Unstable angina

Unstable angina describes chest pain that is experienced increasingly often and/or with less and less exertion. This condition represents a severity of coronary artery disease (CAD) between stable angina pectoris and a heart attack (myocardial infarction).

Angina is a symptom of temporarily inadequate blood flow to a part of the heart (ischemia).Myocardial infarction involves a permanent loss of a part of the heart, a death of heart muscle cells. Not all individuals with unstable angina go on to infarction though it is considered a serious symptom.

Unstable angina is also referred to as crescendo angina, acute coronary insufficiency, intermediate coronary syndrome, and pre-infarction angina. Unstable angina may be described as a new onset of angina within the past two months, increasing angina in previously diagnosed angina, which has become more frequent, longer in duration, or precipitated by less exercise within the past two months, and angina occurring at rest, usually of more than twenty minutes duration, experienced within the past week.

History: In an individual with new onset of chest pain, it is important to distinguish coronary artery disease from other possible causes. A definitive diagnosis often cannot be made immediately. In such cases, angina is presumed until it can be ruled out, due to the seriousness of the diagnosis.

Unstable angina is presumed if the symptoms are described by any of the above criteria. In an individual with previously diagnosed angina, the diagnosis of unstable angina is usually straightforward. The pain is similar in nature, but comes more frequently than before. In cases of prolonged angina at rest that is not relieved by sublingual nitrates, unstable angina may be difficult to differentiate from acute myocardial infarction.

Physical exam will not contribute to the diagnosis.

Tests: An electrocardiogram (EKG) may indicate ischemia to the heart, especially if it can be done during an episode of angina. However, the EKG may also be normal. Echocardiogram, stress test, and angiography are usually performed.

The choice of initial treatment depends on the risk of an imminent cardiac event (heart attack or death), as assessed at the time of the initial examination. Low risk of an imminent cardiac event is assumed if the following criteria for intermediate or high risk are not met.

Intermediate risk criteria include one or more of the following: a recent episode of pain at rest lasting longer than twenty minutes but pain-free at the time of examination, rest pain less than twenty minutes relieved by sublingual nitrates, new onset of pain within the past two weeks with moderate to high likelihood of coronary artery disease, and/or an abnormal EKG.

High-risk criteria include one or more of the following: ongoing pain while at rest lasting longer than twenty minutes, signs or symptoms of cardiovascular instability such as congestive heart failure and/or low blood pressure, and/or and abnormal EKG.

Treatment of low risk unstable angina may be done as an outpatient. Individuals with new onset chest pain are given a trial of antianginal medication, starting with a sublingual nitrate for use during anginal attacks, and an oral beta-blocker for ongoing use. If this does not control the symptoms, a long-acting nitrate in either oral or skin patch/paste (topical) form may be added to the beta-blocker. Calcium channel blockers are indicated if coronary artery spasm (Prinzmetal's or variant angina) is thought to be a contributing factor. In addition, an antiplatelet drug is given to help prevent a heart attack by inhibiting blood clotting. Individuals with increasing angina are usually on antianginal medications already. The medications are reviewed and are altered as necessary until the symptoms are controlled or until higher doses cannot be tolerated.

Further evaluation is usually required to confirm the diagnosis in new onset individuals, to define risk more accurately, and to plan further treatment. In most cases a cardiac stress test is performed, preferably within 72 hours, unless the individual is felt to be at very low risk for CAD.

If stress tests show ischemia despite medication, coronary arteriography is performed. This will demonstrate whether CAD can be successfully treated by coronary bypass surgery or balloon angioplasty.

Individuals with intermediate risk unstable angina may be treated similarly to low risk individuals when the individual is pain free and has a normal EKG at the time of examination. But, those with ongoing symptoms and/or ischemia on EKG at the time of examination are hospitalized, admitted to either a CCU or a monitored bed in a less intensive setting. An oral beta-blocker may be prescribed. A cardiac stress test is performed after the individual has been pain free for 48 hours. The results are used to reassess risk and plan further treatment. If the stress test shows no ischemia, the individual is reclassified as low risk. Medical management is usually sufficient, and the individual may be discharged from the hospital in one to two days. If the stress test shows ischemia only at high workloads, and there is no evidence of left heart dysfunction such as hypotension, difficulty breathing, or excessive fatigue, further diagnostic testing is needed. This may be accomplished by either an alternative type of stress test or coronary arteriography. If the stress test shows ischemia at low workloads, or if there is evidence of left heart dysfunction, the individual is reclassified as high risk.

Coronary arteriography is indicated, followed by revascularization if the results show that this is feasible.

High-risk unstable angina requires hospitalization and continuous EKG monitoring in a coronary care unit (CCU). Initial treatment includes bedrest, oxygen, anti-platelet drugs, heparin (a blood thinner), and antianginal medications. Sublingual nitrates are tried first, and the individual is also started on a beta blocker. If the individual still continues to have ischemia, a calcium channel blocker may be added if coronary artery spasm is suspected. In severe cases, narcotics may be necessary to relieve pain. Symptoms that continue after an hour or more of medical treatment are an indication for immediate coronary arteriography, followed by coronary bypass surgery or angioplasty to improve blood flow to the heart (revascularization), if appropriate.

If the individual's heart is failing seriously, intra-aortic balloon counterpulsation may be needed to support circulation until coronary bypass or angioplasty can be performed. However, most individuals can be stabilized with medical treatment. After the individual has been pain free and stable for 24 hours, the individual is allowed to walk progressively more, and is moved to a regular bed when symptoms have clearly been controlled.

Further evaluation is the next step. In high-risk individuals, revascularization improves the prognosis. Therefore, coronary arteriography is performed, usually within 24 hours, to determine whether these procedures are feasible. After revascularization, ongoing treatment includes anti-platelet drugs and modification of risk factors (discussed in the section on coronary artery disease). Antianginal drugs are not required unless there is residual ischemia. High-risk individuals who do not receive revascularization may require prolonged hospitalization. Ongoing treatment is the same as for stable angina (discussed in the section on angina pectoris), including antianginal drugs, anti-platelet drugs, and modification of risk factors.