Significance of ventricular and pseudoventricular arrhythmias appearing after D.C. countershock

D.C. countershock is an effective method for terminating cardiac arrhythmias. Seven hundred and thirty-one synchronized electrical discharges were employed for the purpose of abolishing 310 episodes of diverse arrhythmias in 207 patients. There was only one episode of ventricular fibrillation in the present series. It was attributed to improper synchronization. Iatrogenic ventricular tachycardia was observed five times in 2 patients. Rapid idioventricular beats occurred on six occasions. The induced ventricular paroxysms were initially rapid, with the rate declining progressively until its extinction (Munk-Gaskell phenomenon). All iatrogenic arrhythmias were short lived and disappeared spontaneously. They were easily differentiated from aberration of supraventricular impulses. Ventricular arrhythmias related to D.C. countershock can be manifested immediately after the procedure, as well as from a few seconds to hours after electrical conversion to sinus rhythm. The former group may either result as a consequence of improper synchronization or represent a direct effect of countershock on the myocardium. These toxic effects appear to be transient and have posed no threat to the life of the patients in our series or in other similar cases reported in the literature. The relationship between electrical depolarization of the heart and ventricular arrhythmias appearing after the return of sinus rhythm is not clear, although some of these paroxysms seem to have a significant connection with quinidine or digitalis premedication.