Electrophysiological Effects of Direct Current Countershock before and after Ouabain Sensitization and after Diphenylhydantoin Desensitization in the Dog

Abstract

The effects of synchronized direct current countershock on ventricular automaticity, intraventricular conduction, and atrioventricular conduction were studied before and after ouabain administration and after diphenylhydantoin. At the level of electrical energy that induced ventricular arrhythmias, averaging 159 watt-seconds, countershock transiently increased ventricular automaticity and prolonged both intraventricular and atrioventricular conduction time. Immediately after ouabain-induced ventricular tachycardia returned to regular sinus rhythm, underlying ventricular automaticity and intraventricular and atrioventricular conduction times were increased. An average of 23 watt-seconds produced overt and persistent ventricular tachycardias due to enhanced automaticity or re-entry. Atrioventricular and inrraventricular conduction times were also prolonged, and transient complete heart block occurred in two experiments. Diphenylhydantoin administration at this time depressed ventricular automaticity, caused a speeding of atrioventricular and intraventricular conduction times and increased the electrical energy necessary to produce ventricular tachycardia to 355 watt-seconds.ADDITIONAL KEY WORDS intraventricular conduction heart block ventricular automaticity atrioventricular conduction re-entry• Synchronized direct current countershock is an accepted procedure for the termination of a number of cardiac arrhythmias. However, despite its widespread use, the electrophysiological effects of direct current countershock on the heart have only recently received attention (1). This is particularly important in understanding why some patients taking digitalis develop serious postshock arrhythmias (2-5). Although it has been demonstrated experimentally that digitalis administration greatly increases the sensitivity to postshock arrhythmias (6), the electrophysio- Accepted for publication March 20, 1968. logical mechanism for this sensitivity phenomenon remains unknown. In addition, a recent experimental study in our laboratory demonstrated that diphenylhydantoin greatly increases the amount of electrical energy required to produce an arrhythmia by countershock after digitalis sensitization (7). The electrophysiological effects of these interventions were explored in the present study by ascertaining the effects of direct current countershock on ventricular automaticity, intraventricular conduction and atrioventricular conduction before and after ouabain sensitization and after diphenylhydantoin desensitization. MethodTwenty-three adult mongrel dogs were anesthetized with intravenous sodium pentobarbital (30 mg/kg) after an overnight fast. A polyethylene catheter was inserted into the femoral

Antiarrhythmic Drugs: Electrophysiological Actions

“…These results are in accord with the demonstration that the drug suppresses slow diastolic depolarization in isolated Purkinje fibers. This property of the drug may explain its ability to increase the en ergy needed to produce some types of arrhythmias which occur after direct current shock in digitalis-treated animals (114) . DPH also antagonizes the toxic effect of digitalis on the A-V node by reversing glycoside-in duced A-V block in contrast to the effects of procaine amide on depressed A-V conduction (115,116).…”

Diphenylhydantoin: Ein Wirkungsvergleich an der gesunden und an der digitalisvergifteten Katze

“…Von einer anderen New Yorker Gruppe [Hel]ant,Scherlag,Damato (8,[18][19][20]45)] wurden die Ergebnisse bezfiglich der Leitungsgeschwindigkeit weiter differenziert, aber im wesentlichen best~itigt. Einen gewissen Widerspruch zu den Befunden des Arbeitskreises Hel-]ant- [18][19][20]45) Singh (48, 49) aus dem gleichen Arbeitskreis und vor allem Jensen und Katzung (24, 25) aus San Francisco haben dann in mehreren Publikationen dargelegt, dal~ qualitative Wirkungsunterschiede des DPH durch Anderung der Wirkstoffkonzentration einerseits und der extrazellul~iren Kaliumkonzentration andererseits entstehen.…”

Treatment of Ventricular Extrasystoles and Tachyarrhythmias in Acute Myocardial Infarction

“…DPH appears to be most efficacious in digitalis toxicity and ventricular arrhythmias (43,44,56,57); it may also prevent or abolish postcountershock arrhythmias which occur consequent to digitalis administration (58). In spite of some clear-cut theoretical advantages of DPH over other antiarrhythmic agents, experi ence with this drug in myocardial infarction is relatively sparse, and the drug should probably be given lower priority than lidocaine in most ventricular rhythm disturbances.…”