventricular defibrillation using biphasic wave-
`forms of different phasic duration” PACE 10:Abstract No. 47
`(1987).
`Tang et al. “Strength duration curve for ventricular defibril—
`lation using biphasic waveforms” PACE, 10: Abstract No. 49
`(1987).
`Wetherbee et al. “Subcutaneous patch electrode—A means
`to obviate thoracotomy for implantation of the automatic
`cardioverter defibrillation system?” Circ.
`72:111—384,
`Abstract No. 1536 (1985).
`Kerber et al. “Energy, current. and sucess in defibrillation
`and cardioversion: clinical studies using an automated
`impedance—based method of energy adjustment.” Circ.
`77(5):1038—1046 (1988).
`Len-nan et al. “Current—based versus energy—based ventricu-
`lar
`defibrillation:
`A prospective
`study”
`JACC
`12(5):1259—1264 (1988).
`Alferness, et al ‘The influence of shock waveforms on
`defibrillation efficacy” IEEE Engineering in Medicine and
`Biology pp. 25—27 (Jun. 1990).
`Blilie et al. “Predicting and validating cardiothoracic current
`flow using finite element modeling” PACE 152563, Abstract
`219 (Apr. 1992).
`Chapman et al. “Non—thoracotomy internal defibrillation:
`Improved efficacy with biphasic
`shoc ” 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):612: Abstract No. 2433 (1991).
`Cooper et al. “The effect of phase separation of biphasic
`waveform defibrillation” PACE 16:471—482 (Mar. 1993).
`Cooper et al. "The effect of temporal separation of phases on
`biphasic Waveform defibrillation efficacy” The Annual Inter-
`national Conference of the IEEE Engineering in Medicine
`and Biology 13(2):O766—0767 (1991).
`Crampton et aL “Low energy ventricular defibrillation and
`miniature defibrillators” JAMA 235(21):2284 (1976).
`Dahlback et
`a1. “Ventricular defibrillation with square
`waves” The Lancet (Jul. 2, 1966).
`Echt et al. “Biphasic waveform is more eflicacious than
`monophasic waveform for
`transthoracic cardioversion”
`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 14:443-451 (Mar. 1991).
`Jones et al. “Defibrillator waveshape optimization” Devices
`and Tech Meeting NlI-l (1982).
`Jones et al. “Reduced excitation threshold in potassium
`depolarized myocardial cells with symmetrical biphasic
`waveforms” J. Mol. Cell. Cordial. 17(39):)Q(V11, Abstract
`No. 39 (1985).
`Jude et al. “Fundamentals of cardiopulmonary resuscitation”
`EA. Davis & Company, Philadelphia, PA, pp. 98—104
`(1965).
`
`3,706,313 12/ 972 Milani et a1.
`3,782,389
`1/1974 Bell.
`3,860,009
`1/ 975 Bell et a]. .
`3,862,636
`1/_975 Bell et al. .
`.
`3,886,950
`6/ 975 Ukkestad et al.
`.
`4,023,573
`5/1977 Panuidge et al.
`4,328,808
`5/1982 Charbonnier et a].
`4,419,998 12/1983 Heath.
`4,473,078
`9/ 984 Angel .
`4,494,552
`1/1985 Heath.
`4,504,773
`3/ 985 Suzuki et al. .
`4,574,810
`3/1986 Lei-man.
`4,595,009
`6/ 986 Leinders.
`4,610,254
`9/ 986 Morgan et a1.
`4,619,265
`10/ 986 Morgan et al.
`4,637,397
`1/1987 Jones et al.
`.
`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 Charbonnier et a1.
`4,848,345
`7/1989 Zenkieh .
`4,850,357
`7/1989 Bach,Jr..
`4,953,551
`9/1990 Mehra et a1.
`.
`4,998,531
`3/1991 Bocchi et al.
`.
`5,078,134
`1/1992 Heilman et a1.
`5,083,562
`1/1992 de Coriolis et al. .
`5,097,833
`3/1992 Campos.
`.
`5,107,834
`4/1992 Ideker et a1.
`5,111,813
`5/1992 Charbonnier et a1.
`5,111,816
`5/1992 Pless et al. .
`5,207,219
`511993 Adams etal..
`5,215,081
`6/1993 Ostroff .
`5,222,480
`6/1993 Couche er a1.
`5,222,492
`6/1993 Morgan et a1.
`5,230,336
`7/1993 Fain et a]. ,
`5,237,989
`8/1993 Morgan et al.
`.
`5,249,573 10/1993 Fincke et a1.
`5,275,157
`1/1994 Morgan er a1.
`5,306,291
`4/1994 Kroll et al. .
`5,334,219
`8/1994 Kroll.
`5,334,430
`8/1994 Berg et a1.
`5,352,239 10/1994 Pless.
`5,370,664 12/1994 Morgan et a1.
`5,372,606 12/1994 Lang ct al.
`.
`5,385,575
`1/1995 Adams.
`5,411,525
`5/1995 Swanson et a1.
`5,411,526
`511995 Kroll et al. .
`5,431,686
`7/1995 K1011 et a1.
`.
`5,489,293
`2/1996 Pless et al.
`.
`
`.
`
`.
`
`.
`.
`
`.
`
`.
`
`.
`
`.
`
`,
`
`.
`
`.
`
`.
`
`.
`
`.
`
`OTHER PUBLICATIONS
`
`Anderson et al. “The efficacy of trapezoidal wave forms for
`ventricular defibrillation” Chesfl0(2):298—300 (1976).
`
`Jones et al. “Decreased defibrillator—induced dysfunction
`with biphasic rectangular waveforms” Am. J. Physiol.
`247:H792—796 (1984).
`Jones et a1. “Improved defibrillator waveform safety factor
`with biphasic waveforms” Am. J. Physiol. 245:H60—65
`(1983).
`Schuder et al. “Defibrillation of 100 kg calves with asym-
`metrical, bi—directional, rectangular pulses” Card. Res.
`18:419—426 (1984).
`Schuder et al. “Transthoracic ventricular defibrillation in the
`100 kg calf with symmetrical one—cycle bidirectional rect-
`angular wave stimuli” IEEE Trans. BME 30(7):415—422
`(1983).
`
`2
`
`

