What is Considered ST-Segment Elevation on ECG
ST-segment elevation is defined by specific voltage thresholds measured at the J-point that vary by lead location, patient age, and sex, and must be present in 2 or more anatomically contiguous leads to diagnose STEMI. 1
Standard Criteria for Men ≥40 Years
Age and Sex-Specific Thresholds
Men <40 Years
- ≥2.5 mm (0.25 mV) in leads V2-V3 (higher threshold due to normal early repolarization patterns in younger men) 1
- ≥1.0 mm (0.1 mV) in all other leads 1
Women (All Ages)
- ≥1.5 mm (0.15 mV) in leads V2-V3 (lower threshold than men due to physiologic differences) 1
- ≥1.0 mm (0.1 mV) in all other leads 1
Posterior and Right Ventricular Leads
- ≥0.5 mm (0.05 mV) in leads V7-V9 (posterior MI detection) 1
- ≥1.0 mm in leads V3R-V4R (right ventricular infarction) 1
Critical Requirement: Contiguous Leads
The elevation must appear in 2 or more anatomically contiguous leads to diagnose acute ischemia/infarction. 1 This requirement reduces false positives from normal variants or measurement artifact.
Contiguous Lead Groups
ST-Segment Depression Thresholds
Horizontal or downsloping ST-depression ≥0.5 mm at the J-point in 2 or more contiguous leads suggests myocardial ischemia, particularly when maximal in leads V1-V3 (indicating posterior MI). 1
Special Circumstances and STEMI Equivalents
Left Bundle Branch Block (LBBB)
The 2022 ACC guidelines provide a scoring system where ≥3 points indicates STEMI: 1
- Concordant ST-elevation ≥1 mm in leads with positive QRS = 5 points 1
- Concordant ST-depression ≥1 mm in V1-V3 = 3 points 1
- Discordant ST-elevation ≥5 mm in leads with negative QRS = 2 points 1
De Winter Sign
Tall, prominent, symmetrical T-waves arising from upsloping ST-depression >1 mm at the J-point in precordial leads represents acute LAD occlusion without classic ST-elevation. 1 This is a STEMI equivalent requiring immediate reperfusion.
Hyperacute T-Waves
Broad, asymmetric, peaked T-waves may precede ST-elevation in early STEMI. 1 Serial ECGs over very short intervals (5-10 minutes) help detect progression to frank STEMI. 2
Common Pitfalls
Timing Issues
25% of STEMIs are missed because significant ST-elevation occurs at an earlier or later time point than the initial ECG. 3 Serial ECGs are essential when clinical suspicion remains high despite initial non-diagnostic findings.
Measurement Errors
30% of STEMIs are missed due to incorrect J-point identification. 3 The J-point is where the QRS complex ends and the ST-segment begins—this must be measured precisely, not estimated visually.
Borderline Elevations
36% of STEMIs present with non-significant or borderline ST-elevation that doesn't meet voltage thresholds. 3 In patients with ongoing ischemic symptoms, activate the catheterization laboratory even with borderline findings rather than waiting for criteria to be met. 1, 2
Posterior MI Recognition
ST-depression in V1-V3 with upright T-waves represents posterior STEMI (a STEMI equivalent). 1 Always obtain posterior leads (V7-V9) when inferior MI is suspected, as 9% of missed STEMIs involve inferoposterior localization. 3
Single-Lead Elevation
ST-elevation in only lead III with maximal precordial ST-depression in V4-V6 indicates high-risk inferior MI with 62% rate of severe heart failure, despite not meeting the 2-contiguous-lead criterion. 4 These patients require aggressive intervention.
Diagnostic Performance Reality
Current guideline criteria identify only 35% of adjudicated STEMIs when applied to a single ED ECG (sensitivity 35%, PPV 54%). 3 This underscores that clinical context, serial ECGs, and liberal use of emergency angiography are essential—do not rely solely on meeting voltage thresholds when ischemic symptoms are convincing. 1, 2