Lecture Notes: Understanding Left Bundle Branch Block and Scar Bosa Criteria

Left Bundle Branch Block (LBBB) Basics

• LBBB is characterized by an alteration in the sequence of repolarization in the heart.
• It is normal to have discordance in LBBB:
  • ST segment and T wave vectors are in the opposite direction to the QRS complex (discordance).
  • This is termed "appropriate discordance."
• Important to identify this since it can mask signs of myocardial ischemia such as ST segment depression and T wave inversions.

Scar Bosa Criteria in LBBB

• Purpose: Helps to identify EKG changes suggestive of myocardial ischemia in the presence of LBBB.
• Criteria composed of three components with a scoring range from 0 to 5:

Criteria 1: Concordant ST Elevation

• Description: ST elevation > 1 mm in leads with a positive QRS complex.
• Score Assigned: 5 points.
• Example: When both the QRS complex and ST segment elevation align (go in the same direction).

Criteria 2: Concordant ST Depression

• Description: ST depression > 1 mm in leads V1 through V3 with a negative QRS complex.
• Score Assigned: 3 points.
• Example: Both the QRS and ST segments align in leads V1 to V3.

Criteria 3: Excessively Discordant ST Elevation

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

Interpretation of Scar Bosa Criteria

• A score ≥ 3:
  • Highly specific (98%) for myocardial ischemia but less sensitive (20%).
  • Indicates a higher likelihood of ischemia, especially when concordance is present.
• Improving Sensitivity: Compare with previous EKGs for changes or use serial EKGs to observe dynamic changes.

Case Example

• Patient with chest pain:
  • EKG shows:
    • Concordant ST elevation in leads II, V5, V6.
    • Concordant ST depressions in leads V1, V2, V3.
  • Scar Bosa score: > 3, suggesting possible myocardial ischemia despite the LBBB.

Conclusion

• Scar Bosa Criteria is a vital tool for assessing EKGs in patients with LBBB and suspected myocardial ischemia.
• Practitioners should use it in conjunction with other methods (like serial EKG comparisons) to enhance diagnostic accuracy.