Platypnea-orthodeoxia

Platypnea-orthodeoxia is a relatively uncommon but striking clinical syndrome characterized by dyspnea and deoxygenation accompanying a change to a sitting or standing from a recumbent position. Since Burchell et al1 described this rare syndrome over half a century ago, no more than 50 cases have been reported in the literature.Platypnea-orthodeoxia has been described to occur in pulmonary arteriovenous shunts, pulmonary parenchymal shunts (as in the hepatopulmonary syndrome), or with intra-cardiac right-to-left shunts.

Two conditions must coexist to cause platypnea-orthodeoxia: an anatomical component in the form of an interatrial communication and a functional component that produces a deformity in the atrial septum and results in a redirection of shunt flow with the assumption of an upright posture. The former may be an atrial septal defect, a patent foramen ovale, or a fenestrated atrial septal aneurysm. The latter may be cardiac, such as pericardial effusion or constrictive pericarditis; pulmonary, such as emphysema, arteriovenous malformation, pneumonectomy, or amiodarone toxicity; abdominal, such as cirrhosis of the liver or ileus; or vascular, such as aortic aneurysm or elongation.2

Under normal conditions an interatrial communication allows blood to shunt from left to right due to a higher pressure in left atrium than right atrium and a greater compliance of the right ventricle than the left ventricle. Right-to-left interatrial shunting is usually associated with spontaneous or induced pulmonary hypertension and, therefore, in the absence of a right-to-left pressure gradient, what is the mechanism for a right-to-left shunt? Or put in another way, what causes water to flow uphill?2 A persistent Eustachian valve can cause interatrial right-to-left shunting with a normal right atrial pressure.3 Platypnea-orthodeoxia could be explained on the basis of positional modification of abnormal shunting. Standing upright could stretch the interatrial communication, be it a patent foramen ovale, an atrial septal defect, or a fenestrated atrial septal aneurysm, thus allowing more streaming of venous blood from inferior vena cava through the defect, whether or not a persistent Eustachian valve coexists.3 This redirection of flow caused by an anatomic distortion of the right atrium or the atrial septum also might occur from a loculated pericardial effusion, an aortic aneurysm, or aortic elongation.2