From the Department of Cardiology (P.S., F.S., B.D., A.M., K.E., P.H.,
C.S.) and the Department of Thoracic and Cardiovascular Surgery (F.A.S., M.G.,
H.D., B.J.M.), University Hospital-RWTH Aachen (Germany).
Correspondence to Patrick Schauerte, MD, Department of Cardiology, University Hospital-RWTH Aachen, Pauwelsstraße 30, 52057 Aachen, FRG. E-mail psch{at}pcserver.mk1.rwth-aachen.de
Background—Phase duration of
biphasic shocks may be an important determinant of defibrillation
success. The purpose of this study was to investigate the effect of
changing phase duration of biphasic pulses delivered by 70-µF
capacitors on defibrillation energy requirements. This may be
clinically relevant for the optimization of implantable
cardioverter-defibrillator design and programming.
Methods and Results—Defibrillation thresholds (DFTs) were
determined for 13 waveforms in 13 pigs by application of a 70-µF
capacitance and a transvenous/submuscular lead system. In part I,
phase-1 duration varied, preserving a phase-1/phase-2 duration ratio of
60%/40%. The phase-1 durations were 1, 2, 3, 4, 5, and 6 ms. The DFT
was lowest (22.9±7 J) for phase 1=3 ms compared with phase 1=1 ms
(36.4±7.5 J), 2 ms (25±6.5 J), 4 ms (25±7.6 J), 5 ms (30.7±7.3 J),
or 6 ms (32.9±8.1 J) (P<.001). In part II, phase-1
duration was 3 ms but phase-2 duration varied: 0.7, 1.3, 2, 2.7, 3.3,
4, and 6 ms. Significant DFT minima were found at phase 2=2 ms
(22.5±4.2 J) and phase 2=4 ms (22.5±4.2 J) compared with phase 2=0.7
ms (31.7±9.3 J), phase 2=3.3 ms (26.7±6.1 J), or phase 2=6 ms
(28.3±6.8 J) (P<.05).
Conclusions—The strength-duration curve of biphasic
defibrillation shocks demonstrates a single optimum for phase-1
duration. In contrast, two optima with minimal energy requirements were
found for phase-2 duration. Optimization of both phases of
low-capacitance biphasic shocks may reduce energy requirements for
defibrillation.
© 1998 American Heart Association, Inc.
Basic Science Reports
Influence of Phase Duration of Biphasic Waveforms on Defibrillation Energy Requirements With a 70-µF Capacitance
Key Words: fibrillation • defibrillation • death, sudden
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