Abstract
Conduction delay in the ischemic or reperfused myocardium is regarded as a warning sign of life-threatening ventricular arrhythmias. In this study, the effects of calcium antagonists on conduction delay were evaluated in two-step coronary ligated hearts of 32 dogs, 8 dogs as control, 8 treated with verapamil (0.15mg/kg bolus followed by 7.5μg/kg/min), 8 with nifedipine (0.1mg/kg bolus) and 8 with diltiazem (0.02mg/kg/min) . Conduction delay was expressed as ΔCT (difference in conduction time before and after coronary ligation) and was measured by special intramyocardial electrodes. A reperfused area was made by releasing the artery after 30min ligation. The values of ΔCT obtained from normal, ischemic, reperfused and borderline areas were compared in the treated and control groups.
As a result, (1) The control group showed no change in the normal area, but the valve increased in the ischemic and border areas and decreased aftex reperfusion. (2) Verapamil reduced ΔCT significantly in the ischemic, reperfused and border areas. (3) Diltiazem also reduced ΔCT in the same way as verapamil, except in the reperfused area. (4) Nifedipine did not alter ΔCT in any myocardial areas except in the retrograde direction in the border area. (5) Diltiazem reduced ΔCT in both the treated and untreated ischemic areas, while verapamil produced a greater reduction in the treated area. The magnitude of reduction in ΔCT, however, was greater in the verapamil than in the diltiazem group. Nifedipine did not affect either ischemic areas. (6) In conclusion, verapamil and diltiazem appear to be useful agents in protecting against ischemic or reperfusion-induced ventricular arrhythmias.