Abstract
Effects of calcium antagonists and lidocaine on the conduction delay observed in the ischemic myocardium were studied in 24 open-chest anesthetized dogs. Acute myocardial ischemia was produced by complete occlusion of the left anterior descending coronary artery (LAD) for 5 or 10 minutes. The conduction time was measured from the initial deflection of V waves on the His bundle electrograms to the major deflection of the bipolar electrograms recorded from the ischemic and non-ischemic subepicardium under a constant atrial pacing. LAD occlusion produced conduction delay in the ischemic zone (14.3±2.3 msec, p<0.001) with no effect on the normal zone. This ischemia-induced conduction delay was reversible and rate-dependently increased. Administration of lidocaine (2 mg/kg bolus, 4.3 mg/kg/hr constant infusion) prior to the second occlusion increased conduction delay by 12.9±1.9 msec (p<0.001) whereas diltiazem (0.4 mg/kg i.v.) and verapamil (0.3 mg/kg i.v.) reduced the ischemia-induced conduction delay by 12.7±4.9 msec (p<0.05) and 8.4±1.8 msec (p<0.001), respectively. These results indicate that slow channel blocking agents reduce the conduction delay induced by the myocardial ischemia, in contrast with the prolonging effect of lidocaine.
