Atypical atrial flutter after AF ablation vs De Novo atypical flutter: are they the same?

Background

Atypical atrial flutter (AAFL) may occur de novo or following catheter ablation for atrial fibrillation (AF). Post-AF ablation AAFL may reflect distinct atrial substrate modification, but whether these patients differ clinically and electrophysiologically from those with de novo AAFL remains unclear.

Methods

A total of 98 AAFL ablation procedures were performed between January 2023 and September 2025. Of these, 7 were redo procedures in previously included patients and 11 patients with prior flutter-only ablation were excluded. The final cohort comprised 80 unique patients: 41 with de novo AAFL and 39 with post-AF ablation AAFL. Baseline characteristics included age, sex, BMI, CHA2DS2-VASc score, LVEF, and CT-derived left atrial volume index (LAVi). Procedural variables included energy modality (radiofrequency [RF] or pulsed-field ablation [PFA]), flutter circuit location, procedure duration, and fluoroscopy time. Arrhythmia recurrence was assessed by ECG, Holter monitoring, or clinical documentation.

Results

Patients with de novo AAFL were significantly older (73 ± 10 vs. 68 ± 12 years; p = 0.03) and had higher CHA2DS2-VASc scores (3.2 ± 1.4 vs. 2.5 ± 1.6; p = 0.035) compared with those with post-AF ablation AAFL. Body mass index, left ventricular ejection fraction, and CT LAVi were similar between groups. Procedural characteristics, including total procedure duration, fluoroscopy time, and radiation dose, did not differ significantly. Regarding energy modality, de novo AAFL ablations used RF in 31 cases and PFA in 10, whereas post-AF ablation procedures used RF in 18, PFA in 18, and a combined RF+PFA strategy in 3 cases.

Termination sites differed markedly between groups. De novo AAFL circuits were predominantly anterior mitral line–dependent (34%), whereas post-AF ablation AAFL most frequently terminated along the posterior mitral line (23%), with additional posterior wall– and roof-dependent circuits. These patterns suggest distinct mechanisms: anatomical macroreentry in de novo AAFL versus scar-related perimitral macroreentry due to conduction gaps in post-ablation patients. Arrhythmia recurrence showed a non-significant trend toward higher AFL/AF recurrence in the post-AF ablation group (41% vs. 22%; p = 0.066).

Conclusions

De novo AAFL and post-AF ablation AAFL represent distinct clinical and electrophysiological entities. Post-ablation AAFL demonstrated differing circuit distribution and a trend toward higher recurrence despite comparable procedural characteristics. These findings highlight the evolving complexity of atrial arrhythmias in the era of widespread AF ablation.