C43-03 Platypnea-Orthodeoxia Syndrome: A 90-Year-Old Patient Presenting With Persistent Hypoxemia

Abstract Introduction Platypnea-orthodeoxia syndrome (POS) is a rare, often underrecognized condition characterized by positional dyspnea—shortness of breath that worsens when sitting or standing and improves when reclining. This postural variation in oxygenation results from an abnormal right-to-left intracardiac or intrapulmonary shunt that becomes hemodynamically significant in the upright position. If left untreated, POS can lead to profound hypoxemia and significant functional impairment. Because its presentation is often subtle and easily misattributed to more common cardiopulmonary disorders, POS poses considerable diagnostic challenges and requires a high index of clinical suspicion. This case highlights the importance of considering POS in patients with unexplained hypoxemia, particularly when symptoms exhibit positional variation. We present a case of severe, refractory hypoxemia in a 90-year-old man due to a large patent foramen ovale (PFO), successfully treated with percutaneous closure. Case Presentation A 90-year-old man with hypertension, hyperlipidemia, hypothyroidism, and no prior cardiac disease presented with persistent hypoxemia discovered during pre-procedure evaluation for a spinal injection. He reported progressive exertional dyspnea over several months but denied chest pain, cough, or fever. On admission, oxygen saturation was 98% on 6 L/min nasal cannula but fell to the low 80s when upright, triggering a rapid response. Arterial blood gases showed hypoxemia and respiratory alkalosis. Chest CTA revealed no pulmonary embolism or parenchymal disease. Notably, oxygenation improved when supine, suggesting a positional component. Initial transthoracic echocardiography (TTE) showed preserved ejection fraction but an inconclusive bubble study. Transesophageal echocardiography (TEE) demonstrated an aneurysmal interatrial septum with a large PFO and significant right-to-left shunting. The patient underwent percutaneous closure with a 30-mm GORE CARDIOFORM septal occluder. Post-procedure, oxygen saturation improved to 94% on room air in the upright position, with resolution of symptoms. Follow-up TTE at one month showed no residual shunt. Discussion POS results from postural changes that facilitate right-to-left shunting despite normal right-sided pressures. Intracardiac shunts, particularly PFO, account for ∼87% of cases; extracardiac causes include pulmonary arteriovenous malformations and severe parenchymal lung disease. Because oxygenation often fails to improve with supplemental oxygen, clinicians should suspect POS when hypoxemia is disproportionate to pulmonary findings and improves when supine. In this case, the striking positional hypoxemia and confirmatory TEE findings were key to the diagnosis. Percutaneous closure of the PFO promptly resolved hypoxemia and restored functional status, underscoring the therapeutic value of targeted intervention. This abstract is funded by: none