Developmental Transitions in Cardiac Conduction

Summary

The proper sequence of electrical activation of the mature four-chambered heart requires specialized conduction pathways including the His–Purkinje system and a nearly complete separation of the atrial and ventricular myocardium. We tracked the emergence of the structure of the mature His–Purkinje system in the developing chicken embryo with anti-polysialylated neural cell adhesion molecule (PSA-NCAM) and the HNK1 antibody against a sulfated carbohydrate epitope. The function of the His–Purkinje system was assayed using extracellular electrodes and high-resolution voltage-sensitive two-dimensional optical mapping. The appearance of the mature form of the His–Purkinje system delineated by the markers coincided with the onset of the mature electrophysiological pattern of ventricular activation. These data suggest that, at the completion of ventricular septation, the His–Purkinje system undergoes critical structural and functional transitions that impact on the global pattern of conduction and contraction of the developing four-chambered heart.