Three-dimensional anatomy of the conduction system of the early embryonic rabbit heart.

The complete embryonic cardiac conduction system is difficult to view in three dimensions, primarily because there has not been a marker of all segments of the normal system throughout all stages of development. Imaging of the conduction system components within the atria has been particularly controversial because different markers reveal different pathways that may or may not represent conduction system components. The conduction system of the adult and embryonic rabbit, however, can be labeled in its entirety with the neurofilament marker, NF-160. The conduction system of rabbit embryos at several stages of development spanning cardiac septation was therefore investigated. Optical mapping of the electrical signature of the conduction system previously revealed a close correlation between the cardiac activation patterns and the anatomy as shown by serial sections. The 3D relationship between the components of the conduction system could only be inferred from the 2D sections. The sections were consequently reconstructed using a commercial software program (AutoQuant). This is the first demonstration of the three-dimensional complete normal rabbit embryonic cardiac conduction system at several stages of development.