Significance of myocardial bridge upon atherosclerosis in The LAD coronary artery

左冠状动脉前降支在心外膜脂肪组织中的一部分常被心肌组织所覆盖。这种情况称为心肌桥（MB）。我们之前注意到，被MB覆盖的LAD内膜从未受到动脉粥样硬化过程的影响。我们通过免疫组化和电镜观察了MB对动脉粥样硬化的保护作用。MB下的内膜厚度与MB入口前和MB出口后相比明显变薄，仅由几层平滑肌细胞组成，胶原纤维少，基质少。所有的平滑肌细胞都呈收缩状态。此外，不仅没有脂质沉积，而且巨噬细胞或平滑肌细胞衍生的两种类型的泡沫细胞都缺失。扫描电镜显示，冠状动脉内皮细胞呈梭形轴向排列，沿冠状动脉走行规律排列。这说明在MB作用下，血流交替进入高剪切应力状态。

A part of the left anterior descending coronary artery running in the epicardial adipose tissue is often covered by myocardial tissue. This condition is designated as myocardial bridge (MB). We have previously noticed that the intima of the LAD covered by MB is never affected by atherosclerotic process. We investigate such protective effect of MB against atherosclerosis by immunohistochemical and electron microscopy. The intimal thickness beneath MB is remarkably thin in comparison with that before the entrance of MB and after the exit of MB. It consists of only few layers of smooth muscle cell with few collagen fibers and little matrix. All of the smooth muscle cells there show contractile form. In addition, not only there is no lipid deposition, but both types of foam cells derived from either macrophage or smooth muscle cells are absent. By scanning electron microscopy, the spindle-shaped endothelial cells are axially and regularly arranged along the course of the coronary artery. This denotes that the blood flow alternates into the condition of high shear stress under the MB.