Pharmacologic exposure of an occult atrial septal defect

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ObjectiveTo describe the diagnostic technique used to identify the presence of a symptomatic interatrial shunt obscured by normal intracardiac pressures and to discuss the unusual findings in this case and their relevance to the investigation of patients with unexplained hypoxemia.DesignCase report.SettingIntensive care unit of a university teaching hospital.PatientA patient with a variant of the platypnea-orthodeoxia syndrome.InterventionsIntravenous administration of metaraminol.Measurements and Main Results Clinical examination and routine investigations ruled out pneumonia or myocardial infarction as a cause of respiratory failure, and pulmonary angiography was normal other than for the demonstration of an interatrial communication. Repeated transthoracic echocardiograms failed to indicate the presence of a significant interatrial shunt that was eventually detected following temporary shunt reversal with intravenous metaraminol and confirmation by bubble-contrast transesophageal echocardiography and right heart catheter studies.ConclusionsSymptomatic right-to-left intracardiac shunt may occur in patients with normal intracardiac and pulmonary artery pressures. The presence of a significant shunt cannot be ruled out by transthoracic echocardiography without the use of bubble contrast.

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