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Understanding LBBB and Scarbosa Criteria

Oct 1, 2024

Lecture Notes on Left Bundle Branch Block and Scarbosa Criteria

Introduction

  • Left Bundle Branch Block (LBBB):
    • A condition that alters the sequence of heart depolarization and repolarization.
    • This alteration leads to discordance, where ST segment and T wave vectors move in opposite directions to the QRS complex, termed 'appropriate discordance'.
    • Normal discordance can mask myocardial ischemia signs such as ST segment depression and T wave inversions.

Scarbosa Criteria

  • Purpose:
    • A tool used to interpret EKGs in patients with LBBB to identify potential myocardial ischemia.
    • Composed of three criteria, scored on a scale from 0 to 5.

Criteria and Scoring

  1. Concordant ST Elevation:

    • Description: ST elevation > 1 mm in leads with a positive QRS complex.
    • Score: Assign 5 points.
    • Details: Concordance is when the QRS complex and ST segment elevation move in the same direction.

  2. Concordant ST Depression:

    • Description: ST depression > 1 mm in leads V1 to V3.
    • Score: Assign 3 points.
    • Details: Concordance is observed when both QRS complex and ST segment depression move in the same direction within these leads.

  3. Excessively Discordant ST Elevation:

    • Description: ST elevation > 5 mm in leads with a negative QRS complex.
    • Score: Assign 2 points.
    • Details: Discordance in LBBB is normal, but excessive discordance indicates potential ischemia.

Interpretation of Scarbosa Score

  • Score Interpretation:
    • A score ≥ 3 is highly specific (98%) for identifying myocardial ischemia but less sensitive (20%).
    • Concordance yields higher points and indicates a higher risk of ischemia compared to excessive discordance.

Increasing Sensitivity

  • Methods:
    • Compare changes with previous EKGs.
    • Observe dynamic changes with serial EKGs.

Clinical Example

  • Case Study:
    • A patient with chest pain showing concordant ST elevation in leads V5 and V6, and concordant ST depression in leads V1 to V3.
    • The patient achieves a Scarbosa score > 3, suggesting myocardial ischemia despite LBBB.

Conclusion

  • Scarbosa Criteria:
    • Effective in identifying ischemia in LBBB patients with high specificity.
    • Important for clinicians to recognize concordance as more alarming compared to excessive discordance alone.

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