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EKG Interpretation in Left Bundle Branch Block

Oct 1, 2024

Lecture Notes on EKG Interpretation with Left Bundle Branch Block

Introduction

  • Discussion on challenges of detecting ST segment changes in patients with left bundle branch block (LBBB) during chest pain events.
  • Importance of Scar Bosa Criteria in analyzing EKGs with LBBB for myocardial ischemia.

Understanding Left Bundle Branch Block

  • Normal Discordance: In LBBB, the repolarization sequence is altered causing the ST segment and T wave vectors to be in opposite directions to the QRS complex.
  • Appropriate Discordance: This is typical in LBBB and can obscure signs of ischemia like ST segment depression and T wave inversions.

Scar Bosa Criteria for EKG Interpretation

  • Purpose: Helps to identify potential ischemic changes in EKGs with LBBB.
  • Scoring System: Ranges from 0 to 5 based on three criteria:

Criteria

  1. Concordant ST Elevation
    • ST elevation >1mm in leads with a positive QRS complex.
    • Assign a score of 5.
    • Concordance: When ST segment and QRS complex are in the same direction.
  2. Concordant ST Depression
    • ST depression >1mm in leads V1 through V3.
    • Assign a score of 3.
    • Occurs when both QRS complex and ST segment are in the same direction.
  3. Excessively Discordant ST Elevations
    • ST elevation >5mm in leads with a negative QRS complex.
    • Assign a score of 2.
    • Excessive Discordance: Normal discordance in LBBB should not exceed 5mm, beyond which suggests ischemia.

Interpretation of Scores

  • Score ≥ 3: Indicates myocardial ischemia with high specificity (up to 98%) but low sensitivity (20%).
  • Concordance vs. Excessive Discordance:
    • Concordance is more indicative of ischemia than excessive discordance.

Enhancing Sensitivity

  • Compare with previous EKGs for changes.
  • Observe dynamic changes with serial EKGs.

Case Example

  • Patient with chest pain showing:
    • Concordant ST elevation in leads II, V5, V6.
    • Concordant ST depression in leads V1, V2, V3.
  • Score > 3, suggesting myocardial ischemia even with LBBB.

Conclusion

  • The Scar Bosa Criteria is a valuable tool for interpreting EKGs with LBBB, focusing on specific patterns of concordance and discordance to identify ischemia.

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