Arterial desaturation dependent on posture.

A 60-year-old woman developed subacute bacterial endocarditis following a minor operation. She presented the unusual picture of breathlessness with cyanosis related to posture, confirmed by laboratory measurement. She had an atrial septal defect with right-to-left shunt, and had sustained multiple pulmonary infarcts, resulting in the obliteration of a large section of her pulmonary vascular bed. The puzzling absence of pulmonary hypertension was explained by tricuspid incompetence, although there was no clinical evidence of this, and on two occasions the right atrial pressure tracing was normal. The use of a balloon catheter to predict the results of operation is described. At operation the severely damaged tricuspid valve was replaced, and the septal defect was closed. There was an immediate improvement in the arterial oxygen tension after operation. She subsequently survived an episode of ventricular fibrillation, left hospital 11 months after her original admission and is now leading a normal life.