When is ST elevation considered significant in electrocardiogram (ECG) readings?

Significant ST Elevation in Electrocardiogram

ST-segment elevation is considered significant when it measures ≥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, occurring in at least 2 contiguous leads. 1

Gender and Age-Specific Criteria

The definition of significant ST elevation varies based on specific factors:

• 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 (I, II, III, aVL, aVF): ≥1 mm (0.1 mV) 1, 2

Special Lead Considerations

• Right ventricular leads (V3R-V4R): ST elevation ≥1 mm indicates right ventricular involvement, particularly important in inferior MI 2
• Posterior leads (V7-V9): ST elevation ≥0.5 mm suggests posterior (inferobasal) MI 1, 2

Clinical Context

ST elevation must be interpreted within the appropriate clinical context:

• ST elevation should be measured at the J-point (where the QRS complex ends and the ST segment begins) 1
• ST elevation must be present in at least two contiguous leads to be considered significant 1
• The elevation should be new or presumed new (comparison with previous ECGs is valuable when available) 1
• ST elevation should be persistent rather than transient 1

Pitfalls and Caveats

1. Normal ECG does not exclude ACS: Approximately 5% of patients with normal ECGs who were discharged from emergency departments were ultimately found to have acute myocardial infarction or unstable angina 1

2. Left Bundle Branch Block (LBBB): New or presumably new LBBB is no longer considered a standalone STEMI equivalent due to its infrequent occurrence and potential to interfere with ST-elevation analysis 1, 2

3. Non-STEMI presentations: ST depression >1 mm in two or more contiguous leads can indicate non-ST elevation ACS and should not be overlooked 1

4. False positives: Conditions that can mimic STEMI ECG patterns include:

   • Left ventricular hypertrophy
   • Pericarditis
   • Early repolarization
   • Takotsubo cardiomyopathy 3
   • Brugada syndrome 1

5. Posterior MI: ST depression in leads V1-V3 may represent posterior wall MI and should prompt consideration of additional posterior leads (V7-V9) 1

6. Automated ECG interpretation limitations: A study found that computerized analysis of ECG criteria for STEMI showed suboptimal diagnostic performance when applied to a single 12-lead ECG at ED presentation 4

Improving Diagnostic Accuracy

• Compare with previous ECGs when available 1
• Perform serial ECGs at 10-minute intervals during the first hour if clinical suspicion is high but initial ECG is non-diagnostic 1
• Consider additional leads (right-sided and posterior) in appropriate clinical scenarios 1
• The presence of reciprocal changes (ST depression in leads opposite to those with ST elevation) significantly improves diagnostic accuracy 5

The accurate identification of significant ST elevation is critical for timely reperfusion therapy in STEMI patients, which directly impacts morbidity and mortality outcomes.