Significance of anatomical properties of myocardial bridge on atherosclerosis evolution in the left anterior descending coronary artery.

Myocardial bridge (MB) is frequently detected in the left anterior descending coronary artery (LAD), and LAD intima under MB is significantly spared from atherosclerotic evolution. Significance of anatomical features of MB on the extent of atherosclerosis of LAD was histomorphometrically investigated. Full-length 200 LADs with MB and 100 control LADs without MB were cross-sectioned at 5 mm intervals, and atherosclerosis ratio and intimal lesion types were evaluated. In cases with MB located within 5 cm from the left coronary ostium, atherosclerosis ratio in the proximal part of LAD was significantly lower than in control group, but, in cases with MB locating more than 5 cm from the ostium, atherosclerosis ratio in this part was similar to that in control cases. MB thickness was significantly correlated with its length, and the longer the MB the more proximally it tended to be located in LAD. Atherosclerosis ratio under MB was lower in cases with thick or long MBs than in cases with thinner or shorter MBs. In addition, intimal lesion in segments proximal to MB tended to be eccentric. Our results suggest that these anatomical properties of MB are the critical modulators for atherosclerosis evolution in the entire course of LAD.