Importance of identifying the direction of pulmonary venous flow in diagnosing a cavopulmonary window: A case report and review of literature.

A 75-year-old male suffered from dyspnea on exertion. In a referring hospital, cardiac catheterization demonstrated a 25% increase in oxygen saturation between the high superior vena cava (SVC) and the right atrium, suggesting a pre-tricuspid left-to-right shunt. However, neither an intracardiac shunt nor a partial anomalous pulmonary venous connection was detected. Therefore, he was referred to our hospital for further evaluation. A transesophageal echocardiogram revealed a retrograde-dominant bidirectional flow in the right upper pulmonary vein (RUPV). A contrast agent injected via the left upper limb appeared in the SVC and thereafter some contrast entered into the RUPV. A three-dimensional reconstructed computed tomography showed a side-to-side communication between the RUPV and the SVC. A cavopulmonary window was definitively diagnosed, in which the RUPV not only drained into the left atrium but also connected to the SVC side-to-side. < In a suspected case of a pre-tricuspid left-to-right shunt without atrial septal defect and anomalous pulmonary venous connection, a cavopulmonary window would be another differential diagnosis. This rare cardiac anomaly should be taken into consideration in diagnosing a pre-tricuspid left-to-right shunt. Identifying the direction of pulmonary venous flow can be an opportunity to find it.>.