Coronary artery bypass grafting (CABG), also known as bypass surgery, has been proven to be one of the most effective treatments for coronary heart disease after nearly 30 years of clinical practice. In recent years, there has been a rapid development in the treatment of coronary artery disease. Along with the development of technologies such as percutaneous transluminal coronary angioplasty (PTCA), also known as stenting, CABG technology has also made great progress, especially the widespread use of arterial graft materials, the popularity of minimally invasive CABG, the increase in the success rate of surgery and the decrease in mortality, making CABG more competitive. Large domestic and international clinical studies have confirmed that CABG has a lower incidence of reoperation and better long-term results compared to PTCA. All this has led to a re-examination of the indications for the procedure. The clinical manifestations of coronary artery disease (CAD) are mainly angina pectoris, and due to the diversity of clinical manifestations of angina pectoris, the clinical typing of CAD is also diverse.
I. Clinical typing.
1. Asymptomatic or mild angina patients have coronary artery stenosis, but the patients have not been feeling angina, or only have chest discomfort during episodes of myocardial ischemia. Sometimes myocardial ischemia is so severe that there is no pain even during myocardial infarction (MI) episodes. These asymptomatic myocardial ischemic events can be detected before serious cardiac events, such as abnormal ECG, arrhythmias, and positive imaging results. The poor prognosis of multiple episodes of asymptomatic myocardial ischemia on the dynamic ECG and the recent increase in episodes of ST-segment depression identify these CAD patients as being at increased risk for subsequent cardiac events. Early morning or nocturnal episodes of asymptomatic ST-segment changes are almost always associated with left coronary artery trunk stenosis, 2- or 3-branch coronary artery disease. Patients with ST-segment depression induced by exercise testing are expected to have 4-5 times higher cardiac mortality.
2. Chronic stable angina with typical anginal symptoms that do not worsen significantly over a period of weeks. Typical symptoms occur with increased myocardial oxygen consumption and are quickly relieved by rest or nitrate medication. The ECG cannot confirm and exclude CAD , because it is not uncommon for a resting ECG to show normal myocardial blood supply even when the coronary atherosclerotic lesion is severe. However, other manifestations of CAD may be found. The sensitivity of exercise test ECG changes for the diagnosis of CAD is about 70% and the specificity is about 90%. Compared to exercise testing, ambulatory ECG is difficult to provide additional important clinical information. Echocardiography provides accurate and repeated measurements of cardiac size, wall thickness and LV systolic and diastolic function, pulmonary artery pressure, and identifies complications such as ventricular wall aneurysms and appendage thrombosis, mitral valve insufficiency, septal perforation, and calcified plaques in the ascending aorta and carotid arteries. In patients who cannot tolerate ECG exercise testing, dobutamine loading echocardiography can be used as a complementary method to observe the presence and location of myocardial ischemia during exercise. Radionuclide imaging has been a reliable noninvasive test for the diagnosis of coronary artery disease, the degree and extent of coronary artery lesions, myocardial viability, the estimation of therapeutic efficacy, and the prognosis. Coronary angiography is still the most reliable method for evaluating coronary artery lesions and is the main basis for drug therapy, interventional therapy and coronary artery bypass grafting (CABG) for coronary artery disease. Coronary artery enhancement CT can clearly show the degree and scope of coronary artery lesions, which is a more reliable, non-invasive and low-cost method to evaluate coronary artery lesions.
3.Unstable angina (UA)/non-ST-segment elevation myocardial infarction (NSTEMI)/non-Q-wave myocardial infarction (NQMI).
According to the Canadian Cardiovascular Society classification method, unstable angina (UA) includes:1. New onset angina: occurring in the last 1 month, with a tendency to worsen, degree 3 or more. 2. Aggravated angina: frequent episodes of previous angina, with prolonged duration and increased degree. 3. Resting angina: episodes of angina at rest, and lasting for 20 minutes or more. UA can be manifested on the ECG as ST-segment elevation, or no elevation. Most people with ST-segment elevation eventually develop Q-wave myocardial infarction (QMI), and a few develop NQMI. people without segment elevation often develop NQMI, and very few develop QMI. UA/NSTEMI/NQMI and QMI are a group of clinical syndromes with similar etiology and clinical manifestations, but different severity – acute coronary syndromes. The main difference between the two is whether the ischemia is severe enough to allow detection of the myocardial damage markers troponin I, T or CK-MB. UA is diagnosed when the marker concentration is normal, and NSTEMZ or NQMI when the marker concentration is above normal.
