Are there stereoselective electrophysiologic effects of intravenously administered (S)- or (R)-propafenone...

The electrophysiological effects of intravenously administered pure (S)- and (R)-propafenone hydrochloride has been determined for the first time in humans-12 patients with supraventricular tachycardia.

Measurements were performed before and during drug therapy.

(S)- and (R)-propafenone prolonged the AH interval from 82 to 107 ms and 75 to 84 ms, respectively, and significantly increased the V nodal Wenckebach cycle length by 58 ms and 37 ms, respectively. The AV nodal effective refractory period in both groups was increased significantly to the same extent (45 vs 42 ms). Sinus node recovery times were not significantly influenced by either enantiomers. Both (S)- and (R)-propafenone significantly prolonged the HV interval to the same extent (from 41 to 51 ms, and 42 to 53 ms). Changes in the electrophysiological characteristics of the myocardium were more pronounced in the atria than in the ventricles. Only (S)-propafenone significantly increased the atrial effective refractory period from 204 to 230 ms, and the ventricular effective refractory period from 225 to 241 ms compared to (R)-propafenone (from 221 to 239 ms, and from 219 to 222 ms, respectively). There was a more pronounced electrophysiological effect on AV nodal conduction of (S)- than (R)-propafenone, probably as a result of its beta-blocking activity.

The electrophysiological effects of (S)-compared to (R)-propafenone were not very pronounced, so it still remains questionable whether one of the enantiomers might be clinically superior to the other, or to the racemic mixture.