The heart muscle's putative "secondary structure'. Functional implications of a band-like anisotropy.

Opinions are divided as to whether the rope-like secondary structure, which Torrent-Guasp dissected out of the myocardial body by the blunt unwinding technique (BUT) reveals some kind of functional compartmentation of the heart muscle. The myocardial fibres are aligned parallel to the fibre disruption (cleavage) plane, along which the band has been prepared but they are not necessarily aligned parallel to the long axis of the band. Inconsistencies in the myocardial rope model arise from the obligatory zones of transmural inflection, which are obvious in the base and the apex of both ventricles. They are, however, merely discernible in the midzone of the left ventricular cone. The investigator experienced in BUT knows that the cleavage plane is not unique. We doubt the assumption that the rope structure is the predominant stress transmission pathway, because the fibre strand peel-off technique (SPOT) delivers irregular fibre disruption planes which are definitely different from those which Torrent-Guasp prepares. The rope-like fibre arrangement could be just a redundant structure, a remnant of past developmental steps without, however, any functional implication to the human heart. On the other hand, peeling-off fibre strands from the ventricular wall produces deeply perforating, i.e., oblique transmurally grooved surfaces. Putative functions of force transmission in an oblique transmural direction are (1) ventricular dilation as a function of the variable inclination angle with respect to the epicardial surface, (2) monitoring of ventricular wall stress and ventricular size and (3) segmental stiffening which could serve other dependent segments as a punctum fixum.