The Long Shadow of Repair: Late-Onset Atrioventricular Block and Atrial Arrhythmias After Scimitar Syndrome and Mitral Annuloplasty.

Background and Clinical Significance: Scimitar Syndrome is a rare congenital cardiopulmonary anomaly characterized by partial anomalous pulmonary venous return, often requiring early surgical correction. It may coexist with other congenital or acquired cardiovascular anomalies, including valvular diseases such as mitral regurgitation. When surgical correction of Scimitar Syndrome is combined with mitral valve annuloplasty, the proximity to the atrioventricular node may potentially predispose patients to late-onset conduction disturbances, although causality remains speculative. Case Presentation: We describe the case of a 53-year-old male who developed paroxysmal atrial fibrillation, atrial flutter, and intermittent second-degree AV block decades after undergoing surgical correction of Scimitar Syndrome with concomitant mitral annuloplasty. Multimodal echocardiographic evaluation revealed preserved left atrial volume, normal intra-atrial conduction time, mildly reduced strain, and maintained atrial synchrony. The patient was treated with direct oral anticoagulants and beta-blockers and underwent the implantation of a ventricular leadless pacemaker. Conclusions: This case highlights the supportive role of atrial function imaging in assessing atrial health and informing rhythm management and procedural choices in surgically corrected congenital heart disease.