`

`5,749,905
`Page 3
`
`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).
`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).
`Mirowsln' et al. “Clinical treatment of life threatening ven—
`tricular tachyarrhythmias with the automatic implantable
`defibrillator” American Heart J. 102(2):265—270 (1981).
`Mirowski et al. mTermination of malignant ventricular
`arrhythmias with an implanted automatic defibrillator in
`human beings” New Engl J. Med. 303(6):322—324 (198D).
`Podolsky “Keeping the beat alive” U.S. News & World
`Report (Jul. 22. 1991).
`Product Brochure for the Shock Advisory System (1987).
`Physio—Control. 11811 Willow Road Northeast, PO. Box
`97006, Redmond WA 980739706.
`Redd (editor), “Defibrillation with biphasic waveform may
`increase safety. improve survival" Medlines 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.—0ct.
`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 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. Arzif. Int. Organs XVIH2514—519 (1972).
`Schuder et al. “Development of automatic implanted
`defibrillator” 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 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 2563.
`Abstract 218 (Apr. 1992).
`Walthen et al. “Improved defibrillation efficacy using four
`nonthoracotomy leads for sequential pulse defibrillation”
`PACE 15:563. Abstract 220 (Apr. 1992).
`Winkle et al. ‘The implantable defibrillator in the ventricular
`arrhythmias” Hospital Practice, pp. 149—165 (Mar. 1983).
`Zipes “Sudden cardiac death” Circulation 85(1):160—-166
`(1992).
`Schuder et al. “Waveform dependency in defibrillation”
`Devices 6’: Tech Meeting NIH (1981).
`Product Brochure for First Medical Semi—Automatic
`Defibrillator (1994). Spacelabs.
`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. “Comparison of efiectiveness of relay—
`switched, one—cycle quasisinusoidal waveform with criti—
`cally damped sinusoid waveform in transthoracic defibril-
`lation of IOU—kilogram calves” Medical Instrumentation
`22(6):281—285 (1988).
`
`3
`
`

