What are the electrocardiographic criteria for diagnosing ST‑segment elevation myocardial infarction (STEMI) on an electrocardiogram (EKG)?

STEMI Electrocardiographic Diagnostic Criteria

The diagnosis of ST-segment elevation myocardial infarction requires ST-segment elevation measured at the J-point in at least 2 anatomically contiguous leads, with specific voltage thresholds that vary by age, sex, and lead location. 1

Standard ST-Elevation Thresholds

Precordial Leads V2-V3

The voltage criteria for leads V2-V3 are stratified by age and sex:

• Men ≥40 years: ≥2.0 mm (0.2 mV) 1, 2
• Men <40 years: ≥2.5 mm (0.25 mV) 1, 2
• Women (all ages): ≥1.5 mm (0.15 mV) 1, 2

These age- and sex-specific thresholds account for normal J-point elevation that is physiologically higher in younger men and generally lower in women. 1

All Other Leads

For leads I, II, III, aVL, aVF, and V4-V6:

• All patients: ≥1.0 mm (0.1 mV) 1, 2

Special Lead Locations

• Leads V4-V5: ≥0.5 mm (0.05 mV), except males <30 years where ≥1.0 mm is more appropriate 1
• Posterior leads V7-V9: ≥0.5 mm (0.05 mV) 1, 2
• Right-sided leads V3R-V4R: ≥0.5 mm (≥1.0 mm in men <30 years) 1, 2

Contiguous Lead Requirement

ST-elevation must appear in at least 2 anatomically contiguous leads to meet diagnostic criteria. 1, 2 This requirement reduces false-positive diagnoses from measurement artifact or normal variants. 2

Contiguous Lead Groups

• Anterior: V1-V6 1, 3
• Inferior: II, III, aVF 1, 3
• Lateral: I, aVL, V5-V6 1, 3
• Septal: V1-V2 3

STEMI Equivalents Requiring Immediate Reperfusion

Posterior Myocardial Infarction

Isolated ST-depression ≥0.5 mm in leads V1-V3 with upright (positive) terminal T-waves represents a posterior STEMI equivalent. 1, 2, 3 This pattern reflects acute circumflex artery occlusion and is frequently missed when only standard 12-lead ECG is evaluated. 2, 3

• Confirmation: Record posterior leads V7-V9; ST-elevation ≥0.5 mm confirms transmural posterior infarction 1, 2, 3
• Management: Treat identically to anterior STEMI with immediate reperfusion 2, 3

New or Presumed New Left Bundle Branch Block

New LBBB in a patient with ischemic symptoms is a STEMI equivalent requiring immediate reperfusion therapy. 2, 3 Emergency angiography should not be delayed even if specific concordance criteria are not met. 2, 3

• Concordant ST-elevation (elevation in leads with positive QRS deflections) is the most reliable marker of acute coronary occlusion in LBBB 1, 2
• Previous ECG is valuable to determine if LBBB is new 1, 2

Left Main or Proximal LAD Occlusion Pattern

Diffuse ST-depression in ≥8 leads combined with ST-elevation in aVR and/or V1 signals left main or severe multivessel disease. 2, 3 This pattern mandates immediate catheterization. 3

Hyperacute T-Waves

Tall, peaked, symmetric (hyperacute) T-waves may precede overt ST-elevation in the earliest phase of coronary occlusion. 2, 3 When present with high clinical suspicion, activate the catheterization laboratory without waiting for ST-elevation to develop. 3

Right Ventricular Infarction

In inferior STEMI, record right-sided leads V3R-V4R; ST-elevation ≥1.0 mm indicates RV involvement. 1, 2, 3 This finding mandates specific hemodynamic management: avoid nitrates and diuretics, maintain preload with intravenous fluids. 3

Measurement Technique

Measure ST-segment deviation at the J-point (the junction between the end of the QRS complex and the beginning of the ST segment). 1, 2 Standard ECG calibration is 10 mm/mV, so 0.1 mV equals 1 mm on the vertical axis. 2

Reciprocal ST-Depression

Reciprocal ST-depression in anatomically opposite leads increases diagnostic specificity for acute coronary occlusion. 1, 4 For example:

• Inferior STEMI (II, III, aVF elevation) typically shows reciprocal depression in I, aVL 1
• Anterior STEMI (V1-V6 elevation) typically shows reciprocal depression in II, III, aVF 1

The presence of reciprocal changes improves positive predictive value from approximately 50% to >90%. 4

Critical Diagnostic Pitfalls

Conditions Mimicking STEMI

• Left ventricular hypertrophy can produce ST-elevation in precordial leads 1, 3
• Early repolarization (especially in young males) may show J-point elevation 1
• Acute pericarditis shows diffuse ST-elevation without reciprocal depression 1
• Brugada syndrome shows characteristic right precordial ST-elevation 1
• Ventricular pacing obscures ST-segment interpretation 3

Missed STEMI Patterns

Up to 30% of patients with acute coronary occlusion may not meet standard STEMI criteria. 2, 3, 5 Common reasons include:

• Circumflex artery occlusion often produces only posterior changes (ST-depression V1-V3) 2, 3
• Timing: ST-elevation may not yet be present (hyperacute T-waves only) or may have already resolved 6
• Borderline voltage: ST-elevation just below diagnostic thresholds 6
• Incorrect measurement: J-point not properly identified 6

Clinical Implementation Algorithm

1. Obtain 12-lead ECG within 10 minutes of first medical contact 2, 3
2. Measure ST-deviation at the J-point in all leads 1, 2
3. Apply age- and sex-specific voltage criteria for V2-V3 1, 2
4. Verify presence in ≥2 contiguous leads 1, 2
5. If inferior STEMI, add right-sided leads V3R-V4R 1, 2, 3
6. If ST-depression V1-V3 with upright T-waves, add posterior leads V7-V9 1, 2, 3
7. Assess for reciprocal changes to increase specificity 1, 4
8. If initial ECG non-diagnostic but high clinical suspicion, perform serial ECGs at 5-10 minute intervals 3

Diagnostic Performance Limitations

Current guideline criteria, when applied to a single ED ECG, identify only 35-50% of adjudicated STEMIs. 7, 6 Sensitivity ranges from 17-50% with conventional criteria, though specificity remains high at 97-98%. 7, 6, 8 Adding ST-depression criteria increases sensitivity to 79-84% but reduces specificity to 79-93%. 9, 8 This underscores the critical importance of clinical context, serial ECGs, and liberal use of emergency angiography when clinical suspicion remains high despite non-diagnostic initial ECG. 2, 3, 6