NSTEMI (Non-ST-Elevation Myocardial Infarction)
The acronym that pairs with STEMI is NSTEMI, which stands for Non-ST-Elevation Myocardial Infarction. 1
Definition and Key Distinction
NSTEMI is defined as myocardial infarction with elevated cardiac troponin levels (above the 99th percentile upper reference limit with a rise and/or fall pattern) occurring in the absence of persistent ST-segment elevation on ECG. 1, 2
The critical distinction between STEMI and NSTEMI lies in the ECG presentation:
STEMI shows persistent ST-segment elevation in 2 or more anatomically contiguous leads, indicating complete coronary artery occlusion requiring immediate reperfusion therapy 1
NSTEMI includes all other acute coronary syndrome presentations with myocardial necrosis: lesser ST-segment elevation, ST-segment depression, T-wave inversion, or even a completely normal ECG 1
Clinical Spectrum
NSTEMI exists on a continuum with unstable angina (UA), with both conditions sharing similar pathogenesis and clinical presentations 1. The sole differentiating factor between NSTEMI and unstable angina is the presence of detectable cardiac biomarkers of myocardial necrosis—if troponin is elevated, it's NSTEMI; if troponin is normal, it's unstable angina. 2
ECG Patterns in NSTEMI
The ECG in NSTEMI may demonstrate several patterns 2, 3:
- ST-segment depression (≥0.5 mm), particularly in multiple leads, correlating with increased mortality risk 3
- T-wave inversions (≥2 mm), especially deep symmetrical inversions in precordial leads 3
- Transient ST-segment changes that resolve when symptoms improve 3
- Completely normal ECG despite ongoing myocardial necrosis 2, 3
Critical Pitfall to Avoid
Abnormalities on ECG and elevated troponins in isolation are insufficient to diagnose NSTEMI—they must be interpreted within the appropriate clinical context of acute myocardial ischemia. 1, 2 A completely normal ECG does not exclude acute coronary syndrome, as 1-6% of patients with normal ECGs presenting with chest pain will have myocardial infarction 3.