Bundle Branch Block

Bundle Branch Block

  • Acute (infarct, inflammation) or chronic (remodeling from CAD, HTN, fibrosis)

    • ➔ damage to conduction system (bundle branches)

    • ➔ delayed conduction ➔ widened QRS (> 0.12s or 3 small boxes)

Normal conduction

Down left and right bundle ➔ typical QRS


Signal progression:

  • SA node ➔ AV node ➔ Bundle of His

  • Right bundle ➔ RV depolarization

    • ➔ RV contraction

  • Left bundle blocked

    • Slower LV Depolarization comes from septum

    • Delayed conduction ➔ widened QRS

The M, W may not be present or obvious

  • Stick with: V1 - Broad S & V6 - Broad R

  • Generally, chest pain + new LBB: think STEMI

    • Difficult to dx MI in presence of LBB

      • Need to understand concordance, appropriate vs excessive discordance, Sgarbossa criteria


Signal progression:

  • SA node ➔ AV node ➔ Bundle of His

  • Left bundle ➔ LV depolarization

    • ➔ LV contraction

  • Right bundle blocked

    • RV Depolarization comes from LV & septum

    • Delayed conduction ➔ widened QRS

Normally activated left ventricle ➔ early part of the QRS appears normal (not all wide like LBB)

Initial part of QRS is unchanged

V1 - RSR' and inverted T

(An extra R wave & appropriate discordance)

V6 - Wide & slurred S (& lateral leads)

  • The LV contributes the most electrically to how the QRS looks

  • In RBB the signal makes it down left bundle just fine

    • ➔ the initial part of the QRS appearing normal-ish