A heart attack, also known as a myocardial infarction, usually occurs when a blood clot forms inside a coronary artery at the site of an atherosclerotic plaque. The blood clot severely limits or completely cuts off blood flow to part of the heart. In a small percentage of cases, blood flow is cut off when the muscles in the artery wall contract suddenly, constricting the artery. This constriction, called vasospasm, can occur in an artery that is only slightly narrowed by atherosclerosis or even in a healthy artery. Regardless of the cause of a heart attack, the oxygen deprivation is so severe and prolonged that heart muscle cells begin to die for lack of oxygen. About 1.1 million people in the United States have a heart attack every year; …show more content…

in the pathogenesis in the initiating events are coronary occlusion, but the Q wave infarction usually results from sustained coronary occlusion and extensive necrosis, whereas the non-Q-wave type may have early spontaneous reperfusion for at least a part of the affected area. All acute MIs have a central area of necrosis or infarction that is surrounded by an area of injury; the area of injury is surrounded by a ring of ischemia. The amount of myocardial dysfunction that results depends not only the size of the necrotic lesion, but also on the amount injury and ischemia in the area. Each area emits characteristic ECG patterns that help to localize and determine the extent of the infarct of a 12-lead ECG. When myocardial muscles cells die, they liberate the intramyocardial cellular enzymes. These enzymes can be used to date and infarct and partially to judged its severity. Because the affected myocardial muscle does not regenerate after an infarction, healing requires the formation of scar tissue that replaces the necrotic myocardial muscle. This involves a series of morphologic changes ranging from no apparent cellular change in the first six hours to total replacement by scar tissue. Scar tissue inhibits contractility, and the significance of this depends of the amount of the scar tissue form. As