A trifascicular block is the combination of a right bundle branch block, left anterior or posterior fascicular block and a first-degree AV block (prolonged PR interval). The term “trifascicular block” is a misnomer, since the AV node itself is not a fascicle. A trifascicular block is a precursor to complete heart block. While a trifascicular block itself does not require any treatment, high doses of AV blocking agents likely should be avoided. Some series report a 50% lifetime need for a permanent pacemaker in the setting of a trifascicular block.
1. Surawicz B et al. ACC/AHA recommendations for the standardization and interpretation of the electrocardiogra. Circulation. 2009;119:e235-240.
2. Chou's Electrocardiography in Clinical Practice: Adult and Pediatric, Sixth Edition, Saunders, Philadelphia, 2008.