Effect of amiodarone on retrograde conduction and refractoriness of the His-Purkinje system in man

The effects of long term treatment with oral amiodarone on retrograde conduction (S₂H₂ interval) and refractoriness of the His-Purkinje system were studied in 11 patients using His bundle electrograms and the ventricular extrastimulus method. Ten patients had ventricular tachycardia and one supraventricular tachycardia. Electrophysiological studies were carried out before and after the patients had been taking their maintenance dose for a mean duration of 84 days. After amiodarone treatment the HV interval was prolonged in seven patients and unchanged in four. At comparable S ₁S₂ intervals, the S₂H₂2 intervals were longer after treatment with amiodarone in all patients than before. Similarly, the longest S₂H₂2 intervals achieved after amiodarone were longer than the control values. Amiodarone significantly increased the relative, effective, and functional refractory periods of the His-Purkinje system. Thus amiodarone exerts important effects on the His-Purkinje system.