Vijayamma Kunnath Narayanan1, Ushavathy Padmanabhan2

Myocardial bridges are bands of cardiac muscle fibers, which bridges across the coronary arteries and its main branches. It is considered as a congenital anatomical variant mainly seen across the left anterior descending artery. Myocardial bridges may cause coronary heart disease either by compressing the underlying artery during cardiac systole or inducing atherosclerotic changes in the artery proximal to the myocardial bridge. The degree of coronary obstruction depends on the position, length, breadth and thickness of the muscle bridges. In this study, the myocardial bridges over the two coronary arteries and its main branches, gross anatomical changes of the tunnelled arteries and coronary dominance were observed.
Ninety human heart specimens including five foetal were collected and fixed in 10% formalin. Coronary arteries were traced and myocardial bridges were looked for along the course of the artery and its position, type, measurements and dominance were tabulated. The gross features of the tunnelled arteries were also observed.
The incidence of myocardial bridges in 90 heart specimens was 63.3%. It is most prevalent in the middle third of the Left Anterior Descending (LAD) artery 61.4%. The percentage bridges over Posterior Descending Artery (PDA) 15.79, right coronary artery 7, left circumflex 8.77 and diagonal 7 were tabulated. The average length, breadth and thickness of MB in LAD was 38 mm x 10 mm x 2 mm. The largest and deep bridges were noticed over the diagonal artery with an average measurement of 45 mm x 25 mm x 20 mm. Right coronary dominance was observed in 77.12% hearts having MB.
Myocardial bridges are congenital anatomical variants and asymptomatic when it is thin and superficial. But, it produces coronary arterial compression and haemodynamic changes when it appears thick and deep. Myocardial bridges are more common in middle third of the LAD and also found in multiple sites in the same LAD and other branches. The association of right dominance with myocardial bridges in LAD may protect the myocardium from ischaemic changes.