Myocardial Bridge Muscle on Left Anterior Descending Coronary Artery Differs from Subepicardial Myocardium of the Left Ventricle in Dogs

Abstract

The myocardial bridge (MB) is a muscle band found sporadically above the coronary artery (CA) in humans and certain animals such as the dog, cat and sheep. The purpose of our study was to compare the structure of the MB muscle with that of tissue from the subepicardial myocardium. The histological studies included toluidine blue staining of 1-µm-thick sections and Gomori’s trichrome staining of canine cardiac samples. The MB muscle of the dog heart is characterized by a distinctive spatial arrangement, with individual fibers separated by substantial elements of intercellular connective tissue in cross-section. Longitudinally, the long, slender fibers are aligned continuously with intermediation of intercalated disks lying peφendicular to the long axis of the fibers. In other regions of the left ventricular subepicardial myocardium, each myocyte is tightly packed in transverse view. There is great variation in the thickness (0.11-2.24 mm, average 0.45 mm) of MBs and the distance (24-236 µm, average 103 µm) between MBs and the left anterior descending coronary artery (LAD) among the 13 affected dogs examined, with no apparent relationship between the occurrence of MBs and either age or sex. These results on MB alignment suggest that the MB muscle generates force along the long axis of the fiber orientation as skeletal muscle does, and with minimal constriction of the CA; if so, the function of MB myocytes may differ from that of common cardiac myocytes, as does the structure. Then, the long-supposed downward compressive force of MBs on the LAD would be minimal in most cases; however, when the MB produces a systolic narrowing of the LAD known as the milking effect, the degree of lateral compression and its influence should depend not only on the substantial size of the MB muscle but also on the distance between the MB muscle and LAD. The environment surrounding the LAD may be a crucial factor in determining whether the MB influences the induction of heart disorders or not.

Myocardial bridges over the ramus intervetricularis anterior and its branches in Cercopithecus aethiops sabeus

“…The most frequent position of MBs in regard to RIA of the LCA found in our study is similar to that reported by Yamaguchi et al, (1996) in dogs. It can be compared with the incidence of MBs reported in different species.…”

“…The frequency of MB, their location, morphology and clinical significance arouse some controversies (Nikoli} and Teofilovski Parapid, 1995;Nikoli} et al, 1996;Mohlenkamp et al, 2002;Bharambe and Arole, 2008). The same thing is with the most of the fundamental questions based in relation to hearts muscle coverage of coronary arteries (Morales et al, 1993), as whether MBs are normal variants of the coronary arteries anatomy (Yamaguchi et al, 1996) or are an anomaly. Angelini et al (2002) proposed that a coronary artery anomaly should be defined as any coronary pattern with a morphological feature encountered in <1%.…”

The investigation of perivasculary space under the myocardial bridge in different species

“…The myocardial bridges (MB) are defined as a short segment of the superficial muscular bands that run across coronary arteries (CA) (1–4). Myocardial bridge is a muscle band found sporadically above the CA in both humans and certain animals such as the dog, cat, sheep, goat, chimpanzee and orangutan (5–10).…”

Ponte miocárdica associada a lesões cardiovasculares em bovinos adultos da raça Canchim

“…the coronary artery 21 , and with results reporting that the presence of the myocardial bridge may influence the arterial tissue through haemodynamic forces alterations through its contractions 5 . Therefore, the highest obliquity of fibers 3 , as well as the environment in which this artery is involved [21][22][23] could be a compensatory disposition…”

“…Therefore, the highest obliquity of fibers 3 , as well as the environment in which this artery is involved [21][22][23] could be a compensatory disposition…”