What is the level of evidence for pacemaker implantation in patients with syncope and new left bundle branch block (LBBB)?

Level of Evidence for Pacemaker in Syncope with New LBBB

For patients with syncope and new left bundle branch block (LBBB), pacemaker implantation is supported by Level B evidence according to European Society of Cardiology guidelines, with a Class IIb recommendation indicating that it may be considered in selected patients with unexplained syncope and bundle branch block. 1

Evidence-Based Recommendations for Pacemaker Implantation

Strong Indications for Pacing (Class I)

• Syncope + BBB + Abnormal Electrophysiology Study: Pacing is strongly indicated (Class I, Level B) in patients with syncope, BBB, and positive electrophysiological study showing HV interval ≥70 ms, or second/third-degree His-Purkinje block during incremental atrial pacing or pharmacological challenge 1
• Alternating BBB: Pacing is strongly indicated (Class I, Level C) in patients with alternating BBB with or without symptoms 1

Possible Indications for Pacing (Class IIb)

• Unexplained Syncope + BBB: Pacing may be considered (Class IIb, Level B) in selected patients with unexplained syncope and BBB after reasonable diagnostic workup 1

Not Indicated (Class III)

• Asymptomatic BBB: Pacing is not indicated (Class III, Level B) for BBB in asymptomatic patients 1

Diagnostic Algorithm for Syncope with LBBB

1. Initial Evaluation:

   • 12-lead ECG to confirm LBBB and identify other conduction abnormalities 2
   • Transthoracic echocardiogram to exclude structural heart disease 2
   • Assess for symptoms: syncope characteristics (prodrome, position, relation to effort) 1

2. Further Testing:

   • Carotid sinus massage to evaluate carotid sinus hypersensitivity 1
   • Electrophysiological study (EPS) to measure HV interval and assess for infranodal block 1
   • Implantable loop recorder (ILR) if EPS is negative 1

3. Decision Points:

   • If EPS shows HV interval ≥70 ms or infranodal block → Pacemaker implantation (Class I) 1
   • If alternating BBB is documented → Pacemaker implantation (Class I) 1
   • If syncope remains unexplained after workup → Consider empiric pacemaker (Class IIb) 1

Recent Evidence Supporting Empiric Pacing

The SPRITELY trial (2023) demonstrated that pacemaker implantation compared to ILR monitoring significantly reduced major study-related events in patients with syncope and bifascicular block, regardless of BBB morphology (LBBB: 23.8% vs 78.9%, p=0.001; RBBB: 27% vs 72.9%, p<0.0001) 3. This suggests that empiric pacing may be beneficial even without documented bradycardia.

Special Considerations

• Age Factor: Older patients with BBB and unexplained syncope after reasonable workup might benefit more from empiric pacemaker implantation, especially if syncope is unpredictable (no/short prodrome) or occurs in supine position or during effort 1

• Risk of Heart Failure: Patients with LBBB and LVEF <50% have higher rates of heart failure hospitalization or death after pacemaker implantation (HR 3.50 for LBBB; HR 5.1 for LVEF <50%) 4

• Pacing Mode: For patients requiring pacing, physiological pacing techniques like left bundle branch area pacing may better preserve ventricular electrical synchrony compared to right ventricular pacing 5

Clinical Pitfalls to Avoid

1. Overreliance on ECG findings alone: Less than half of patients with BBB and syncope have a final diagnosis of cardiac syncope 1

2. Premature pacemaker implantation: Complete diagnostic workup before deciding on pacemaker implantation to avoid unnecessary device implantation 1

3. Ignoring non-cardiac causes: Always exclude non-cardiac causes of syncope before attributing symptoms to conduction system disease 1

4. Overlooking risk of heart failure: Right ventricular pacing can worsen left ventricular function, especially in patients with pre-existing LBBB or reduced LVEF 4

In summary, while the level of evidence for pacemaker implantation in syncope with new LBBB is moderate (Level B), recent evidence suggests that empiric pacing may be beneficial in selected patients, particularly older individuals with unexplained syncope after thorough evaluation.