Pharmacologic exposure of an occult atrial septal defect

Objective: To describe the diagnostic technique used to identify the presen ce of a symptomatic interatrial shunt obscured by normal intracardiac press ures and to discuss the unusual findings in this case and their relevance t o the investigation of patients with unexplained hypoxemia. Design. Case report. Setting. Intensive care unit of a university teaching hospital. Patient. A patient with a variant of the platypnea-orthodeoxia syndrome. Interventions. Intravenous administration of metaraminol. Measurements and Main Results. Clinical examination and routine investigati ons ruled out pneumonia or myocardial infarction as a cause of respiratory failure, and pulmonary angiography was normal other than for the demonstrat ion of an interatrial communication. Repeated transthoracic echocardiograms failed to indicate the presence of a significant interatrial shunt that wa s eventually detected following temporary shunt reversal with intravenous m etaraminol and confirmation by bubble-contrast transesophageal echocardiogr aphy and right heart catheter studies. Conclusions. Symptomatic right-to-left intracardiac shunt may occur in pati ents with normal intracardiac and pulmonary artery pressures. The presence of a significant shunt cannot be ruled out by transthoracic echocardiograph y without the use of bubble contrast.