Coronary artery bypass surgery, also coronary artery bypass graft surgery, and colloquially heart bypass or bypass surgery is a surgical procedure performed to relieve angina and reduce the risk of death from coronary artery disease. Arteries or veins from elsewhere in the patient's body are grafted to the coronary arteries to bypass atherosclerotic narrowings and improve the blood supply to the coronary circulation supplying the myocardium (heart muscle). This surgery is usually performed with the heart stopped, necessitating the usage of cardiopulmonary bypass; techniques are available to perform CABG on a beating heart, so-called "off-pump" surgery.
Arteriosclerosis is a common arterial disorder characterized by thickening, loss of elasticity, and calcification of arterial walls, resulting in a decreased blood supply.
Atherosclerosis is a common arterial disorder characterized by yellowish plaques of cholesterol, lipids, and cellular debris in the inner layer of the walls of large and medium-sized arteries.
A greater number of bypasses does not imply a person is "sicker," nor does a lesser number imply a person is "healthier. A person with a large amount of coronary artery disease (CAD) may receive fewer bypass grafts due to the lack of suitable "target" vessels. A coronary artery may be unsuitable for bypass grafting it if it is small (< 1 mm or < 1.5 mm depending on surgeon preference), heavily calcified (meaning the artery does not have a section free of CAD) or intramyocardial (the coronary artery is located within the heart muscle rather than on the surface of the heart). Similarly, a person with a single stenosis ("narrowing") of the left main coronary artery requires only two bypasses (to the LAD and the LCX). However, a left main lesion places a person at the highest risk for death from a cardiac cause.
The surgeon reviews the coronary angiogram prior to surgery and identifies the lesions (or "blockages") in the coronary arteries. The surgeon will estimate the number of bypass grafts prior to surgery, but the final decision is made in the operating room upon examination of the heart.
Both PCI and CABG are more effective than medical management at relieving symptoms, (e.g. angina, dyspnea, fatigue). CABG is superior to PCI in multivessel CAD (more than one diseased artery), although the ARTS II registry suggests PCI with drug-eluting stents (DES) may be not inferior to CABG.
The ARTS II registry compared a cohort of patients treated with DES and contemporary medical management to the historical CABG cohort in the ARTS I trial and concluded drug-eluting stenting is not inferior to CABG for treatment of multivessel coronary disease. The Surgery or Stent (SoS) trial was a randomized controlled trial that compared CABG to PCI with bare-metal stents. The SoS trial demonstrated CABG is superior to PCI in multivessel coronary disease.
No randomized trial comparing CABG and DES has been completed, although two trials of DES versus CABG are currently enrolling patients - SYNTAX (Synergy Between Percutaneous Coronary Intervention With Taxus and Cardiac Surgery) and FREEDOM (Future Revascularization Evaluation in Patients With Diabetes Mellitus—Optimal Management of Multivessel Disease). The registries of the nonrandomized patients screened for these trials may provide as much robust data regarding revascularization outcomes as the randomized analysis.
A recent study comparing the outcomes of all patients in New York state treated with CABG or percutaneous coronary intervention (PCI) demonstrated CABG was superior to PCI with DES in multivessel (more than one diseased artery) coronary artery disease (CAD). Patients treated with CABG had lower rates of death and of death or myocardial infarction than treatment with a coronary stent. Patients undergoing CABG also had lower rates of repeat revascularization. The New York State registry included all patients undergoing revascularization for coronary artery disease, but was not a randomized trial, and so may have reflected other factors besides the method of coronary revascularization.
The 2005 ACC/AHA guidelines further state: CABG is the likely the preferred treatment with other high-risk patients such as those with severe ventricular dysfunction (i.e. low ejection fraction), or diabetes mellitus.
Graft patency is dependent on a number of factors, including the type of graft used (internal thoracic artery, radial artery, or great saphenous vein), the size or the coronary artery that the graft is anastomosed with, and, of course, the skill of the surgeon(s) performing the procedure. Arterial grafts (e.g. LITA, radial) are far more sensitive to rough handling than the saphenous veins and may go into spasm if handled improperly.
Generally the best patency rates are achieved with the in-situ (the proximal end is left connected to the subclavian artery) left internal thoracic artery with the distal end being anastomosed with the coronary artery (typically the left anterior descending artery or a diagonal branch artery). Lesser patency rates can be expected with radial artery grafts and "free" internal thoracic artery grafts (where the proximal end of the thoracic artery is excised from its origin from the subclavian artery and re-anastomosed with the ascending aorta). Saphenous vein grafts have worse patency rates, but are more available, as the patients can have multiple segments of the saphenous vein used to bypass different arteries.
Veins that are used either have their valves removed or are turned around so that the valves in them do not occlude blood flow in the graft. LITA grafts are longer-lasting than vein grafts, both because the artery is more robust than a vein and because, being already connected to the arterial tree, the LITA need only be grafted at one end. The LITA is usually grafted to the left anterior descending coronary artery (LAD) because of its superior long-term patency when compared to saphenous vein grafts.
People undergoing coronary artery bypass are at risk for the same complications as any surgery, plus some risks more common with or unique to CABG.
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