Unstable angina is closely linked to heart attack

Q: For several years my husband has had anginal chest pains due to a bad heart. Recently he was hospitalized with a diagnosis of unstable angina. I would like to know the difference between regular and unstable angina.

A: Angina and heart attacks (myocardial infarction) are almost always caused by narrowings of the coronary arteries limiting the supply of blood to the heart muscle. A moderate reduction in blood flow produces angina, while a more severe and prolonged reduction in blood flow causes a heart attack and permanent damage to the heart muscle.

Angina is generally a deep and poorly localized discomfort, usually in the chest or left arm, that is triggered by physical activity or emotional stress. While a feeling of pressure is typical, angina may also bring a tightness, squeezing, burning, aching, heaviness or choking sensation. The most common type of angina is termed "stable" angina because a predictable amount of activity or stress triggers an attack. The amount and duration of the pain are similar in each attack, and the pain is promptly relieved by rest or nitroglycerin.

"Unstable" angina can be broadly defined as a condition in between stable angina and a myocardial infarction. There are three major types of unstable angina: angina occurring at rest and usually lasting for more than 20 minutes; angina severe enough to cause a marked limitation of ordinary activity (for example, pain on climbing one flight of stairs at a normal pace); and a change in the pattern of stable angina so that pain is distinctly more frequent, lasts longer and is brought on by a smaller amount of physical activity.

The risk of a heart attack or sudden death is greatly increased in those with unstable angina because it usually signals the rupture of an atherosclerotic plaque in one of the coronary arteries. That, in turn, leads to a blood clot which can grow rapidly and completely block the artery. A heart attack occurs in about half of those with unstable angina. Because these risks are greatest when the symptoms begin, prompt medical attention is essential.

Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.