Histopathologic profiles of coronary atherosclerosis by myocardial bridge underlying myocardial infarction.

Objective: Anatomic properties of myocardial bridge (MB) are sometimes responsible for myocardial infarction (MI) through the changes in the atherosclerosis distribution in the left ascending coronary artery (LAD). The purpose of this study was to investigate histopathologic profiles of atherosclerotic lesions resulting from the MB presence in the LAD in the MI cases.

Methods: In 150 consecutive autopsied MI hearts either with MBs [MI(+)MB(+); n = 67] or without MBs [MI(+)MB(-); n = 83] and 100 normal hearts with MBs [MI(-)MB(+)], LADs were consecutively cross-sectioned at 5-mm intervals. The most advanced intimal lesion and unstable plaque-related lesion characteristics (UPLCs) in each section were histopathologically evaluated in conjunction with the anatomic properties of the MB, such as its thickness, length, location, and MB muscle volume burden (MMV: the total volume of MB thickness multiplied by MB length).

Results: The MB showed a significantly greater thickness (P = 0.0090), length (P = 0.0300), and MMV (P = 0.0019) in MI(+)MB(+) than in MI(-)MB(+). Mean age of acute MI cases was significantly younger (P = 0.0227) in MI(+)MB(+) than in MI(+)MB(-). Frequency of plaque fissure/rupture in the proximal LAD was significantly higher in acute MI cases of MI(+)MB(+) than in MI(+)MB(-). UPLCs tended to be located proximally in MI(+)MB(+) and frequent 2.0 cm or more proximal to the MB entrance in MI(+)MB(+).

Conclusion: In MI(+)MB(+), UPLCs tend to be located more proximally, and a plaque in the LAD proximal to the MB is prone to rupture, resulting in MI at younger age.