Left Atrial Septal Pouch Thrombus: A Rare Contraindication to Percutaneous Transmitral Commissurotomy.

BACKGROUND

Thrombus formation within a left atrial septal pouch is uncommon but may critically impact septostomy-based interventions.

CASE SUMMARY: A 55-year-old woman with severe rheumatic mitral stenosis and chronic atrial fibrillation on anticoagulation was evaluated for percutaneous transmitral commissurotomy. Transesophageal echocardiography revealed a large bilayered interatrial septal pouch containing a semimobile thrombus, whereas the left atrial appendage was thrombus-free. Cardiac computed tomography angiography confirmed a focal septal filling defect. Given the embolic risk associated with transseptal puncture, the procedure was deferred, and anticoagulation was intensified.

DISCUSSION: This case highlights the thrombogenic potential of the left atrial septal pouch in low-flow states and underscores the importance of systematic septal evaluation before transseptal interventions.