Chapter 8: Non–ST-Segment Elevation Acute Coronary Syndromes

PATIENT CASE

A 67-year-old man with a history of type 2 diabetes mellitus (DM) and hypertension presents with chest pain that began the night before while watching television. The pain is midsternal, nonradiating, sharp, nonpleuritic, nonpositional, and 6 out of 10 in intensity. It has waxed and waned since onset. Physical activity has been minimal. Aside from mild shortness of breath, his review of systems is negative.

The patient has no history of chest pain or coronary artery disease (CAD). He takes aspirin 81 mg daily, metformin 500 mg twice daily, lisinopril 10 mg daily, and simvastatin 40 mg daily. His initial vital signs are as follows: temperature 37.6°F, blood pressure 153/94 mm Hg, heart rate 96 bpm, respiratory rate 17 breaths/min, and oxygen saturation 98% on room air. An electrocardiogram (ECG) shows sinus rhythm with a normal axis, right bundle branch block, normal ST segments, and flattened T waves in V₄-V₆, with no prior available ECG for comparison. A point-of-care troponin assay is negative.

What additional workup, if any, is required to establish a diagnosis, and what are the next best steps in management?

DEFINITIONS

An acute coronary syndrome (ACS) occurs when a patient experiences the acute onset of myocardial ischemia. The ACS spectrum (Figure 8-1) is divided into the following:

• ST-segment elevation myocardial infarction (STEMI), in which patients have a clinical picture consistent with myocardial ischemia and ST-segment elevations in 2 or more contiguous leads on the surface ECG. Biomarkers of myocardial necrosis, such as serum troponin, may not yet be detectable.

• Non–ST-segment elevation myocardial infarction (NSTEMI), in which patients have elevated biomarkers consistent with myocardial infarction (MI) but do not meet STEMI criteria.

• Unstable angina (UA), in which patients have chest pain characteristic of myocardial ischemia but negative biomarkers. Unlike chronic stable angina, the pain is either new or has become more severe, longer lasting, or provokable with minimal or no exertion.

Patients with chest pain can be rapidly assessed for STEMI; however, biomarkers of myocardial necrosis may not become positive until several hours after initial presentation. Thus, NSTEMI and UA are often indistinguishable early in the clinical course and are therefore grouped together as non–ST-segment elevation ACS (NSTEACS).

EPIDEMIOLOGY

Each year in the United States, 635,000 patients have a first-time coronary event causing hospitalization or death, 155,000 patients have a clinically silent event, and 300,000 patients have a recurrent event.¹ The average age at presentation is 65 years for men and 72 years for women.

Data from the National Registry of Myocardial Infarction ...