Incidence of Arrhythmias in the Dog Following Transthoracic Ventricular Defibrillation with Unidirectional Rectangular Stimuli

The incidence of the various types of arrhythmia induced by defibrillation in anesthetized dogs that had had continous ventricular fibrillation for 30 seconds was studied as a function of the current strengh and the duration of the unidirectional rectangular pulse used to terminate the fibrillation. Shocks at 10, 20, 40, 80, and 100 amp with durations in the range of 80 µsec through 64 msec were used. At any given energy level the incidence of induced arrhythmias was much larger for the 40-, 80-, and 100-amp shocks than for the 10- and 20-amp shocks. At 10 and 20 amp, the incidence of induced arrhythmias increased with increasing energy content. Premature ventricular contractions were observed at nearly all levels of energy and current, in contrast to other types of arrhythmias that appear to be strongly related to energy content or current amplitude or both.