A case report of a triad causing platypnoea–orthodeoxia synd
Platypnoea–orthodeoxia syndrome (POS) is a rare condition characterized by hypoxaemia and dyspnoea when changing from a recumbent to an upright position. Diagnosis requires a high clinical suspicion and is often underdiagnosed.

Authors report a case of POS in a 50-year-old woman with dyspnoea and new-onset atrial fibrillation. Oxygen saturation and dyspnoea worsened as she changed from a supine to a sitting position (96 vs. 86%, respectively). Transoesophageal echocardiography demonstrated enlargement of both atria and right ventricle with reduced systolic function and a large Chiari network (CN). Colour Doppler discovered severe tricuspid regurgitation with tenting and tethering of the valve leaflets. Finally, a bubble test revealed the cause of POS to be a patent foramen ovale along with the severe tricuspid regurgitant jet moving into the left atrium and favoured by the CN. Surgical closure of the foramen ovale resulted in the resolution of symptoms.

Platypnoea–orthodeoxia syndrome is most commonly caused by a right-to-left shunt through an anatomical defect of the interatrial septum, typically a patent foramen ovale, combined with elevated right atrium pressure. This case illustrates an uncommon cause of POS in the absence of elevated atrium pressure due to the interplay of three key elements: a patent foramen ovale, tricuspid regurgitation, and the CN. The aim is to alert physicians to the possibility of an intracardiac shunt as the cause of unexplained and/or refractory hypoxaemia related to position changes. Early recognition of this syndrome promotes timely treatment, greatly improving patient outcomes.

Source: https://academic.oup.com/ehjcr/article/5/7/ytab236/6316556