myocardial bridge
Introduction
Introduction to myocardial bridge The myocardial bridge is a congenital vascular malformation. Coronary artery and its branches usually walk in the subepicardial fat on the surface of the heart or deep in the epicardium. When a coronary artery is surrounded by the myocardium, this segment of the myocardium is called a myocardial bridge. The coronary artery is called a wall coronary artery. artery. Myocardial bridge may be related to the local factors of coronary heart disease, and may also cause myocardial ischemia. The coronary artery covered by the myocardial bridge during compression of the heart is compressed, and systolic stenosis occurs, and coronary artery compression is relieved when the heart is dilated, and coronary artery stenosis is also relieved. basic knowledge The proportion of illness: 0.004% Susceptible people: no special people Mode of infection: non-infectious Complications: angina pectoris myocardial infarction arrhythmia sudden death
Cause
Myocardial bridge etiology
Congenital factors (70%)
Myocardial bridge is a common congenital anatomic deformity. The cause is the intramyocardial segment of the coronary artery, especially the intramyocardial segment of the left anterior descending artery. It can be squeezed during systole, and myocardial ischemia occurs after middle age. symptom.
Pathogenesis
The direction of myocardial bridge myocardial fibers is at a right angle to the long axis of the anterior descending and posterior descending branches, while the right anterior branch and the left anterior branch are at a smaller angle. The cross-section of the wall coronary artery shows that the lumen is small and the wall is thin. When the myocardial bridge is thicker, the wall coronary artery segment is less likely to form atherosclerosis, and the proximal and distal endothelium are often seen. Atherosclerosis. Due to the above anatomical features, when the heart contracts, the myocardial bridge compresses the wall coronary artery, causing the lumen to be further narrowed. The longer and thicker the myocardial bridge, the greater the angle between the myocardial fibers and the blood vessels, and the heavier the wall coronary artery stenosis. The more severe the distal myocardial ischemia, even the myocardial infarction.
Prevention
Myocardial bridge prevention
Because myocardial bridge is a common congenital anatomic deformity, there are no effective preventive measures at present. It should pay attention to prevent various risk factors of coronary heart disease and prevent atherosclerosis of coronary artery, because it can further aggravate the condition.
Complication
Myocardial bridge complications Complications, angina pectoris, myocardial infarction, arrhythmia, sudden death
There are complications such as angina, less myocardial infarction, and occasional arrhythmia and sudden death after exercise.
Symptom
Myocardial bridge symptoms common symptoms cardiac hypertrophy arrhythmia myocardial ischemia ECG abnormal atherosclerosis angina pectoris myocardial infarction
The coronary artery and the myocardium of the myocardium originate normally, and there are no congenital malformations such as abnormal passages. Some of the epicardial coronary arteries are covered by superficial myocardium in the proximal or middle part of the coronary artery. After a short distance, they are exposed to the myocardium. The covered coronary artery segment is called the wall coronary artery or the intra tunneled major coronary artery, and the superficial myocardium covering the coronary artery is called the muscle bridge.
The wall coronary artery can also be seen in the left diagonal branch or the left blunt edge branch. The wall coronary artery segment is generally less prone to atherosclerotic lesions, but the proximal wall of the coronary artery is prone to atherosclerosis due to the proximal end of the muscle bridge. The pressure is higher than the normal intracoronary pressure and higher than the intra-aortic pressure. Coronary angiography shows that the wall coronary artery lumen is significantly less than the diastolic phase during the systole, and the lighter diameter is 60%-70 of the diastolic phase during the systolic phase. %, the severity is only 25% or less, or even completely occlusion. According to the data of the Department of Cardiovascular Hospital, 123 cases of wall systolic systolic lumen were less than 25% of the diastolic lumen (18.6%), especially Patients with cardiac hypertrophy had significant luminal compression during systole, and the systolic diameter was less than 25% of diastolic phase. 201(201Tl) motor myocardial perfusion imaging and coronary sinus pacing metabolites showed myocardial ischemia. Most coronary perfusion is in the diastolic phase. The cause of myocardial ischemia caused by simple systolic compression may be abnormal or paralyzed wall coronary artery tension. Some patients with symptoms may have coronary artery pressure extended to early diastolic or Left ventricular hypertrophy due to an excess of myocardial oxygen consumption.
The clinical manifestations of myocardial bridges are closely related to typing.
1. Superficial type due to thin and short myocardial bridge, has little effect on coronary blood flow, most of which may have no myocardial ischemia symptoms and corresponding ECG changes.
2. The depth type is long due to the thickness of the myocardial bridge, which has a great influence on the coronary blood flow, and angina pectoris occurs. The ECG shows ST-T changes of myocardial ischemia. If the myocardial bridge is complicated by coronary atherosclerosis, thrombosis or plaque Shedding, that is, the clinical symptoms of myocardial infarction and the corresponding changes in electrocardiogram, myocardial ischemia and rapid arrhythmia are more likely to appear myocardial ischemia.
Examine
Myocardial bridge examination
1. Coronary angiography: If coronary systolic stenosis or delayed diastolic relaxation is found, it suggests the presence of myocardial bridge, but coronary angiography can only detect myocardial bridges that have a significant effect on coronary blood flow, myocardial The detection of the bridge is related to its length, the direction of the muscle bridge fibers, and the myocardial bridge is related to the tissue between the related arteries. Some myocardial bridges limit the crown due to the almost complete occlusion of the proximal coronary artery or the fixed stenosis caused by atherosclerosis. Blood flow perfusion masks the systolic stenosis, or because of the presence of vasospasm, angiography is difficult to find, coronary angiography often can not find atherosclerotic stenosis at the myocardial bridge.
2. Intracoronary Doppler examination: It was found that the coronary blood flow velocity of the myocardial bridge was significantly increased in the early stage of diastole, and then decreased rapidly, followed by a platform until the systolic phase decreased again. The peak appeared. Due to the presence of the maximum perfusion pressure in the coronary artery and the corresponding decrease in the vascular area, a significant pressure gradient occurs at both ends of the myocardial bridge. When the diastolic phase of the myocardial bridge is relaxed, the pressure gradient at both ends disappears and the vascular area is rapid. Expanded, blood flow rate also dropped quickly.
3. Intravascular ultrasound: It can be found that atherosclerosis often occurs in the proximal coronary artery of the myocardial bridge, and intracoronary Doppler induces a decrease in coronary blood flow reserve.
Diagnosis
Myocardial bridge diagnosis
In addition to clinical symptoms and corresponding ECG changes, myocardial bridge diagnosis depends on coronary angiography and intracoronary Doppler and ultrasonography.
The diagnosis of myocardial bridge is difficult. The superficial type is difficult to diagnose because of asymptomatic or mild symptoms. Even coronary angiography can only detect those deep myocardial bridges. This may explain why myocardial bridges in autopsy and coronary angiography. There is such a big difference in the detection rate.
