The Conducting Tissues of the Mouse Heart

Background: Since the study of Lev and Thaemert in 1973, little has been published concerning the overall arrangement of the murine conduction tissues, in particular with relation to gross anatomical landmarks. We recently emphasised the potential value of the mouse as an experimental animal in determining the role, if any, of the superior septal pathways in ventricular activation, comparing the findings to the arrangement in the human heart. Our previous study, however, was confined to the atrioventricular conduction axis. In the light of recent controversies regarding atrial conduction, we have now extended our study to evaluate the overall arrangement of the conduction tissues in the murine heart. Methods: We have re-examined serially sectioned histological datasets previously prepared from adult mouse hearts, incorporating new datasets to permit assessment in the three orthogonal planes, correlating the histological findings with the gross anatomy as revealed in episcopic datasets prepared from late foetal and neonatal mice. Results: The overall arrangement of the conduction tissues is comparable with the human arrangement, but with subtle differences. The sinus node straddles the superior cavoatrial junction, rather than being embedded within the terminal groove. Conduction from the node to the atrial walls is through working atrial myocardium. The atrioventricular conduction axis, as we have recently emphasised, is much more comparable, in particular with presence of well-formed nodo-ventricular and fasciculo-ventricular pathways. In many of the hearts it is also possible to recognise a well-formed retro-aortic node. Conclusions: Despite the differences in the arrangement of the sinus node, mouse is an ideal model for further investigations of cardiac conduction, in particular to clarify the potential roles of the superior septal pathways and the retro-aortic node.