What is TAPVC?
TAPVC stands for total anomalous pulmonary venous connection. The other term used parallel to this is total anomalous pulmonary venous drainage. They both imply the same.
What are pulmonary veins?
Pulmonary veins are tubes (2 usually on each side) which bring back the oxygenated red blood from lungs back to the heart.
These are relatively thin tubes and connect to the left upper chamber of the heart. The red blood form the left upper chamber goes then to the left lower pump, the left ventricle. This pushes the blood into the whole body which can function because it receives the oxygen.
What goes wrong in TAPVC?
In TAPVC, the 4 tubes coming into the left upper chamber do not enter the heart there. They infact usually form a chamber behind the left upper chamber and from that chamber they could re-enter the heart by several different routes into the right chambers!
This would imply the red blood does not enter the left pump! If that does not happen, survival would not be possible. But, there is a hole between the upper chambers of the heart which does allow some blood to enter the left side of the heart. This is usually a small quantity of blood. And it is not pure red blood.
When the red blood enters the right upper chamber, it mixes with the blue blood here. Most of this mixed blood enters the lungs as rest of the blue blood usually does. Small part of the mixed blood enters the left pump via the left upper chamber. This quantity is decided by the size of the hole between the upper chambers!
What is the problem with children with TAPVC?
Majority of them are very blue after they are born. This is because mixed blood (red+blue) enters the body circulation instead of the pure red blood. This is equivalent to a low quality fuel running a vehicle.
The additional problem is related to a much larger (usually more than twice the normal quantity) of blood flowing into the lungs. This results in lungs being affected significantly. Usually the child has high lung pressures. Sometimes in addition to high blood flow to lungs if the blood going out of lungs is blocked (the abnormal pulmonary veins) then the pressure may be too high in the first few days of life of the baby and a very special type of Obstructed TAPVC !
What are the types of TAPVD ?
This depends on where the abnormal pulmonary veins open up . It also depends on what course the veins take ! On the basis of this the TAPVC patients are divided into the following:
Whether the veins drain from a course above the heart: S up racardiac
Whether the veins drain into the right heart directly: Cardiac type (here they do drain into the heart directly but into the wrong chamber, the right upper)
If they course below the heart and into the liver and then reach the right up per chamber: Infracardiac
In addition any of these may be having blockage within the pulmonary veins (Obstructed). So, either of these could be further sub grouped into:
With Obstruction to the Pulmonary Veins or Without Obstruction within the Pulmonary Veins
What happens if the pulmonary veins are obstructed ?
We have noted above that in all patients with TAPVC, the amount of blood going to lungs is usually more than twice normal. This in itself causes some increase in pressure in the lungs from increased flow. In addition, if the amount of blood coming out of the lungs is blocked (as in obstructed TAPVD) then, due to back pressure, the lung pressure would increase too much to a point of affecting survival. It results in a double injury to the lungs with very high flow and blockage in addition.
This results in a true emergency where correction is required almost immediately.
What is the treatment of TAPVD ?
The treatment is to surgically reconnect the pulmonary veins to the normal connecting chamber of the heart, the left atrium. The only way to do this is to do it by open heart on pump surgery.