| Abstract: | The electrophysiologic and antiarrhythmic actions of bretylium tosylate were studied after acute coronary artery occlusion and reperfusion in pentobarbital-anesthetized dogs. Three groups of animals were studied: Group I (n = 8) served as saline controls, Group II (n = 7) received bretylium tosylate (10 mg/kg i.v.) 60 min prior to coronary artery occlusion, and Group III (n = 5) received bretylium tosylate (30 mg/kg i.v.) in three divided doses over the 24 h prior to coronary artery occlusion. In Groups II and III the effective refractory period of the nonischemic myocardium was not altered by bretylium before or during the occlusion period, nor was it influenced by bretylium during the subsequent reperfusion period. In Group I the effective refractory period of the ischemic myocardium decreased 24 +/- 3.0% after coronary occlusion and increased 12 +/- 3% above the preocclusion level on reperfusion. In Group II the effective refractory period of the ischemic myocardium decreased 28 +/- 3.2% after coronary occlusion but did not overshoot preischemic levels on reperfusion. In Group III the effective refractory period decreased 15 +/- 3.8% following coronary occlusion and did not overshoot preocclusion levels during reperfusion. The ventricular activation times of the normal and ischemic myocardium were not affected by bretylium tosylate during occlusion or reperfusion in Group II or III. Significant reperfusion arrhythmias were observed only in Groups I and II. These data suggest that bretylium tosylate exerts its antiarrhythmic actions in ischemic myocardium by reducing the dispersion of cardiac refractoriness produced by coronary artery occlusion and, consequently, abolishing the abrupt change in cardiac refractoriness that follows coronary artery reperfusion. These antiarrhythmic actions of bretylium are pronounced in the chronically treated group, suggesting an electrophysiologic basis of the delayed antiarrhythmic actions of bretylium. |
