Excerpt from Myocardial Infarction

Synonyms, Key Words, and Related Terms: acute coronary syndromes, ACS, MI, heart attack, myocardial infarction, unstable angina, non–ST-elevation MI, NSTEMI, coronary artery disease, CAD, ischemic heart disease, chest pain, impaired systolic function, impaired diastolic function, myocardial necrosis, atherosclerosis, coronary thrombus, plaque rupture, coronary emboli, infected cardiac valve, coronary occlusion secondary to vasculitis, primary coronary vasospasm, variant angina, cardiovascular disease, congestive heart failure, CHF, coronary heart disease, smoking, diabetes mellitus, hypertension, dyslipidemia, obesity, elevated homocysteine levels, male pattern baldness, sedentary lifestyle, psychosocial stress, peripheral vascular disease, poor oral hygiene, vasculitis, congenital coronary anomalies, coronary trauma, coronary spasm, necrosis of heart muscle,coronary thrombosis, pulmonary rales, lower extremity edema, elevated jugular venous pressure, cocaine use, heavy exertion, hyperthyroidism, severe anemia

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Background: Myocardial infarction (MI) is the irreversible necrosis of heart muscle secondary to prolonged ischemia. This usually results from an imbalance of oxygen supply and demand. The appearance of cardiac enzymes in the circulation generally indicates myocardial necrosis. MI is considered, more appropriately, part of a spectrum referred to as acute coronary syndromes (ACSs), which also includes unstable angina and non–ST-elevation MI (NSTEMI). Patients with ischemic discomfort may or may not have ST-segment elevation. Most of those with ST-segment elevation will develop Q waves. Those without ST elevations will ultimately be diagnosed with unstable angina or NSTEMI based on the presence of cardiac enzymes.

MI may lead to impairment of systolic function or diastolic function and to increased predisposition to arrhythmias and other long-term complications.

Pathophysiology: Atherosclerosis is the disease primarily responsible for most ACS cases. Approximately 90% of MIs result from an acute thrombus that obstructs an atherosclerotic coronary artery. Plaque rupture is considered to be the major trigger of coronary thrombosis. Following plaque rupture, platelet activation and aggregation, coagulation pathway activation, and endothelial vasoconstriction occur and lead to coronary thrombosis and occlusion.

Consider nonatherosclerotic causes of acute MIs in younger patients or if no evidence of atherosclerosis is noted. Such causes include coronary emboli from sources such as an infected cardiac valve, coronary occlusion secondary to vasculitis, primary coronary vasospasm (variant angina), cocaine use, or other factors leading to mismatch of oxygen supply and demand, as may occur with a significant GI bleed.

Frequency:

In the US: Approximately 1.5 million cases of MI occur each year.

Internationally: Cardiovascular diseases cause 12 million deaths throughout the world each year, according to the third monitoring report of the World Health Organization, 1991-93. They cause half of all deaths in several developed countries and are one of the main causes of death in many developing countries; they are the major cause of death in adults everywhere.

Mortality/Morbidity:

Cardiovascular disease is the leading cause of death in the United States; approximately 500,000-700,000 deaths related to the coronary artery occur each year.

Ischemic heart disease is the leading cause of death worldwide.

Approximately 6.3 million deaths due to heart disease occurred in 1990 worldwide, which represents 29% of all deaths. The prevalence of coronary artery disease (CAD) is increasing rapidly in nonindustrialized countries.

Race:

Cardiovascular disease is the leading cause of morbidity and mortality among African American, Hispanic, and white populations in the United States.

Sex:

A male predominance in incidence exists up to approximately age 70 years, when the sexes converge to equal incidence.

Premenopausal women appear to be somewhat protected from atherosclerosis, possibly owing to the effects of estrogen.

Age:

Incidence increases with age.

Most patients who develop an acute MI are older than 60 years. Elderly people also tend to have higher rates of morbidity and mortality from their infarcts.