1. Department of Histology and Cell Biology, Faculty of Medicine, Zagazig University, Zagazig 44519, Egypt.
Background: Despite the fact that the exact architecture and orientation of left ventricular myocardial fibers are critical to cardiac functions either in health or disease, it is still debated.
Aim of the work: Histological demonstration of the transverse alignment of the myofibers making the left ventricular mass was applied to validate different anatomical speculations of cardiac myofibers organization; mainly Streeter’s conjecture and the ventricular myocardial band model of Torrent-Guasp.
Material and methods: Six healthy adult male C57BL/6N mice were utilized. Their hearts were separated into atria and ventricles. Then, both ventricles were divided into four levels [base, upper mid, lower mid and apex]. Paraffin step-serial transverse sections were stained with H&E and Masson’s trichrome stains. Morphometrical measurements of the thickness of the anterior, posterior, and lateral walls of the left ventricle (LV) as well as the inter-ventricular septal wall were realized with ImageJ software. For data analyses among the four levels of LV, Scheffé’s method was applied for multiple comparisons when a significant difference was observed by Kruskal-Wallis test (p<0.05).
Results: Examination of the LV from its base to its apex revealed obvious changes in the thickness of its walls and inter-ventricular septum as well as in its cavity shape. Interestingly, the myocardial fibers showed different running patterns [longitudinal, oblique and circular] among different levels as well as within the same level from sub-epicardial to the endocardial region. Throughout all levels, the subepicardial myofibers showed longitudinal orientation while that of the intermediate wall revealed either oblique [in upper mid-level] or circular orientations in other levels. The sub-endocardial fibers were mostly longitudinal with the presence of some circular fibers in the base and upper-mid regions. Masson’s trichrome sections revealed a trivial amount of collagen fibers just around each individual myocyte without any bundle formation.
Conclusion: The presence of different running patterns of the myocardial fibers among different levels of LV as well as within the same level indicates multiple rolling of the myocardial fibers. Thus, we suggested that the band model by Torrent-Guasp accounts for the patterns of myocardial fiber architecture forming the left ventricle.
Keywords: Left ventricle, myocardial band, Torrent-Guasp, C57BL/6N mice