The most literal meaning of trifascicular block is complete heart block: all three fascicles are blocked. A second, and clinically distinct, definition of trifascicular block is a circumstance in which right bundle branch block (RBBB) and left bundle branch block occur in the same patient, but at distinct points in time. For example, a patient that is found to have a RBBB one day and a LBBB another can be said to have "alternating bundle branch blocks". In this context, because all three fascicles show evidence of block at different points in time, the term trifascicular block is often used.
The treatment of trifascicular block is highly dependent on which clinical entity (one of the three above) is being described.
Diagnosis
An electrophysiology study of the conduction system can help discern the severity of conduction system disease. In an electrophysiology study, trifascicular block due to AV nodal disease is represented by a prolonged AH interval (denoting prolonged time from impulse generation in the atria and conduction to the bundle of His) with a relatively preserved HV interval (denoting normal conduction from the bundle of His to the ventricles). Trifascicular block due to distal conduction system disease is represented by a normal AH interval and a prolonged HV interval. In the absence of symptoms, a prolonged AH interval is likely benign while a prolonged HV interval is almost always pathologic.[citation needed]
Treatment
An implantable cardiac pacemaker or permanent pacemaker is recommended in the following clinical circumstances. Class 1 recommendation is the strongest recommendation. Level A evidence is the highest level of evidence. [citation needed]
