A comparison of the electrophysiologic effects of intravenous and oral amiodarone in the same patient.

In 12 patients (nine with Wolff-Parkinson-White syndrome and three with ventricular tachycardia) the electrophysiologic effects of intravenous (5 mg/kg body weight in 1 min) and oral (total dose 9800 to 11,200 mg) amiodarone were studied with programmed stimulation of the heart. Intravenous and oral amiodarone had a similar (p less than .05) effect of lengthening on the effective refractory period of the atrioventricular node. Only intravenous amiodarone prolonged (p less than .05) the AH interval. Oral amiodarone was more effective than intravenous amiodarone in lengthening the anterograde effective refractory period of the accessory atrioventricular pathway. Only oral amiodarone prolonged the effective refractory period of atrium and ventricle and the HV interval, all significantly (p less than .05). Intravenous amiodarone slowed (p less than .05) the rate of circus-movement tachycardia in patients with Wolff-Parkinson-White syndrome, and further slowing was observed after oral amiodarone. Termination of tachycardia by intravenous amiodarone predicted prevention of reinitiation of tachycardia during oral amiodarone. These data indicate that intravenous and oral amiodarone do not have the same electrophysiologic effects. It is not clear whether cumulative effects, active metabolites, or both are responsible for these differences.