Definition of ST Elevation on 12-Lead ECG
ST-segment elevation on a 12-lead ECG is defined as new elevation at the J-point in at least 2 contiguous leads with elevation of ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2-V3, and/or ≥1 mm (0.1 mV) in other contiguous chest leads or limb leads. 1
Detailed Criteria by Lead Location
The definition of ST elevation varies based on lead location, gender, and age:
Precordial Leads (V1-V6)
- Leads V2-V3:
- Men ≥40 years: ≥2 mm (0.2 mV)
- Men <40 years: ≥2.5 mm (0.25 mV)
- Women: ≥1.5 mm (0.15 mV)
- Other chest leads (V1, V4-V6): ≥1 mm (0.1 mV)
Limb Leads
- All limb leads (I, II, III, aVL, aVF): ≥1 mm (0.1 mV)
Special Lead Considerations
- Right ventricular leads (V3R-V6R): ≥1 mm ST elevation indicates right ventricular involvement, especially in inferior MI 1
- Posterior leads (V7-V9): ≥0.5 mm (0.05 mV) ST elevation suggests posterior (inferobasal) MI 1
Clinical Significance
ST elevation is a key diagnostic criterion for ST-elevation myocardial infarction (STEMI), which represents acute coronary artery occlusion requiring urgent reperfusion therapy. The presence of ST elevation in specific lead groups correlates with the anatomical location of myocardial injury:
- Anterior wall: V1-V4 (LAD territory)
- Lateral wall: I, aVL, V5-V6 (LCx or diagonal branches)
- Inferior wall: II, III, aVF (RCA or LCx territory)
- Posterior wall: ST depression in V1-V3 with tall R waves (mirror image of posterior ST elevation)
- Right ventricle: V3R-V4R (proximal RCA)
Contiguous Leads
"Contiguous leads" refers to leads that view adjacent regions of the heart:
- Inferior: II, III, aVF
- Lateral: I, aVL, V5, V6
- Anterior: V1-V4
- Posterior: V7-V9 (or reciprocal changes in V1-V3)
Common Pitfalls and Caveats
Left Bundle Branch Block (LBBB): The ACCF/AHA guidelines have eliminated new LBBB as a standalone STEMI equivalent criterion due to its infrequent occurrence 1. However, LBBB with appropriate clinical presentation should still prompt consideration of acute coronary syndrome.
Early Repolarization: Can mimic ST elevation but typically shows:
- Notching or slurring of the terminal QRS complex
- Concave upward ST elevation
- Widespread distribution
- Stable pattern over time
Reciprocal Changes: The presence of reciprocal ST depression in leads opposite to those with ST elevation significantly increases the positive predictive value for myocardial infarction (>90%) 2.
Left Circumflex Occlusion: May present with minimal or no ST elevation on standard 12-lead ECG. Additional posterior leads (V7-V9) may increase diagnostic sensitivity 3.
Lead aVR: ST elevation in aVR alone is not part of the STEMI criteria but may indicate left main or proximal LAD disease when accompanied by widespread ST depression 4.
The diagnosis of STEMI requires both appropriate ECG findings and a clinical presentation consistent with acute myocardial ischemia. ST elevation criteria are most useful when applied in the appropriate clinical context, as they help identify patients who would benefit from urgent reperfusion therapy 1.