OPTIMIZED FIRST-PHASE TILT IN PARALLEL-SERIES BIPHASIC WAVE-FORM

Introduction: A biphasic defibrillation waveform can achieve a large s econd phase leading-edge voltage by a ''parallel-series'' switching sy stem. Recently, such a system using two 30-mu F capacitances demonstra ted better defibrillation threshold than standard waveforms available in current implantable devices, However, the optimized tilt of such a ''parallel-series'' system had not been defined. Methods and Results: Defibrillation thresholds were evaluated for five different biphasic ' 'parallel-series'' waveforms (60/15 mu F) and a biphasic ''parallel-pa rallel'' waveform (60/60 mu F) in 12 anesthetized pigs. The five ''par allel-series'' waveforms had first phase tilts of 40%, 50%, 60%, 70%, and 80% with second phase pulse width of 3 msec, The ''parallel-parall el'' waveform had first phase tilt of 50% with second phase pulse widt h of 3 msec. The defibrillation lead system comprised a left pectoral ''hot can'' electrode (cathode) and a right ventricular lead (anode), The stored energy at defibrillation threshold of the ''parallel-series '' waveform with first phase tilts of 40%, 50%, 60%, 70%, and 80% was 7.0 +/- 2.1, 6.1 +/- 2.8, 6.8 +/- 2.8, 7.2 +/- 2.9, and 8.4 +/- 3.1 J, respectively, The stored energy of the ''parallel-series'' waveform w ith a 50% first phase tilt was 16% less than the nonswitching ''parall el-parallel'' waveform (7.3 +/- 2.8 J, P = 0.006). Conclusions: A firs t phase tilt of 50% maximized defibrillation efficacy of biphasic wave forms implemented with a ''parallel-series'' switching system. This op timized ''parallel-series'' waveform was more efficient than the compa rable ''parallel-parallel'' biphasic waveform having the same first ph ase capacitance and tilt.