Abstract
The electrophysiologic effects of verapamil, a slow channel blocker, were investigated during diagnostic cardiac catheterization in 24 children premedicated with lytic cocktail. The ages ranged from 50 days to 12 years. Twenty had congenital and 4 had rheumatic heart disease. Surface EKG, high intra-atrial and His bundle electrograms were obtained in all before and 5min after a single dose of verapamil (0.15mg/Kg, max 5mg iv). In 14 cases complete electrophysiologic studies were performed using the atrial pacing and extrastimulus technique. Due to variability of the resting heart rates and the effect of cycle length on refractory periods each patient was paced with identical S1-S1 interval before and after verapamil, thus allowing each case to serve as his own control. Verapamil prolonged the corrected AH interval in all (mean±SD; from 116±37 to 152±41 msec, p<0.01) and shortened the HV interval in 15/24 (mean±SD: from 55±13 to 47±9.9 msec, p<0.05). The effective and functional refractory periods of the total conduction system, the AV node (ERPAVN) and atrium (ERPA) increased significantly in 10/14. The most profound effect was on ERPAVN and ERPA (25.54±29 and 19.27±21.81 percent mean percent increase±SD respectively, p<0.01 and p<0.02). Our findings show that verapamil prolongs the effective and functional refractory periods of the cardiac conduction system with maximal effects on the AV node, thus suggesting the mechanism of its effectiveness in the treatment of reentrant supraventricular arrhythmias.
