THE ELECTROPHYSIOLOGIC EFFECTS OF INTRAVENOUS VERAPAMIL IN THE INTACT IMMATURE MAMMALIAN HEART

Abstract

Verapamil (V) is currently utilized in the therapy of cardiac arrhythmias in the neonate and young infant. However, there is little data concerning the electrophysiologic (EP) effects of V on the intact neonatal myocardium and conducting system. We studied the EP effects of intravenous V in doses of 0.075 mg/kg, 0.15 mg/kg and 0.30 mg/kg in 6 neonatal puppies (3-15 days of age) utilizing His bundle recording and programmed stimulation techniques. Verapamil resulted in a dose dependent slowing of sinus cycle length (37 ± 6%, p <0.05) but no changes in either %SNRT or CSNRT. Verapamil also resulted in a significant prolongation of the atrial ERP in the neonatal heart (32 ± 12%, p 0.30 mg/kg V). Concerning AV conduction, V produced a small increase in the resting AH interval (50.5 ± 2.4 msec, control, vs. 57.3 ± 4.7 msec, p 0.30 mg/kg V) and a dose related increase in the paced cycle length resulting in AV nodal Wenckebach (170 ± 12.8 msec, control, → 246 ± 23 msec, p 0.30 mg/kg V). The ERP and FRP of the neonatal AV node prolonged in a dose dependent fashion (ERP-AVN - ↑75 ± 19%; FRP ↑42 ± 14%). Retrograde conduction, present in all, was abolished in 4/6 or significantly prolonged (1/6) by V, particularly at doses >0.15 mg/kg. No changes were observed in ventricular ERP or FRP. Compared with data obtained in the adult dog studied by identical protocol, V has more of an effect on the neonatal sinus node and atrium. Suppression of AV nodal conduction appears comparable in both neonatal and adult subjects.

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