Left Atrial Slow-Conduction Channels Predict Pulmonary Vein Isolation Outcomes in Paroxysmal Atrial Fibrillation.

Introduction: The mechanisms underlying recurrent atrial fibrillation (AF) despite durable pulmonary vein isolation (PVI) in patients with paroxysmal AF (PAF) remain unclear. This study investigates whether left atrial (LA) slow-conduction channels act as a substrate for recurrence following durable PVI.

Methods: High-density LA mapping was performed in 120 PAF patients. LA conduction velocities were calculated using the Local Velocity Vector algorithm. Channels were defined as narrow regions with slow conduction (< 0.5 m/s) and fragmented electrograms. All patients underwent PVI using radiofrequency energy. One-year freedom from recurrent AF was compared based on baseline LA channel presence. A control group of five patients with atrioventricular reentrant tachycardia was included.

Results: Among 120 patients, 42 (35%) had 54 LA channels identified. Channels represented ~1% of total LA surface area, exhibited slow conduction (~0.23 m/s), were bordered by lines of block, displayed abnormal electrograms, and demonstrated decremental conduction, suggesting a potential role in reentry. Half were in low-voltage areas while the remainder were in regions with preserved voltage. At 1 year, 3 of 78 patients without channels (4%) had PAF recurrence, all due to PV reconnections, compared to 7 of 42 patients with channels (17%) who experienced recurrence (p = 0.02), 6 of whom had durably isolated PVs on repeat study. No channels were identified in controls.

Conclusion: The absence of LA channels may indicate a PAF phenotype with high PVI success. Conversely, patients with channels are less likely to respond to PVI. It remains unclear whether channels serve as risk indicators or targets for ablation.