Comparison of Effectiveness of Relay-Switched, One-Cycle Quasisinusoidal Waveform with Critically Damped Sinusoid Waveform in Transthoracic Defibrillation of 100-Kilogram Calves

Studies o f 240 transthoracic fibrillation-defibrillation episodes in calves of 91-108 kg are reported. The waveform in 120 o f the episodes was a one-cycle, quasisinusoidal waveform having peak currents o f 64 and 3 2 A and half-cycle durations o f 4 and 6 ms. The episodes were interlaced with 120 others involving critically dam ped sinusoid wave­ forms having a 70.2-A peak current at 1.1 m s to peak. Applied after 30 s o f fibrillation, the biphasic shock (201 J o f delivered energy) was successful on the initial attem pt in 106 o f 120 episodes (88%), and the uniphasic shock (206 J ) was successful in only 44 of 120 episodes (37%). The biphasic waveform, producible by a sim ple relay-armature shift in a passive circuit, yielded significantly better results (p < 0 .001) and should be evaluated clinically.