Atrioventricular block during fetal heart rate decelerations.

Electrocardiograms (ECG) was examined in 15 fetuses during fetal heart rate decelerations in labour. Sinus bradycardia was demonstrated in six cases and in two cases inversion of the P wave was seen. In seven cases there was complete dissociation of the P wave from the QRS complex, indicating complete atrioventricular heart block. Many decelerations are vagally mediated, but such cases associated with complete atrioventricular heart block may be due to the effect of hypoxia on the bundle of His.