Antiarrhythmic and electrophysiological effects of SD-3212, a novel Na+ and Ca++ channel blocker,in anaesthetized dogs with myocardial infarction in comparison with its stereoisomer (SD-3211) and bepridil

Summary Antiarrhythmic and electrophysiological effects of SD-3212, a novel antiarrhythmic agent, which has both Na⁺ channel and Ca⁺⁺ channel blocking activites, were compared with those of its (+)-stereoisomer, SD-3211, which has only a Ca⁺⁺ channel blocking activity, and bepridil, a known Ca⁺⁺ channel blocker with additional Na⁺ channel blocking activity, using the two-stage coronary ligation induced arrhythmia (24h after the ligation of the left anterior descending coronary artery) and 7 day-old myocardial infarcted hearts in anaesthetized dogs.SD-3212 showed a dose-dependent antiarrhythmic effect on the two-stage coronary ligation induced arrhythmia. SD-3212 at a dose of 3 mg/kg reduced the arrhythmic ratio, i.e. ectopic beats per min divided by the sum of ectopic beats and sinus beats per min, significantly from 1 up to 12 min after the administration. Neither bepridil (1–6 mg/kg) nor SD-3211 (1 mg/kg) had an antiarrhythmic effect. SD-3212 (0.3–3 mg/kg) prolonged both the conduction time in the normal myocardium and the delayed potential in the infarcted myocardium in the 7 day-old myocardial infarcted hearts in anaesthetized dogs in a dose-dependent manner. This effect of SD-3212 was shown at coupling intervals of 150–1000 ms increasing with decreasing interval. In this respect, SD-3212 is similar to drugs which show fast recovery of V_max from use-dependent block such as lidocaine. Bepidril (1–6 mg/kg) also prolonged these parameters in a dose-dependent manner, however, the prolongation induced by bedripil was limited to shorter coupling intervals as compared with that induced by SD-3212. SD-3212 (0.1–1 mg/kg) did not show this prolonging effect. SD-3212 increased the refractory period in the infarcted zone to a small extent (not significantly) at all strengths tested between 0.5–4 mA and also in the normal zone between 0.2–1 mA to an even lesser extent than in the infarcted zone. Bepridil produced a significant increase of refractory period in the infarcted zone. In the normal zone, bepridil produced a non-significant, but greater increase of the refractory period as compared with SD-3212. SD-3211 did not affect the refractory period in the infarcted zone or in the normal zone. None of the three drugs produced a significant change in the excitation threshold.Thus, SD-3212 showed electrophysiological properties of a drug with fast recovery kinetics without producing a significant increase of refractory period, and these properties are very similar to those of class Ib antiarrhythmic agents such as lidocaine. The present study suggests that there might be a possibility of SD-3212 to become a safe and unique antiarrhythmic agent with suppresses both Na⁺ and Ca⁺⁺ inward current.Send offprint requests to S. Nagashima at the above address