A macroscopic anatomical investigation of atrioventricular bundle locational variation relative to the membranous part of the ventricular septum in elderly human hearts.

Although several gross anatomical investigations on the cardiac conducting system have been published, most have presented gross anatomical observations after histological confirmation. This is because of the difficulty in dissecting the conducting system itself. Additionally, the conducting system has hitherto been represented schematically and/or histologically, even in recent regional anatomical color atlases of the heart. Therefore most researchers and clinicians rarely view a conducting system at the macroscopic level. In this study we reveal the detailed-gross anatomical architecture and normal variations in the conducting system using 105 elderly human hearts. In particular, we focused on the location of the atrioventricular bundle relative to the membranous part of the interventricular septum because it has commonly been used as a landmark to identify the conducting system. Consequently we found locational variations in the atrioventricular bundle to be relatively more frequent in 56 cases (53.3%), in contrast to 49 (46.7%) ordinary cases in which this bundle ran just along the lower border of the membranous part of the interventricular septum. In the former cases we also emphasized the clinical significance of the naked atrioventricular bundle running on the membranous part of the interventricular septum in 22 cases (21.0%). Some types of lower atrioventricular bundle variation would be important for cardiac surgery, especially the operation of the interventricular septal defect and can be explained from the developmental viewpoint, i.e., the atrioventricular bundle has its origin in the mixture of specialized myocardial rings.