Fetal arrhythmias.

Fetal arrhythmias may be benign or life-threatening. Benign disturbances in fetal cardiac rhythm are relatively common, and their clinical manifestations are reviewed. Life-threatening fetal arrhythmias include supraventricular tachycardias, atrial flutter, ventricular or junctional tachycardia, chaotic atrial tachycardia, and bradyarrhythmias such as second or third degree AV block. The incidence, diagnostic characteristics and treatment of each of these are reviewed. In addition, the pathophysiology of hydrops fetalis, embryology of the conduction system and transplacental drug transfer characteristics are reviewed.