DIFFERENT EFFECTS OF FLECAINIDE ON ATRIOVENTRICULAR-CONDUCTION PROPERTIES IN THE ADULT AND IMMATURE RABBIT HEART

The influence of flecainide (0.1, 0.5, 1.0, and 2.0 mu g/mL) on atriov entricular (AV) conduction was studied in neonatal and adult perfused rabbit hearts using extracellular bipolar surface electrograms and pre mature atrial and ventricular pacing. Flecainide produced a concentrat ion and rate-related increase in the steady-state nodal conduction (AH (min)) and an increase in slow AH conduction (AH(max)) in both age gro ups. The drug produced significant increases in the refractory periods of the atrium, AV node, His-Purkinje system, and ventricular myocardi um. The neonatal refractory periods were significantly greater at lowe r or the same drug concentrations than those of the adult. The neonata l Wenckebach cycle length was significantly greater with a lower conce ntration of drug (0.5 mu g/mL) than was the adult Wenckebach cycle len gth. The His-Purkinje system steady-state conduction time (HVmin) was increased by a lower concentration of drug in the neonate (0.5 mu g/mL ) as compared with 2.0 mu g/mL in the adult. These data show that acro ss a wide range of AV conduction parameters, the neonatal preparations responded to a lower concentration of flecainide than did the adult p reparations. These findings may, in part, be the basis for the reporte d greater efficacy of the drug in children than in adults.