Electrophysiologic effects of encainide following acute coronary occlusion in dogs.

ABSTRACT

Encainide, a benzanilide derivative, is a local anesthetic antiarrhythmic drug. To determine its effects on infarcted and normal tissue in situ, we infused encainide (1.0 mg/kg) for 15 min intravenously followed by 0.01 mg/kg/min for an additional 105 min in 8 adult open-chest, pentobarbital-anesthetized, atrially paced dogs after left anterior descending coronary occlusion. We monitored plasma concentration, blood pressure, and surface electrocardiogram (ECG). We determined conduction intervals from the onset of the QRS in the limb lead ECG to the major deflection of bipolar electrograms recorded in the infarcted and normal zones. We found that the blood pressure did not change significantly. Encainide did significantly prolong the atrial stimulus artifact-to-QRS interval and the QRS duration, as previously reported, and also prolonged intraventricular conduction intervals. In the infarcted zone, the drug prolonged conduction in both subendocardium and subepicardium, and prolongation was of somewhat greater magnitude in this zone than in the normal zone. Encainide prolonged the effective refractory period only in the infarcted zone (19 +/- 5 msec at peak; p less than 0.01). The above electrophysiologic effects may explain in part the previously demonstrated antiarrhythmic properties of this drug.