TAPVC is a condition where all four pulmonary veins drain directly or indirectly into the right atrium instead of into the left atrium.

Pathology

Supracardiac TAPVC is the commonest and comprises half of all cases. Cardiac and infracardiac are equal in frequency at 20% each. Mixed variety accounts for 10%.

Usually, all four pulmonary veins join to form a pulmonary venous sinus which drains to right atrium directly or indirectly.

In supracardiac TAPVC, the pulmonary venous sinus drains into the left vertical vein (left superior vena cava) which drains into the left brachiocephalic vein.

In cardiac TAPVC, the pulmonary venous sinus drains into the coronary sinus. Less commonly, the pulmonary veins drain into the right atrium.

In infracardiac TAPVC, the pulmonary venous sinus descends into the abdomen via the esophageal hiatus to drain into portal vein, hepatic vein, inferior vena cava or ductus venosus.

Infracardiac TAPVC is four times more common in males.

In the mixed type, usually left upper pulmonary vein drains into left SVC, while other pulmonary veins drain into coronary sinus. 

Since all pulmonary veins drain into the right atrium, there will be a large ASD to allow blood to flow to the left atrium. Still, the left sided chambers are small as blood preferentially goes to the pulmonary artery due to lower resistance.

Features

Some patients have obstruction to pulmonary venous drainage. This causes two problems- decrease in pulmonary blood flow leading to cyanosis and increased back pressure leading to pulmonary artery hypertension. Chest X-ray may show pulmonary edema.

In those patients without obstruction to pulmonary venous drainage, there is good pulmonary blood flow leading to good oxygenation of blood in the lungs. Still, they have mild cyanosis due to mixing of oxygenated blood and deoxygenated blood in right atrium, before blood enters the left atrium to go to the entire body. These patients have right sided volume overload due to large amount of blood in the right atrium, which prefers to go to the right ventricle due to higher compliance. This produces pulmonary congestion leading to increased respiratory infections and also produces right heart failure.

In patients with pulmonary vein obstruction, S2 will be single and loud due to PAH. In patients without pulmonary vein obstruction, there is fixed split of S2, just as in an ASD, due to the large pulmonary blood flow delaying pulmonary valve closure and due to reciprocal changes in the ASD shunt with respiration. Quadruple or quintiple sounds can also occur in patients without pulmonary vein obstruction.

In patients with pulmonary vein obstruction, v1 has a tall R due to RV pressure overload, while in patients without pulmonary vein obstruction, v1 has rsR’ pattern due to RV volume overload.

In patients without pulmonary vein obstruction, chest X-ray shows cardiomegaly due right atrial and right ventricular enlargement. In supracardiac TAPVC, after 4 months age, there is snowman appearance- this refers to superior mediastinal shadow due to superior venacaval and left brachiocephalic enlargement.

Patients with pulmonary vein obstruction die in the first month of life. Patients without pulmonary vein obstruction die in the first year of life.

 Echo shows large RA, RV and pulmonary artery and small LA and LV. A large ASD is present. 

Surgery

If TAPVC with pulmonary vein obstruction is diagnosed, immediate surgery is to be done. If there is no pulmonary vein obstruction, surgery is done at 6 months.

The ASD is closed. For supracardiac TAPVC, the pulmonary venous sinus is connected to the left atrium. For the cardiac type which drains into the coronary sinus, the coronary sinus is deroofed and its ostium into the right atrium is closed. The coronary sinus drains into the left atrium, but this is not of much consequence. For the cardiac type in which pulmonary veins drain into the right atrium, part of the interatrial septum is excised to divert blood from these veins into the lefat atrium. For infracardiac TAPVC, the pulmonary venous sinus is connected into the left atrium.

After surgery, pulmonary vein obstruction can occur in 10%. So, careful follow up is needed.