This study evaluates whether the electrophysiologic effects of i.v.
amiodarone in patients with reentrant
supraventricular tachycardia (SVT) can predict the efficacy of long-term oral
therapy with this
drug. The effects of oral and i.v.
amiodarone were studied in 27 patients with SVT. In 14 the SVT circuit involved a concealed atrioventricular bypass for retrograde conduction (Group I), and in 13 a concealed atrio-His bypass (Group II). Intravenous
amiodarone induced significant prolongation of the AH interval, the refractory periods of the atrium, atrioventricular node, His-Purkinje system and ventricular myocardium. The ventriculoatrial interval was slightly prolonged in Group I patients and did not change in Group II patients after i.v. administration of the
drug. In both groups, the effective refractory period (ERP) of the concealed bypass was prolonged by i.v.
amiodarone. During control state, SVT could be induced in all patients; after i.v. administration of the
drug, SVT was presented in 6 patients in Group I and in 8 patients in Group II. In all cases, in which i.v.
amiodarone prolonged the ERP of the concealed bypass to more than 350 ms, the
drug always prevented SVT even when given orally. All but 2 patients--1 from Group I and 1 from Group II--remained asymptomatic after oral
amiodarone. In the patient from Group I, SVT had been prevented by i.v.
amiodarone, whereas in the patient from Group II SVT could not be induced by ventricular stimulation during the control state, but appeared after i.v. administration of the
drug.(ABSTRACT TRUNCATED AT 250 WORDS)