Myocardial Infarction
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; the heart attacks prove fatal for about 40 percent of these people (Microsoft Encarta, 2004).
ETIOLOGY
The most common cause of acute myocardial infarction (AMI) is complete or nearly complete occlusion of a coronary artery usually precipitated by rupture of the vulnerable atherosclerotic plaque and subsequent thrombus formation. Plaque rupture can be precipitated by both internal and external factors. Internal factors include plaque characteristics, such as the size and consistency of the lipid core and the thickness of the fibrous cap, as well ac conditions to which it is exposed, such as coagulation status and degree of arterial vasoconstriction. Vulnerable plaques most frequently occur in areas with less than 70% stenosis and are characterized by an eccentric shape with an irregular border, a large, thin lipid core, and a thin, fibrous cap. External factors result from actions of the client or from external conditions that affect the client. Strenuous physical activity and severe emotional stress, such as anger, increased sympathetic activity, which in turn, increases hemodynamic stress that may lead to plaque rupture. At the same time, sympathetic activity increases myocardial oxygen demand. Scientists have
ETIOLOGY
The most common cause of acute myocardial infarction (AMI) is complete or nearly complete occlusion of a coronary artery usually precipitated by rupture of the vulnerable atherosclerotic plaque and subsequent thrombus formation. Plaque rupture can be precipitated by both internal and external factors. Internal factors include plaque characteristics, such as the size and consistency of the lipid core and the thickness of the fibrous cap, as well ac conditions to which it is exposed, such as coagulation status and degree of arterial vasoconstriction. Vulnerable plaques most frequently occur in areas with less than 70% stenosis and are characterized by an eccentric shape with an irregular border, a large, thin lipid core, and a thin, fibrous cap. External factors result from actions of the client or from external conditions that affect the client. Strenuous physical activity and severe emotional stress, such as anger, increased sympathetic activity, which in turn, increases hemodynamic stress that may lead to plaque rupture. At the same time, sympathetic activity increases myocardial oxygen demand. Scientists have