[Atrioventricular conduction time in premature infants is about half of that in adults].

OBJECTIVE

To determine the atrioventricular (AV) conduction time in prematurely born infants as part of a comparative electrocardiological study of conduction times versus heart size.

DESIGN

Recording and analysis of electrocardiograms.

SETTING

Department of Neonatology, University Hospital of the Free University of Amsterdam, the Netherlands.

METHODS

Using bipolar precordial leads of standard monitoring equipment in 28 babies, born at a gestational age of 26-36 weeks, ECGs were recorded as soon after birth as possible. The ECGs were analysed and relevant conduction times, such as PR intervals and QRS durations, were measured by hand. These data were related to the birth weights of the infants. (The heart weight amounts to approximately 0.6% of body weight.)

RESULTS

Average birth weight of the babies was 1374 g (SD: 491), average PR interval 93 ms (9), QRS duration 40 ms (4), and average heart rate 148/min (14).

CONCLUSION

Human hearts weighing 6-10 g have conduction times half that of the adult human heart which weighs 50 times as much. The contribution of the AV node to the total AV conduction time increases with diminishing heart size.