C63-08 Platypnea-Orthodeoxia Syndrome Due to Patent Foramen Ovale in Chronic Lung Disease

Abstract Introduction Platypnea-Orthodeoxia Syndrome (POS) is an uncommon disorder characterized by dyspnea and arterial desaturation in the upright position that improves when supine. The condition is most often attributed to intracardiac shunting, particularly through a patent foramen ovale (PFO), but may also arise from extracardiac or functional anatomic factors that alter atrial geometry and redirect inferior vena cava flow (IVC) toward the PFO without elevated right atrial pressure. We present a case of POS secondary to PFO in an elderly man with pulmonary fibrosis and emphysema that resolved following percutaneous closure. Case Description An 86-year-old male with chronic respiratory failure on 4 L/min oxygen, pulmonary fibrosis, emphysema, atrial flutter status post ablation, and known PFO presented from a preoperative clinic for evaluation of worsening hypoxemia. He was alert and asymptomatic despite oxygen saturation of 80-85% when sitting upright, which improved to 94-96% when supine. Arterial blood gas analysis confirmed a postural drop in PaO2 from 75 mm Hg (Supine) to 54 mm Hg (Upright). Computed tomography of the chest excluded pulmonary embolism, and ventilation-perfusion scanning revealed no perfusion mismatch. Pulmonary function testing showed mild diffusion impairment with near-normal lung volumes. Transesophageal echocardiogram with bubble study demonstrated a large 0.6 cm PFO with right-to-left shunting. The patient underwent a percutaneous PFO closure with a 35 mm Amplatzer occluder device, post-procedure TTE showing complete closure without residual shunt. He was subsequently discharged with stable oxygenation and no further recurrence of hypoxemia following intervention. Discussion POS is an uncommon but reversible cause of hypoxemia, most frequently linked to intracardiac shunts such as PFO. Approximately 87% of cases are intracardiac in origin and can redirect venous outflow without elevated right atrial pressure. In this patient, the shunting is posture-dependent with inferior displacement of the atrial septum and aligns the IVC inflow towards the PFO, transiently redirecting venous blood into the left atrium despite normal right-sided pressures due to widening of interatrial communication. Chronic pulmonary changes likely compounded the septal distortion and further augmented shunting when upright. Diagnosis requires a 5% drop in SpO2 or 4 mm Hg reduction in PaO2 between supine and upright positions, with contrast echocardiography serving as the diagnostic standard. In select patients, percutaneous closure can result in complete resolution of positional hypoxemia. Given the 25% prevalence of PFO in the population, clinicians should consider POS in patients with unexplained positional desaturation. This abstract is funded by: None