What is the management of bifascicular block?

Management of Bifascicular Block

Permanent pacemaker implantation is indicated for bifascicular block with intermittent complete heart block associated with symptomatic bradycardia or when bifascicular block is accompanied by intermittent type II second-degree AV block, even without symptoms. 1

Definition and Risk Assessment

Bifascicular block refers to electrocardiographic evidence of impaired conduction below the AV node in two of the three fascicles of the right and left bundles. This typically presents as:

• Right bundle branch block (RBBB) with left anterior fascicular block
• Right bundle branch block with left posterior fascicular block
• Left bundle branch block (LBBB)

The primary concern with bifascicular block is the potential progression to complete heart block, which can lead to significant morbidity and mortality.

Risk Stratification

The risk of progression from bifascicular block to complete heart block is generally low (approximately 2-3% annually) 1, but increases with:

• HV interval >100 milliseconds (higher risk)
• Presence of syncope without other identifiable causes
• Presence of intermittent complete heart block
• Association with structural heart disease

Management Algorithm

Class I Indications for Permanent Pacemaker (Highest Priority)

1. Bifascicular block with intermittent complete heart block associated with symptomatic bradycardia 1
2. Bifascicular or trifascicular block with intermittent type II second-degree AV block (even without symptoms) 1
3. Alternating bundle-branch block (bilateral bundle-branch block) 1

Class II Indications (Reasonable to Consider Pacing)

1. Bifascicular or trifascicular block with syncope not proven to be due to complete heart block, but where other causes have been excluded 1
2. Markedly prolonged HV interval (≥100 milliseconds) found incidentally during electrophysiological study 1
3. Pacing-induced infra-His block (non-physiological) found during electrophysiological study 1
4. Bifascicular block in patients with neuromuscular diseases (e.g., myotonic muscular dystrophy) 1

Class III Indications (Pacing NOT Indicated)

1. Asymptomatic bifascicular block without AV block 1
2. Bifascicular block with first-degree AV block without symptoms 1

Special Circumstances

Perioperative Management

For patients with bifascicular block undergoing surgery:

• Routine prophylactic temporary pacing is not necessary for asymptomatic patients with bifascicular block, even with first-degree AV block 2, 3
• Consider temporary transcutaneous pacing standby for high-risk patients 1

Acute Myocardial Infarction

In the setting of acute MI with bifascicular block:

• Higher risk of progression to complete heart block
• Consider temporary pacing for new bifascicular block with first-degree AV block 1
• Permanent pacing is indicated for persistent second-degree AV block in the His-Purkinje system with bifascicular block or complete heart block after acute MI 1

Diagnostic Evaluation

For patients with bifascicular block:

1. Transthoracic echocardiogram: Recommended for all patients with newly detected LBBB to exclude structural heart disease 1

2. Ambulatory ECG monitoring: Useful in symptomatic patients to document suspected higher-degree AV block 1

3. Electrophysiological study (EPS): Consider in:

   • Symptomatic patients with unexplained syncope 1
   • Patients with symptoms suggestive of intermittent bradycardia 1

Prognosis

Despite the theoretical risk, the progression rate from bifascicular block to complete heart block is relatively low in the absence of other factors. However, when complete heart block does develop, it carries significant morbidity and mortality risks.

Recent evidence suggests that while patients with bifascicular block and prolonged PR interval have a high incidence of complete AV block and mortality, cardiac implantable electronic device implantation may not significantly improve survival when accounting for the time-varying nature of device implantation 4.

Key Pitfalls to Avoid

1. Don't assume all syncope in patients with bifascicular block is due to progression to complete heart block. Consider other causes including ventricular tachyarrhythmias 1

2. Don't implant permanent pacemakers in asymptomatic patients with isolated bifascicular block without evidence of higher-degree AV block 1

3. Don't overlook the possibility of ventricular tachyarrhythmias in patients with bifascicular block and syncope, as sudden death may be due to ventricular arrhythmias rather than complete heart block 1

4. Avoid unnecessary temporary pacing in asymptomatic patients with bifascicular block undergoing surgery, as the risk of progression to complete heart block is low 2, 3