Anatomical and Ultrastructural Study of the Electrophysiological Atrioventricular Node of the Rabbit

Abstract

The structure of the tissue forming the atrioventricular node of the rabbit heart was studied with the light and the electron microscope. The observations were correlated and compared with the electrophysiological properties of the region. A technique was developed which allows identification of tissue examined by microscopy with that examined using microelectrode techniques to within 0.5 mm. Although the cells which form the connecting neck between the atrial tissue and the His bundle are basically muscle cells, their development has led to tissue structure different from that of the remaining myocardium. This tissue often displayed structural characteristics similar to those observed in pathological skeletal and cardiac muscle. Variation in the abundance of "tight" intercellular junctions in the region of the node were noted. The possible significance of the morphological characteristics in terms of electrical impulse transmission is discussed, and some tentative suggestions are made concerning the mechanisms by which the slow impulse conduction is effected in this region.