COMPARATIVE EFFECTS OF D-SOTALOL AND L-SOTALOL ON THE ATRIOVENTRICULAR NODE OF THE RABBIT HEART

The purpose of this study was to compare the dose-dependent effects of d-sotalol and 1-sotalol (3 x 10(-7) M to 10(-4) M) on electrophysiological parameters in isolated preparations of the rabbit atrioventricular (AV) node. Standard microelectrode techniques were used in recording transmembrane action potentials from cells of the upper and lower AV node. Twelve New Zealand white Rabbits of either sex weighing between 1.5 and 2.6 kg were used. In both cell types studied, d-sotalol as well as 1-sotalol prolonged action potential duration to the same extent. No significant effects were observed with either isomer on maximum diastolic potential, action potential amplitude, or maximum upstroke velocity of the action potential (V(max)). The rate of spontaneous discharge in AV nodal cells was decreased to the same extent by both isomers; this effect was caused by action potential prolongation; no effect on the rate of diastolic depolarization or V(max) was observed. Both d-sotalol and I-sotalol prolonged AV nodal conduction to the same degree by lengthening the action potential duration in AV nodal cells. The effects of 10(-4) M d-sotalol on AV nodal reentrant tachycardia were studied in one preparation in which AV nodal reentrant tachycardias could reproducibly be initiated by atrial premature stimulation. d-Sotalol abolished the occurrence of this tachycardia by lengthening refractoriness in AV nodal cells; this effect can be ascribed to a Class III antiarrhythmic effect.