Abstract Body (Do not enter title and authors here):
Background: Recurrent atrial fibrillation (AF) following catheter ablation remains a significant clinical challenge, affecting 20–40% of patients. While current guidelines recommend a 3-month “blanking period” before considering reintervention, the optimal timing for repeat ablation remains undefined.

Objectives: To compare long term rates of AF recurrence among patients undergoing repeat ablation based on timing of re-intervention.

Methods:
We conducted a multicenter retrospective observational study using the ITHACA database, including patients who experienced AF after an initial ablation and underwent a repeat procedure. The primary outcome was a composite of AF recurrence defined as clinical AF recurrence, anti-arrhythmic use, cardioversion post-blanking period or a third ablation. Time-to-repeat ablation between patients who experience recurrence post second ablation was compared to patients who did not have a second recurrence using a two-sample t-test. A decision tree classifier was used to identify time intervals between index and repeat atrial fibrillation (AF) ablation that best predicts risk of recurrence. The Gini index guided the tree's construction, optimizing the separation of patients into recurrence and non-recurrence groups based on the time interval.

Results:
Of 3129 patients, 616 (19.6%) underwent repeat ablation. Among them, 105 (17%) had no AF recurrence, while 511 (83%) did. Median time to repeat ablation was 576 days (IQR 744 days). Patients who remained AF-free had a significantly shorter mean interval between ablations (656 vs. 833 days; p < 0.0001). The decision tree identified three distinct timing intervals differentiating our cohort into patients who were more or less likely to have AF recurrence post repeat ablation. Among patients with repeat ablation >1274 days after the index, 95% had recurrence. For those with repeat ablation between 273–1274 days, 84% had recurrence. Patients undergoing repeat ablation within 272 days of index ablation had the lowest rate of recurrence (77%).
Conclusion:
Patients who underwent repeat ablation after a shorter interval between index and repeat intervention had lower rates of long-term AF recurrence. Our decision tree model identified reintervention within <272 days post index as a potential marker of improved long-term outcomes.