Platypnea-Orthodeoxia Syndrome Due to a Functional Patent Foramen Ovale: Aortic Dilatation and Possible Contribution of Obstructive Sleep Apnea.

Platypnea-orthodeoxia syndrome (POS) is an uncommon and underrecognized cause of positional hypoxemia, usually related to dynamic right-to-left shunting. We report the case of a 74-year-old man with obesity and unexplained presyncopal episodes associated with severe positional oxygen desaturation. Initial transthoracic echocardiography with agitated saline contrast performed in the supine position was negative. However, contrast-enhanced transesophageal echocardiography performed in the sitting position revealed a patent foramen ovale with a dynamic right-to-left shunt associated with aortic root dilatation and interatrial septal distortion. Percutaneous closure using a NobleStitch system resulted in immediate improvement in oxygenation. Subsequent respiratory polygraphy identified moderate obstructive sleep apnea, interpreted as a possible contributing factor rather than a proven mechanism. This case highlights the importance of considering POS in unexplained positional hypoxemia and emphasizes that a negative supine transthoracic contrast study does not exclude a dynamic intracardiac shunt.