Usefulness of intravenous diltiazem in predicting subsequent electrophysiologic and clinical responses to oral diltiazem.

Diltiazem, 0.25 mg/kg, was given intravenously during induced tachycardias in 6 patients with atrioventricular (AV) nodal reentrant tachycardia (group I) and in 24 patients with AV reentrant tachycardia incorporating a retrogradely conducting accessory pathway (group II). In all 6 group I and in 15 of 24 group II patients, tachycardias terminated within 1 minute after diltiazem administration, with a weak link in the anterograde direction. In 3 other patients in group II, tachycardias were terminated by a premature ventricular complex within 1 minute. In the remaining 6 patients in group II, in whom tachycardias failed to terminate, rates of tachycardias decreased as a result of suppression of anterograde AV nodal conduction by diltiazem. Electrophysiologic studies were performed subsequently 2 hours after the third dose of 90 mg of diltiazem, which was given orally at 8-hour intervals. In 18 responders to intravenous diltiazem who were subjected to oral diltiazem testing, sustained supraventricular tachycardia (SVT) could be induced in only 2. Of the 6 nonresponders, sustained tachycardias could not be induced in 3. Twelve patients, including 11 responders and 1 nonresponder to intravenous diltiazem who responded to oral diltiazem testing, were discharged with oral diltiazem therapy, 90 mg every 8 hours, with follow-up periods of 2 to 13 months (mean 7 +/- 4 [+/- standard deviation]). The frequency of recurrent SVT decreased significantly; 8 patients were free of tachycardias and 4 had occasional recurrences of SVT that required no hospital visit. In conclusion, intravenous diltiazem is effective in terminating SVT. Termination of SVT by intravenous diltiazem predicts subsequent electrophysiologic and clinical responses to oral diltiazem.