Atrial septal aneurysm with right-to-left interatrial shunting.

Interatrial shunting in the presence of an atrial septal aneurysm is an uncommon but well recognized abnormality. Previous case reports have demonstrated that elevated right atrial pressure secondary to pulmonary embolism or right ventricular infarction may cause right-to-left interatrial shunting in the presence of an atrial septal aneurysm. We describe a unique situation in which an atrial septal aneurysm was associated with a right-to-left shunt secondary to severe systemic hypotension and normal right atrial pressure. In this patient, we used midodrine, an oral alpha-1 agonist, to increase systemic arterial pressure, decrease the severity of the shunt, and treat the severe hypoxemia. This case establishes that right-to-left interatrial shunting can result from a decrease in left ventricular afterload with normal right atrial pressure. Oral alpha-1 agonist therapy can be used successfully to treat patients such as ours and possibly others with similar functional abnormalities.