SESSION TITLE: Cardiovascular Disease 1 SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/09/2018 01:15 PM - 02:15 PM INTRODUCTION: Platypnea-orthodeoxia syndrome (POS) is a rare clinical entity characterized by dyspnea and hypoxemia that occurs in the upright position and improves with recumbency. We report the case of a woman who developed POS in the setting of a PFO and aortic aneurysm. CASE PRESENTATION: An 88-year-old woman with a history of repaired ascending aortic dissection presented with progressive shortness of breath for the past three years. Bending down exacerbated her dyspnea while lying supine improved it. She had no other cardiopulmonary complaints. Her prior work-up including pulmonary function testing, transthoracic echocardiogram, chest CT with contrast, and bronchoscopy were non-diagnostic. Additionally, right and left heart catheterizations showed normal right-sided pressures and non-obstructive coronary artery disease. During her visit, saturation was 78% sitting upright, while in the supine position, saturation increased to 95% with the patient breathing more comfortably. Since her prior chest imaging did not show pulmonary arteriovenous malformations, and she did not have a history to suspect pulmonary parenchymal shunts (eg hepatopulmonary syndrome), we pursued transesophageal echocardiogram with bubble study to evaluate for intracardiac shunting. The study revealed aortic root dilation to 5.2 cm at the level of the sinuses of Valsalva. Furthermore, a large patent foramen ovale showed predominantly right-to-left shunting across the atrial septum. The bubble study was positive in all positions; however, more bubbles crossed in the sitting position. The patient was subsequently referred to interventional cardiology for PFO closure. DISCUSSION: The proposed mechanism behind intracardiac causes of POS features two components, a structural defect that allows abnormal communication of blood flow, and a functional defect that promotes abnormal shunting. In the upright position, gravity causes anterior and inferior displacement of the aortic root, increasing its size. This decreases the atrial septum size while increasing its mobility. The resulting floppy atrial septum acts as a spinnaker in venous blood flow; its billowing to the left keeping the PFO open. Concurrently, ascending aorta enlargement causes the IVC to shift relative to the atrial septum due to counterclockwise rotation of the heart, as well as compression onto the right atrium that results in horizontal re-orientation of the atrial septum plane, allowing part of the inflow from the IVC to course directly across the PFO. CONCLUSIONS: Intracardiac causes of platypnea-orthodeoxia syndrome are under-recognized but potentially reversible causes of dyspnea. Small studies have shown that percutaneous PFO closure is safe and effective. Reference #1: Cheng TO. Platypnea-orthodeoxia syndrome: etiology, differential diagnosis, and management. Catheter Cardiovasc Interv.1999;47:64–66. Reference #2: Agrawal A, Palkar A, Talwar A. The multiple dimensions of Platypnea-Orthodeoxia syndrome: A review. Respir Med. 2017 Aug;129:31-38. Reference #3: Chopard R, Meneveau N, Rival G, Maitre J, Westeel V, Bernard Y, Bassand JP. Right-to-left atrial shunting associated with aortic root aneurysm: A rare cause of platypnea-orthodeoxia syndrome. Heart Lung Circ. 2013 Jan;22(1):71-5. DISCLOSURES: No relevant relationships by Jessie Chai, source=Web Response No relevant relationships by Alvaro Velasquez, source=Web Response