Contrasting effects of verapamil and procainamide on rate-dependent bundle branch block: Pharmacologic evidence for the role of depressed sodium channel responses

Abstract

The mechanisms responsible for intermittent bundle branch block are still under debate. The role of the time-dependent behavior of the slow calcium channel has recently been emphasized. To test this hypothesis and ascertain the possible involvement of the fast sodium channel, the effects of the slow calcium channel blocker verapamil and the fast sodium channel blocker procainamide were compared in 10 patients with intermittent bundle branch block. All 10 patients showed bundle branch block during spontaneous sinus rhythm. Maneuvers to slow cardiac rate (that is, carotid sinus massage, Valsalva maneuver) were performed to identify normal conduction as well as phase 4 bundle branch block. Thus, the ranges of diastolic intervals (RR) resulting in phase 3 (tachycardia-dependent) bundle branch block, phase 4 (bradycardia-dependent) bundle branch block and normal conduction were measured in two control studies performed before intravenous administration of verapamil (control 1) and procainamide (control 2) and at the peak effect of both drugs. In the control studies, all 10 patients showed phase 3 bundle branch block, whereas phase 4 bundle branch block occurred in only 4 patients. The ranges of phase 3 bundle branch block, phase 4 bundle branch block and normal conduction were very similar in control studies 1 and 2. The phase 3 bundle branch block range was slightly shortened by verapamil (983 +/- 83.5 ms in control 1; 930 +/- 69.4 ms at the peak effect of verapamil), whereas phase 4 bundle branch block remained unchanged. In contrast, conduction was systematically worsened by procainamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Overdrive Suppression of Antegrade Conduction Over A Kent Bundle Induced by Disopyramide

“…Recently, Chiale et al (Chiale, et al, 1990) studied effects of procainamide on rate-dependent bundle branch block, and concluded that clinical intermittent bundle branch block was related to depressed fast responses and not to slow calcium mediated responses. Previous experimental data on overdrive suppression of conduction in canine His-Purkinje system (Takahashi et al.…”

Argentina’s most important contributions in the field of electrophysiology

“…Intracellular studies were carried out on the pharmacodynamics of antiarrhythmic drugs. 39 , 40 , 41 , 42 In vitro studies with microelectrode technique in normal and abnormal human myocardial tissues obtained from explanted hearts were performed. 43 Two original contributions were related to Brugada syndrome with reference to its etiopathogenesis and diagnosis.…”