A heart attack, clinically known as a myocardial infarction, occurs when an artery supplying the heart with blood carrying oxygen and nutrients suddenly becomes blocked, causing part of the heart muscle to die Figure 01. Because your heart is a muscle, it needs oxygen to function, just like any other tissue. The special blood vessels that feed the heart are called coronary arteries. Coronary artery disease is a process of narrowing that occurs over time in these important vessels and can lead to a heart attack. The narrowing is caused by the build-up of fats and plaques in arteries, and can exist and grow without any symptoms.
When the artery becomes blocked, your heart does not receive the blood and oxygen it needs to survive. A heart attack can leave your heart much weaker and less able to pump blood around to the rest of your body, as a portion of the muscle has died and is no longer functioning as well.
Figure 01. What happens during a heart attack
Heart attacks are the most common cause of cardiovascular death. Worldwide, about 20% to 30% of patients suffering from a heart attack die from it, one-third within the first few hours.
Most heart attacks occur because the walls of an artery have a built up a fatty material called cholesterol plaque. The plaque ruptures, exposing a new, rough surface and releases a substance that causes the blood to clot. The clot forms on the plaque and blocks the artery Figure 02. The buildup of fatty material (cholesterol plaque) in the arteries is called artherosclerosis. It is the underlying cause of most heart attacks. The plaque buildup causes the arteries to harden and narrow, which makes may reduce blood delivery to the heart during exercise or stress. This can cause momentary chest pain that comes on when the heart is stressed (a condition known as angina). The plaque eventually ruptures, and its rough surface attracts the type of blood cells that cause clotting. Once the clot forms, no more blood reaches the heart, and part of the muscle usually dies as a result.
Figure 02. Healthy artery vs. an artery with plaque buildup
High blood pressure (hypertension), as well as smoking cigarettes, pipes, or cigars, may contribute to plaque buildup. Your heart also has to work harder when pushing against a “high-pressure” system. This increased workload makes your heart larger and more inefficient. High blood pressure also can lead to congestive heart failure, kidney damage or kidney failure, dementia, and blindness.
Occasionally, inflammatory diseases or cocaine abuse can also cause a heart attack.
Stress, anger, or physical exertion may trigger a heart attack if your arteries are clogged and you have heart disease. Doctors do not understand why a heart attack often follows physical or emotional stress. One reason may be that during a stressful episode, your heart’s need for oxygen increases but the body is unable to increase the blood flow through the diseased heart (ischemia). Stress hormones also make arteries narrow, which may cause a break in the fatty material built up in the blood vessel. Researchers have noticed that number of heart attacks increases during earthquakes and other natural disasters.
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