Total anomalous pulmonary venous return (TAPVR) is a congenital heart defect in which one or all of the pulmonary veins between the lungs and heart are not connected properly. The most common form of this defect occurs when all four pulmonary veins drain into a single vessel. This vessel could be a vein that drains the circulation of the liver, the heart or the upper body (e.g., the superior vena cava).

That single vein then connects into the right atrium, which normally receives only oxygen-poor blood. From there, the oxygen-rich blood flows into the right ventricle, through the pulmonary artery and back into the lungs. In short, oxygen-rich blood cycles endlessly to and from the lungs and never gets delivered out to the oxygen-starved tissues and organs of the body.

In addition to causing low oxygen levels in the body’s blood supply, TAPVR adds additional strain to the lungs and the heart as they work to meet the body’s demand for oxygen-rich blood. Without treatment, lung congestion and heart failure will occur within days or weeks. Obstructions of the pulmonary veins, as well as overall congestion in the heart due to the overload, are not uncommon.

TAPVR occurs in about one in every 15,000 live births, or 1.5 percent of newborns with congenital heart disease.

There are a number of different types of TAPVR, which are classified according to the site of the pulmonary vein mis-connection:

For an infant to survive with TAPVR, even for a short while, other heart defects must be present that allow oxygen-rich blood on the right side of the heart to mix with oxygen-poor blood on the left side of the heart. The most common associated congenital defect is known as an atrial septal defect (ASD) – a hole in the wall (septum) between the two upper chambers of the heart (the atria). The ASD improves the circulation of an infant with TAPVR by allowing some oxygen-rich blood to travel from the right atrium through the ASD and into the left atrium, from where it can travel to the left ventricle and through the aorta to the rest of the body. The result is a blood supply to the body that carries at least some available oxygen.

Another associated defect is known as a patent ductus arteriosus (PDA). This is a defect in which a normal fetal blood vessel (ductus arteriosus) between the aorta and the pulmonary artery remains open (patent) after birth. By keeping the connection open between the aorta and the pulmonary artery, some of the oxygen-rich blood that is abnormally traveling through the pulmonary artery and back to the lungs can travel through the aorta and to the rest of the body.

Like some other congenital heart defects, the cause of TAPVR is unknown.