A combined electrophysiological and anatomical study of the human fetal heart.

Five human fetal hearts of gestational ages ranging from 12 to 16 weeks were studied with both electrophysiological and anatomical techniques. The electrophysiological behavior of these hearts was comparable with results obtained with other animal species and adult human hearts. This indicates that the fetal heart is functionally mature from an early stage of development; however the tissues are not fully differentiated from an anatomical standpoint. Results of mapping experiments indicated that atrial activation occurred through broad wave fronts, and no electrophysiological evidence was found to support the concept of "specialized internodal conduction." In two hearts, the node and bundle were found to be anatomical contiguity with ventricular myocardium throughout their length, but the conducting tissues were already functionally insulated from the ventricles. The results have significance with regard to concepts of the "sudden death in infancy syndrome" and ventricular pre-excitation.