Management of New Right Bundle Branch Block with Existing Left Axis Bifascicular Block

Risk Assessment and Indications for Pacing

The American College of Cardiology and the European Society of Cardiology recommend permanent pacemaker implantation for patients with alternating bundle branch block (new right bundle branch block with existing left axis bifascicular block) even in the absence of symptoms, due to the high risk of progression to complete atrioventricular block 1, 2, 3
Patients with alternating bundle branch block have clear ECG evidence of block in all three fascicles manifested on successive ECGs, and will benefit from cardiac pacing, with a strong consensus among guidelines 2, 3
The combination of right bundle branch block with left anterior fascicular block constitutes a bifascicular block, which when combined with a new conduction abnormality represents a high-risk situation, according to the European Heart Journal 1, 4
The European Society of Cardiology gives a Class I recommendation (Level of Evidence C) for permanent pacing in patients with alternating BBB with or without symptoms 2, 3

An electrocardiogram should be performed to confirm the diagnosis and exclude other structural heart disease, although this fact is from Praxis Medical Insights, a similar recommendation can be found in the European Heart Journal, which suggests that electrophysiological study (EPS) is highly sensitive in identifying patients with intermittent or impending high-degree AV block 2

The European Society of Cardiology notes that while isolated bifascicular block generally has a slow rate of progression to complete heart block (1-2% per year), the presence of alternating bundle branch block significantly increases this risk 2, 3
The American College of Cardiology indicates that the risk of sudden death is higher in patients with alternating bundle branch block, and pacing can reduce this risk 1

The American College of Cardiology and the European Society of Cardiology recommend referring patients with new RBBB with existing left axis deviation/left anterior fascicular block for urgent cardiology consultation for pacemaker evaluation, and proceeding with permanent pacemaker implantation even in the absence of symptoms 1, 2, 3

The European Society of Cardiology advises against delaying pacemaker implantation in patients with alternating BBB, as they are at high risk for progression to complete heart block, and recommends avoiding medications that can further suppress AV conduction until a pacemaker is implanted, although the latter is from Praxis Medical Insights, a similar recommendation can be found in the European Heart Journal 2, 3