What is the difference between concordant and discordant ST elevation?

Understanding Concordant and Discordant ST Elevation

Concordant ST elevation occurs when the ST segment is elevated in the same direction as the main QRS complex, while discordant ST elevation occurs when the ST segment is elevated in the opposite direction of the main QRS complex. This distinction is particularly important in the setting of bundle branch blocks and ventricular paced rhythms when evaluating for acute myocardial infarction (AMI).

Normal Electrical Patterns and Pathological Changes

• In normal conduction, the ST segment and T wave are typically discordant (opposite direction) to the major terminal portion of the QRS complex 1
• Loss of this normal QRS complex-T wave axes discordance may indicate myocardial injury or ischemia 1
• This loss of discordance usually manifests as concordance, where the ST segment/T wave complex occurs on the same side of the isoelectric baseline as the major terminal portion of the QRS complex 1

Sgarbossa Criteria for AMI in LBBB

The Sgarbossa criteria utilize concordance and discordance patterns to identify AMI in the setting of left bundle branch block (LBBB):

• Concordant ST elevation ≥1 mm in leads with a positive QRS complex (sensitivity 73%, specificity 92%) 1
• ST depression ≥1 mm in leads V1-V3 (sensitivity 25%, specificity 96%) 1
• Discordant ST elevation ≥5 mm in leads with a negative QRS complex (sensitivity 19%, specificity 82%) 1

Clinical Significance

• Concordant ST elevation is highly specific for AMI but has limited sensitivity 1, 2
• In the setting of LBBB, concordant ST elevation of ≥1 mm has a specificity of 92% and positive predictive value of 96% for AMI 1
• Discordant ST elevation is less specific but more commonly seen in AMI (19% prevalence in AMI patients with LBBB) 1, 2
• Excessive discordant ST elevation (≥5 mm) can indicate myocardial injury despite being in the expected direction 1

Diagnostic Challenges

• Observer variability in identifying these patterns can be significant, with better agreement for ST depression than for both discordant and concordant ST elevation 2
• The low prevalence and poor sensitivity of these criteria make diagnosis of AMI in the setting of LBBB challenging 2
• Similar principles can be applied to right bundle branch block (RBBB) and ventricular paced rhythms, though research has primarily focused on LBBB and paced rhythms 1

Clinical Application

• When evaluating patients with bundle branch blocks and suspected AMI, look for:

  • Concordant ST elevation in any lead (highly specific for AMI) 1
  • Excessive discordant ST elevation (≥5 mm in leads with opposite QRS polarity) 1
  • ST depression in leads V1-V3 in the setting of LBBB 1

• Figure 3 in the guidelines demonstrates an ECG with concordant ST elevation in leads I, aVL, V5, and V6, as well as excessive discordant ST elevation in leads V1-V4, indicating AMI in the setting of LBBB 1

Understanding these patterns is crucial for accurate diagnosis and timely treatment decisions in patients with conduction abnormalities who present with suspected acute coronary syndromes.