Abstract
Multiple responses secondary to pacemaker stimuli falling after the end of the T wave (ventricular diastole) were seen in 3 patients. In 1 of them, the induced QRS deflections were identical to those seen during a previously present spontaneous ventricular tachycardia. Another patient had two areas of repetition, one in late systole (Q-spike intervals ranging between 0.25 and 0.33 sec) and the other in early diastole (Q-spike intervals between 0.32 and 0.43 sec). A third patient with a malfunctioning pacemaker unit showed stimulation during the supernormal phase after variable periods of pacemaker failure. Capture during the supernormal phase was followed either by bursts of spontaneous multiple responses or by a series of effective pacemaker stimuli. These unusual arrhythmias were abolished, respectively, by the administration of lidocaine, after a change to a demand mode of operation, and by pacemaker replacement. It is believed that a Wedensky-like effect best explains the genesis of diastolic repetition. However, the presence of two areas of vulnerability, one for ventricular fibrillation and the other for ventricular tachycardia, cannot be definitely excluded in Case 1.