Intraventricular conduction disturbance due to delayed recovery from ventricular inactivation in chlorpromazine-treated dogs.

In in situ canine hearts, chlorpromazine induced a time (preceding cycle length)-dependent decrease in conduction velocity within the ventricle. Thus, QRS duration of nonpremature beats was lengthened at rapid pacing rates while QRS duration of atrial premature beats was lengthened at short coupling intervals. These slow conductions were not due to reduced take-off potential of ventricular action potentials but to drug-induced slow recovery of the rapid Na+ system. The phenomenon may be responsible for reported QRS prolongation and fatal ventricular arrhythmias encountered in patients receiving phenothiazines.