From the Guidelines
Platypnea-orthodeoxia syndrome (POS) caused by a patent foramen ovale (PFO) occurs through a specific anatomical and physiological mechanism, where a right-to-left shunt develops through the PFO when a patient assumes an upright position, leading to systemic hypoxemia that worsens in the upright position and improves when lying down. This condition involves both anatomical and functional components. Anatomically, the PFO creates a potential passage between the right and left atria. When a patient stands up, there can be distortion of the interatrial septum, causing the foramen ovale to open wider. Additionally, structures like an enlarged aortic root, persistent Eustachian valve, or atrial septal aneurysm can direct blood flow from the inferior vena cava preferentially toward the PFO. Functionally, positional changes alter the pressure relationship between the atria. Though right atrial pressure is typically lower than left atrial pressure (preventing right-to-left shunting), certain conditions like pulmonary hypertension, right ventricular dysfunction, or decreased right heart compliance can reverse this gradient when upright, as noted in patients with pulmonary embolism 1. This creates a pressure differential that forces deoxygenated blood through the PFO into the left atrium, causing systemic hypoxemia.
The diagnosis of POS should be considered in patients with unexplained positional hypoxemia. Key points to consider in the diagnosis and management of POS include:
- The role of PFO in causing right-to-left shunting and systemic hypoxemia
- The importance of positional changes in altering the pressure relationship between the atria
- The potential for structures like an enlarged aortic root or persistent Eustachian valve to direct blood flow toward the PFO
- The need for definitive treatment, typically involving PFO closure, to prevent recurrent episodes of hypoxemia.
Recent guidelines on the management of cryptogenic stroke and PFO suggest that PFO closure may be considered in certain patients, particularly those with a high Risk of Paradoxical Embolism (RoPE) score and at least one clinical risk factor 1. However, the effectiveness of PFO closure in preventing recurrent stroke or transient ischemic attack is still uncertain, and the procedure is associated with potential complications 1. Therefore, definitive treatment typically involves PFO closure, but the decision to proceed with closure should be made on a case-by-case basis, taking into account the individual patient's risk factors and clinical characteristics.
From the Research
Mechanism of Platypnea-Orthodeoxia Syndrome
The mechanism of platypnea-orthodeoxia syndrome (POS) caused by patent foramen ovale (PFO) involves an increase in right atrial pressure or a change in the degree of right-to-left shunting with upright posture 2. This can lead to dyspnea and hypoxemia when upright, which improves upon recumbency.
Key Factors Contributing to POS
Several factors contribute to the development of POS in patients with PFO, including:
- Anatomical distortion of the atrial septum related to a dilated aortic root or shortening of the distance between the aortic root and posterior atrial wall 2
- Right-to-left shunt through the PFO, which can be exacerbated by upright posture 3, 4
- Association with other cardiac defects, such as atrial septal aneurysm or persistent prominent Eustachian valve 4
- Non-cardiac pathologies, such as pulmonary AV malformations, lung parenchymal diseases, and hepatopulmonary syndrome 3
Diagnosis and Treatment
Diagnosis of POS typically involves transthoracic echocardiography, contrast-enhanced transthoracic echocardiography, or right-and-left cardiac catheterization to confirm the presence of a right-to-left shunt 3, 4. Treatment usually involves percutaneous closure of the PFO, which has been shown to be a safe and effective method for alleviating symptoms and improving oxygen saturation 2, 4, 5.
Clinical Outcomes
Studies have demonstrated significant improvements in clinical outcomes, including: