Unstable angina describes a syndrome that is intermediate between stable angina and myocardial infarction: an accelerating or "crescendo" pattern of chest pain that lasts longer than stable angina, occurs with less exertion or at rest, or is less responsive to medication.

Unstable angina and myocardial infarction are considered acute coronary syndromes, while stable angina is a chronic condition.

Unstable angina occurs in approximately 6 out of every 10,000 people. Coronary artery disease due to atherosclerosis is by far the most common cause of unstable angina. A coronary artery spasm is a rare cause of angina.

Initially, narrowing (in the form of atheroschlerotic plaques) of the coronary arteries may be severe enough to cause stable angina with exertion or stress. This narrowing, however, sometimes causes no symptoms at all.

For reasons that are not well understood, the plaques reach a point at which they rupture. Under these circumstances, a plug formed by platelets and blood clots may form, causing an already narrowed blood vessel to become highly susceptible to becoming completely blocked. This unstable situation may progress to complete occlusion of the vessel, with infarction of the heart muscle (heart attack).

Once this type of lesion exists in a coronary artery, and whether the event leads to a heart attack or not, the chest pain produced by the extreme narrowing of the coronary artery may become unstable. Unlike stable angina, in which chest pain can be induced by exercise or stress, chest pain in unstable angina may occur at rest and without any precipitating factors. Pain may increase in severity, frequency, or duration at low levels of activity or for no identifiable reason. This type of angina may also occur soon after a heart attack.

Risk factors for unstable angina are similar to those for stable angina and coronary artery disease, including:

• male gender
• age
• cigarette smoking
• high cholesterol levels (in particular, high LDL cholesterol and low HDLcholesterol)
• high blood pressure
• diabetes
• family history of coronary heart disease before age 55
• sedentary lifestyle
• being more than 30% over ideal body weight

Occasionally, sudden overwhelming stress can precipitate an episode of angina.

Typical anginal pain usually originates in the chest and may radiate to shoulder, arm, jaw, neck, back or other areas. The pain is often described as tightness, squeezing, crushing, burning, choking or aching. Unstable angina is differentiated from stable angina in that the pain may:

• occur at rest
• be new in conditions of onset or last longer than previous anginal attacks
• be less responsive to medication

In other words, if a pattern of stable angina has been present previously, the development of unstable angina may be defined by a change in the pattern, frequency, or severity of the pain. If a pattern of stable angina has not been present previously, the beginning of chest pain episodes also constitutes unstable angina.

• Physical examination may reveal a change in blood pressure. Transient heart murmur or arrhythmias (irregular heartbeats) may occur as well.
• ECG changes that occur at rest, during pain, are often diagnostic.
• Heart scans or coronary angiography of the heart are often performed.
• Echocardiography may reveal changes in the heart caused by decreased coronary blood flow.
• Blood tests such as CPK, CPK-MB, troponin I, troponin T, and myoglobin are used to diagnose unstable angina and can predict likelihood of progression to heart attack.

An individual experiencing unstable angina usually requires rest and hospitalization to prevent complications.

A cornerstone of therapy for unstable angina is antiplatelet medication (to prevent platelet aggregation, which is the initial event in the blood circulation leading to clot formation within a vessel). One antiplatelet agent widely used is aspirin. More recently, a medication called clopidogrel has shown in clinical studies to be even more effective than aspirin in reducing the likelihood of heart attacks. Clopidogrel and aspirin may be used together. They are also often administered during heart attacks.

Heparin and nitroglycerin are also given during unstable angina, often sublingually (under the tongue) or intravenously (IV). Other medications include beta-blockers, calcium channel blockers, anti-anxiety medications, and medications to control blood pressure and abnormal heart rhythms.

Surgery may be recommended. CABG (coronary artery bypass grafting) or PTCA (balloon angioplasty), often with the implantation of a stent, may be necessary.

The outcome varies depending on many factors. The most important factor is the severity of the underlying coronary artery disease. Other factors include the severity of the episode, past history of heart attack, and the number of medications a patient was taking when the episode began. Associated arrythmias and heart attacks can cause sudden death.

The best prevention of unstable as well as stable angina is to modify those risk factors that can be changed.

• stop smoking
• lose weight if overweight
• control blood pressure, diabetes, and cholesterol

In fact, some studies have shown that modifying risk factors can prevent the progression of arterial blockages and can lead to decrease in the severity of blockages.

Aspirin, antianginal medications such as nitrates (nitroglycerin), beta-blockers, calcium channel blockers, or others may be prescribed to prevent the occurrence of angina and lessen its severity. Aspirin and clopidogrel may reduce the likelihood of heart attacks in predisposed patients.