What is Tetralogy of Fallot?
TOF
When a VSD is associated with obstruction at the level of the pulmonary valve known as Pulmonary stenosis (PS), the whole condition is known as Tetralogy of Fallot (TOF). It is one of the commonest causes of “Blue Baby” .
TOF is a cardiac condition that includes a series of 4 defects in the heart. These defects are the result of and are caused by an unequal separation of the great arteries into a larger aorta and a smaller pulmonary artery.
When child develops in the mother’s womb, the aorta and pulmonary arteries did not separate with equal diameters in the normal way, from a single tube known as the truncal artery. The separation of the great arteries and ventricles happens simultaneously, one separates from above downwards and the other separates from below upwards. Both are supposed to meet and fuse together to complete the formation of the normal heart.
As the abnormal arterial septum moves to one side, it misses the meeting point with the ventricular septum. This makes the pulmonary artery small, the aorta big and the ventricular septum has a defect (hole in the heart) below the Aortic valve.
This defect which connects the left (LV) and the right ventricle(RV) is known as a VSD. The high pressure in the LV is transmitted to the Right ventricle now. Which, when associated with the PS, results in the right ventricle become stronger and thicker resulting in a Hypertrophic Right ventricle. This quartet of features is known as TOF.
We treat this condition by closing the hole (VSD) and opening the PS. We have to do open heart surgery and when we open (cut) the pulmonary artery the block is relieved. Once we have relieved the PS we need to reconstruct the pulmonary artery with a patch of Pericardium, known as the transannular patch (TAP) but unfortunately the underlying abnormal Pulmonary valve is sacrificed by this step. This is the repair of tetralogy of Fallot.
Sometimes the small child may not be ready for complete correction. This is because of small pulmonary arteries. Yet the child is blue and occasionally loses consciousness. This symptom is called a spell and is an emergency, (the lack of oxygen) we use an operation to increase blood flow to the lungs and thereby increase oxygen uptake.
A source of blood supply to the lung is provided from another blood vessel that goes to the arm using a PTFE (plastic) tube from the subclavian artery to the Pulmonary artery. This operation is known as the BT shunt operation. It makes the child pink until the pulmonary artery grows to the size that is sufficient to obtain a complete repair. So we stage the repair in some of these children to give a very good result.