From the Research
Platypnea-Orthodeoxia syndrome is a rare condition characterized by decreased oxygen levels and shortness of breath that worsens when sitting or standing upright and improves when lying flat, typically caused by an intracardiac shunt, most commonly a patent foramen ovale (PFO) or atrial septal defect (ASD) 1.
Causes and Pathophysiology
The syndrome is usually caused by an intracardiac shunt, hepatopulmonary syndrome, or shunting resulting from severe pulmonary disease 1. The primary mechanisms of Platypnea-Orthodeoxia syndrome can be broadly classified based on intracardiac abnormalities, extracardiac abnormalities, and miscellaneous etiologies 2.
- Intracardiac shunts, such as a patent foramen ovale (PFO) or atrial septal defect (ASD), are the most common causes of the syndrome.
- Extracardiac causes include intra-pulmonary arteriovenous malformations and lung parenchymal diseases.
- Miscellaneous etiologies may also contribute to the development of the syndrome.
Diagnosis and Treatment
Diagnosis requires demonstration of positional changes in oxygenation, with arterial blood gases showing decreased PaO2 and oxygen saturation in the upright position compared to supine 3.
- Echocardiography with bubble study is the preferred diagnostic test to identify cardiac shunts.
- Treatment depends on the underlying cause but often involves closure of the shunt, typically through transcatheter closure of a PFO or ASD if present.
- For patients with pulmonary arteriovenous malformations, embolization may be necessary.
- Supportive care includes supplemental oxygen therapy while definitive treatment is arranged.
- Patients should be advised to avoid prolonged standing or sitting positions that worsen symptoms until the underlying cause is addressed. The syndrome occurs because gravity enhances right-to-left shunting in the upright position, allowing deoxygenated blood to bypass the lungs and enter systemic circulation 4.
Clinical Implications
Platypnea-Orthodeoxia syndrome should be suspected when normal arterial oxygen saturations are recorded while an individual is supine, followed by abrupt declines in those saturations when upright 3.
- A high clinical suspicion is necessary to diagnose the syndrome, as it is probably underdiagnosed.
- Identification of the syndrome has therapeutic implications and can have a huge impact on the patient's everyday life.
- Percutaneous closure of a small secundum atrial septal defect can eliminate right-to-left shunting and substantially improve the patient's functional status 1.