Effects of verapamil and propranolol on ventricular vulnerability after coronary reperfusion

This study was designed to determine whether or not verapamil and propranolol affect the lowering of the ventricular multiple response threshold (VMRT) that is seen following release of a previously ligated coronary artery. In mongrel dogs, the left anterior descending coronary artery was occluded for 15 min and then the ligation was released. The dogs were divided into three groups: in the control group, saline was administrated immediately before the release of ligation; in the two other groups, verapamil or propranolol were administrated immediately before the release of ligation. In the control group, VMRT was decreased during coronary occlusion and did not recover immediately after coronary recirculation. That is, significantly lowered values were observed at 5 and 10 min after reperfusion. The administration of verapamil prevented the lowering of VMRT after reperfusion, whereas propranolol had no effect. In all three groups, an increase in the difference of the concentration of K+ between the great cardiac vein and the femoral vein (delta K+) was observed soon after occlusion; however, delta K+ returned to normal soon after reperfusion. These results and the known anti-arrhythmic mechanism of verapamil suggests that Ca++-dependent action potentials might play an important role in lowering VMRT after release of a previously occluded coronary artery, whereas the effects of K+ and catecholamine do not play a role in causing the lowering of VMRT.