A method for evaluating different modes of action of an antiarrhythmic drug in man. The effects of propafenone on sinus nodal functions

Effects of propafenone on ventricular arrhythmias: double-blind, parallel, randomized, placebo-controlled dose-ranging study

Propafenone is a new class Ic antiarrhythmic compound with a broad pharmacologic profile. In this study, its dose-response relationship was examined in a double-blind, randomized, placebo-controlled five treatment parallel design protocol. Patients enrolled had heart disease with Lown grade 2 premature ventricular contractions (PVCs) (greater than or equal to 30/hr) documented on 24-hour Holter recordings. Propafenone was compared in four doses (337.5, 450, 675, and 900 mg/day) to placebo. The double-blind phase lasted 2 weeks. Two hundred twenty-six patients were enrolled, of whom 171 were men and 55 were women; their mean age was 59.8 years and 85% were Caucasian and 4% were black. The arrhythmias were symptomatic in 173. Twenty (8.8%) withdrew from the study before completion: 15 had adverse reactions, two had intercurrent illnesses, and three withdrew for administrative reasons. In one patient, the density of arrhythmia appeared to increase with propafenone. Side effects were of central nervous system or gastrointestinal origin; less than 5% of patients developed first-degree atrioventricular block or intraventricular conduction defect. There were no deaths in the study. The occurrence of side effects was not related to dose. Propafenone had no effect on heart rate. It increased the PR interval at all doses (9% to 22% compared to placebo at baseline; p less than 0.01) at 450 to 900 mg/day after 2 weeks of therapy. The drug increased the QRS duration at all doses, highly significantly at 675 mg/day (8.5 msec; p less than 0.01) and at 900 mg/day (15.7 msec; p less than 0.01) after 2 weeks of therapy. Only at the highest dose was the QTc slightly but significantly (14.3 msec; p less than 0.01) increased. Propafenone exerted a dose-dependent effect on PVCs recorded on serial 24-hour Holter recordings: compared to placebo, at 2 weeks 337.5 mg/day reduced PVCs by 70.8% (p less than 0.05), 450 mg/day reduced PVCs by 82.0% (p less than 0.01), 675 mg/day reduced PVCs by 90.2% (p less than 0.01) and 900 mg/day reduced PVCs by 95.3% (p less than 0.01). The effects of the two highest doses of propafenone were significantly greater than those of 337.5 mg/day. In 68% of the patients receiving 900 mg/day, 80% or greater reduction in total PVCs was found. In addition, there was a greater than 90% decrease in ventricular couplets, and 96% decrease in ventricular tachycardia (VT) beats. Propafenone eliminated PVCs in 8% of all patients, ventricular couplets in 58%, and VT beats in 91%.(ABSTRACT TRUNCATED AT 400 WORDS)

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 less than 0.01). Flecainide significantly prolonged the atrioventricular node variables both in the basal state and after autonomic blockade (p less than 0.01), but the degree of increase was more marked after autonomic blockade (p less than 0.05). These data show dual effects of oral flecainide: a direct depressant action and an autonomically mediated opposing action, likely of vagolytic type.

Intrinsic electrophysiologic properties of reentrant supraventricular tachycardia involving bypass tracts

This study evaluates the effects of autonomic blockade (propranolol, 0.2 mg/kg, and atropine, 0.04 mg/kg) in 20 patients with paroxysmal supraventricular tachycardia (SVT). In 8 patients the SVT circuit involved a concealed atrioventricular bypass for retrograde conduction (group I) and in 12 a concealed atrio-His pathway (group II). Autonomic blockade did not significantly change atrial and ventricular refractory periods, whereas it prolonged atrioventricular nodal refractoriness without varying AH interval. The ventriculoatrial interval did not change in any patient. The H2A2 interval was unchanged in all but 2 group II patients. In both groups, the effective refractory period of the concealed bypass was prolonged by autonomic blockade. In the basal state, SVT was induced in all patients; after autonomic blockade, SVT was induced in 7 patients in group I (87%) and in 7 in group II (58%) (p less than 0.05). Cycle length of SVT was prolonged after autonomic blockade in 11 of these 14 patients. The variations were observed only in the anterograde conduction (Ae-H interval), whereas retrograde conduction (H-Ae interval) was unchanged in all patients. These data indicate that the autonomic system appears to facilitate induction of SVT in patients with concealed atrio-His bypass as well as shorten the cycle length of SVT in both groups of patients.