Bifascicular Block

Bifascicular Block (RBBB + LAFB)

Background

• 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

• Left anterior fascicular block
• Left bundle branch block
• Left posterior fascicular block
• Right bundle branch block
• Trifascicular block

Further Reading

• ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
• ECG Reference Sites on the WEB – the best of the rest

Author Credits

References

• 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.