Detection of right-to-left shunt with radionuclide angiocardiography in refractory hypoxemia.

A significant right-to-left shunt at the atrial level was diagnosed by radionuclide angiocardiographic examination in a patient with hypoxemia whose perfusion scan showed no pulmonary uptake. The shunt occurred through a patent foramen ovale due to increased right ventricular afterload, subsequently confirmed at autopsy. It is concluded that radionuclide angiocardiography with technetium 99m macroaggregated albumin (99mTc MAA), followed immediately by a perfusion lung scan, may have a place in the evaluation of patients with refractory hypoxemia, since pulmonary embolism and/or right-to-left shunting are two of several causes of hypoxemia in the absence of congenital heart disease. A review of the literature on different pathophysiologic factors is presented and some therapeutic implications, specifically the adverse effect of PEEP in such situations, are discussed.