- Email: [email protected]
VII pulse generators for ICDs
640
Symposium
abstracts
American
September 1994 Heart Journal
. VII PULSE GENERATORS FOR ICDs HOW IMPORTANT IS CAPACITOR SIZE FOR IMPLANTABLE DEFIBRILLATORS? Charles D. Swerdlowand Mark W. Kroll. Rm. #5342, Division of Cardiology, Cedars-SinaiMedical Center, 8700 Beverly Blvd, LosAngeles,CA 90048.
EFFECT OF TILT ON WAVEFORM PHASE EFFICACY FOR VENTRICULAR DEFIBRILLATION IN HUMANS. Andrew EL Foster, StephenR Shorofsky,and Michael R. Gold. University of Maryland, 22 S.GreeneSt, Baltimore, MD 21201.
Theoreticalpredictionsindicate that optimal capacitor size (C) for truncated exponentialpulsesis smaller than that used by ICDs; but the effect on stored-energy defibrillationthreshold(DFI’) is not known. A modelbased on the Weiss-Lapicqueand average-current approximationswasusedto calculatethe effect of varying C on monophasic DFT for programmable-durationand fixed-tilt pulses.For pulseswith the bestduration for eachC, the effect dependsonly on the ratio of actual C to optimal C and is independent of pathway resistance (R) and chronaxie.Increasesin C by factors of 2,3,6, and 10 result in DFT increasesof 7%, 19%, 59%, and 114%.For fixedtilt pulses,DFT dependson the ratio of the systemtime constant(RC) to the chronaxie. For 63% tilt, valuesof this ratio of 2,3,6, and 10resultin DFT increases of 14%,36%, lOll%, and 208%. If R&O ohmsand chronaxie = 3.0 ms, optimalC is 48 pLF,150pF C resultsin a DFT increaseof 21%, if duration is optimized,and 25% if tilt Is 63%; 300 pF C resultsin increasesof 62% and 208%. This model predicts that optimizing C will decreaseDFT for ICDs moderately; but increasing C will increase DFT substantially.
The optimal waveform (W) for humandefibrillation hasnot beendetermlaed.We have previouslyshownthat biplutsicW (bW) resultsIn 20% reductionsin defibrillation thresbdd (DFT) comparedto monophaaicW (mW). To determine the optimal tilt for mW and bW, we prospectivelya&died the e&et of alterbig tilt on DFT duringdefibrillator implantationin 36 patients(pts).DFT’ was deter-r&ad using a step-down protocol (3 lead coaflgurations; 150 pF capacitor). DFT leading edge voltagewas measuredfor truncated exponentialmW (17 pts)andfor asymmetric,equalphasebW (19 pts).DFT was relatively insensitiveto tilts 250% for mW and for bW. In only 1 of 36 pts wasthe optimal tilt c!lO%. Storedenergy requirements(Ja) were reducedsignifieantiyfor mW and for bW at fflts X096.
Valuesmm, *p<.OSvs mW 65% tilt; t pc.05 vs 65%bW tilt. Conclusion:LowesteffectiveJ,t for mW and for bW is observedat tilts Lso%. Biphasic W delivery reduces energy require~~entsfor human ventricular deflbrilhttionover the full rangeof tilts studied. EFFECT OF CAPACITANCE ON DEFIBRILLATION THRESHOLDS IN DOGS. Paul JDeGroot, Marye Sue Norenberg,Rahul M&a. Medtronic, Inc., 7000Central Ave.N& Miuaeapolls,MN 5,432. Defibrillation thresholds(DFT) are known to vary with capacitance(C). However,no study hasdirectly reported DFI’ for multiple C. h this investigation,we determined the DFT for S vahmsof C and 4 dlffarant tilts. Slnglecapacitorbiphaaicwaveformsweretestadin 6 dogs.DFI wasdeterminedby shot&lagbetweena subcutaneous patch (40sq cm) and an RV cdl (I.+=5cm). Mean resistaace was 6&U ohms, Up and down thresholdwas determinedin randomorder, aad their meaneomputi. Stored Energy DFTs(me, joules)were: COLF) 30 60 90 120 150 A%
35/35% 13.8rt2.6 9.5i1.3 11.7ti.3 9.8f1.8 11.3i3.5 11.2zt1.7
SO/SO% 13.x22 8.2fl.l lO.O%YJ 9.w.7 1 l.lzt2.8 10.5520
65165% 12.1i1.8 8.OkO.9 8.1i1.6 10.4i1.8 11.7zt3.0 lO.ktl.9
80180% 10.52.6 9.6Lt1.7 14.1i2.3 15.1i2.9 16.6k5.2 13.2s.o
AT 12.5k1.5 8.8kO.8 1 l.Oi2.6 11.2t2.6 127f2.6
Conclusions: Multiple comparisontestsreveal that 60 pF hassignlfieautly lower DFT than all other capacitances, and80% tilt ESUI~S in @~ffi~~tly higherDFT than0th~ tilts.
