Bifascicular Block Overview
- 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 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)
- Left anterior fascicular block
- Left bundle branch block
- Left posterior fascicular block
- Right bundle branch block
- Trifascicular block
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e