Causes
Coronary artery bypass surgery is performed on people who suffer from severe CAD, a condition involving the clogging of arteries that bring blood to the heart muscle caused by fatty deposits on the inner walls of the arteries. The surgery is also performed on people who suffer from severe angina (pain that occurs when the heart muscle isn't receiving enough oxygen). Angina is usually caused by CAD, which is the major cause of heart disease in North America.
The coronary arteries lie on the heart's surface. They bring oxygen-rich blood to the heart muscle (myocardium). For the heart to pump blood normally, the heart muscle needs a constant supply of oxygen-rich blood from the coronary arteries. When coronary arteries become blocked, the oxygen supply to the heart is reduced.
There are two general patterns of blockage. In the first pattern, blockage develops slowly and only partially blocks the artery. This usually results in chest pain or angina because the heart is not getting enough oxygen. The second pattern is a complete blockage that usually develops quickly. With a complete blockage, parts of the heart muscle are not getting oxygen and heart muscle cells begin to die. This is called a myocardial infarction, or heart attack.
The most common cause of a partial blockage is cholesterol and fat deposits on the inner walls of the coronary arteries. The gradual buildup of these substances may form fatty deposits called plaques in a process known as atherosclerosis (hardening of the arteries). The plaques bulge into the large branches of the two main coronary arteries and restrict the ability of blood to flow through them. Eventually an artery can become blocked or occluded, and no blood can flow through it. Plaque can also help to form blood clots (thrombosis). The slow buildup of a blood clot can narrow the affected artery even more, while a quickly developing clot can abruptly close off the artery.