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Electrophysiologic effects of verapamil in children
Insights
Verapamil, a slow channel blocker, prolongs cardiac conduction system refractory periods, particularly in the AV node. This suggests its effectiveness in treating supraventricular arrhythmias.
Area of Science:
- Cardiology
- Electrophysiology
- Pharmacology
Background:
- Verapamil is a slow channel blocker used in cardiac conditions.
- Pediatric cardiac patients with congenital or rheumatic heart disease often require electrophysiologic assessment.
Purpose of the Study:
- To investigate the electrophysiologic effects of verapamil in pediatric patients.
- To determine the impact of verapamil on cardiac conduction intervals and refractory periods.
Main Methods:
- Diagnostic cardiac catheterization was performed on 24 children (50 days to 12 years).
- Electrophysiologic studies included surface EKG, intra-atrial, and His bundle electrograms before and after verapamil administration (0.15 mg/Kg IV).
- Atrial pacing and extrastimulus techniques were used to assess refractory periods.
Main Results:
- Verapamil significantly prolonged the corrected AH interval (p < 0.01).
- The HV interval was shortened in 15/24 patients (p < 0.05).
- Effective and functional refractory periods, especially of the AV node and atrium, increased significantly (p < 0.01, p < 0.02).
Conclusions:
- Verapamil prolongs the effective and functional refractory periods of the cardiac conduction system.
- The maximal effect of verapamil was observed on the AV node.
- These findings support verapamil's mechanism in treating reentrant supraventricular arrhythmias.
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 5 min after a single dose of verapamil (0.15 mg/Kg, max 5 mg iv). In 14 cases complete electropysiologic 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 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 less than 0.01) and shortened the HV interval in 15/24 (mean +/- SD: from 55 +/- 13 to 47 +/- 9.9 msec, p less than 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 less than 0.01 and p less than 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.