RESUMEN
BACKGROUND: Atrial fibrillation is the most common sustained cardiac arrhythmia in adults and it is associated with a high burden of mortality and morbidity worldwide. Catheter ablation is increasingly used to improve symptoms and prognosis in selected patients. Lower limb venous access with subsequent transseptal approach to the left atrium is the standard procedure for atrial fibrillation catheter ablation. CASE PRESENTATION: We report an unusual case of complex venous anomaly with a left-sided inferior vena cava with hemiazygos continuation to a persistent left superior vena cava draining in an enlarged coronary sinus in a patient with persistent atrial fibrillation scheduled for transcatheter ablation. DISCUSSION: Lower limb venous anomalies may limit a standard transseptal approach to the left atrium thus precluding an effective catheter ablation procedure for atrial fibrillation. Alternative interventions, such as unconventional percutaneous access, thoracoscopic approach and "ablate and pace" procedures, may be necessary in patients with symptomatic atrial fibrillation and complex venous anomalies.