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Bundle Branch Blocks

Bundle Branch Blocks is a topic covered in the 5-Minute Emergency Consult.

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  • Blockage of intraventricular electrical impulses through the right and left bundles
  • Complete bundle branch block:
    • Absence or delay of conduction down one bundle, with normal conduction down the other bundle
    • Affected ventricle depolarizes from muscle to muscle in a slower and more disorganized fashion.
    • Quasi-random signal (QRS) complex at 120 msec or longer
  • Incomplete bundle branch block:
    • Delayed depolarization, but less than complete bundle branch block
    • QRS complex duration 100–120 msec
  • Right bundle branch block (RBBB):
    • Delayed depolarization of the right ventricle
  • Left bundle branch block (LBBB):
    • Delayed depolarization of the left ventricle
    • LBBB can be caused by delay of conduction in main left bundle or delay in both fascicles of the left bundle.
    • Causes early activation of the right side of the septum and the right ventricular myocardium (so explaining loss of “septal Q” on ECG)
    • Left bundle branches into 2 fascicles:
      • Left anterior fascicle: Initial septal activation proceeds inferiorly, anteriorly, and to the right.
      • Left posterior fascicle: Isolated blockage rare; activation begins in the midseptum and finishes in inferior and posterior walls.
  • Bifascicular block:
    • RBBB with concomitant block of the left anterior or left posterior fascicle


  • Myocardial infarction
  • Cardiomyopathy
  • Hypertension
  • Age-related fibrosis of Purkinje fibers
  • Valvular disease
  • Exercise induced
  • Congenital/atrial septal defect
  • Brugada syndrome (RBBB): Cause of sudden cardiac death in otherwise healthy patients.
  • Chagas disease (especially Central/South America)
  • Postoperative, following cardiac surgery
  • Drugs:
    • β-Blockers
    • Calcium blockers
    • Tricyclic antidepressants
    • Type Ia and Ic antiarrhythmics
    • Digitalis

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Rosen, Peter, et al., editors. "Bundle Branch Blocks." 5-Minute Emergency Consult, 5th ed., Lippincott Williams & Wilkins, 2016. Emergency Central, emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307334/all/Bundle_Branch_Blocks.
Bundle Branch Blocks. In: Rosen P, Shayne P, Barkin AZ, et al, eds. 5-Minute Emergency Consult. 5th ed. Lippincott Williams & Wilkins; 2016. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307334/all/Bundle_Branch_Blocks. Accessed April 25, 2019.
Bundle Branch Blocks. (2016). In Rosen, P., Shayne, P., Barkin, A. Z., Wolfe, R. E., Hayden, S. R., Barkin, R. M., & Schaider, J. J. (Eds.), 5-Minute Emergency Consult. Available from https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307334/all/Bundle_Branch_Blocks
Bundle Branch Blocks [Internet]. In: Rosen P, Shayne P, Barkin AZ, Wolfe RE, Hayden SR, Barkin RM, Schaider JJ, editors. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2016. [cited 2019 April 25]. Available from: https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307334/all/Bundle_Branch_Blocks.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Bundle Branch Blocks ID - 307334 ED - Rosen,Peter, ED - Shayne,Philip, ED - Barkin,Adam Z, ED - Wolfe,Richard E, ED - Hayden,Stephen R, ED - Barkin,Roger M, ED - Schaider,Jeffrey J, BT - 5-Minute Emergency Consult UR - https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307334/all/Bundle_Branch_Blocks PB - Lippincott Williams & Wilkins ET - 5 DB - Emergency Central DP - Unbound Medicine ER -