CORONARY ARTERY DISEASE AND ATHEROSCLEROSIS

Coronary artery disease results in decreased blood flow to the myocardium. If blood flow is diminished but not completely obstructed, the person may experience difficulty breathing and angina, which is chest pain caused by lack of oxygen to part of the heart muscle. If blood flow is completely blocked, however, the result is a myocardial infarction (necrosis of cardiac muscle).

The most common cause of coronary artery disease is atherosclerosis. Plaques of cholesterol form in the walls of a coronary artery; this narrows the lumen (cavity and creates a rough surface where a clot (thrombus) may form. A predisposing factor for such clot formation, one that cannot be changed, is a family history of coronary artery disease. There is no “gene for heart attacks,” but we do have genes for the enzymes involved in cholesterol metabolism. Many of these are liver enzymes that regulate the transport of cholesterol in the blood in the form of lipoproteins and regulate the liver’s excretion of excess cholesterol in bile.
Some people, therefore, have a greater tendency than others to have higher blood levels of cholesterol and certain lipoproteins. In women before menopause, estrogen is believed to exert a protective effect by lowering blood lipid levels. This is why heart attacks in the 30- to 50-year-old age range are less frequent in women than in men.

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Other predisposing factors for atherosclerosis include cigarette smoking, diabetes mellitus, and high blood pressure. Any one of these may cause damage to the lining of coronary arteries, which is the first step in the abnormal deposition of cholesterol. A diet high in cholesterol and saturated fats and high blood levels of these lipids will increase the rate of cholesterol deposition. A possible chemical marker of risk is a high bloodlevel of Homocysteine. Homocysteine is a metabolic product of the essential amino acid Methionine,and may be converted back to Methionine or further changed and excreted by the kidneys. A high blood level of Homocysteine may indicate inflammation of the walls of arteries. Yet another chemical marker of inflammation is C-reactive protein (CRP). There is still much to learn about the role of inflammation in atherosclerosis, but simple blood tests for chemical markers may someday provide a diagnosis before heart damage occurs.

When coronary artery disease becomes life threatening, coronary artery bypass surgery may be performed. In this procedure, a synthetic vessel or a vein (such as the Saphenous vein of the leg) is grafted around the obstructed coronary vessel to restore blood flow to the myocardium. This is not a cure, for atherosclerosis may occur in a grafted vein or at other sites in the coronary arteries.