This study investigates developmental differences in ventriculoatrial conduction during incremental ventricular pacing in the perfused rabbit heart. In 16 adult and 13 neonatal perfused preparations, ventricular prematures S2 were introduced after a train of 10 S1 stimuli. S2 was progressively shortened until the ventricular refractory period was reached. Parameters of retrograde conduction and refractoriness were then compared.

Results:

As the Table shows, there were no developmental differences in retrograde conduction through the atrioventricular node or infra-Hisian system. In both age groups, retrograde conduction was maintained until ventricular refractoriness was reached. However, the ventricular effective refractory period of the neonate was significantly shorter than that of the adult (p=.002).

Table 1
Full size table

Conclusion: Developmental differences in retrograde conduction in the rabbit heart are not due to intrinsic properties of the AV node or infra-Hisian system, but may be a manifestation of the shorter refractory period of the neonatal ventricular myocardium. This difference may partially explain the faster rates of reentrant supraventricular tachycardia in the neonate.