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Definition: coronary artery bypass graft from The Macquarie Dictionary

noun Medicine a surgical procedure in which veins removed from one part of the body, usually the leg, or arteries redirected from the chest wall are used to bypass a narrowed or blocked section of artery on the heart, allowing the heart to receive sufficient blood to function effectively.

(plural coronary artery bypass grafts)


Summary Article: Heart Bypass Surgery
from Encyclopedia of Global Health

Heart bypass surgery, also known as coronary artery bypass graft surgery (CABG), is the most commonly performed surgical procedure performed on the heart to bypass the obstructed artery (the coronary artery) of the heart and improve blood flow to the heart. The coronary arteries supply oxygen and nutrients to the cardiac muscles; due to the small size of the arteries, they are often prone to accumulation of fats and cholesterol which can lead to plaque formation and the development of atherosclerosis. If these arteries are blocked there is also a risk of developing ischemic heart disease or coronary artery disease leading to the development of angina. Factors increasing plaque accumulation include high blood pressure, increased cholesterol levels, smoking and the presence of diabetes. The increase in age (greater than 55 years for women and 45 years for men) also increases the risk as does a positive family history for early heart disease. To determine the presence of coronary artery disease, a stress test accompanied by electrocardiogram monitoring of the heart and cardiac catheterisation is performed. The latter is performed by insertion of a catheter through the artery in the groin or arm to the heart, with injection of contrast medium into the arteries.

CABGs are generally performed to relieve the chest pain and reduce the risk of death from coronary artery disease. A CABG generally takes four to six hours to complete. There are many techniques of performing a CABG; a detour is created to bypass the obstructed artery. Various arteries and veins may be used as grafts, these conduits include the saphenous vein, the internal thoracic artery (internal mammary artery) and the radial artery. Before the surgery the surgeon will use a coronary angiogram to identify the blockages. The surgical procedure begins with an incision of the middle of the chest followed by a median sternotomy (cutting of sternum). Through this incision the surgeon is able to view the heart and the aorta. To achieve the cardiopulmonary bypass tubes are inserted into the right atrium of the heart which will collect venous blood from the body to the membrane oxygenator in the bypass pump (heartlung machine) thus enabling circulation of oxugenated blood to other parts of the body. The aorta is cross claped to allow bypasses to be connected to the aorta. The heart is stopped using a mixture of chemicals called cardioplegia.

Standard CABG surgery may be associated with concerns over neurological and inflammatory complications related to the bypass and thus many patients receive the off-pump CABG (OPCABG). This technique is used to perform the bypass without the use of the bypass pump. The advantage of this type of surgery is that it may be perfomed whilst the heart is still beating, thus reducing the risk of loss of memory. OPCABG has been reported to be superior in terms of length of stay in hospital following surgery and incidence of stroke; however it associated with a higher rate of mediastinal infection than CABG surgery. A technique known as minimally invasive direct coronary artery bypass (MIDCAB) is also used where the normal action of incision of the chest during the other techniques is avoided.

Heart bypasses differ in the numbers of coronary arteries bypassed in the procedure. There may be single bypass (one coronoary artery bypassed), double (two), triple (three), quadruple (four), and quintiple (five). For the coronary arteries to be bypassed, it must be ensured that the arteries are not too small, not heavily calcified, and not located within the heart muscle (intramycocardial). The recovery period after CABG (the first four to eight weeks after the surgery) is associated with higher risks of complications and hospital readmission. CABGs are associated with several risks; they are associated with significant postoperative cardiovascular morbidity and mortality in high-risk patients. Possible risks in receiving a CABG are myocardial infarctions which occur in five to 10 percent of patients. Stroke occurs in one to two percent, primarily in elderly patient. Depression is common after surgery, but is generally improved with the use of cognitive behavioral therapy. Research suggests that risks of CABG are worse in women than men. Overall mortality related to CABG is three to four percent. Mortality may be higher in women, primarily due to their advanced age at the time of CABG surgery and smaller coronary arteries as women are generally smaller than men. Mortality and complications increase with factors such as age (older than 70 years), kidney failure and presence of other diseases such as diabetes mellitus. Approximately 25 to 30 percent of patients undergoing CABG have diabetes mellitus, these patients have increased risk due to respiratory, renal and cerebral complications, and wound infections. Diabetes mellitus represents an independent risk factor for late graft failure and mortality from cardiac causes. CABGs are however performed on these patients as it results in better quality of life in the diabetic patient with severe coronary artery disease, as compared to medical treatment and the use of other surgical procedures such as percutaneous coronary angioplasty.

The long-term results after CABG surgery include possible blockage of vein grafts after surgery due to blood clotting. After a successful CABG, a patient’s anginal chest pain generally resolves; however they may experience chest discomfort due to the incision of the chest prior to the bypass. In general, the success rate of CABG is approximately 90 percent; many of these patients experience significant improvements after the surgery.

    SEE ALSO:
  • Heart Attack; Heart Diseases (General).

BIBLIOGRAPHY
  • A. Jalal, et al., “Coronary Artery Bypass Grafting on Beating Heart. Does it Provide Superior Myocardial Preservation than Conventional Technique?” Saudi Medical Journal (v.28/6, 2001).
  • Farhana Akter
    King’s College, London
    Copyright © 2008 by SAGE Publications, Inc.

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