Benign fetal bradycardias diagnosed by echocardiography.

Five cases of benign fetal arrhythmias presented with dramatic pictures of sustained irregular bradycardias. These cases were not associated with structural heart disease, the development of hydrops fetalis, or maternal autoantibodies. In all but one case, the arrhythmias resolved before delivery. Two fetuses had 2:1 atrioventricular block and the other three showed group beating due to blocked atrial trigeminy. With regular intermittent reevaluation, and if no signs of hydrops occur, watchful waiting is the suggested therapeutic modality.