Unstable Angina

Most clinicians use the term "unstable angina" to denote an accelerating or "crescendo" pattern of pain in cases where previously stable angina occurs with less exertion or at rest, lasts longer, and is less responsive to medication. Coronary angioscopy has shown that a high proportion of patients with this pattern of symptoms have "complex" coronary stenoses characterized by plaque rupture, ulceration, or hemorrhage with subsequent thrombus formation. This inherently unstable situation may progress to complete occlusion and infarction or may heal, with reendothelialization and a return to a stable though possibly more severe pattern of ischemia. New-onset angina is sometimes considered unstable, but if it is exertional and responsive to rest and medication, it does not carry the same poor prognosis.

Diagnosis

Most patients with unstable angina will exhibit electrocardiographic changes during pain - commonly ST segment depression or T wave flattening or inversion but sometimes, and more ominously, ST segment elevation. They may exhibit signs of left ventricular dysfunction during pain and for a time thereafter.

Chest pain is one of the most frequent reasons for emergency department visits, and the consequences of misdiagnosis are significant (clinically for false-negative diagnoses and economically for false-positives). Up to half of patients have noncardiac diagnoses, and even many of those with coronary disease are at low risk for early events (< 1% 30-day event rate). However, those with recent, prolonged, or recurrent episodes and accompanying electrocardiographic changes indicative of ischemia (ST segment depression > 1 mm, ischemic ST segment elevation, T wave inversions, or new LBBB) may have much higher event rates. Many hospitals have developed chest pain observation units to provide a longer period of observation and immediate testing in patients determined to be at low risk in order to improve the triage process. In many cases those who have not experienced new chest pain and have no electrocardiographic changes or cardiac enzyme elevations undergo treadmill exercise tests or imaging procedures to exclude ischemia at the end of a 6-24 hour period and are discharged directly from the emergency department if these tests are negative.

Treatment

A. General Measures
Treatment of unstable angina should be multifaceted and vigorous. Patients should be hospitalized, maintained at bed rest or at very limited activity, monitored, and given supplemental oxygen. Sedation with a benzodiazepine agent may help if anxiety is present. The systolic blood pressure is usually maintained at 100-120 mm Hg, except in previously severe hypertensives, and the heart rate should be lowered to 60/min.

B. Anticoagulation, Antiplatelet, and Thrombolytic TherapyBecause intravascular thrombosis plays a prominent role in the pathophysiology of unstable angina and its progression to myocardial infarction, antithrombotic therapy is an important part of treatment for unstable angina. Most patients should receive a combination of two or more agents. Aspirin, 325 mg daily, should be commenced on admission, and intravenous heparin should be started if symptoms have been recent (past 24 hours) or if they recur. Heparin therapy, when necessary, should be continued for at least 2 days. Several trials have shown that low-molecular-weight heparin is marginally superior to unfractionated heparin in preventing recurrent ischemic events in the setting of acute coronary syndromes. Enoxaparin (1 mg/kg subcutaneously every 12 hours) is the best-studied member of this class of agents. The Clopidogrel in Unstable Angina to Prevent Recurrent Events (CURE) trial demonstrated a 20% reduction in the composite end point of cardiovascular death, myocardial infarction, and stroke with the addition of clopidogrel (300 mg loading dose, 75 mg daily for 12 months) in patients with non-ST segment elevation acute coronary syndromes.