Chapter 124. Acute Coronary Syndromes

1. What are the available tools to diagnose and risk stratify patients with suspected acute coronary syndrome (ACS)?

2. What are the American College of Cardiology and American Heart Association (ACC/AHA) class I guideline recommendations for anti-ischemia and antithrombotic therapy for unstable angina (UA) and non-ST-elevation myocardial infarction (NSTEMI)? For STEMI? Which drugs reduce mortality?

3. What are the benefits of an invasive versus a conservative strategy for managing UA/NSTEMI?

4. Which patients should undergo early invasive therapy in the setting of ACS?

The term acute coronary syndrome (ACS) refers to a group of clinical symptoms consistent with acute myocardial ischemia, whether from unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), or ST-segment elevation myocardial infarction (STEMI). The definition of STEMI is based on the electrocardiographic (ECG) criteria of ST-segment elevation, and this diagnosis accounts for 330,000 hospital admissions per year in the United Sstates. The definition of NSTEMI is based on the absence of ST-segment elevations on the ECG, but ST depression and T-wave inversions may be evident, and there is sufficient ischemic damage to cause biochemical evidence of myonecrosis. NSTEMI accounts for 570,000 hospital admissions per year. UA and NSTEMI have similar pathogenesis and clinical presentations, but UA is not associated with release of cardiac troponins and/or creatine kinase (CK-MB). UA accounts for 670,000 admissions per year. According to the American Heart Association (AHA), an estimated $177 billion has been spent on the treatment of coronary heart disease in 2010.

Although tremendous strides have been made in the management of cardiovascular disease, coronary heart disease currently accounts for almost 20% of deaths in the United States. The 30-day mortality associated with the diagnosis of ACS varies from 1.7% for patients with UA to 7.4% for patients with NSTEMI to 11.1% for those with STEMI.

Despite chest pain pathways to guide clinicians in risk stratification, approximately 5% of symptomatic patients with myocardial infarction are inappropriately discharged from the emergency department to the outpatient setting. In addition, nearly 50% of all myocardial infarctions (MIs) produce no symptoms.

This chapter will focus on patients diagnosed with ACS, encompassing STEMI, NSTEMI, and UA, and review the best medical evidence based on the latest pertinent clinical trials reporting diagnosis and management of ACS. Recommendations will be referenced according to the American College of Cardiology (ACC)/AHA guidelines for the management of patients with STEMI and UA/NSTEMI along with the 2007 focused update of these guidelines. This chapter will not review the rapid rule-out protocols for the more than 75% of 5 million patients who present to emergency departments in the United States annually and have no evidence of ACS. Noncardiac chest pain and chronic stable angina are covered elsewhere in this book (Specific treatments/interventions may be described in relation to ACC/AHA guideline recommendations as per the class scheme explained in Table 124-1).