Bifascicular Block

Bifascicular Block Overview

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

ECG Bifascicular Block (RBBB + LAFB)
Bifascicular Block (RBBB + LAFB)

Main Causes of Bifascicular Block

  • 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

LITFL Further Reading

Advanced Reading




Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

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