The electrophysiological effects of intravenous verapamil were compared in six intact neonatal puppies ages 3-15 days and in adult dogs. Utilizing standard intracardiac recording and programmed stimulation techniques, sinus and AV nodal function and atrial and ventricular refractory periods were determined following incremental intravenous doses of 0.075 mg/kg, 0.15 mg/kg, and 0.30 mg/kg of verapamil. In the neonate, intravenous verapamil resulted in a significant increase of the sinus cycle length (37 ± 6%) but no changes occurred in either the percent sinus node recovery time or the corrected sinus node recovery time. The atrial effective refractory period was prolonged by verapamil (32 ± 12%). Concerning atrioventricular (AV) nodal function, verapamil produced a small but significant prolongation of resting AH interval (50.5 ± 2.4 ms (control) versus 57.3 ± 4.7 ms post 0.30 mg/kg) and a dose-related prolongation of the paced cycle length resulting in AV nodal Wenckebach (170 ± 12.8 ms control, 190 ± 10.3 ms post 0.075 mg/kg, 215.8 ± 13.0 ms post 0.15 mg/kg and 246.7 ± 22.8 ms post 0.30 mg/kg). The effective refractory period (ERP) and functional refractory period (FRP) of the atrioventricular node (AVN) were prolonged in a dose-dependent fashion (ERP-AVN; 75 ± 19% increase, FRP-AVN: 42 ± 14% increase). Retrograde conduction, present in all six neonates, was completely abolished in four of six subjects and significantly prolonged in one other puppy by verapamil. No changes in ventricular refractory periods were observed. Comparison of the neonatal data with data obtained in adult dogs studied by identical protocol, suggested that in the neonate verapamil tends to have more of an effect on sinus cycle and atrial ERP. The suppression of AVN conduction by verapamil appeared comparable in both the neonatal and adult subjects.
- Immature heart
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine