Tetralogy of Fallot

Tetralogy of Fallot (TOF) is a major heart defect, which is a combination of 4 heart defects. It causes affected children to have a bluish tinge of their lips and nails, especially when they walk/run. It worsens with time. Surgical repair of the defect is needed for children to get better.  

The ideal age of repair is six months to 1year of age. The quality and quantity of life are good after repair.  

Causes of TOF

If the parents are wondering why their child got TOF, there is no straightforward answer. TOF is a developmental disorder present at birth. What exactly causes it is not very clear. There are certain factors affecting mothers during pregnancy that increase the risk of TOF and other heart defects in babies. 

Some of the known risk factors are a family history of heart defects, mother on certain medications in early pregnancy, diabetes in mother from early pregnancy, IVF pregnancy, anomaly scan showing a defect in any other organ system of the fetus (brain, gut, kidney, etc.). 

In 30-40% of children with TOF, one of the chromosomes may have an abnormal arrangement of genes in it. This abnormal arrangement causes TOF in the heart. 

It also causes problems in other body parts like a cleft in the palate or the lip, immunity issues, developmental delay, and calcium level maintenance issues.

What are the four heart defects in TOF?

1. VSD: a hole in the lower two chambers of the heart
2. Pulmonary stenosis: narrowing of the exit point of the Right Ventricle(RV)
3. Thickening of the muscular wall of  RV
4. The aorta arising from both Left Ventricle(LV) and RV

How blood flows in a heart with a TOF

It is important to know how the normal heart works for you to understand TOF better. See figure 1 below 

The left heart has two chambers, and the right heart has two chambers. The top 2 chambers (Right Atrium or RA and Left Atrium or LA) are the collecting chambers, while the bottom two chambers (RV and LV) are pumping chambers. The LV pumps pure (red) blood to the whole body. 

The body’s organs use the oxygen in that blood and make the blood impure (blue). The impure (blue) blood returns to the RA and is pumped by the RV to the lungs. 

When we breathe, the oxygen in our breath enters the blood and makes it pure again. The pure blood enters LA and is pumped out to the body by the LV. 

Thus the heart supports two circuits. The left circuit pumps pure blood to the body, and the right circuit pumps impure blood to the lungs.  

In a child with a TOF, blood cannot leave the RV easily as the exit (1) is narrow. So some blue blood of the RV goes across the VSD (2) and out through the aorta to the body. (3) and (4) are also seen in figure 2. 

Effects of Tetralogy of Fallot

Narrowing of the pulmonary valve and artery decreases the blood flow to the baby’s lungs. So blood from the RV exits through the VSD into the aorta, and this blue blood mixes with the red, and the baby’s skin tone, lips, nail beds look blue. The blue-ness increases when the baby cries or is feeling cold.

Symptoms and Signs of TOF 

The most common symptoms are:

• The baby will have bluish discoloration of the skin, lips, etc.
• Difficulty in breathing
• Rapid breathing
• Clubbing of fingers and toe- The baby’s fingertips will have the shape of a bulb
• Extreme tiredness even with mild activity
• Fainting
• Irritability
• Crying spells

The most common signs are

• A tendency to squat- A child with TOF will show a tendency to squat if he or she finds it difficult to breathe. Squatting helps improve the flow of blood to the lungs that make breathing more easier. Children also tend to sit/lie cross-legged.
• Tet spells- Tet spells are episodes where the body of a baby turns blue suddenly. Crying, feeding, agitation, and exposure to cold are the usual triggers. The baby may faint after turning blue to purple. It is a life-threatening condition. 
• A heart murmur- Murmurs are abnormal heart sounds that a doctor can hear while listening with the help of a stethoscope. It is due to the flow of blood across the pulmonary valve. 

Diagnosis of TOF

Echocardiography-This is the main test to diagnose TOF. Other tests include ECG, CT scan, cardiac catheterization, genetic tests (FISH for chromosome 22q11 deletion). 

How is TOF treated?

TOF requires surgical correction. The best time for the surgery is between 6 months to 1 year age. Certain babies who become very sick from it or possess tiny pulmonary arteries need an additional bypass shunt surgery (called BT shunt) even earlier. The BT shunt helps the baby become less sick or helps the tiny pulmonary arteries grow. Your pediatric cardiologist/surgeon can give you more details about this. 

The main steps in the surgery planned for total correction (called intracardiac repair) are

Closure of VSD

Widening of the narrow pulmonary valve and pulmonary artery

The baby’s heart will then have normal circulation. The surgery will be for around 4-5 hours. The post-operative ICU course is also critical. The major milestones in the ICU are getting off the ventilator safely and coming off the infused intravenous medications to maintain normal vital signs.

Follow up for your child with repaired TOF

Lifelong follow up is essential. The child will have to go for Echocardiography/ECG/exercise stress test, and occasionally CT scans for surveillance of the repair. Certain children with leaky pulmonary valves develop heart failure and may need repeat surgery or a cardiac catheterization procedure. 

There are other less common complications of a repaired TOF.

Overall, the quality and quantity of life after repair of TOF is good. Your child can have a normal childhood and adult life. As mentioned above, constant visits to pediatric cardiac OPD is essential