Coronary arteries typically run through the connective tissue beneath the epicardium. However, when a segment of a coronary artery passes through the myocardium, the overlying bundle of myocardial fibers is referred to as a myocardial bridge, and the coronary artery segment beneath it is called a tunneled artery. This condition is most observed in the midsection of the left anterior descending artery (LAD). On coronary angiography, the tunneled artery appears compressed during systole and returns to normal or shows significantly reduced compression during diastole, a phenomenon known as milking effect. The detection rate of myocardial bridges on coronary angiography ranges from 0.51% to 16%, while autopsy studies report a much higher prevalence of 15%-85%, indicating that most myocardial bridges are clinically insignificant.
Since the tunneled artery is compressed during systole in each cardiac cycle, severe compression can lead to distal myocardial ischemia. Clinically, this may manifest as angina-like symptoms, arrhythmias, or even acute myocardial infarction (AMI) or sudden cardiac death. Additionally, the systolic compression caused by the myocardial bridge can result in retrograde blood flow in the proximal segment, damaging the endothelium at that location and increasing the risk of atherosclerotic plaque formation in the proximal segment.
Medications such as beta-blockers and calcium channel blockers, which reduce myocardial contractility and heart rate, can effectively alleviate symptoms. However, stent implantation is generally not recommended due to the increased risks of coronary perforation, intimal hyperplasia, and restenosis. Surgical unroofing of the tunneled artery (myotomy) was once considered a definitive treatment, but cases of recurrence have been reported. Additionally, since diastolic perfusion pressure in the tunneled artery is not significantly reduced, bypass grafts have a high occlusion rate after surgery. Therefore, medical therapy remains the primary treatment for myocardial bridges. Patients with significant systolic compression should avoid strenuous exercise. For those who continue to experience ischemic symptoms despite medical therapy and have severe diastolic compression of the tunneled artery, internal mammary artery bypass surgery may be considered.
Unless absolutely necessary, the use of nitrates and positive inotropic agents should be avoided.