The pulmonary veins are the four blood vessels (two on each side) that return oxygen-rich blood from the lungs to the left atrium of the heart.
Total anomalous pulmonary venous return (TAPVR) is a rare congenital malformation in which all four pulmonary veins do not connect normally to the left atrium. Instead all four pulmonary veins drain abnormally to the right atrium by way of an abnormal (anomalous) connection.
Total anomalous pulmonary venous return is classified into different types, based on how and where the pulmonary veins drain to the heart:
Supracardiac Total Anomalous Pulmonary Venous Return
The pulmonary veins drain to the right atrium via the superior vena cava. In this type of TAPVR, the pulmonary veins first come together behind the heart and then drain upwards to an abnormal “vertical vein.” This vertical vein joins the innominate vein which connects to the right superior vena cava and drains to the right atrium.
Cardiac Total Anomalous Pulmonary Venous Return
The pulmonary veins come together behind the heart and then drain to the right atrium through the coronary sinus. The coronary sinus is the vein that normally returns blood from the heart muscle itself back to the right atrium after its oxygen has been depleted. The coronary sinus drains directly into the right atrium.
Infracardiac Total Anomalous Pulmonary Venous Return
The pulmonary veins drain to the right atrium via the hepatic (liver) veins and inferior vena cava. In this type, the pulmonary veins join together behind the heart and then typically drain downwards, connecting to the liver's portal vein system. They then drain through the vascular bed of the liver and enter the right atrium from the hepatic veins.
All types of total anomalous pulmonary venous return have to have an atrial septal defect (ASD). Because none of the pulmonary veins connect normally to the left side of the heart (and thus out to the body), blood is shunted from the right atrium across the atrial septal defect. Absence of an atrial septal defect in total anomalous pulmonary venous return is not compatible with survival.