Effect of calcium antagonists on the electrical alternans of the ST segment during acute coronary occlusion in dogs.

Effects of antagonists on the ST alternans during acute coronary occlusion were examined in dogs. The intravenous administration of verapamil at doses of 0.1 mg/Kg and 0.2 mg/Kg prominently attenuated the degree of alternans. Diltiazem at dose of 0.2 mg/Kg also attenuated the degree of alternans. Dipyridamole at dose of 0.5 mg/Kg did not significantly attenuate the degree of alternans. Verapamil significantly inhibited the ST-segment elevation. After verapamil, ST alternans did not occur even after a longer period of occlusion when changes in QRS complex and the ST-segment elevation were remarkable. It is possible that verapamil inhibits ST alternans by both the protecting effect against ischemic injury and a direct effect on the electrical activity of the myocardial cell membrane.