`

`US. Patent
`
`May 12, 1993
`
`Sheet 1 of 7
`
`5,749,905
`
`VOLTAGE
`
`a——>__.
`
`
`VOLTAGE
`
`f I
`
`VOLTAGE
`
`1
`
`A
`
`VTHRESHI
`
`FIG. 4
`
`+——— F—._.___>
`
`E
`-D
`
`
`
`tTHFlESH
`
`
`TIME
`
`4
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 2 of 7
`
`5,749,905
`
` 10»
`
`
`INITIATE DISCHARGE
`
`IN FIRST POLARITY
`
`
` 12
`
`VOLTAGE < VTHRESH
`IN FIRST PHASE
`
`
`
`STOP DISCHARGE
`
` WAIT FOR
`INTERIM TIME G
`
`
` CHANGE
`
`POLARITY
`
`
`16
`
`18
`
`2O
`
`RESUME DISCHARGE
`FOR SECOND PHASE
`
`DURATION F
`
`
`
`
`
`
` 22
` 24
`
`
`STOP DISCHARGE
`
`FIG. 3
`
`5
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 3 of 7
`
`5,749,905
`
`VOLTAGE
`
`VTHHESH HGj
`
`|
`
`tTHRESH
`
`VOLTAGE
`
`1A
`
`VTHRESH}
`
`LFG-fi
`tTHRESH
`
`VOLTAGE
`
`
`
`A
`VTHRESHi
`
`l1
`
`6
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 4 of 7
`
`5,749,905
`
` 50
`INITIATE DISCHARGE
`
`IN FIRST POLARITY
`
`
`
`
`
`
`
`STOP DISCHARGE
`IN FIRST PHASE
`
`58
`
`60\
`
`
`
`
` WAIT FOR
`
` INTERIM TIME G
`
` 62
`
`
` 64
` STOP DISCHARGE
`
` CHANGE
`POLARITY
`
`RESUME DISCHARGE
`FOR SECOND PHASE
`DURATION F
`
`FIG. 6
`
`7
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 5 of 7
`
`5,749,905
`
`INITIATE DISCHARGE
`IN FIRST POLARITY
`
`90
`
`NO
`
` VOLTAGE < VTHRESH
`
`
` NO
` VOLTAGE < VTHRESH
`
`
`
`
`FIG. 9
`
`94
`
`95-
`
`96
`
`97
`
`STOP DISCHARGE
`
`OF FIRST PHASE
`
`WAIT FOR
`
`INTERIM TIME G
`
`CHANGE
`POLARITY
`
`RESUME DISCHARGE
`FOR SECOND PHASE
`DURATION F
`
`STOP DISCHARGE
`
`98
`
`8
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 6 of 7
`
`5,749,905
`
`
`
`FIG. 10
`
`9
`
`

`

`US. Patent
`
`May 12, 1998
`
`Sheet 7 of 7
`
`5,749,905
`
`2..0.”—
`
`moEjEmEmo
`
`$305,200
`
`mm<1$m
`
`105%
`
`$2;
`
`vm
`
`mm
`
`Amok<m<mzoo
`
`Imam;
`
`
`
`
`
`mmooEomdEmilEooEbmd
`
`mm
`
`ww<mo._.w
`
`m0to<m<o
`
`
`
`m0<._r._o>IQ:
`
`inanm
`
`10
`
`10
`
`
`
`
`

`

`5,749,905
`
`1
`ELECTROTHERAPY METHOD UTILIZING
`PATIENT DEPENDENT ELECTRICAL
`PARAMETERS
`
`This application is a CONTINUATION of application
`Ser. No. 08/ 103 .837 filed Aug. 6. 1993 now abandoned.
`
`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 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 clectrotherapy 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 useful in the emergency
`room. the operating room, emergency medical vehicles or
`other situations where there may be an unanticipated need to
`provide elecn'otherapy to a patient short notice. The advan
`tage of external defibrillators is that they may be used on a
`patient as needed. then subsequently moved to be used with
`another patient. However, because external defibrillators
`deliver their electrotherapeutic pulses to the patient’s heart
`indirectly (i.e.. fi'om 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 [7.8. Pat. No. 4.821.723 to Baker. IL. et 111.; US.
`Pat. No. 5.083.562 to de Coriolis et 211.; US. Pat. No.
`4,800,883 to Winstrom; US. Pat. No. 4.850.357 to Each. In;
`and US. Pat. No. 4,953,551 to Mehra 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 elfec-
`tively titrated to the physiology of the patient to optimize the
`defibrillator’s eifectiveness. 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
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4s
`
`50
`
`55
`
`65
`
`11
`
`2
`amount of energy or to achieve that desired start and end
`voltage diflerential (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
`and duration parameters that will be eifective 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 eflecfive to treat low
`impedance patients do not necessarily deliver effective and
`energy efiicient 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
`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
`risk. What is needed. therefore. is an external defibrillation
`method and apparatus that maximizes energy efliciency (to
`minimize the size of the required energy storage medium)
`and maximizes therapeutic eflicacy across an entire popu—
`lation of patients.
`SUMMARY OF THE INVENTION
`
`This invention provides an external defibrillator and
`defibrillation method that automatically compensates for
`patient—to—patient impedance diiferences 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. This method and apparatus of altering the delivered
`biphasic pulse thereby compensates for patient impedance
`difierences 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.
`FIG. 3 is a flow chart demonstrating part of an electro—
`therapy method according to a second aspect of this inven—
`tion.
`
`11
`
`

