Endocardial Ablation of Atrial Flutter with Involvement of the Vein of Marshall: A Case Report

: Background: Atypical atrial flutter (AFL) is a complex clinical challenge, particularly in patients with prior atrial fibrillation (AF) treated with pulmonary vein isolation (PVI). Arrhythmias involving the vein of Marshall (VOM) often require extensive lesion sets, including ethanol infusion, to effectively target the epicardial substrate. To minimize tissue damage, an alternative strategy has been proposed, emphasizing advanced electroanatomical mapping, entrainment maneuvers, and highly targeted ablation techniques. Case Presentation: We describe a 72-year-old woman with recurrent atrial arrhythmias following pulmonary vein isolation (PVI), who presented with palpitations as her primary symptom. After ineffective pharmacological therapy, she underwent a catheter ablation procedure. Electroanatomical mapping revealed significant left atrial scarring and suggested a macroreentrant circuit involving the VOM. Entrainment maneuvers confirmed the VOM's involvement. A single targeted endocardial ablation guided by the ablation index terminated the arrhythmia within 12 s, without the need for ethanol infusion or extensive lesion sets. Discussion: This case underscores the VOM's role in sustaining atypical AFL post-PVI and highlights the effectiveness of precise electroanatomical mapping combined with targeted endocardial ablation. Unlike broader ablation or ethanol infusion strategies, a focused lesion at the critical isthmus achieved arrhythmia termination with minimal tissue damage. Conclusions: Endocardial ablation at the site of entrainment can safely and effectively treat VOM-related AFL, offering symptom relief and restoration of sinus rhythm. This approach may reduce procedural risks and expand the feasibility of VOM-related arrhythmia management in centers without access to ethanol infusion.