bifascicular block

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In the normal heart there are differences between the anatomy of the right and left branches of the His bundle. The right bundle branch has no main divisions but the left bundle has two - the anterior fascicle and the posterior fascicle.

A bifascicular block occurs when both the right bundle branch and either the left anterior or posterior fascicle are blocked

  • most common type of bifascicular block is RBBB with LAFB
    • has been described in about 1% of a hospitalized population
    • most commonly seen with coronary artery disease
    • approximately 11% of patients with RBBB and LAFB progress to complete heart block
  • RBBB with LPFB is an uncommon finding - however it is more common than isolated LPFB
    • appears to progress to complete heart block more frequently than does the combination of RBBB and LAFB


  1. Harrigan RA et al. Electrocardiographic manifestations: bundle branch blocks and fascicular blocks. The Journal of Emergency Medicine 2003;25(1):67–77

Last reviewed 01/2018