Serial electrophysiologic studies of the effects of oral diltiazem on paroxysmal supraventricular tachycardia

In 16 patients with paroxysmal supraventricular tachycardia, electrophysiologic studies were done before and serially at hourly intervals for 8 hours after the 3rd oral dose of 90 mg diltiazem given every 8 hours. Diltiazem increased both the longest atrial paced cycle length producing type 1 atrioventricular block and the effective refractory period of the atrioventricular conducting system at all measurements. Before diltiazem, all 16 patients had induction of sustained tachycardia. After diltiazem, sustained tachycardia could not be induced in 10 patients at any measurements; in these patients, either echo or nonsustained tachycardia was induced. In the remaining 6 patients, sustained tachycardia was induced, particularly after 6 hours. Follow-up observations in 12 patients receiving the same dosage of oral diltiazem for 6±2 months (mean±SD), showed that of the 8 patients in whom electrophysiologic testing induced either echo or nonsustained tachycardia, 6 were asymptomatic and 2 experienced transient palpitation. Of the other 4 patients with induction of sustained tachycardia, 3 had transient palpitation and one had occasional attacks of sustained tachycardia requiring modification of therapy. Thus, oral diltiazem increases atrioventricular nodal refractoriness, with an effect lasting up to 8 hours. It is an effective agent for the prophylaxis of paroxysmal supraventricular tachycardia.