Symposium
abstracts
American
September 1994 Heart Journal
. VII PULSE GENERATORS FOR ICDs HOW IMPORTANT IS CAPACITOR SIZE FOR IMPLANTABLE DEFIBRILLATORS? Charles D. Swerdlowand Mark W. Kroll. Rm. #5342, Division of Cardiology, Cedars-SinaiMedical Center, 8700 Beverly Blvd, LosAngeles,CA 90048.
EFFECT OF TILT ON WAVEFORM PHASE EFFICACY FOR VENTRICULAR DEFIBRILLATION IN HUMANS. Andrew EL Foster, StephenR Shorofsky,and Michael R. Gold. University of Maryland, 22 S.GreeneSt, Baltimore, MD 21201.
Theoreticalpredictionsindicate that optimal capacitor size (C) for truncated exponentialpulsesis smaller than that used by ICDs; but the effect on stored-energy defibrillationthreshold(DFI’) is not known. A modelbased on the Weiss-Lapicqueand average-current approximationswasusedto calculatethe effect of varying C on monophasic DFT for programmable-durationand fixed-tilt pulses.For pulseswith the bestduration for eachC, the effect dependsonly on the ratio of actual C to optimal C and is independent of pathway resistance (R) and chronaxie.Increasesin C by factors of 2,3,6, and 10 result in DFT increasesof 7%, 19%, 59%, and 114%.For fixedtilt pulses,DFT dependson the ratio of the systemtime constant(RC) to the chronaxie. For 63% tilt, valuesof this ratio of 2,3,6, and 10resultin DFT increases of 14%,36%, lOll%, and 208%. If R&O ohmsand chronaxie = 3.0 ms, optimalC is 48 pLF,150pF C resultsin a DFT increaseof 21%, if duration is optimized,and 25% if tilt Is 63%; 300 pF C resultsin increasesof 62% and 208%. This model predicts that optimizing C will decreaseDFT for ICDs moderately; but increasing C will increase DFT substantially.
The optimal waveform (W) for humandefibrillation hasnot beendetermlaed.We have previouslyshownthat biplutsicW (bW) resultsIn 20% reductionsin defibrillation thresbdd (DFT) comparedto monophaaicW (mW). To determine the optimal tilt for mW and bW, we prospectivelya&died the e&et of alterbig tilt on DFT duringdefibrillator implantationin 36 patients(pts).DFT’ was deter-r&ad using a step-down protocol (3 lead coaflgurations; 150 pF capacitor). DFT leading edge voltagewas measuredfor truncated exponentialmW (17 pts)andfor asymmetric,equalphasebW (19 pts).DFT was relatively insensitiveto tilts 250% for mW and for bW. In only 1 of 36 pts wasthe optimal tilt c!lO%. Storedenergy requirements(Ja) were reducedsignifieantiyfor mW and for bW at fflts X096.
Valuesmm, *p<.OSvs mW 65% tilt; t pc.05 vs 65%bW tilt. Conclusion:LowesteffectiveJ,t for mW and for bW is observedat tilts Lso%. Biphasic W delivery reduces energy require~~entsfor human ventricular deflbrilhttionover the full rangeof tilts studied. EFFECT OF CAPACITANCE ON DEFIBRILLATION THRESHOLDS IN DOGS. Paul JDeGroot, Marye Sue Norenberg,Rahul M&a. Medtronic, Inc., 7000Central Ave.N& Miuaeapolls,MN 5,432. Defibrillation thresholds(DFT) are known to vary with capacitance(C). However,no study hasdirectly reported DFI’ for multiple C. h this investigation,we determined the DFT for S vahmsof C and 4 dlffarant tilts. Slnglecapacitorbiphaaicwaveformsweretestadin 6 dogs.DFI wasdeterminedby shot&lagbetweena subcutaneous patch (40sq cm) and an RV cdl (I.+=5cm). Mean resistaace was 6&U ohms, Up and down thresholdwas determinedin randomorder, aad their meaneomputi. Stored Energy DFTs(me, joules)were: COLF) 30 60 90 120 150 A%
35/35% 13.8rt2.6 9.5i1.3 11.7ti.3 9.8f1.8 11.3i3.5 11.2zt1.7
SO/SO% 13.x22 8.2fl.l lO.O%YJ 9.w.7 1 l.lzt2.8 10.5520
65165% 12.1i1.8 8.OkO.9 8.1i1.6 10.4i1.8 11.7zt3.0 lO.ktl.9
80180% 10.52.6 9.6Lt1.7 14.1i2.3 15.1i2.9 16.6k5.2 13.2s.o
AT 12.5k1.5 8.8kO.8 1 l.Oi2.6 11.2t2.6 127f2.6
Conclusions: Multiple comparisontestsreveal that 60 pF hassignlfieautly lower DFT than all other capacitances, and80% tilt ESUI~S in @~ffi~~tly higherDFT than0th~ tilts.