NSTEMI (Non-ST-Elevation Myocardial Infarction)
A patient with a normal ECG and elevated troponin has NSTEMI, not unstable angina, stable angina, or STEMI. 1
Diagnostic Criteria
The diagnosis of NSTEMI requires:
- Elevated cardiac troponin (above the 99th percentile) with a rising and/or falling pattern 1
- Clinical evidence of myocardial ischemia (symptoms, ECG changes, or imaging findings) 1
- Absence of persistent ST-segment elevation on the ECG 1
In your scenario, the normal ECG excludes STEMI (which requires persistent ST-elevation) and the elevated troponin excludes both stable angina and unstable angina. 1
Why Not the Other Options?
Stable angina (Option A): Ruled out because stable angina does not cause troponin elevation—it represents predictable, exertional chest pain without myocardial necrosis. 1
Unstable angina (Option B): Ruled out because unstable angina is defined by ischemic symptoms without troponin elevation above the diagnostic threshold. 1, 2 With contemporary high-sensitivity troponin assays, the diagnosis of unstable angina has declined markedly—approximately 30% of patients previously diagnosed with unstable angina are now reclassified as NSTEMI when cardiac-specific troponins are measured. 1, 3
STEMI (Option D): Ruled out because STEMI requires persistent ST-segment elevation on the ECG, which is absent in this case. 1
Critical Diagnostic Nuances
Serial troponin measurements are essential: A single elevated troponin is insufficient for diagnosis. You must demonstrate a dynamic rise and/or fall pattern (≥20% change between measurements) to distinguish acute NSTEMI from chronic troponin elevation. 1, 4, 5 Obtain troponins at presentation and 3-6 hours after symptom onset (or 0h/1h with high-sensitivity assays). 1, 6
Troponin elevation is not specific to NSTEMI: Multiple non-ACS conditions cause troponin elevation including heart failure, tachyarrhythmias, hypertensive emergencies, myocarditis, Takotsubo cardiomyopathy, pulmonary embolism, renal dysfunction, and critical illness. 1, 4, 5 In one ED study, only 51% of patients with elevated troponins had true ACS—the remainder had alternative explanations. 7
Quantitative interpretation matters: The higher the troponin level, the greater the likelihood of type 1 MI. Elevations >5-fold the upper reference limit have >90% positive predictive value for acute MI. 4, 5, 6 Troponin should be interpreted as a quantitative marker, not simply positive/negative. 1, 6
Common Pitfalls to Avoid
Do not diagnose NSTEMI based solely on elevated troponin. You must integrate clinical presentation (ischemic symptoms), ECG findings (even if "normal," look for subtle ST-depression, T-wave inversions, or dynamic changes), and demonstrate dynamic troponin changes. 1, 7 A completely normal ECG during chest pain should prompt consideration of alternative diagnoses. 1
Recognize that "normal" ECG does not mean completely unremarkable. Look carefully for subtle findings: ST-depression ≥1mm, T-wave inversions >1mm in leads with predominant R waves, transient ST-changes during symptoms, or deep symmetrical T-wave inversions in anterior leads suggesting proximal LAD stenosis. 1 Approximately 5% of patients with normal ECGs ultimately have ACS. 1
Point-of-care troponin assays are inferior. Central laboratory high-sensitivity troponin assays provide superior diagnostic accuracy, sensitivity, and negative predictive value compared to point-of-care tests. 6 Results should be available within 60 minutes, preferably 30 minutes. 1