Large Change in Voltage at Phase Reversal Improves Biphasic Defibrillation Thresholds

Abstract

Background Multiple factors contribute to an improved defibrillation threshold of biphasic shocks. The leading-edge voltage of the second phase may be an important factor in reducing the defibrillation threshold. Methods and Results We tested two experimental biphasic waveforms with large voltage changes at phase reversal. The phase 2 leading-edge voltage was twice the phase 1 trailing-edge voltage. This large voltage change was achieved by switching two capacitors from parallel to series mode at phase reversal. Two capacitors were tested (60/15 microfarads [μF] and 90/22.5 μF) and compared with two control biphasic waveforms for which the phase 1 trailing-edge voltage equaled the phase 2 leading-edge voltage. The control waveforms were incorporated into clinical (135/135 μF) or investigational devices (90/90 μF). Defibrillation threshold parameters were evaluated in eight anesthetized pigs by use of a nonthoracotomy transvenous lead to a can electrode system. The stored energy at the defibrillation threshold (in joules) was 8.2±1.5 for 60/15 μF ( P <.01 versus 135/135 μF and 90/90 μF), 8.8±2.4 for 90/22.5 μF ( P <.01 versus 135/135 μF and 90/90 μF), 12.5±3.4 for 135/135 μF, and 12.6±2.6 for 90/90 μF. Conclusions The biphasic waveform with large voltage changes at phase reversal caused by parallel-series mode switching appeared to improve the ventricular defibrillation threshold in a pig model compared with a currently available biphasic waveform. The 60/15-μF capacitor performed as well as the 90/22.5-μF capacitor in the experimental waveform. Thus, smaller capacitors may allow reduction in device size without sacrificing defibrillation threshold energy requirements.