Right Atrial Thrombus Presenting as Platypnea-Orthodeoxia Secondary to Reverse Lutembacher Syndrome: A Case Report.

Platypnea-orthodeoxia syndrome (POS) is defined by dyspnea and deoxygenation due to a change in body position from lying down to an upright position. We present a case of a large right atrial (RA) thrombus likely due to a right coronary artery fistula in a patient with a patent foramen ovale (PFO). On imaging, the thrombus was thought to be an atrial myxoma involving the tricuspid valve; however, after surgical excision and histopathological analysis, it was noted to be a cystic thrombus. Red-brown material along with vascular elements was noted on histopathology. Post-surgery, the patient was critically ill and died due to severe tricuspid regurgitation (TR) and hypotension despite using a right ventricle assist device and multiple vasopressors. Reverse Lutembacher syndrome (RLS) is defined as a triad of tricuspid stenosis (TS), elevated RA pressure, and right-to-left atrial shunting. The location of the mass and positional changes could be causing transient RLS from positional TS and interatrial shunting via the PFO causing POS. Cardiac magnetic resonance imaging can help differentiate between intracardiac masses. T1 and T2 signal characteristics and differences in contrast enhancement can help differentiate between a thrombus and a tumor. Treatment options include anticoagulation, thrombolysis, and thrombectomy. If severe TR occurs after surgery, treatment modalities such as caval valves could be an option in the future. Extracorporeal membrane oxygenation to provide right ventricle support in such cases could be considered.