Heart attack

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Acute MI	Anterior heart arteries	Heart, front view	Heart, section through the middle
Heart attack symptoms	Posterior heart arteries	Post myocardial infarction ECG wave tracings	Progressive build-up of plaque in coronary artery

A heart attack (myocardial infarction) occurs when an area of heart muscle dies or is permanently damaged because of an inadequate supply of oxygen to that area.

Myocardial infarction; MI; Acute MI

Most heart attacks are caused by a clot that blocks one of the coronary arteries (the blood vessels that bring blood and oxygen to the heart muscle). The clot usually forms in a coronary artery that has been previously narrowed from changes related to atherosclerosis. The atherosclerotic plaque (buildup) inside the arterial wall sometimes cracks, and this triggers the formation of a clot, also called a thrombus.

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A clot in the coronary artery interrupts the flow of blood and oxygen to the heart muscle, leading to the death of heart cells in that area. The damaged heart muscle loses its ability to contract, and the remaining heart muscle needs to compensate for that weakened area.

Occasionally, sudden overwhelming stress can trigger a heart attack.

It is difficult to estimate exactly how common heart attacks are because as many as 200,000 to 300,000 people in the United States die each year before medical help is sought. It is estimated that approximately 1 million patients visit the hospital each year with a heart attack.

The risk factors for coronary artery disease and heart attack include:

• Smoking
• High blood pressure
• Too much fat in your diet
• Poor blood cholesterol levels, especially high LDL ("bad") cholesterol and low HDL ("good") cholesterol
• Diabetes
• Male gender
• Age
• Heredity

Many of the risk factors listed are related to being overweight.

Newer risk factors for coronary artery disease have been identified over the past several years. These include elevated homocysteine, C-reactive protein, and fibrinogen levels. Homocysteine is an amino acid. C-reactive protein is connected with inflammatory reactions, and fibrinogen is a blood clotting component. High homocysteine can be treated with folic acid supplements. Studies are still ongoing about the practical value of these new factors.

Heart attacks account for 1 out of every 5 deaths. It is a major cause of sudden death in adults.

Review Date: 11/14/2005
Reviewed By: Steven Kang, MD, Division of Cardiac Pacing and Electrophysiology, Cardiovascular Consultants Medical Group, Oakland, CA. Review provided by VeriMed Healthcare Network.