- 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)
- 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)
- 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.