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Understanding Left Bundle Branch Block EKG

Oct 1, 2024

Lecture on Left Bundle Branch Block and the Scar Bosa Criteria

Introduction

  • Left Bundle Branch Block (LBBB):
    • A condition affecting the heart's electrical conduction system.
    • Alters the sequence of repolarization.
    • Results in normal discordance between the ST segment, T wave vectors, and the QRS complex.

Understanding Discordance

  • Discordance in LBBB:
    • The ST segment and T wave vectors are in the opposite direction to the QRS complex.
    • This is termed "appropriate discordance" and is considered normal in LBBB.

Challenges in EKG Interpretation

  • ST Segment Changes:
    • Chest pain with LBBB makes it difficult to identify ST segment changes compared to a normal EKG.
    • Normal discordance in LBBB can mask signs of myocardial ischemia, such as ST segment depression and T wave inversions.

Scar Bosa Criteria

  • Purpose:
    • Helps identify potential ischemia on EKGs of patients with LBBB.
    • Consists of three criteria, scored from 0 to 5.

Criteria for Scoring

  1. Concordant ST Elevation

    • Definition: ST elevation > 1 mm in leads with a positive QRS complex.
    • Score: 5 points.

  2. Concordant ST Depression

    • Definition: ST depression > 1 mm in leads V1 through V3 with a negative QRS complex.
    • Score: 3 points.

  3. Excessively Discordant ST Elevation

    • Definition: ST elevation > 5 mm in leads with a negative QRS complex.
    • Score: 2 points.

Interpretation of Scores

  • Score of ≥3:
    • Highly specific (up to 98%) for myocardial ischemia but less sensitive (about 20%).
    • Concordance is a strong indicator of ischemia compared to excessive discordance.

Enhancing Sensitivity

  • Compare changes with previous EKGs or observe dynamic changes with serial EKGs.

Example Case

  • Patient with Chest Pain:
    • EKG shows concordant ST elevation in leads V5 and V6.
    • Concordant ST depressions in leads V1, V2, and V3.
    • Scar Bosa score > 3, indicating potential myocardial ischemia despite LBBB.

Conclusion

  • Using Scar Bosa criteria can help diagnose myocardial ischemia in patients with LBBB and chest pain.
  • Important to note the significance of concordance in the scoring system.

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