INFLUENCE OF PHASE DURATION OF BIPHASIC WAVE-FORMS ON DEFIBRILLATION ENERGY-REQUIREMENTS WITH A 70-MU-F CAPACITANCE

Background-Phase duration of biphasic shocks may be an important deter minant of defibrillation success. The purpose of this study was to inv estigate the effect of changing phase duration of biphasic pulses deli vered by 70-mu F capacitors on defibrillation energy requirements. Thi s may be clinically relevant for the optimization of implantable cardi overter-defibrillator design and programming. Methods and Results-Defi brillation thresholds (DFTs) were determined for 13 waveforms in 13 pi gs by application of a 70-mu F capacitance and a transvenous/submuscul ar 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 c ompared with phase 1=1 ms (36.4+/-7.5 J), 2 ms (25+/-6.5 J), 4 ms (257.6 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 phas e 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 phas e-1 duration. In contrast, two optima with minimal energy requirements were found for phase-2 duration. Optimization of both phases of low-c apacitance biphasic shocks may reduce energy requirements for defibril lation.