The cause of total anomalous pulmonary venous return (TAPVR) is unknown. In normal circulation, blood is oxygenated in the lungs and then returns to the left atrium, flowing from there to the left ventricle, through the aorta, and around the body. In TAPVR, oxygenated blood returns to the right atrium instead. From there it goes to the right ventricle, through the pulmonary artery and back to the lungs. In other words, blood simply circles to and from the lungs and never gets out to the body. This condition is incompatible with life.
If the infant is to live, a large atrial septal defect (ASD) or patent foramen ovale (passage between the left and right atria) must exist to allow oxygenated blood to flow to the left side of the heart and subsequently the body.
The severity of this condition depends on whether the pulmonary veins are obtructed. There are two subtypes of TAPVR. In one, the veins course into the abdomen, passing through a muscle (diaphragm). This muscle squeezes the veins and narrows them, causing the blood to back up into the lungs. This type causes symptoms early in life. The second type of TAPVR has no obstruction; the veins do not course through the abdomen.
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