The interatrial or internodal conduction tracts are bands of specialised myocytes which are believed to lie between the sinuatrial node and the atrioventricular node. Previously, conduction between the two nodes was thought to occur through direct stimulation and conduction between normal atrial myocytes. The latter theory does not explain why the SAN impulses arrive at the AVN more quickly than would be expected by just atrial myocyte conduction.
However, ultrastructural evidence for discrete bands of rapidly-conducting myocytes is sparse. Where clear differentiation has been made, the myocytes appear to resemble the Purkinje cells of the ventricles. Three discrete internodal tracts have been reported:
Last reviewed 01/2018