4, ST-segment elevation myocardial infarction/myocardial infarction with Q waves (STEMI/QMI) In the World Health Organization study on disease incidence, myocardial infarction (MI) is diagnosed with two of the following three characteristics: typical symptoms (angina lasting longer than 20 minutes) elevated myocardial marker concentrations and typical ECG manifestations of Q waves.
MI is caused by prolonged myocardial ischemia, resulting in myocardial cell death and complete necrosis of the affected myocardium, which takes at least 4-6 hours; it also depends on the persistence of coronary artery obstruction and collateral blood flow in the myocardial ischemic area. Infarcts are usually classified according to the size and location of the infarct and staged according to the pathological manifestations: acute phase (6h-7d), healed phase (8d-28d), and healed phase (more than 29d). However, it should be emphasized that the pathological changes of the staging are not the same as the clinical manifestations in time: if the pathology has shown that the infarct is in the healing phase, the ECG may still show progressive S-T segment changes. Cardiac troponin remains increased.
Echocardiography can clarify left ventricular function and the presence of mechanical complications of acute infarction such as left ventricular wall tumor, septal perforation, and mitral valve insufficiency.
When determining the treatment method, it is important to consider which is the most effective, lowest risk and least expensive treatment method for the patient compared with drug therapy, PTCA and CABG.
Coronary artery bypass grafting (CABG) is currently one of the most widely used surgical procedures with the best long-term outcome in China and abroad. The indications for the procedure are
1. Asymptomatic or mild angina pectoris
(1) Severe stenosis of the left main trunk and similar left main trunk lesions (70% or more stenosis of the proximal diameter of the left anterior descending and gyral branches) confirmed by coronary angiography, with distal patency and greater than 1.5 mm, are absolute indications for surgery.
(2) A three-branch lesion, especially in combination with left heart insufficiency (EF less than 50%), is a clear indication for CABG surgery with greater benefit than other means.
(3) Single or two-branch lesions including severe stenosis of the proximal left anterior descending branch are favored for surgical treatment.
(4) For single or two-branch lesions not involving the proximal left anterior descending branch, CABG is strongly recommended if other tests reveal a large cardiac emergency with imminent death and hypoplastic left heart.
For such patients, the purpose of CABG is not to eliminate symptoms, but to extend life and improve survival as compared to non-surgical treatments.
2. In chronic stable angina, the indications for surgery are the same as for asymptomatic or mild angina.
Due to the heavier symptoms than the former, CABG is also strongly recommended for single or two lesions with significant proximal stenosis of the left anterior descending branch if the left ventricular EF is below 50%, or if other tests reveal the presence of myocardial ischemia.
In such patients, the aim of CABG is to eliminate symptoms and prolong life.
Indications for unstable angina (UA)/non-ST-segment elevation myocardial infarction (NSTEMI) surgery are the same as for asymptomatic or mild angina and chronic stable angina.
However, the timing of surgery becomes a critical issue, as the acute phase of UA/NSTEMI/NQMI has a 2-3 times higher mortality rate than stable angina, so it is emphasized to treat these patients with the maximum dose of medication they can tolerate and wait for their condition to stabilize and progressive ischemia to resolve before performing CABG.
If angina recurs despite the maximum dose of medication (approximately 33% of patients), CABG must be performed immediately, with the same long-term outcome as in stable angina, although the perioperative mortality is high.
In such patients, CABG can clearly eliminate symptoms and prolong life.
The later the surgery is performed after AMI, the lower the perioperative mortality rate.
For progressive myocardial ischemia/infarction despite intensive nonoperative therapy (thrombolysis or PTCA), CABG may be attempted if there is still surviving myocardium and a suitable target vessel.
Patients with cardiogenic shock or mechanical complications (e.g., septal perforation, papillary machine infarction/segmental inferior mitral valve closure insufficiency, left ventricular rupture) must be operated on urgently to resuscitate the patient.
5. For patients with significant evidence of ischemia with combined left ventricular insufficiency, fatal arrhythmias, PTCA failure or restenosis, or after previous CABG (obstruction of more than 1 vessel bridge, or atherosclerotic lesions dilating into other vessels), CABG should be aggressively performed if there is still surviving myocardium and a suitable target vessel.
Contraindications to surgery.
1, multiple organ failure, severe chronic congestive heart failure combined with pulmonary hypertension in the heart, who cannot tolerate surgery.
2. No surviving myocardium and suitable target vessels.