Electrophysiologic effects of bepridil in the anesthetized dog studied by endocardiac electrodes.

The electrophysiologic effects of bepridil in the anesthetized closed-chest dog were studied with intracardiac electrodes using the extrastimulus technique to measure the refractory periods of atria, atrioventricular (AV) junction and ventricles. Intravenous administration of 5 mg/kg of bepridil caused a reduction in sinus node rate and prolonged the sinus node recovery time. Refractory periods in the atrium, especially the effective refractory period, increased. Anterograde AV nodal conduction was slowed and refractoriness increased, often resulting in AV nodal Wenckebach periods, during atrial pacing, and retrograde conduction was always completely abolished. Refractory periods of the AV junction were altered in a comparable fashion to conduction through the AV node. No significant actions on conduction or the refractory period were noticed in the His-Purkinje system or the ventricle. The mechanism of action of bepridil seems to be correlated to its membrane effects, namely, inhibition of pathways responsible for the slow inward current, which explains its selective action on myocardial sites where this current is particularly involved.