Lesson 7: Bundle Branch Blocks

Summary of Learning points

• Etiology of BBB

  • Acute inflammation

  • Ischemia/scar

  • Infiltrative disease

• Left bundle branch block criteria

  • QRS > 120 ms

  • Broad R wave in I and V6 (no Q)

  • Broad S wave in V1 (+/- small r wave)

• Right bundle branch block criteria

  • QRS > 120 ms

  • Slurred S wave in I and V6

  • RSR’ in V1

• Fascicular blocks

  • LAFB

    • Left axis deviation (positive in I, neg in aVF)

    • qR or R wave in I, rS in III

  • LPFB

    • Much less common in isolation than LAFB

    • Right axis deviation (neg in I, pos in II, aVF)

    • S wave in I, Q in III

    • Exclude RVH/RAE

  • Bifascicular block

    • RBBB + LAFB/LPFB

• Workup of BBB

  • Young people may have RBBB but this typically resolves

  • If EKG with BBB (L or R) without other pathology (hypertension, etc) consider work-up with echocardiography to evaluate for cardiomyopathy

  • LBBB presence makes it difficult to use EKG for diagnosis of ACS; use other diagnostic tools instead or in conjunction

Practice ECG

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