National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: Clinical Characteristics and Utilization of Biochemical Markers in Acute Coronary Syndromes

Acute coronary syndrome (ACS)1 refers to a constellation of clinical symptoms caused by acute myocardial ischemia (1)(2). Owing to their higher risk for cardiac death or ischemic complications, patients with ACS must be identified among the estimated 8 million patients with nontraumatic chest symptoms presenting for emergency evaluation each year in the US (3). In practice, the terms suspected or possible ACS are often used by medical personnel early in the process of evaluation to describe patients for whom the symptom complex is consistent with ACS but the diagnosis has not yet been conclusively established (1). Patients with ACS are subdivided into 2 major categories based on the 12-lead electrocardiogram (ECG) at presentation (Fig. 11 ): those with new ST-segment elevation on the ECG that is diagnostic of acute ST-elevation myocardial infarction (STEMI) and those who present with ST-segment depression, T-wave changes, or no ECG abnormalities (non–ST elevation ACS, NSTEACS). The latter term (NSTEACS) encompasses both unstable angina and non–ST elevation myocardial infarction (NSTEMI). This terminology has evolved along clinical lines based on a major divergence in the therapeutic approach to STEMI vs NSTEACS (see section IB). Unstable angina and NSTEMI are considered to be closely related conditions, sharing a common pathogenesis and clinical presentation but differing in severity (1). Specifically, NSTEMI is distinguished from unstable angina by ischemia sufficiently severe in intensity and duration to cause irreversible myocardial damage (myocyte necrosis), recognized clinically by the detection of biomarkers of myocardial injury (4).