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Coronary artery bypass surgery

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Coronary artery bypass surgery

Coronary artery bypass surgery, also called coronary artery bypass graft (CABG /ˈkæbɪ/ KAB-ij, like "cabbage"), is a surgical procedure to treat coronary artery disease (CAD), the buildup of plaques in the arteries of the heart. It can relieve chest pain caused by CAD, slow the progression of CAD, and increase life expectancy. It aims to bypass narrowings in heart arteries by using arteries or veins harvested from other parts of the body, thus restoring adequate blood supply to the previously ischemic (deprived of blood) heart.

There are two main approaches. The first uses a cardiopulmonary bypass machine, a machine which takes over the functions of the heart and lungs during surgery by circulating blood and oxygen. With the heart in cardioplegic arrest, harvested arteries and veins are used to connect across problematic regions—a construction known as surgical anastomosis. In the second approach, called the off-pump coronary artery bypass (OPCAB), these anastomoses are constructed while the heart is still beating. The anastomosis supplying the left anterior descending branch is the most significant one and usually, the left internal mammary artery is harvested for use. Other commonly employed sources are the right internal mammary artery, the radial artery, and the great saphenous vein.

Effective ways to treat chest pain (specifically, angina, a common symptom of CAD) have been sought since the beginning of the 20th century. In the 1960s, CABG was introduced in its modern form and has since become the main treatment for significant CAD. Significant complications of the operation include bleeding, heart problems (heart attack, arrhythmias), stroke, infections (often pneumonia) and injury to the kidneys.

Coronary artery bypass surgery aims to prevent death from coronary artery disease and improve quality of life by relieving angina, the associated feeling of chest pain. The decision to perform surgery is informed by studies of CABG's efficacy in different patient subgroups, based on the lesions' anatomy or how well the heart is functioning. These results are compared with that of other strategies, most importantly percutaneous coronary intervention (PCI).

Coronary artery disease is caused when coronary arteries of the heart accumulate atheromatous plaques, causing stenosis (narrowing) in one or more arteries and risking myocardial infarction, the interruption of blood supply to the heart. CAD can occur in any of the major vessels of the coronary circulation: the left main stem, left ascending artery, circumflex artery, and right coronary artery, and branches thereof. CAD symptoms vary from none, to chest pain only when exercising (stable angina), to chest pain even at rest (unstable angina). It can even manifest as a myocardial infarction; if blood flow to the heart is not restored within a few hours, whether spontaneously or by medical intervention, the blood-deprived part of the heart becomes necrotic (dies) and is scarred. It may lead to other complications such as arrhythmias, rupture of the papillary muscles of the heart, or sudden death.

There are various methods of detecting and assessing CAD. Apart from history and clinical examination, noninvasive methods include electrocardiography (ECG) at rest or during exercise, and X-ray of the chest. Echocardiography can quantify heart functioning by measuring, for example, enlargement of the left ventricle, the ejection fraction, and the situation of the heart valves. The most accurate ways to detect CAD are the coronary angiogram and the coronary CT angiography. An angiogram can provide detailed anatomy of coronary circulation and lesions. The significance of each lesion is determined by the diameter loss. A diameter loss of 50% translates to a 75% cross-sectional area loss, considered moderate by most groups. Severe stenosis constitutes a diameter loss of 2/3 or more—a greater-than-90% loss of cross-sectional area. To more accurately determine the severity of stenosis, interventional cardiologists may also employ intravascular ultrasound, which can determine the severity and provide information on the composition of the atheromatous plaque. With the technique of fractional flow reserve, the pressure after the stenosis is compared to mean aortic pressure. If the ratio is less than 0.80, then the stenosis is deemed significant.

People with angina during exercise are usually first treated with medical therapy. Noninvasive tests help estimate which patients might benefit from undergoing coronary angiography. Generally, if portions of cardiac wall are receiving less blood than normal, coronary angiography is indicated; then, lesions are identified and inform a decision to undergo PCI or CABG.

CABG is generally preferred over PCI when there is a significant burden of plaque on the coronary arteries, that is extensive and complex, due to survival benefit. Other indicators that a patient will benefit more from CABG rather than PCI include: decreased left-ventricle function; left main disease; diabetes; and complex triple system disease (including LAD, Cx and RCA), especially when the lesion in the LAD is at its proximal part.

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