Am J Physiol Heart Circ Physiol

Cardiac fiber direction is an important factor determining the propagation of electrical activity, as well as the development of mechanical force. In this paper, we imaged the ventricles of several species with special attention to the intraventricular septum to determine the functional consequences of septal fiber organization. First, we identify a dual-layer organization of the fiber orientation in the intraventricular septum of ex-vivo sheep hearts using diffusion tensor imaging at high field MRI. To expand the scope of the results, we investigate the presence of similar fiber organization on five mammalian species (rat, canine, pig, sheep, human) and highlight the continuity of the layer with the moderator band in large mammalian species. We implemented the measured septal fiber fields in 3D electromechanical computer models to assess the impact of the fiber orientation. The downward fibers produced a diamond activation pattern superficially in the RV. Electromechanically, there was very little change in pressure volume loops although the stress distribution was altered. In conclusion, we clarified that the RV septum has a downwardly directed superficial layer in larger mammalian species, which can have modest effects on stress distribution