Induced right-to-left cardiac shunt during pulmonary perfusion imaging.

Ventilation-perfusion lung scans are routinely performed using Tc-99m labeled MAA particles administered intravenously which are subsequently trapped in the pulmonary artery capillary bed. In the presence of a right-to-left shunt, activity may be seen in the systemic circulation. Right-to-left shunts may be worsened by inducing hypoxemia which causes pulmonary artery constriction, and also by increasing venous return to the heart. In this case, the authors used various maneuvers to increase right-to-left shunting and thereby demonstrated the presence of fixed pulmonary hypertension. These findings suggested that the patient's dyspnea on exertion was not primarily because of left ventricular dysfunction, and proposed coronary bypass surgery was deferred for medical management.