[Etiology].
The pathogenesis of coronary atherosclerosis is complex and not yet fully understood. According to a large number of epidemiological and experimental studies, the main causative factors are: high-calorie, high-fat, high-sugar diet, smoking, high blood lipids, hypertension, diabetes, obesity, low physical activity, intense mental work, emotional stress, mental tension, middle-aged and older men, low high-density lipoprotein, abnormal coagulation function, etc. In a few cases, there may be familial genetic factors. Xiao Shiliang, Department of Cardiac Surgery, Wuhan Union Medical College Hospital
[Pathological changes
Coronary artery anatomy: Coronary artery is the blood vessel supplying blood and oxygen to the heart muscle, and its anatomical form is quite variable. Under normal circumstances, there are two branches of coronary artery, left and right, which open to the left and right coronary sinus of ascending aorta respectively, and sometimes another smaller coronary artery is issued from the aorta.
The left coronary artery trunk is about 4-5 mm in diameter and 0.5-2 cm in length. After issuing from the ascending aorta, it travels downward to the left behind the common pulmonary artery trunk and divides into the anterior descending branch and the gyrus branch along the left atrioventricular sulcus between the common pulmonary artery trunk and the left auricle.
The anterior descending branch is a continuation of the main trunk of the left coronary artery and travels down the anterior interventricular sulcus, then around the apical notch to the posterior wall of the heart, where it coincides with the posterior descending branch of the right coronary artery in the lower 1/3 of the posterior interventricular sulcus. The anterior descending branch gives off branches such as the left conical branch, the oblique branch, the anterior left ventricular branch, the anterior right ventricular branch and the anterior septal branch. The blood supply area includes the root of the aorta and the common pulmonary artery trunk, part of the left atrial wall, the anterior left ventricular wall, part of the anterior right ventricular wall, most of the ventricular septum (upper and anterior), the apical region and the anterior papillary muscle.
The gyral branch emanates from the left coronary artery trunk and travels along the left atrioventricular sulcus immediately anterior to the base of the left auricle, to the left and back, and then down through the left edge of the heart to the diaphragm. The main branches are several left marginal branches, posterior left ventricular branches, and atrioventricular branches along the left atrioventricular sulcus. The atrioventricular branches are sometimes (about 10%) longer, and from their ends they give rise to the posterior descending branches and the atrioventricular node artery. 30% of humans have a gyral branch that also gives rise to the sinus node artery. The gyral branches supply the lateral and posterior walls of the left ventricle, the left atrium, and sometimes the diaphragmatic surface of the ventricle, the anterior and posterior papillary muscles, part of the ventricular septum, the AV node, the AV bundle, and the sinoatrial node.
The right coronary artery emanates from the right coronary valve sinus close to the base of the right auricle and travels outward and downward along the right atrioventricular sulcus. It reaches the posterior junction of the ventricle, atrium, and interventricular septum with the ventricular septum in the atrioventricular sulcus and divides into two branches, the right posterior descending branch in the posterior interventricular sulcus toward the apical region, and the other smaller atrioventricular node artery that turns upward. The main branches of the right coronary artery include the right conus branch, right atrial branch, sinus node branch, right anterior ventricular branch, right posterior lateral ventricular branch, posterior septal branch, posterior descending branch, and AV node artery. The right coronary artery supply area includes the right atrium, sinus node, right ventricular outflow tract, pulmonary cone, anterior right ventricular wall, posterior right ventricular wall, inferior 1/3 of the ventricular septum, and atrioventricular node. Patients with a predominant right coronary artery also supply blood to part of the left ventricle and the apical portion of the heart. The distribution of the right and left coronary arteries on the diaphragmatic surface of the myocardium is quite variable, and when a stenotic lesion occurs in a coronary artery branch with a larger blood supply, the area of myocardial ischemic injury is more extensive and more severe (Figure 3).
