Bifascicular Block ECG Review

A bifascicular block on ECG is defined by the combination of a right bundle branch block and either a left anterior fascicular block or left posterior fascicular block. When these occur in combination, significant conduction disease is usually present, and there is a risk for higher degrees of atrioventricular block in the future causing symptomatic bradycardia and requiring pacemaker implantation.


Note: A bifascicular block is related to a trifascicular block, which also includes a first-degree AV block. Even though technically incorrect, the AV node in this situation is considered the third fascicle.

A bifascicular block can occur as a part of the ischemic heart disease or as a part of the normal degeneration of the conduction system (Lev's disease). Although the 2009 American College of Cardiology/American Heart Association scientific statement on ECG interpretation does not recommend the use of the terms bifascicular ortrifascicular, they are quite commonly used.

ECG Examples:

1. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
2. Surawicz B, et al. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram. Circulation. 2009; doi:10.1161/CIRCULATIONAHA.108.191095.