What is the recommended management for a patient with a new right bundle branch block (RBBB) and an existing left axis bifascicular block?

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

Permanent pacemaker implantation is indicated for patients with alternating bundle branch block (new right bundle branch block with existing left axis bifascicular block) even in the absence of symptoms. 1

Risk Assessment and Indications for Pacing

• Patients with alternating bundle branch block (also known as bilateral bundle branch block) have clear ECG evidence of block in all three fascicles manifested on successive ECGs 1
• These patients progress rapidly toward complete atrioventricular block, with a strong consensus among guidelines that they will benefit from cardiac pacing 1
• The combination of right bundle branch block (RBBB) with left anterior fascicular block constitutes a bifascicular block, which when combined with a new conduction abnormality represents a high-risk situation 1, 2
• The 2013 ESC Guidelines give a Class I recommendation (Level of Evidence C) for permanent pacing in patients with alternating BBB with or without symptoms 1
• The ACC/AHA guidelines similarly indicate permanent pacemaker implantation for alternating bundle-branch block 1

Evaluation Before Pacemaker Implantation

• An electrocardiogram should be performed to confirm the diagnosis and exclude other structural heart disease 2
• Ambulatory electrocardiographic monitoring may be useful to detect intermittent atrioventricular block, especially if the patient reports symptoms 2
• Cardiac imaging may be considered to evaluate for underlying structural heart disease that could be contributing to the conduction abnormalities 2
• Electrophysiological study (EPS) is highly sensitive in identifying patients with intermittent or impending high-degree AV block, though not mandatory in cases of alternating BBB 1

Special Considerations

• 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 1
• The SPRITELY trial demonstrated that pacemaker implantation compared to monitoring with implantable loop recorders significantly reduced major study-related events in patients with bifascicular block, regardless of the specific type of bundle branch block 3
• Perioperative risk is increased in these patients, with potential for progression to complete heart block during procedures requiring anesthesia 4
• The risk of sudden death is higher in patients with alternating bundle branch block, and pacing can reduce this risk 1

Management Algorithm

1. Confirm the diagnosis with a 12-lead ECG showing new RBBB with existing left axis deviation/left anterior fascicular block 2
2. Refer for urgent cardiology consultation for pacemaker evaluation 1
3. Proceed with permanent pacemaker implantation even in the absence of symptoms 1
4. For patients awaiting pacemaker implantation, ensure close monitoring for progression to complete heart block 4
5. If the patient requires surgery or procedures requiring anesthesia before pacemaker implantation, consider temporary pacing capabilities during the procedure 4, 5

Pitfalls and Caveats

• Do not delay pacemaker implantation in patients with alternating BBB, as they are at high risk for progression to complete heart block 1
• Avoid medications that can further suppress AV conduction (such as beta-blockers, calcium channel blockers, and digoxin) until a pacemaker is implanted 2
• Do not confuse this high-risk situation with isolated asymptomatic bifascicular block, which has different management recommendations 1
• In patients undergoing transcatheter aortic valve replacement (TAVR) with pre-existing RBBB, prophylactic permanent pacemaker implantation should be strongly considered, as studies show it can prevent early cardiac rehospitalization related to complete heart block 6