(1) Anterior view (2) Posterior view
(3) Right anterior oblique view (4) Left anterior oblique view
Figure 3 Coronary artery anatomy
[Typing].
The distribution of the left and right coronary arteries can be divided into three main types according to the source of blood supply in the cross region of the heart, i.e., the intersection of the ventricles, atria and atrial septum on both sides of the posterior wall of the heart.
(1) Right coronary artery dominant type This type is the most common, accounting for about 80%. The right coronary artery is thick and long, supplying blood to the posterior wall of the right ventricle and crossing the cardiac cross by the posterior descending branch to part of the posterior wall of the left ventricle and the posterior part of the ventricular septum.
2) Dominant left coronary artery The right coronary artery is small, and the posterior descending branch from the left coronary artery emanates to supply blood to the posterior wall of the left and right ventricles and the ventricular septum.
(3) Left and right coronary artery homogeneous type The left and right coronary arteries each send a posterior descending branch to supply blood to the posterior wall of the left and right ventricles (Figure 4).
(1) Right coronary artery dominant type
(2) Left coronary artery dominant type
(3) Homogeneous left and right coronary arteries
Figure 4 Distribution types of left and right coronary arteries
Pathological anatomy: Most of the coronary atherosclerotic lesions occur in the proximal segment of the main branches of the coronary arteries, within about 5 cm from the opening of the aorta, often located in the atrioventricular groove, surrounded by the main branches of the coronary arteries surrounded by adipose tissue, and the lesion sites provide favorable conditions for surgical treatment. In cases with hypertension or diabetes, the lesion is extensive and can involve small branches of the coronary arteries. Atherosclerotic lesions mainly involve the coronary artery intima. In the early stage of the lesion, lipid and lipid-containing macrophages infiltrate the intima and mesangial cells, and the intima thickens with yellow spots. With endothelial cell injury and increased intimal permeability due to multiple causes, lipid infiltration increases and the spots gradually increase and enlarge, forming plaques or streaks. Focal dense lamellar collagen also appears in the intima, and lesions involving the entire perimeter of the intima result in luminal narrowing or obstruction. The lesioned coronary artery has reduced blood flow, and the local myocardial blood and oxygen supply is insufficient during exercise or even at rest, which may lead to myocardial infarction in severe cases. Coronary atherosclerotic lesions can be complicated by bleeding, thrombosis and aneurysm. When atherosclerotic lesions rupture and bleed, lipids enter the vascular lumen, easily causing distal vessel embolism and inducing thrombosis, and vessel wall hematoma may in turn gradually form granulation tissue and fibrosis. The acute phase of endothelial hemorrhage may induce spasm of the coronary arteries and branches of the collateral circulation, aggravating the degree of myocardial ischemia. Thrombosis often exists in combination with hemorrhage and may lead to distal vessel embolism and vessel wall fibrosis. In most cases, aneurysms occur in only one vessel, with a diameter of up to 2.5 cm, and the lumen may contain blood clots, but the vessel lumen remains open. If atherosclerotic lesions cause coronary artery stenosis that is limited to only one branch of the coronary artery and develops slowly, the traffic branch between the lesioned vessel and the adjacent coronary artery is significantly dilated and an effective collateral circulation can be established, and the myocardium in the affected area can still receive adequate blood supply. If the lesion involves more than one vessel, or if the stenosis progresses faster, the collateral circulation is not fully established, or if the cake emits blood, hematoma, thrombosis, or spasm of the vessel wall, it may lead to severe myocardial ischemia, or even myocardial infarction. Myocardial atrophy, or even necrosis to the point of rupture or subsequent formation of fibrous scars in the lesioned area may result in severe impairment of myocardial contractile function, resulting in arrhythmia or cardiac pumping failure. The greater the extent of myocardial ischemia, the more serious the damage caused. The left coronary artery supplies the most blood flow to the coronary circulation, therefore, the heart disease caused by obstruction of the left coronary artery and its branches is more serious than that of the right coronary artery.