Significance of the site of injection in unexpected right-to-left shunting

Lung perfusion scintigraphy, with Tc-99m MAA injected into a left antecubital vein, revealed extensive uptake in the myocardium, kidneys, spleen, thyroid, and brain. After a right antecubital injection, a normal pulmonary perfusion pattern was found. This finding is specific for right-to-left shunting due to anomalous systemic venous drainage into the left atrium.