Myocardial Infarction

Myocardial infarction or acute myocardial infarction is the medical term for an event commonly known as a heart attack. It happens when blood stops flowing properly to part of the heart and the heart muscle is injured due to not receiving enough oxygen. Usually this is because one of the coronary arteries that supplies blood to the heart develops a blockage due to an unstable buildup of white blood cells, cholesterol and fat. The event is called "acute" if it is sudden and serious.

A person having an acute MI usually has sudden chest pain that is felt behind the breast bone and sometimes travels to the left arm or the left side of the neck. Additionally, the person may have shortness of breath, sweating, nausea, vomiting, abnormal heartbeats, and anxiety. Women experience fewer of these symptoms than men, but usually have shortness of breath, weakness, a feeling of indigestion, and fatigue. In many cases, in some estimates as high as 64%, the person does not have chest pain or other symptoms. These are called "silent" myocardial infarctions. Important risk factors are previous cardiovascular disease, old age, tobacco smoking, high blood levels of certain lipids and low levels of high density lipoprotein cholesterol, diabetes, high blood pressure, lack of physical activity, obesity, chronic kidney disease, excessive alcohol consumption, and the use of cocaine and amphetamines.

The onset of symptoms in myocardial infarction is usually gradual, over several minutes, and rarely instantaneous. Chest pain is the most common symptom of acute MI and is often described as a sensation of tightness, pressure, or squeezing. Chest pain due to ischemia of the heart muscle is termed angina pectoris. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and epigastrium, where it may mimic heartburn. Levine's sign, in which patients localize the chest pain by clenching their fists over their sternums, has classically been thought to be predictive of cardiac chest pain, although a prospective observational study showed it had a poor positive predictive value.

Shortness of breath occurs when the damage to the heart limits the output of the left ventricle, causing left ventricular failure and consequent pulmonary edema. Other symptoms include diaphoresis, weakness, light-headedness, nausea, vomiting, and palpitations. These symptoms are likely induced by a massive surge of catecholamines from the sympathetic nervous system which occurs in response to pain and the hemodynamic abnormalities that result from cardiac dysfunction. Loss of consciousness and sudden death can occur in MIs. Women also report more numerous symptoms compared with men . Women may also experience back or jaw pain during an episode.

At least one-fourth of all MIs are silent, without chest pain or other symptoms. These cases can be discovered later on electrocardiograms, using blood enzyme tests or at autopsy without a prior history of related complaints. Estimates of the prevalence of silent MIs vary between 22 and 64%. and after heart transplantation, probably because the donor heart is not fully innervated by the nervous system of the recipient. In people with diabetes, differences in pain threshold, autonomic neuropathy, and psychological factors have been cited as possible explanations for the lack of symptoms.

Immediate treatments for a suspected MI include aspirin, which prevents further blood from clotting, and sometimes nitroglycerin to treat chest pain and oxygen. STEMI is treated by restoring circulation to the heart, called reperfusion therapy, and typical methods are angioplasty, where the arteries are pushed open, and thrombolysis, where the blockage is removed using medications. Non-ST elevation myocardial infarction may be managed with medication, although angioplasty may be required if the person is considered to be at high risk. People who have multiple blockages of their coronary arteries, particularly if they also have diabetes, may also be treated with bypass surgery . Ischemic heart disease, which includes MI, angina, and heart failure when it happens after MI, was the leading cause of death for both men and women worldwide in 2011.

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