`

`5,749,905
`
`3
`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.
`
`DETAJLED 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. Theprinciples 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:
`
`lAl-lDl
`:A:
`
`H:
`
`x100
`
`As shown in FIGS. 1 and 2, Ais 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 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
`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 aflect 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 alfect defibrillator battery and
`capacitor choices.
`We have determined that. for a given patient, externally-
`applied truncated exponential biphasic waveforms defibril-
`
`4
`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
`high—tilt waveforms. However,
`low-tilt waveforms are
`energy ineflicient. since much of the stored energy is not
`delivered to the patient. 0n 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
`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 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
`parameters of the patient and the physical connection
`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
`A to the terminal voltage B during time B 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 F. The values of A, E, G and F are set to
`optimize defibrillation and/or cardioversion efiicacy across a
`population of patients. Thus, high impedance patients
`receive a low—tilt waveform that is more efiective per unit of
`delivered energy, and low impedance patients receive a
`high-tflt 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
`desirable to extend the first phase of the biphasic waveform
`(while the second phase duration is kept constant) to
`increase the overall eflicacy 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 electrolherapeutic pulse.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`4s
`
`50
`
`SS
`
`65
`
`12
`
`12
`
`

`

`5 ,749.905
`
`5
`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.. the defibrillator's capacitor or capacitor bank. to
`the initial first phase voltage A. Block 10 represents initia-
`tion 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
`threshold time trams» as shown by block 12 of FIG. 3. If.
`at the end of time tmflsH. the voltage measured across the
`energy source has not dropped below the minimum first
`phase terminal voltage threshold VmRE5H~ 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 Imus”. as shown in FIG. 4.
`until
`the measured voltage drops below the threshold
`VmaasH- 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 messg 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—
`termined second phase duration F. as represented by block
`22 of FIG. 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
`minimum 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 defibrillators. thereby minimizing defibrillator size,
`weight and expense. It should be noted that the waveforms
`shown in FIGS. 4 and 5 could be expressed in terms of
`current versus time using a predetermined current threshold
`value without departing from the scope of the invention.
`FIGS. 6-8 illustrate a third aspect of this invention that
`prevents the delivered waveform from exceeding a maxi-
`mum tilt (i.e.. maximum delivered energy) in low impedance
`patients. As shown by blocks 52 and 54in FIG. 6, the first
`phase discharge stops either at the end of a predetermined
`time tIHRESH or when the first phase voltage drops below
`V'mmzsy- The second phase begins after an interim period
`G and continues for a preset period F as in the second aspect
`of the invention. Thus, in high impedance patients, the first
`phase ends at time tTHRESH. even if the voltage has not yet
`fallen below V'mmfl. as shown in FIG. 7. In low imped-
`ance patients. on the other hand. the first phase of the
`delivered waveform could be shorter in duration than the
`time tmcsm as shown in FIG. 8.
`Once again. the waveforms shown in FIGS. 7 and 8 could
`be expressed in terms of current versus time using a prede-
`termined current threshold value without departing from the
`scope of the invention.
`FIG. 9 is a flow chart illustrating a combination of the
`defibrillau'on methods illustrated in FIGS. 3 and 6. In this
`combination method. the first phase of the biphasic wave-
`
`6
`form will end if the voltage reaches a first voltage threshold
`V‘mRESH prior to the first phase duration threshold tmRESH.
`as shown by blocks 91 and 92. This defibrillator decision
`path delivers a waveform like that shown in FIG. 8 for low
`impedance patients. For high impedance patients. on the
`other hand. if at the expiration of tZHRESH the voltage has not
`fallen below V'mmzsm the duration of the first phase is
`extended beyond tMRESH until the voltage measured across
`the elecn'odes reaches a second voltage