1.Myocardial bridge overview (what is myocardial bridge?) The coronary artery and its branches usually travel in the subepicardial fat on the surface of the heart or in the deep epicardial surface. When a section of the coronary artery is surrounded by myocardium, the section of myocardium is called myocardial bridge and the section of coronary artery is called wall coronary artery. 2, myocardial bridge signs and symptoms (what are the symptoms of myocardial bridge?) Wall coronary artery and myocardial bridge coronary artery origin is normal, and there is no abnormal channel and other congenital malformations, some epicardial coronary artery proximal or middle section is covered by superficial myocardium, after a short distance and then exposed outside the myocardium. The coronary artery segment covered by myocardium is called wall coronary artery or intratunneled major coronary artery, and the superficial myocardium overlying the coronary artery is called myocardial bridge. Wall coronary arteries can also be seen in left diagonal branches or left obtuse marginal branches. Wall coronary artery segments are generally less susceptible to atherosclerotic lesions, but the proximal end of the wall coronary artery is susceptible to atherosclerosis due to higher intraluminal pressure in the lumen of the myocardial bridge than normal coronary artery and higher than intra-aortic pressure. Coronary angiography reveals that the lumen of the wall coronary artery is significantly smaller in the systolic phase of the heart than in the diastolic phase, and in mild cases the diameter is 60% to 70% of that in the diastolic phase, and in severe cases it is only 25% or less, or even completely occluded. According to the data of Fu Wai Cardiovascular Hospital, the systolic lumen of the wall coronary artery in 123 cases was less than 25% of the diastolic lumen in 18 cases (14.6%), especially in patients with myocardial hypertrophy in which the systolic lumen was significantly compressed. In those with systolic lumen less than 25% of diastolic lumen,201 thallium (201Tl) exercise myocardial perfusion imaging and coronary sinus pacing metabolites showed myocardial ischemia. The majority of coronary perfusion is in diastole, and systolic compression alone may cause myocardial ischemia due to abnormal wall coronary artery tone or spasm, and in some symptomatic patients may be due to prolonged coronary artery compression into early diastole or excessive myocardial oxygen consumption with left ventricular hypertrophy. The clinical presentation of myocardial bridges is closely related to the staging. (1) Superficial type Because the myocardial bridge is thin and short, it has less influence on coronary blood flow, and most of them can have no myocardial ischemic symptoms and corresponding electrocardiographic changes. (2) Longitudinal type Because the myocardial bridge is thick and long, it has great influence on the coronary blood flow, and angina pectoris and ST-T changes of myocardial ischemia appear on the ECG. If myocardial bridge is complicated by coronary atherosclerosis secondary to thrombosis or plaque dislodgement, clinical symptoms of myocardial infarction and corresponding ECG changes may occur. Myocardial ischemia is more likely to occur when myocardial bridges are combined with tachyarrhythmias. (3) Diagnostic tests for myocardial bridge (what tests are needed to confirm the diagnosis of myocardial bridge?) Diagnosis: In addition to clinical symptoms and corresponding electrocardiographic changes, the diagnosis of myocardial bridge still depends on coronary angiography and intracoronary Doppler and ultrasound examinations. The diagnosis of myocardial bridges is difficult. Superficial types are difficult to diagnose because of asymptomatic or mild symptoms, and even coronary angiography can only detect those with longitudinal myocardial bridges. This can also explain why there is such a big difference in the detection rate of myocardial bridges in autopsy and coronary angiography. (1) Coronary angiography If systolic stenosis or delayed diastolic relaxation of coronary arteries is found, it indicates the presence of myocardial bridges. However, coronary angiography can only detect myocardial bridges that have a significant effect on coronary blood flow. The detection of myocardial bridges is related to their length, the direction of travel of the bridging fibers, and the organization between the myocardial bridge and the associated artery. Some myocardial bridges are difficult to detect on angiography because of almost complete occlusion of the proximal coronary artery or because fixed stenosis from atherosclerosis limits coronary perfusion and obscures the systolic stenosis, or because of the presence of vasospasm. Coronary angiography often fails to detect atherosclerotic stenoses at myocardial bridges. (2) Intracoronary Doppler examination reveals a significant increase in coronary flow velocity in the early diastolic phase of the myocardial bridge section as a peak, followed quickly by a decline and then a plateau until it declines again in systole. The peak is due to the presence of the maximum perfusion pressure in the coronary artery and the corresponding continuous reduction of the vascular area, resulting in a significant pressure step difference between the two ends of the myocardial bridge. When the myocardial bridge relaxes in diastole, the pressure step difference between the two ends disappears, the vascular area expands rapidly, and the flow velocity decreases quickly. (3) Intravascular ultrasound reveals frequent atherosclerosis formation in the coronary arteries proximal to the myocardial bridge. Reduced intracoronary flow reserve is detected by intracoronary Doppler. 4.Myocardial bridge treatment plan (how to treat myocardial bridge?) For symptomatic myocardial bridges and those with atherosclerotic plaques at myocardial bridges, pharmacological or surgical treatment can be used. (1) Pharmacological treatment Angina pectoris caused by systolic wall coronary artery compression may be effective with beta-blockers and calcium antagonists such as verapamil (isoptin) and diltiazem. (2) Surgical treatment Surgical treatment should be performed if the angina is difficult to be controlled by medication. There are two types of surgery, namely myocardial bridge resection and coronary artery bypass grafting. Myocardial bridge resection: For superficial type, the myocardial bridge is found under general anesthesia at room temperature and removed to completely relieve the compression of the coronary artery and restore its distal blood flow. Myocardial bridge resection alone is rare and is often performed in conjunction with coronary artery bypass grafting. ② Coronary artery bypass grafting: It is suitable for longitudinal type or combined with atherosclerotic stenosis. Coronary artery bypass grafting can be performed under normothermic general anesthesia, normothermic extracorporeal circulation or hypothermic extracorporeal circulation. The graft material can be autologous saphenous vein or internal mammary artery. 5.Myocardial bridge prevention and prognosis (how to prevent myocardial bridge?) Prognosis: Myocardial bridges generally have a good prognosis, but about 12% of those with uncomplicated coronary atherosclerosis have angina symptoms, occasionally causing acute myocardial infarction, post-exercise ventricular tachycardia or sudden death, so myocardial bridges are not always benign. Angina caused by systolic wall coronary artery compression may be effective with beta-blockers and calcium antagonists such as verapamil and diltiazem. If drug therapy is ineffective, a simple procedure of myocardial bridge removal from the wall coronary artery or stent implantation in the wall coronary artery may be considered to relieve symptoms. If atherosclerotic stenotic lesions are present in the coronary arteries proximal to the myocardial bridge, percutaneous intracavitary balloon dilation should be performed, with attention to the potential risk of thrombosis in the mural coronary arteries. Prevention: Because myocardial bridges are a relatively common congenital anatomical malformation, there are no effective preventive measures. Care should be taken to prevent various risk factors for coronary artery disease and to prevent atherosclerosis of the coronary arteries, which can further aggravate the condition.