LARGE CHANGE IN VOLTAGE AT PHASE REVERSAL IMPROVES BIPHASIC DEFIBRILLATION THRESHOLDS - PARALLEL-SERIES MODE SWITCHING

Background Multiple factors contribute to an improved defibrillation t hreshold of biphasic shocks. The leading-edge voltage of the second ph ase may be an important factor in reducing the defibrillation threshol d. Methods and Results We tested two experimental biphasic waveforms w ith large voltage changes at phase reversal. The phase 2 leading-edge voltage was twice the phase 1 trailing-edge voltage. This large voltag e change was achieved by switching two capacitors from parallel to ser ies mode at phase reversal. Two capacitors were tested (60/15 microfar ads [mu F] and 90/22.5 mu F) and compared with two control biphasic wa veforms for which the phase 1 trailing-edge voltage equaled the phase 2 leading-edge voltage. The control waveforms were incorporated into c linical (135/135 mu F) or investigational devices (90/90 mu F). Defibr illation threshold parameters were evaluated in eight anesthetized pig s by use of a nonthoracotomy transvenous lead to a can electrode syste m. The stored energy at the defibrillation threshold (in joules) was 8 .2+/-1.5 for 60/15 mu F (P<.01 versus 135/135 mu F and 90/90 mu F), 8. 8+/-2.4 for 90/22.5 mu F (P<.01 versus 135/135 mu F and 90/90 mu F), 1 2.5+/-3.4 for 135/135 mu F, and 12.6+/-2.6 for 90/90 mu F. Conclusions The biphasic waveform with large voltage changes at phase reversal ca used by parallel-series mode switching appeared to improve the ventric ular defibrillation threshold in a pig model compared with a currently available biphasic waveform. The 60/15-mu F capacitor performed as we ll as the 90/22.5-mu F capacitor in the experimental waveform. Thus, s maller capacitors may allow reduction in device size without sacrifici ng defibrillation threshold energy requirements.