Myocardial Torsion. Jorge C. Trainini

in this image.

5. Interpretation of the origin and end of the muscle band.

      The cardiac fulcrum

      As previously expressed, the opposite orientation and rotational movement of the left ventricular fibers, both at the basal and distal apical segment levels, explain Torrent Guasp’s myocardial band model. The author considered that the ventricular myocardium is formed by an assembly of muscle fibers coiled unto themselves as a rope (rope theory) (Figure 1.4) and flattened laterally to form a band, which by giving two spiral turns describes a helix limiting the two ventricles and defining their function. In turn, the phylogenetic study allows to theoretically understand, through the 600 million-year evolution of the circulatory system, that the ends of the band are located at the root of the great vessels, as it is formed from a loop of the primitive circulatory duct. (109)

      Figure 1.14. Segment sequence from the myocardial band histological analysis.

      The muscle shaping the right ventricle corresponds to the origin of the myocardial band (right segment), which begins both in the cardiac fulcrum as in the fibrous structures related with the pulmonary artery and the tricuspid annulus (pulmo-tricuspid cord) (Figures 1.15 to 1.17). The ascending segment, which is part of the autochthonous muscle bundles constituting the left ventricle, ends at the base of the aorta, and the cardiac fulcrum constitutes a solid point of attachment of the end of the myocardial band.

      Figure 1.9 demonstrates that the aortic annulus is not continuous. Its circumference is interrupted between the ends of the trigones, in the region where the mitral valve anterior cusp is inserted. Our research has demonstrated that in the course of the aortic annulus septal segment, extending from the left to the right trigone, there is a thickening we have called cardiac fulcrum (below and in front of the right trigone) where most of the myocardial band is attached, since as any muscle needs a supporting point to develop the leverage required to fulfill its function.

      The insertion of the myocardial fibers in the fibrous skeleton of the heart has been considered for three centuries. The development of the myocardial band reported in 1970 by Torrent Guasp (106-108) indicates in the anatomical research that it originates and ends at the root of the great vessels, but that the fibers do not insert in the atrioventricular annuli. The myocardium attaches to these annuli but does not insert in them. In our investigations we have not found insertion of cardiomyociytes in the collagen matrix of the trigones (Figure 1.39).

      However, Torrent Guasp considered that the myocardial band lacked a fixed supporting point as those present in the muscular system to develop force. In this sense, he assumed that it behaved as the circular muscle of the arteries, finding support in its own chamber blood content (hemoskeleton). In our research, we have always considered that the myocardial band should have a fixed point of attachment to allow its helical rotation in order to achieve its motions and the essential muscle force of shortening-twisting and lengthening-untwisting. The study of a supporting point in the myocardial band finds correlation with an organic engine, such as the heart, which without a firm attachment to a resistant nucleus would lack the necessary mechanical faculties for its considerable power.

      Figure 1.15. Detail of the pulmo-tricuspid cord between the tricuspid orifice and the pulmonary artery where the myocardial band begins. The circle shows the site of the cardiac fulcrum, which is visualized when the pulmonary artery and the pulmo-tricuspid cord are removed from their insertion at the beginning of the myocardial band unfolding (observe figure 1.27). The right coronary artery has been cut to reveal the cord trajectory (bovine heart).

      This point of attachment implies, as in any muscle, its ability to achieve the necessary leverage and also to act as a bearing or pad, preventing the force of ventricular rotation, either by torque or torsion strain from transferring to the aorta, thus dissipating the energy produced by the helical muscle motion, and avoiding aortic constriction or bending during systolic ejection. (134)

      Young bovine and human hearts (from spontaneous abortion fetuses, explanted adult hearts and cadaveric hearts retrieved from the morgue) were used to study the myocardial band insertion. The dissection was performed as described in Section 4: “Anatomy of the cardiac band. Dissection”, of this same chapter.

      In anatomical investigations we have found in all the bovine and human hearts studied a nucleus underlying the right trigone, whose osseus, chondroid or tendinous histological structure depends on the specimen analyzed, and is oriented towards the muscle fibers of the ascending segment which intimately penetrate its structure to attach themselves. This point of attachment would serve to support both the origin and end of the myocardial band, as the fibers that initiate the right segment, origin of the myocardial band, attach to the anterior part of this nucleus as well as to the pulmo-tricuspid cord (Figure 1.16).

      Figure 1.16. Descriptive photograph of the muscle bundles emerging from the cardiac fulcrum, which belong to the right segment forming the right ventricle (transverse section of a bovine heart).

      This osseus, chondroid or tendinous attachment point is found in the vicinity of the tricuspid valve (right), the aorta (posterior) and the pulmo-tricuspid cord (anterior) (Figure 1.20). To find it, it is necessary to unfold the myocardial band and move the pulmonary artery, the pulmo-tricuspid cord and the right segment to the left of the observer, stripping the root of the aorta (as a scarf that separates from the neck). Next, the muscular plane of the descending segment is separated from that of the ascending segment to follow the latter up to its insertion in the cardiac fulcrum. This maneuver reveals the fulcrum in front of the aorta and below the right trigone and the origin of the right coronary artery (Figures 1.18 and 1.19), detached from the aortic continuity and inserted as a complementary element between the aorta and the myocardium. This structure, origin and end of the myocardial band, has a more rigid consistency than the trajectory between the trigones.

      Figure 1.17. Panoramic view of the pulmo-tricuspid cord.

      An osseus formation, called os cordis, in bovine and sheep hearts, is reported in the veterinary literature in the same location where we have studied this structure both in bovids and humans. (69, 134) Beyond its mere mention in bovids, no reason for its presence or function was ever assigned to this structure, and it has not been described in humans. In bovids, its consistency is osseus at palpation, which has been confirmed by histological studies, and its size, according to our studies, is of approximately 45 mm × 15 mm, being its triangular shape (Figure 1.20).

      Figure 1.18. The figure shows the ascending segment, which is going to insert in the cardiac fulcrum (bovine heart) (see Figure 1.19).

      Figure 1.19. Cardiac fulcrum below the right trigone (bovine heart). The insert shows the resected piece.

      Figure 1.20. Resected cardiac fulcrum

      (bovine heart).

      The findings in the human hearts are surprising from the point of view of interpretation, since it is logic to consider its presence in all the evolutionary mammalian chain. It should be assumed that this structure, analyzed in different species, has the common function of providing support to the myocardial band to generate the power needed by any muscle, which is different in diverse mammals. Therefore, its presence is constant in all the hearts studied, both in bovids and humans, but its structural characteristic is different, and this diversity in the intimal analysis of the cardiac fulcrum