TETRALOGY OF FALLOT

 

What is Tetralogy of Fallot?
 

This condition describes 4 defects of various degrees that occur in combination:

1. Pulmonary stenosis – obstruction of flow to lung circulation (can occur at various levels)
2. V entricular septal defect– hole between the pumping chambers
3. Over-riding of aorta- the main body artery sits astride both pumping chambers to various degree and sometimes may arise mainly from the right pumping chamber
4. Right ventricular hypertrophy – thickening of the right pumping chamber

 

 

What causes Tetralogy of Fallot?

 

We don’t quite know why these defect occurs. There are certain genetic defects such as 22q11 deletion or Di George syndrome and Down syndrome (trisomy 21) where Tetralogy of Fallot can occur more commonly. Most often, no cause is found.
 

 

What are the symptoms?
 

Depending on the severity of obstruction to the lung circulation, babies could present with high flow to lung circulation – just like with a VSD, (when the obstruction is mild), to presenting as a blue baby with low oxygen levels (cyanosis) where the obstruction is severe, leading to reduced flow to lung circulation and mixing of blue (less oxygenated) blood with pink (more oxygenated) blood through the hole (VSD). Those with a thick muscle below the pulmonary valve that tightens at certain times, (when the baby is upset, straining, or with feeding) can suddenly go blue or very pale and quiet. This presents quite dramatically and is called a hypercyanotic or Tet spell. This requires urgent attention with admission to the hospital. In mild cases, babies or infants may present with a loud heart murmur. With the advent of fetal echocardiography, Tetralogy of Fallot can be diagnosed before birth and a clear plan can be made for early follow-up and treatment.
 

 

How is it diagnosed?
 

A good history, examination, ECG and the classic chest X ray appearance of heart shadow, can strongly suggest Tetralogy of Fallot. Echocardiography is an excellent investigation that usually gives all the information necessary to proceed with treatment. In some cases called complex tetralogy of Fallot additional investigations such as CT angiography or cardiac catheterization and angiography may be necessary before planning treatment.
 

 

How is it treated ?
 

Infants with severe narrowing or obstruction of lung flow may need medications called beta-blockers (propranolol). It reduces the heart rate and mixing of blue blood with pink blood. It only serves as a temporary measure. In babies who have severely reduced flow to the lungs, procedures to increase the flow may be necessary as urgent procedures. Dr Khambadkone can perform balloon dilation of pulmonary valve if that contributes to the main narrowing, or right ventricular outflow tract stenting (RVOT stent) where a slotted metal tube collapsed and mounted on a balloon catheter is delivered through a vein in the leg or neck to open up the outflow by positioning the stent across the narrow muscle below the valve and the valve itself. Both these procedures are done by a key hole technique of cardiac catheterization. The allow better flow to be established to the lung circulation until a definitive surgery could be done.

 

In newborn babies, stenting of patent ductus arteriosus (PDA) could provide better flow to the lung circulation. Surgery is sometimes required to increase flow to the lung circulation by a shunt (Modified Blalock-Taussing shunt or Modified BT shunt). Surgery to repair the defect is performed between 3 – 6 months of age if the infants can wait until that age and if they are more than 3.5 to 4 kg. This involves open heart surgery with use of heart –lung machine (cardio-pulmonary bypass). Dr Khambadkone works closely with renowned cardiac surgeons. Depending upon the extent of surgery and age of the baby, recovery on the Intensive Care Unit could be for 2 – 3 days; the total hospital stay is between 7 to 10 days. The recovery at home after discharge may take a few weeks. Return to school may take up to 4 weeks.

 

 

What is the prognosis?
 

After repair of Tetralogy of Fallot, it is possible that there may be some residual defects such as mild obstruction of flow to lung circulation, lung artery branches, and more likely, leak from the pulmonary valve called pulmonary regurgitation. Rarely, there may be small residual hole around the patch closing VSD. These tend to be less than severe and need only regular monitoring. Sometimes, when the pulmonary valve is removed and a patch is placed across it, regular monitoring to watch the enlargement of the right ventricle may be necessary. In older children, magnetic resonance imaging (MRI) is used to monitor the leak and enlargement of the right ventricle. Life long follow–up is mandatory to detect progression of residual problems and abnormal heart rhythms in later life.
 

 

Would my child need another procedure or operation?
 

If there are residual defects that cause a burden on the circulation, then repeat procedures in form of cardiac catheterization may be needed. Dr Khambadkone can perform balloon dilation or stenting to help alleviate narrowing of the lung artery branches or the outflow of the right ventricle. Narrowing of the outflow area involving the valve (severe pulmonary stenosis) or severe leak from the valve (severe pulmonary regurgitation) would need treatment and in certain patients this is possible by cardiac catheterization and percutaneous pulmonary valve implantation, a procedure that Dr Khambadkone has been one of the pioneers in its introduction, research and as a trainer to many cardiologists in the world. 

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