Effect of bunaphtine on right atrial repolarisation in man

Using a bipolar suction electrode technique, right atrial monophasic action potentials were recorded in 11 patients with recurrent attacks of paroxysmal atrial tachyarrhythmia. The right atrial monophasic action potential total duration, measured at 90 per cent level of repolarisation, in sinus rhythm, ranged between 217 and 394 ms. N(2-diethylamine-ethyl)N(n-buthyl)-naphtamide (Bunaphtine) was administered by an intracardiac catheter at an average dosage of 1-78 mg/kg body weight in order to evaluate its effect on atrial repolarisation. Monophasic action potential recordings were performed during drug administration and thereafter every minute for an average observation period of 12-2 minutes. The drug induced a significant lengthening of atrial repolarisation (mean 18.4%) strongly correlated with a significant reduction of relative repolarisation rate of phase 3 (RRR ph3). The effect was more obvious in patients with short repolarisation and was not correlated with significant variations in heart rate. When basic cycle length was maintained constant by atrial pacing an increase in total duration of right atrial monophasic action potential was seen. Administration of the drug was followed by an appreciable reduction of inhomogeneity of repolarisation as measured from different sites in the atrium. In 2 patients conversion from atrial fibrillation to sinus rhythm occurred during drug infusion with a progressive lengthening of right atrial monophasic action potential; this suggests that the antiarrhythmic properties of Bunaphtine are related to its direct effect on repolarisation. Thus, as far as atrial tissue is concerned Bunaphtine can be considered a Class 3 antiarrhythmic drug according to the classification of Vaughan-Williams.