New-Onset Atrial Fibrillation After Typical Flutter Ablation: Risk-Stratified Monitoring Using Implantable Loop...

Atrial flutter and atrial fibrillation (AF) arise from a common arrhythmogenic atrial substrate and frequently coexist in the same patient over the course of their lifetime. We aimed to examine the true incidence and risk factors associated with new-onset AF after successful typical atrial flutter ablation in a real-world population.

We performed a single-center retrospective cohort study of adults who underwent atrial flutter ablation and received an implantable loop recorder (ILR) between 2019 and 2024 as part of a systematic post-ablation monitoring practice. Demographic and clinical variables were collected from the electronic medical record system. Cox proportional-hazards models and multivariable logistic regression were employed to identify independent predictors of AF, while the cumulative incidence of AF was estimated using the Kaplan-Meier method, and clinically relevant risk thresholds were subsequently derived.

Among 95 patients (mean age 69.5 ± 7.9 years; 77.9% male; mean CHA₂DS₂-VASc 3.3) followed for a median of 44.7 months (IQR 34.5-49.0), AF was detected in 61 (64.2%). By Kaplan-Meier estimation the cumulative incidence of AF was 30% at 3 months, 46% at 1 year, and 58% at 2 years; the median time to detection among affected patients was 124 days (IQR 13-385). Patients with detected AF had a larger left atrial volume index (LAVI; 35.2 vs. 28.2 mL/m², p<0.001) and lower LVEF (53.1% vs. 59.6%, p<0.001) as well as higher incidence of heart failure (p = 0.032). LAVI (adjusted OR 1.10 per mL/m², 95% CI 1.03-1.17; p = 0.006) and a reduced LVEF (≤50%; adjusted OR 9.2, 95% CI 1.9-44.5; p = 0.006) were independent predictors (AUC 0.79), and both remained independent in a Cox model (LAVI adjusted HR 1.04 per mL/m²; LVEF ≤50% adjusted HR 2.2, 95% CI 1.3-3.9). A LAVI threshold of ≥26 mL/m² functioned as a rule-out (sensitivity 92%), whereas LVEF ≤50% functioned as a rule-in (specificity 94%, PPV 92%); no single threshold or combination achieved both high sensitivity and high specificity. On stratified analysis the 2-year cumulative incidence of AF was 70% versus 20% above and below the LAVI threshold (log-rank p<0.001) and 73% versus 53% by the LVEF threshold (p = 0.001).

Continuous post-ablation monitoring revealed AF in roughly two-thirds of patients after flutter ablation, often emerging several months following the procedure. More advanced atrial remodeling and impaired ventricular function were independent predictors of higher risk, providing practical and accessible thresholds to guide clinical decisions about which patients warrant prolonged rhythm surveillance and anticoagulation reinitiation after flutter ablation.