Ultra-Structural Alteration of Human Coronary Arterial Endothelium with Myocardial Bridge

Abstract

The cardiac muscle fibre over the segment of the coronary artery was known as “myocardial bridge”. The myocardial bridge was associated with coronary atherosclerosis and myocardial ischemia because of endothelial damage of coronary with myocardial bridge. The present study explored the ultrastructural changes of coronary arterial endothelium in human adult autopsy hearts with the myocardial bridge. The aim of the study is to compare the scanning electron microscopic features of the endothelium and calcium depositions between four segments of the coronary artery. The sample was collected from North Okkalarpa General and Teaching Hospital, Yangon. Forty-five adults autopsied hearts with myocardial bridge among the 243 cases had measured the length and thickness of the myocardial bridge. Then, four pieces of the coronary artery were taken in proximal, under, and distal segments of the coronary artery with a myocardial bridge and a segment from the coronary artery without a myocardial bridge in the same autopsy hearts to be used as control. The endothelial features and elements composition of each specimen was examined with a scanning electron microscope (Phenom Pro X) operated at 15 kV with energy dispersion X-ray spectrometry (EDS). In the present study, forty-five bridges (18.5%) were observed among the 243 hearts and there were located on the Left Anterior Descending Artery (LAD) (100% in all cases. The mean length of the myocardial bridge was 18.3 mm \(\pm\) 11.7 (range 1.5-59 mm). The mean thickness of the myocardial bridge was 2.8 mm \(\pm\) 1.5 (range 1-6.3 mm). Comparing endothelial cell gradings, the proximal segment was significantly different endothelial grading from the under-bridging segment, distal segment, and control segment. The under-bridging segment was significantly different from the distal segment. The control segment was not significantly different from both the under-bridging segment and the distal segment. Calcium deposition in the proximal segment was significantly different from the under-bridging segment, distal segment, and control segment. The under-bridging segment was a similar deposition of calcium in the distal segment and control segment. The distal segment was not significantly different from the control segment (P<0.05).

The proximal segment was the most endothelial damage site due to haemodynamic changes affected by the myocardial bridge. The under-bridging segment was the least endothelial damage site which might be due to the atheroprotective effect of the myocardial bridge in the under segment.