Histologic and histochemical evidence concerning the presence of morphologically distinct cellular zones within the rabbit atrioventricular node

Abstract The rabbit atrioventricular nodal region has been studied using a method of tissue preparation allowing direct comparison of adjacent sections processed by histological and histochemical techniques. By this means, specialized cardiac tissue is found to occupy the region defined electrophysiologically as the atrioventricular node. This region is more extensive than that previously defined by light microscopy. Within this region three types of cell are distinguishable; transitional cells, and upper and lower nodal cells. The last are continuous with and identical to the cells of the atrioventricular bundle. The cell types also exhibit differences in their pattern of innervation. The significance of these cellular zones and their associated nerves is discussed with reference to previous electrophysiological findings and the mechanism of nodal delay.