Direct and autonomically mediated effects of oral flecainide

This study was undertaken to determine if oral flecainide exerts autonomically mediated actions in addition to its direct depressant effect. Electrophysiologic studies were performed twice in each of 15 patients (mean age 59 years) with normal resting and intrinsic heart rate and normal A-H interval. In the first study, the variables of sinus node and atrioventricular node were evaluated both in the basal state and after autonomic blockade (propranolol 0.2 and atropine 0.04 mg/kg). Oral flecainide was administered for 4 to 5 days (200 to 250 mg daily) and the study was then repeated using the same methods. From comparison of data obtained in the 2 studies in the basal state, the overall effect of flecainide was evaluated and by comparing those obtained after autonomic blockade, the direct action of the drug was assessed. The overall effect of flecainide on sinus node was slight; sinus cycle length, corrected sinus node recovery time and sinoatrial conduction time did not change significantly after the drug. In contrast, after autonomic blockade the variables of sinosal automaticity were increased significantly (p < 0.01). Flecainide significantly prolonged the atrioventricular node variables both in the basal state and after autonomic blockade (p < 0.01), but the degree of increase was more marked after autonomic blockade (p < 0.05). These data show dual effects of oral flecainide: a direct depressant action and an autonomically mediated opposing action, likely of vagolytic type.