Coronary artery disease occurs when atherosclerotic plaque (hardening of the arteries) builds up in the wall of the arteries that supply the heart. This plaque is primarily made of cholesterol. Plaque accumulation can be accelerated by smoking, high blood pressure, elevated cholesterol, and diabetes. Patients are also at higher risk for plaque development if they are older (greater than 45 years for men and 55 years for women), or if they have a family history of early heart artery disease.
The atherosclerotic process causes significant narrowing in one or more coronary arteries. When coronary arteries narrow more than 50% to 70%, the blood supply beyond the plaque is not enough to meet the increased oxygen demand during exercise. The heart muscle in the area of these arteries becomes starved of oxygen (ischemic). Patients often experience chest pain (angina) when the blood oxygen supply cannot keep up with demand. Up to 25% of patients experience no chest pain at all, despite a lack of adequate blood and oxygen supply. These patients have "silent" angina, and have the same risk of heart attack as those with angina.
When a blood clot (thrombus) forms on top of this plaque, the artery becomes completely blocked, causing a heart attack.
When arteries are narrowed 90% to 99%, patients often have accelerated angina or angina at rest (unstable angina). Unstable angina can also occur due to the blockage of an artery by a clot that eventually is dissolved by the body's own protective clot-dissolving system.
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