Bifascicular block

Bifascicular block is characterized by right bundle branch block with left anterior fascicular block, left bundle branch block, or right bundle branch block with left posterior fascicular block on electrocardiography. Complete heart block could be the cause of syncope that is otherwise unexplained if bifascicular block is seen on electrocardiography. It is estimated that less than 50% of patients with bifascicular block have high-degree atrioventricular block, although the exact incidence is unknown.

The European Society of Cardiology (ESC) suggests using electrophysiology studies to look into it (EPS). When pharmacologic stress or incremental atrial pacing induces high-degree atrioventricular block, a permanent pacemaker (PPM) is recommended. If EPS is negative, long-term rhythm monitoring with an implantable loop recorder (ILR) is advised.

Most commonly, it refers to a combination of right bundle branch block (RBBB) and either left anterior fascicular block (LAFB) or left posterior fascicular block (LPFB), with the former being more common.

Signs and symptoms
Patients who suffer from bifascicular block are more likely to experience syncope and unexpected death.

Diagnosis
Diagnostic criteria:

Clinically, bifascicular block presents with one of two ECG patterns:

Right bundle branch block (RBBB) with left anterior fascicular block (LAFB), manifested as left axis deviation (LAD).

RBBB and left posterior fascicular block (LPFB), manifested as right axis deviation (RAD) in the absence of other causes.

Treatment
In those with bifascicular block and no symptoms, little with respect to treatment is needed. In those with syncope, a pacemaker is recommended.