Tetralogy of Fallot(TOF)

What is ToF?
ToF refers to tetralogy of Fallot. This is a collection of 4 abnormalities which always happen in a constellation.  The primary problem is deviation of a part of the upper wall of the hole which obstructs the blood going to the lungs.
What are the 4 abnormalities in ToF?
The VSD or the hole, which is always large; the obstruction to blood flow into the lungs (right ventricular outflow tract obstruction); right pump wall being thicker (right ventricular hypertrophy) and overriding aorta (tilted appearance ) of the main artery coming out of the left ventricular pump.

Which are the main abnormalities of this condition ?
The main conditions associated with this are the VSD and the Blockage to the right pump.

What decides the clinical condition of the baby?

The clinical condition of the baby is decided by the balance between the VSD and the blockage. If the blockage is less, the effect of the VSD is more and the child is not much blue. If the blockage is more, the child will be more blue.

How does a doctor assess if the child is more blue or not ?
This is assessed by the pulse oximeter which reads the saturation of the blood as a number which is percentage. If the number is 94% or more it is referred to as normal; if it is less the child is “desaturated”.  The lower the oxygen the lower the saturation will be. When it gets to be below 80%, plan needs to be made about the next intervention.  If it continues to be in high 80′s and 90′s it is referred to as “Pink Tetralogy”, because these babies are not blue!

When is intervention performed in ToF patients ?
Intervention is planned on the basis of the oxygen saturation. If the saturation is <75% or around this, planning needs to start in the direction of the next step.
The decision to take the next step is decided on the basis of the following:

1. The age of the patient
2. The weight of the patient
3. The cardiac details on echocardiography, specifically:

a. Pulmonary artery size
b. Coronary artery anatomy
c. RVOT anatomy
d. No of VSDs if more than one.

How is decision made on the basis of the age of presentation?
The child may actually turn very blue in the newborn period. When that happens, the child has such severe blockage that enough blood is not going into the lungs. The circulation has to be restored emergently then using a medicine called Prostaglandin. This opens a natural track called PDA which allows blood to go to lungs. The PDA is usually present in all till 7th to 14th day of life in all children and then naturally closes. That is how the child was sustaining itself till the presentation.  

What is to be done when the child presents in newborn period with severe low oxygen ?
When that happens, the child needs a secure blood supply to the lungs because the natural path from heart to lungs may be too severely blocked. A shunt is a connection between 2 arteries, one carrying the red blood (with high pressure) and other to the lungs (pulmonary). The shunt in medical parlance is referred to as B-T shunt or Blalock-Taussig shunt (named after the 2 people who worked to make this happen).


How is treatment planned later on?
If the child is diagnosed in infancy (or in newborn period but has been stable) then the treatment planning is done according to the points mentioned above.  If the babies weight is >7.5 Kg and the cardiac anatomy is amenable to surgery then a total repair where in all the defects related to ToF are taken care of is accomplished.

If the babies weight is < 7.5 Kg or the anatomy is not favorable then the child needs to undergo a BT shunt.

What are the treatment options in a child with ToF ?
Yes. All children with a diagnosis of ToF need to undergo a final surgery called total repair. Some children who have a lower oxygen prior to reaching a point where they can have  total repair need an intermediate surgery called Shunt operation.

BT shunt is a surgery which is only a temporizing measure. Is there an alternative to it
Yes ! In some select patients we have done balloon angioplasty of the pulmonary valve and the outflow tract to improve the pulmonary blood flow.  This will temporarily for a few months improve the situation and the baby will reach a point where finally the total repair operation can be done.  This is a palliative (temporarily improving) intervention which decreases the number of surgeries a child needs.

What is the longterm outlook of a child with ToF ?
Longterm outlook of children with TOF is excellent. This also depends on what type of surgery is performed.

What are the types of surgeries performed for ToF?
The surgical steps involved are :
1. Closure of VSD
2. Reconstruction of the RV outflow tract

  1. This may be done by removing extra muscle. If this is the only procedure done for improving the RVOT then the child is looking forward to an extremely good future.
  2. If the surgery involved widening the ring of the pulmonary valve (trans-annular patch or TAP) then the child needs follow up for evaluating how the right side of the heart is faring. The follow up is usually needed for up to 2 decades. A small percent of patients may require intervention of some nature a couple of decades later.

What is likely to happen if the child has had a surgery with TAP?
The child may require (only a small percent will do so ) an intervention. This is usually so because the pulmonary valve is leaking. This happens because the valve ring once interrupted will cause some leakage. If the leakage over the years and decades results in problems of the RV, the pulmonary valve may need to be replaced.  Interestingly there are options  currently of replacing the pulmonary valve in select patients without surgery i.e. by angioplasty technique. The technique and technology is being improved already to accommodate more patients for this procedure by the transcatheter technique.