Coronary artery bypass surgery
Coronary artery bypass surgery, also called coronary artery bypass graft, is a surgical procedure to treat coronary artery disease, 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 heart.
There are two main approaches. The first uses a cardiopulmonary bypass machine, operated by a Perfusionist, 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, 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 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, stroke, infections and injury to the kidneys.
File:Heart saphenous coronary grafts.jpg|thumb|Three coronary artery bypass grafts, a pedicled LITA to LAD and two saphenous vein grafts – one to the right coronary artery system and one to the obtuse marginal system.
Uses
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.Coronary artery disease
Coronary artery disease is caused when coronary arteries of the heart accumulate atheromatous plaques, causing stenosis 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, to chest pain even at rest. 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 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 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.
Indications for CABG
Stable patients
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, especially when the lesion in the LAD is at its proximal part.
Acute coronary syndrome
During an acute heart event, known as acute coronary syndrome, it is paramount to quickly restore blood flow to heart tissue. Typically, patients arrive at the hospital with chest pain. They are first treated with drugs, particularly the strongest drugs that prevent clots within vessels. Patients at risk of ongoing ischemia undergo PCI to restore blood flow and thus oxygen delivery to the struggling heart. If PCI failed to restore blood flow because of anatomical considerations or other technical problems, urgent CABG is indicated to save heart tissue. The timing of the operation plays a role in survival: It is preferable to delay the surgery if possible.CABG is also indicated when there are mechanical complications of an infarction. There are no absolute contraindications of CABG, but severe disease of other organs such as the liver or brain, limited life expectancy, and patient fragility are considered.
Other cardiac surgery
CABG is also performed when a patient is to undergo another cardiac surgical procedure, most commonly for valve disease, and angiography reveals a significant lesion of the coronary arteries. CABG can also address dissection of coronary arteries, where a rupture of the coronary layers creates a pseudo-lumen and diminishes blood delivery to the heart. Such a dissection may be caused by pregnancy, tissue diseases like Ehlers–Danlos syndromes and Marfan syndrome, cocaine abuse, or PCI. A coronary aneurysm may also indicate CABG: A blood clot might develop within the vessel and travel downstream.CABG versus PCI
CABG and percutaneous coronary intervention are the two methods to restore blood flow caused by stenotic lesions of the coronary arteries. The choice of method is still a matter of debate, but it is clear that in the presence of complex lesions, significant left main disease, or diabetes, CABG yields better long-term survival and outcomes. Strong indications for CABG also include symptomatic patients and impaired left ventricle function. CABG offers better results than PCI in left main disease and in CAD that affects multiple vessels, because of the protection arterial conduits offer to the native arteries of the heart, by producing vasodilator factors and preventing the advancement of plaques. Studies published in 2023 show that CABG in patients with left main disease is associated with lower mortality and fewer adverse events compared to PCI.Patients with unprotected left main disease—when the runoff of the left main artery is not protected by a patent graft since a previous CABG operation—have been studied as a group. A 2016 European study found that in these patients, CABG outperforms PCI in the long run. Another 2016 study found that PCI has similar results to CABG at 3 years, but that CABG becomes better than PCI after 4 years.
A 2012 trial and followup in diabetic patients demonstrated a significant advantage to CABG over PCI. The relative advantage remained evident at 3.8-year and 7.5-year follow ups, which found particular benefits in smokers and younger patients. A 2015 trial compared CABG and the latest technological advancement of PCI, second-generation drug-eluting stents in multivessel disease. Their results indicated that CABG is a better option for CAD patients. A trial published in 2021, comparing results after one year, also concluded that CABG is a safer option than PCI. A large study published in 2023 showed that PCI patients had higher mortality than CABG patients with left main coronary artery disease.
Procedure
Preoperative examination and strategy
Routine preoperative examination aims to check the status of systems and organs besides the heart. The examination typically includes a chest X-ray to check the lungs, a complete blood count, and kidney and liver function tests. Physical examination to determine the quality of the grafts or the safety of removing them, such as varicosities in the legs, or the Allen test in the arm is performed to be sure that blood supply to the arm will not be critically disturbed.A patient taking anticoagulants—aspirin, clopidogrel, ticagrelol and others—will stop taking them several days before, to prevent excessive bleeding during and after the operation. Warfarin is also stopped for the same reason and the patient starts taking heparin products after the INR falls below 2.0.
After the angiogram is reviewed by the surgical team, targets are selected. Ideally, all major lesions in significant vessels should be addressed. Most commonly, the left internal thoracic artery is anastomosed to the left anterior descending artery because the LAD is the most significant artery of the heart and supplies blood to a larger portion of myocardium than other arteries.
A conduit can be used to graft one or more native arteries. In the latter case, an end-to-side anastomosis is performed. In the former, using a sequential anastomosis, a graft can then deliver blood to two or more native vessels of the heart. Also, the proximal part of a conduit can be anastomosed to the side of another conduit. It is preferred not to harvest too much conduit because it might necessitate re-operation.