Platypnea-Orthodeoxia Syndrome: Positional Reversal of the Interatrial Pressure Gradient Demonstrated by Atrial Septal Motion

Platypnea-Orthodeoxia Syndrome (POS) is a rare clinical syndrome characterized by dyspnea and hypoxemia while upright that are relieved when the patient is supine. A right to left shunt in combination with several hypothesized hemodynamic or structural factors are needed to develop the syndrome. It is an important source of dyspnea in a small percentage of often-elderly patients. The exact mechanism for the positional increase in the shunt has remained elusive. We present the case of an 85-year-old woman with severe POS. The patient has an atrial septal aneurysm with a Patent Foramen Ovale (PFO). We were able to demonstrate a significant increase in the right to left intra-atrial shunt in the upright position using transesophageal echocardiography and agitated saline study. By analyzing the atrial septal motion, we were also able to provide evidence that the shunt is caused by a reversal in the inter-atrial pressure gradient in the upright position, thus we are able to show for the first time that a reversal of the interatrial pressure gradient can be responsible for the positional shunt.