A 71-year-old woman presents to the emergency department because of chest pain that began 2 hours ago while she was watching television. She describes a substernal pressure sensation radiating to her left shoulder and jaw. The pain is associated with nausea and diaphoresis and has persisted despite rest. Her medical history is significant for hypertension, hyperlipidemia, type 2 diabetes mellitus, and chronic kidney disease. Medications include amlodipine, atorvastatin, metformin, and aspirin. Temperature is 36.9°C (98.4°F), blood pressure is 154/92 mm Hg, pulse is 104/min, and respiratory rate is 18/min. Oxygen saturation is 97% on room air. ECG demonstrates 1.5-mm ST-segment depressions in leads II, III, aVF, and V4-V6. Initial high-sensitivity troponin I is elevated and rises further on repeat testing 3 hours later.
Which of the following is the most likely diagnosis?
The correct answer is:
B) Non-ST-elevation myocardial infarction (NSTEMI)
This patient has an NSTEMI, a form of acute coronary syndrome caused by acute plaque rupture and partial coronary artery occlusion resulting in myocardial ischemia and myocardial necrosis. The diagnosis is established by evidence of myocardial injury, demonstrated by elevated and rising cardiac troponin levels, in the setting of symptoms consistent with myocardial ischemia.
NSTEMI and unstable angina often present similarly. Patients may develop chest pressure at rest, diaphoresis, nausea, radiation of pain to the arm or jaw, and ischemic ECG changes such as ST-segment depression or T-wave inversion. The key distinction is that NSTEMI causes myocardial cell death, resulting in elevated cardiac biomarkers. Unstable angina produces ischemia without infarction, so troponin levels remain normal.
The ECG in NSTEMI may be normal or may demonstrate ischemic changes. Unlike STEMI, persistent ST-segment elevation is absent because complete transmural infarction has not occurred. Nevertheless, NSTEMI remains a true myocardial infarction and carries significant risk of complications, including arrhythmias, heart failure, and recurrent ischemic events.
A common Step 2 teaching point is that diagnosis of myocardial infarction requires both clinical evidence of ischemia and evidence of myocardial injury. In modern practice, elevated troponin levels are the most sensitive marker of myocardial necrosis.
Answer choice A: Acute pericarditis, is incorrect.
Pericarditis typically causes sharp, pleuritic chest pain that improves when leaning forward. ECG findings classically include diffuse ST-segment elevation and PR-segment depression rather than focal ST-segment depression with elevated troponins due to coronary ischemia.
Answer choice C: Stable angina, is incorrect.
Stable angina causes predictable exertional symptoms that resolve with rest and does not result in elevated troponin levels. This patient’s prolonged chest pain at rest and rising cardiac biomarkers indicate acute myocardial infarction.
Answer choice D: ST-elevation myocardial infarction (STEMI), is incorrect.
STEMI is characterized by acute coronary occlusion causing persistent ST-segment elevation in contiguous leads. This patient’s ECG demonstrates ST-segment depression rather than ST-segment elevation.
Answer choice E: Unstable angina, is incorrect.
Unstable angina can cause identical symptoms and similar ECG findings, but cardiac biomarkers remain normal. The elevated and rising troponin levels confirm myocardial necrosis and therefore establish the diagnosis of NSTEMI.
Key Learning Point
NSTEMI is an acute coronary syndrome characterized by myocardial ischemia and myocardial necrosis without ST-segment elevation. Elevated cardiac troponin levels distinguish NSTEMI from unstable angina.
