Significance of myocardial bridge upon atherosclerosis in The LAD coronary artery

冠状动脉左前降支在心外膜脂肪组织中走行的一部分常被心肌组织覆盖。这种情况被称为心肌桥（MB）。我们之前已经注意到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MB对动脉粥样硬化的保护作用。MB下方内膜厚度明显薄于MB入口前和出口后内膜厚度。它仅由几层平滑肌细胞和少量胶原纤维和基质组成。所有的平滑肌细胞都有收缩的形态。此外，不仅没有脂质沉积，而且不存在来自巨噬细胞或平滑肌细胞的两种类型的泡沫细胞。扫描电镜下可见梭形内皮细胞沿冠状动脉的走行沿着轴向规则排列。这表明血流在MB下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.