Bifascicular Block

Bifascicular Block (RBBB + LAFB)


  • Bifascicular block is the combination of RBBB with either LAFB or LPFB.
  • Conduction to the ventricles is via the single remaining fascicle.
  • The ECG will show typical features of RBBB plus either left or right axis deviation.
  • RBBB + LAFB is the most common of the two patterns.
  • Bifascicular block is a sign of extensive conducting system disease, although the risk of progressing to complete heart block is thought to be relatively low (1% per year in one cohort study of 554 patients).

(NB. Some authors also consider LBBB to be a ‘bifascicular block’, because both fascicles of the left bundle branch are blocked)

Main Causes

  • Ischaemic heart disease (40-60% cases)
  • Hypertension (20-25%)
  • Aortic stenosis
  • Anterior MI (occurs in 5-7% of acute AMI)
  • Primary degenerative disease of the conducting system (Lenegre’s / Lev’s disease)
  • Congenital heart disease
  • Hyperkalaemia (resolves with treatment)

Related Topics

Further Reading

Author Credits


  • Hampton, JR. The ECG in Practice (5th edition), Churchill Livingstone 2008. McAnulty JH, Rahimtoola SH, Murphy E, DeMots H, Ritzmann L, Kanarek PE et al. Natural history of “high-risk” bundle-branch block: final report of a
  • prospective study. N Engl J Med. 1982 Jul 15;307(3):137-43. PMID: 7088050.
  • Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice (6th edition), Saunders 2008.
  • Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
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