A new method for evaluating the effect of antiarrhythmic drugs on atrioventricular nodal conduction.

Electrophysiological variables were studied in 19 patients before and after one of three commonly used antiarrhythmic agents. The pacing rate at which alternating Wenckebach periods appeared in eight patients was significantly reduced by intravenous digoxin (0.01 mg/kg body weight). The atrioventricular nodal conduction time (A-H interval) and Wenckebach point were not significantly altered by digoxin. Intravenous propranolol (0.1 mg/kg body weight) in four patients did not affect the A-H interval, but it reduced the pacing rates at which the Wenckebach point and alternating Wenckebach periods occurred. Intravenous disopyramide (2 mg/kg body weight) significantly increased the pacing rate required to produce alternating Wenckebach periods but did not significantly alter the other indicators of atrioventricular conduction in seven patients. It is concluded that the pacing rate required to produce alternating Wenckebach periodicity may be a useful and sensitive variable in the evaluation of the effect of antiarrhythmic agents on atrioventricular nodal conduction.

Electrophysiology of tiapamil in humans.

Electrophysiological properties of tiapamil, a new calcium antagonist, were studied in 15 patients. His bundle recordings were obtained during sinus rhythm and following atrial and ventricular pacing. Studies were performed before and 20 min after slow injection of tiapamil (1 mg/kg). During sinus rhythm, the main effect was a significant prolongation of the P-R interval owing to lengthening of the A-H interval. QRS, P-A and H-V intervals remained unchanged whereas the R-R interval was significantly shortened. Antegrade Wenckebach point was significantly lower after tiapamil. There was no statistically significant effect of tiapamil on the effective refractory periods of atrium, A-V node and ventricle. Corrected sinus node recovery time and sinoatrial conduction time were unchanged although the V-A conduction interval was prolonged. This study suggests that, in the dosage used, the main effect of intravenous tiapamil is prolongation of both antegrade and retrograde A-V nodal conduction.