Apical Loop and Interventricular Septum
In the continuity of the RS of the BL there is a 180° turn, forming the central fold that divides both loops, being the point of change of direction of the myocardial fibers in a descending direction. The subendocardial fibers in the segment reaching the apex overlap helically to form the ”vortex cordis” described by Richard lower in the 17th-century6. Then they change direction and the subepicardial forms the AS ending in the insertion of the left fibrous trigone at the base of the left ventricle. (Figure 1: Asterik, 5)
The previous configuration leaves two lateral segments (LS, RS) with predominantly transverse fibers covering or ”embracing” the (AL) containing two muscular segments with subendocardial (DS) and subepicardial (AS) direction, interposing each other at an angle of 90°, called septal segments. The 180° central fold dividing both loops preserves the continuity of endo-epicardial directions and the longitudinal axial continuity of the adjacent segments in the unfolded band.
The two large muscle segments are distinguishable by macroscopical anatomical dissection7, can be observed by tractography8, defined as an interseptal hyperechoic line in echocardiography9, and identified as the path of dissection of some hematomas, participating in the formation of septal intramyocardial dissecting agents10.
The BL helix embracing the base of the heart, the 180° central fold, and the helical twist that superimposes AL subendocardium on subepicardial that generates the vortex cordis and the interventricular septum, form the fractal principle of self-similarity and its global three-dimensional structure a non-orientable geometric surface of triple torsion like a Moebius strip.