What are the ECG criteria for diagnosing a ST-Elevation Myocardial Infarction (STEMI) in men and women?

STEMI ECG Criteria

STEMI is diagnosed by new ST-segment elevation at the J-point in at least 2 contiguous leads with sex-specific thresholds: ≥2 mm (0.2 mV) in men ≥40 years or ≥2.5 mm (0.25 mV) in men <40 years in leads V2-V3; ≥1.5 mm (0.15 mV) in women in leads V2-V3; and ≥1 mm (0.1 mV) in all other leads. 1, 2, 3

Standard Diagnostic Criteria

ST-Elevation Thresholds by Lead and Demographics

Precordial Leads V2-V3:

• Men <40 years: ≥2.5 mm (0.25 mV) 4, 3
• Men ≥40 years: ≥2 mm (0.2 mV) 1, 4, 1, 2, 3
• Women (all ages): ≥1.5 mm (0.15 mV) 1, 4, 1, 2, 3

All Other Leads (limb leads and V4-V6):

• All patients: ≥1 mm (0.1 mV) 1, 4, 1, 2, 3

Essential Requirements

• ST elevation must be measured at the J-point (where QRS complex meets ST segment) 3
• Elevation must be present in at least 2 contiguous leads 1, 4, 1, 2, 3
• ST elevation must be new or presumed new 1, 2
• Elevation should persist for ≥20 minutes 1
• Standard ECG calibration: 10 mm/mV (so 0.1 mV = 1 mm vertically) 3

Contiguous Lead Groupings

Anatomically contiguous leads include: 3

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

STEMI-Equivalent Patterns

Posterior MI (True STEMI-Equivalent)

This is the most critical STEMI-equivalent that qualifies for immediate reperfusion therapy. 1, 5

• ST depression ≥0.5 mm in leads V1-V4, maximal in V3-V6, with positive terminal T-waves (upright T-waves) 1, 5
• Represents acute occlusion of posterior descending artery or left circumflex 5
• Confirm with posterior leads V7-V9 showing ST elevation ≥0.5 mm 3, 5
• Activates immediate reperfusion protocols (fibrinolysis or primary PCI) 1, 5

Right Ventricular Infarction

• Obtain right precordial leads V3R and V4R when inferior STEMI is present 3
• ST elevation >0.5 mm in V3R-V4R indicates RV involvement 3, 5
• Critical for management decisions (avoid nitrates, preload reduction) 3

Hyperacute T-Waves

• May appear in very early phase before ST elevation develops 2, 3
• Tall, peaked T-waves in distribution of coronary territory 3
• Requires serial ECGs every 10-20 minutes to detect evolution to ST elevation 3

Left Main or Proximal LAD Occlusion Pattern

• ST elevation in aVR with multilead ST depression (≥8 leads) 2, 5
• Indicates severe three-vessel disease or left main occlusion 5
• Requires urgent (not emergent) catheterization, not fibrinolysis 5

Critical Pitfalls and Confounders

Left Bundle Branch Block

New or presumably new LBBB should NOT be considered diagnostic of STEMI in isolation. 2, 5

• The 2013 ACCF/AHA guidelines removed new LBBB as a STEMI equivalent due to infrequent occurrence and poor diagnostic accuracy 2, 3
• LBBB interferes with ST-segment analysis 2
• Specialized criteria (Sgarbossa criteria) may help but are beyond standard STEMI criteria 2
• Clinical context and serial troponins are essential 2

Non-STEMI vs STEMI Distinction

Isolated ST depression (without posterior MI features) is classified as NSTEMI or unstable angina, NOT STEMI. 5

• ST depression ≥0.5 mm in any leads (except as posterior MI pattern) = NSTEMI if troponin elevated 4, 5
• ST depression ≥0.5 mm with normal troponins = unstable angina 4, 5
• Do NOT activate STEMI protocols or administer fibrinolytics for isolated ST depression 6, 5
• These patients require early invasive strategy within 24-48 hours, not immediate reperfusion 6

Other ECG Confounders

• Left ventricular hypertrophy may cause baseline ST elevation 2
• Ventricular paced rhythm obscures ST-segment interpretation 2
• Benign early repolarization can mimic STEMI 7
• Acute pericarditis shows diffuse ST elevation (not contiguous territory) 7
• Brugada syndrome may show ST elevation in V1-V3 2

Clinical Application Algorithm

Immediate ECG Acquisition and Interpretation

1. Obtain 12-lead ECG within 10 minutes of presentation 4, 3, 5
2. Measure ST elevation at J-point using sex-specific thresholds 3
3. Identify at least 2 contiguous leads with diagnostic elevation 3
4. Check for STEMI-equivalents: posterior MI pattern, hyperacute T-waves 3, 5

When Initial ECG is Non-Diagnostic

• Perform serial ECGs every 10-20 minutes if clinical suspicion remains high 3
• 11% of STEMI patients have initial non-diagnostic ECG, with 72.4% showing diagnostic changes within 90 minutes 3
• Obtain posterior leads V7-V9 if posterior MI suspected 3
• Obtain right-sided leads V3R-V4R for all inferior STEMIs 3
• Consider transthoracic echocardiography to identify focal wall motion abnormalities 2

Activation of Reperfusion Protocols

If diagnostic STEMI or STEMI-equivalent is identified: 5

• Activate catheterization lab immediately for primary PCI within 90 minutes (door-to-balloon) 4, 5
• Administer fibrinolysis within 30 minutes (door-to-drug) if PCI-capable facility cannot be reached within 90 minutes 4, 5
• Do NOT delay reperfusion therapy for cardiac biomarker results 4, 3

Biomarker Considerations

• Cardiac troponin is the preferred biomarker but should not delay reperfusion 4, 2
• Troponins are insensitive in first 4-6 hours after symptom onset 4
• Serial troponins at 0,3, and 6 hours if initial ECG non-diagnostic 4
• Elevated troponin confirms diagnosis but is not required to initiate STEMI treatment 4, 2

Key Clinical Pearls

• Reciprocal ST depression in opposite leads strengthens STEMI diagnosis but does not alter management 5, 8
• Dynamic ST changes (elevation appearing/resolving with symptoms) indicate very high-risk disease 6
• Greater magnitude and number of leads with ST elevation correlate with larger infarct size and worse outcomes 6
• Clinical presentation must be consistent with myocardial ischemia (symptoms >10 minutes) 1, 2
• When in doubt with equivocal ECG but high clinical suspicion, immediate invasive angiography may be necessary to guide therapy 2