When arrhythmia hides a tumor: a case of atrial fibrillation unmasking superior vena cava syndrome

Superior Vena Cava Syndrome (SVCS) is typically caused by thoracic malignancies and may present with a wide range of symptoms, from mild facial edema to severe respiratory compromise. Atrial Fibrillation (AF), although common, is rarely the initial manifestation of SVCS. We report the case of a 65-year-old woman who presented to the emergency department with new-onset AF, and in whom physical examination revealed signs of venous congestion suggestive of SVCS. Imaging studies confirmed a right hilar mass with vascular invasion, thrombosis of the internal jugular vein, and complete obstruction of the superior vena cava. Histological analysis confirmed small-cell lung carcinoma. The patient underwent endovascular stenting and chemoradiotherapy. This case highlights the importance of thorough physical examination in emergency settings and suggests that new-onset AF in the presence of venous congestion may be an early clue to an underlying structural pathology such as SVCS.