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.