Transthoracic Ventricular Defibrillation with Square-wave Stimuli: One-Half Cycle, One Cycle, and Multicycle Waveforms

Abstract

A very high powered amplifier for experimental transthoracic ventricular defibrillation has been described. The effectiveness of both one-half-cycle unidirectional and one-cycle bidirectional square waves in terminating ventricular fibrillation first increases, then reaches a maximum and finally decreases as the duration of the shock is increased. With 10- and 20-ampere unidirectional shocks and 10-ampere bidirectional shocks, a maximal effectiveness of substantially 100% was found under the chosen experimental conditions. Five-ampere unidirectional and bidirectional shocks yielded maximal effectiveness of 70%. The effectiveness of a 128-millisecond, 5-ampere, multicycle square-wave shock is a strong function of frequency and has a maximal value of approximately 70%.