Angina is a term for the discomfort felt when a blockage in a coronary artery prevents enough oxygen-rich blood from reaching part of the heart. In some people, this discomfort manifests not as pain, but as a sensation of tightness or heaviness across the chest. Angina pain or discomfort often is felt not only in the chest, but in the neck, jaw, back, and/or arms. Patients with blockages in their coronary arteries (atherosclerosis) also may experience the following symptoms during an angina attack: sweating or "clamminess," shortness of breath, nausea, and a feeling like indigestion.

Unstable angina is understood as anginal pain that occurs with lesser degrees of exertion, increasing frequency, or at rest (i.e., without exertion). Unstable angina, which occurs at rest, represents the condition in its most serious form. It usually is caused by the formation of a blood clot in a coronary artery at the site of a ruptured plaque and, if left untreated, it may result in a heart attack and irreversible damage to the heart.

Causes

The heart receives its blood supply from the three coronary arteries. Heart tissue requires oxygen-rich blood to perform its pumping function and to survive. Over time, plaques made up of cholesterol and other substances can develop in these arteries and partially block the flow of blood.

Plaques can cause problems in two ways: by (1) creating blockages and (2) forming blood clots. If a plaque grows, it eventually reaches a point where it critically impairs the flow of oxygen-rich blood. This usually happens when the artery becomes more than about 70% blocked (stenosed). A 70% blockage may permit enough blood to reach the heart when its oxygen demand is not high, such as when one is sitting down. With exertion (e.g., climbing stairs), however, the heart works harder and requires more oxygen-rich blood. A 70% or greater blockage will deprive the heart of the volume of blood needed to meet its increased demand and cause angina.

If the surface of a plaque ruptures, a blood clot may form on top of it, creating a larger blockage. If the clot grows large enough, it can completely obstruct the artery. Blood clots may form and spontaneously partially dissolve, intermittently blocking blood flow. Each time this occurs, the patient experiences symptoms of angina. The discomfort can last only a few minutes or half an hour or more.

Because blood clots can form anytime, patients can experience angina even at rest. Chest pains that occur at rest are a warning that plaque in a coronary artery has ruptured and a blood clot may be forming. Heart tissue becomes ischemic (anemic) within 30 minutes of being deprived of oxygen and may die within a few hours. If a blood clot that completely blocks blood flow in the coronary artery does not at least partially dissolve, it will cause a heart attack.

Diagnosis

Unstable angina is a clinical diagnosis based primarily on the observation of symptoms and supported by evidence such as changes on an electrocardiogram (EKG). A patient complaining of chest pain or tightness experienced with minimal exertion, lasting a few minutes to half an hour, often accompanied by discomfort in the neck, jaw, back or arm, nausea, shortness of breath, or clamminess — can reasonably be diagnosed with unstable angina. No single test can diagnose unstable angina.