Atypical atrial flutter is a distinct arrhythmia associated with advanced heart disease, carrying a significant risk of complications and showing limited treatment success rate

Abstract Background Atypical atrial flutter (AtFL) and atrial fibrillation (AF) have similar clinical presentation. However, their underlying substrates and clinical courses may differ significantly. This study aimed to compare the clinical characteristics of patients with AtFL and AF who were admitted for rhythm control therapy via electrical cardioversion or ablation. Methods Data on AtFL patients was prospectively collected in a dedicated database. For comparison, we used data from the Israeli Catheter Ablation Registry for AF patients. Results The multivariant analysis included 176 consecutive patients with AtFL and a comparative group of 1002 patients with AF. Age and Gender: AtFL patients were older, with a median age of 71 years (CI 65-78) compared to 68 years (CI 62-76) for AF patients (p<0.01), with a similar gender distribution (43% and 38% female, respectively). Arrhythmia History: AtFL patients had a longer history of atrial arrhythmia (5 years, median 3-12) compared to AF patients (3 years, median 1-5, p=0.01). A greater proportion of AtFL patients had undergone previous cardioversions and ablations procedure (see Table). In over 50% of cases, AtFL was a "secondary" arrhythmia that developed following AF. Comorbidities: Coronary artery disease, hypertrophic cardiomyopathy, heart failure symptoms, reduced ejection fraction, left atrial enlargement, and significant mitral regurgitation were more common in the AtFL group (see Table). Thromboembolic Complications: Thromboembolic events occurred in 18 AtFL patients (10%) compared to 30 AF patients (3%; p=0.001). One-Year Follow-Up: During one year of follow-up, AtFL patients experienced a higher rate of re-hospitalization due to arrhythmia recurrence, with 56% (23 cases) compared to 24% (219 cases) in the AF group (p<0.001). Conclusions Among patients referred for cardioversion or ablation for rhythm control, those with AtFL had a longer history of atrial arrhythmia, more advanced heart disease, and worse one-year outcomes, compared to patients with AFTable