Acute coronary syndromes

Introduction

Acute coronary syndromes comprise the spectrum of unstable cardiac ischemia from unstable angina to acute myocardial infarction. Rather than the traditional nomenclature of unstable angina, non-Q wave and Q wave myocardial infarction, acute coronary syndromes are now classified based on the presenting electrocardiogram as either "ST elevation" or "non-ST elevation." This allows for immediate classification and guides determination of whether patients should be considered for acute reperfusion therapy. The evolution of cardiac markers then allows determination of whether myocardial infarction has occurred. Acute coronary syndromes represent a dynamic state in which patients frequently shift from one category to another, as new ST elevation can develop after presentation and cardiac markers can become abnormal with recurrent ischemic episodes.

Diagnosis

Many patients with acute coronary syndromes will exhibit electrocardiographic changes during pain - either ST segment elevation, ST segment depression, or T wave flattening or inversion. 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. Algorithms have been developed to aid in determining the likelihood that a patient has an acute coronary syndrome, and for those patients that do have an acute coronary syndrome, the risk of death or death and ischemic events.

Many hospitals have developed chest pain observation units to provide a systematic approach toward serial risk stratification 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 an 8- to 24-hour period and are discharged directly from the emergency department if these tests are negative.

Treatment

Table 10-4 provides a summary of the American College of Cardiology/American Heart Association Guideline recommendations for selected medical treatments.

A. General Measures
Treatment of acute coronary syndromes without ST elevation should be multifaceted and vigorous. Patients who are at high risk 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.

B. Anticoagulation, Antiplatelet, and Thrombolytic Therapy
Coronary thrombosis plays a prominent role in the pathophysiology of unstable angina and its progression to myocardial infarction, and antithrombotic therapy plays an important role in treatment. Patients should receive a combination of antiplatelet and anticoagulant agents. Aspirin, 81-325 mg daily, and heparin (low molecular weight or unfractionated) should be commenced on presentation. Several trials have shown that low-molecular-weight heparin (and specifically enoxaparin 1 mg/kg subcutaneously every 12 hours) is somewhat more effective than unfractionated heparin in preventing recurrent ischemic events in the setting of acute coronary syndromes. However, the recent SYNERGY trial showed that unfractionated heparin and enoxaparin had similar rates of death or (re)infarction in the setting of frequent early coronary intervention. 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/d for 12 months) in patients with non-ST segment elevation acute coronary syndromes. When treated with clopidogrel, the optimal aspirin dose appears to be 81 mg/d (versus 160 mg/d or 325 mg/d) based on similar thrombotic event rates and lower rates of bleeding.