Initial Experience with Ablation to Treat Paroxysmal Bradyarrhythmia

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Initial Experience with Ablation of the Innervation Surrounding Sinus and Atrioventricular Nodes to Treat Paroxysmal Bradyarrhythmia

Introduction

Symptomatic bradyarrhythmias, including sinus node dysfunction (SND) and high-degree atrioventricular block (AVB), represent a significant clinical challenge. While pacemaker implantation remains the standard Class I intervention for these conditions, it is not curative and carries risks such as lead dislodgement, infection, and device-related complications. Emerging evidence suggests that excessive vagal tone plays a critical role in paroxysmal bradyarrhythmias, particularly in patients without structural heart disease. Recent studies have explored cardioneuroablation—targeted ablation of parasympathetic ganglia—as a potential therapy. However, non-selective ablation risks damaging cardiac autonomic regulation. This study introduces a refined approach: restricted ablation of fibrillar myocardium electrical activity around the sinus and atrioventricular nodes (AVNs) to modulate vagal influence while preserving cardiac ganglia.

Methods

Patient Selection

Thirteen patients (9 female, 4 male; mean age 36.0 ± 9.0 years) with recurrent syncope and documented paroxysmal bradyarrhythmias were enrolled between May 2008 and June 2015. Inclusion criteria included:

  1. ≥4 syncopal episodes refractory to medical therapy.
  2. ECG/Holter evidence of SND (sinus bradycardia, sinus pauses) or high-degree AVB.
  3. Normal cardiac structure (LVEF 65.3% ± 4.0%) and positive atropine response.
    Exclusion criteria included structural heart disease, coronary artery disease, or valvular abnormalities.

Electrophysiological Study and Ablation Protocol

  1. Electroanatomic Mapping: Combined fluoroscopy and 3D CT angiography integrated with CARTO-RMT or Niobe II magnetic navigation systems reconstructed right atrial geometry. Activation mapping during sinus rhythm identified earliest activation sites and fractionated electrograms.
  2. Ablation Targets: High-amplitude fractionated potentials (≥100 Hz) near the sinus node and AVN regions, avoiding direct ablation to nodal tissue or phrenic nerve pathways.
  3. Ablation Parameters: Radiofrequency (RF) energy delivered via 4-mm-tip catheter (temperature-controlled mode: 50–60°C, 20–45 W; irrigated catheter used if needed). Ablation continued for 10–15 s after target potential disappearance.
  4. Endpoint Criteria:
    • ≥20% increase in sinus rate.
    • Sinus node recovery time (SNRT) reduction by ≥20%.
    • Wenckebach block point (WP) <500 ms.
    • Atrium-His (AH) interval shortening ≥20 ms.

Post-Procedural Management

Patients received anticoagulation (warfarin) for 1 month followed by aspirin (100 mg/day). Follow-up included clinical evaluations, ECGs, Holter monitoring, and symptom assessment.

Results

Procedural Outcomes

  • Immediate Success: 12/13 patients (92.3%) achieved acute success with elimination of high-frequency potentials. One patient (Case 5) had persistent AVB requiring pacemaker implantation.
  • Heart Rate Improvement: Post-ablation heart rate increased from 49.0 ± 10.0 to 69.0 ± 11.0 bpm (P = 0.008).
  • Electrophysiological Parameters:
    • SNRT decreased from 1386.0 ± 165.0 ms to 921.0 ± 64.0 ms (P = 0.002).
    • WP shortened from 590.0 ± 96.0 ms to 464.0 ± 39.0 ms (P = 0.023).
    • AH interval reduced from 106.0 ± 5.0 ms to 90.0 ± 12.0 ms (P = 0.013).
  • Vagal Reactions: Transient sinus bradycardia or AH prolongation occurred during ablation but resolved spontaneously.

Follow-Up

Over 13.0 ± 5.9 months:

  • 10 patients (76.9%) remained symptom-free.
  • 2 patients (Cases 2 and 8) experienced syncope recurrence due to bradyarrhythmia relapse, necessitating pacemakers.
  • No procedural complications (e.g., phrenic nerve injury, pericardial effusion) were observed.

Discussion

Mechanistic Insights

The study builds on the hypothesis that hypervagotonia induces functional bradyarrhythmias through excessive inhibition of sinus and AV nodal activity. High-frequency potentials (≥100 Hz) near these nodes likely represent fibrillar myocardium electrical activity linked to parasympathetic nerve terminals. Ablation at these sites disrupts vagal input without extensive ganglion destruction, preserving autonomic balance. The immediate vagal reactions (e.g., transient bradycardia) followed by sustained improvement in conduction parameters support this targeted approach.

Technical Innovations

  1. Precision Mapping: Integration of 3D CT with electroanatomic systems enabled precise localization of ablation targets while avoiding nodal tissue (Figure 2). This contrasts with earlier spectral mapping methods requiring complex fast Fourier transform analysis.
  2. Restricted Ablation Strategy: Limiting lesions to peri-nodal areas reduced collateral damage to cardiac ganglia, addressing concerns about non-selective denervation affecting coronary flow or ventricular function.

Clinical Implications

  • Symptom Resolution: 76.9% freedom from syncope at 13-month follow-up demonstrates durable efficacy, particularly in younger patients with structurally normal hearts.
  • Pacemaker Avoidance: Successful ablation deferred permanent pacing in 10 patients, mitigating long-term device-related risks.

Limitations and Future Directions

  1. Small Cohort: The 13-patient sample limits generalizability. Larger studies are needed to validate safety and refine patient selection.
  2. Ablation Depth and Durability: Recurrence in 2 cases suggests incomplete denervation. Extended ablation ranges or adjunctive left atrial targeting (e.g., right superior pulmonary vein ganglia) may improve outcomes.
  3. Uncertainty in Target Identification: Differentiation between fibrillar myocardial potentials and conduction system signals requires further electrophysiological characterization.

Conclusion

Restricted ablation of fibrillar myocardium electrical activity surrounding the sinus node and AVN presents a promising alternative for vagally mediated bradyarrhythmias. By selectively modulating parasympathetic influence, this approach achieves significant improvements in sinus rate, SNRT, and AV conduction with minimal complications. While long-term durability and broader applicability require further investigation, the technique offers a potential paradigm shift in managing functional bradyarrhythmias without permanent pacemaker dependence.

doi.org/10.1097/CM9.0000000000000595

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