Tetralogy of Fallot is a heart defect that refers to a combination of four related heart defects, that occurs together. The four defects that can occur in a child are:
- VSD (Ventricular Septal Defect)
- Overriding Aorta: The Aortic valve is mal-aligned and appears to arise from both the left and the right ventricles instead of left ventricle as it normally does.
- Pulmonary Stenosis: Condition in which the pulmonary valves get narrowed and outflow tract or area below the valve that creates a blockage of blood from the right ventricle to the pulmonary artery.
- Right Ventricular Hypertrophy: Caused due to the thickening of the muscular walls of the right ventricle as the right ventricle is pumping at high pressure.
Rarely a child with TOF or Tetralogy of Fallot also have additional ventricle septal defect or Arterial Septal Defect (ASD) or Abnormalities in the branching pattern of their coronary arteries. In some cases, a patient with TOF have complete blockage of flow of blood from right ventricle that is pulmonary atresia. This can be due to chromosomal abnormalities, such as of 22q11 deletion syndrome.
What happens when a patient has a TOF?
The pulmonary stenosis and right ventricle outflow tract obstruction seen with TOF limits the blood flow to the lungs, the blood flow of the lungs is restricted and combination of ventricle septal defect and overriding aorta allows oxygen-poor blood or blue blood returning to the right atrium and right ventricle to be pumped out the aorta to the body.
This flow of oxygen poor blood from the right ventricle to the body results in a reduction in the arterial oxygen saturation so that babies appearing blue or cyanotic. It is because the oxygen poor blood is darker and blue in color, causing the skin and lips appearing blue.
The extent of cyanosis is determined by the amount of narrowing of the pulmonary valve and right ventricular outflow tract. The narrower the outflow tract from the right ventricle the restrictive is the blood flow to the lungs which in turn lower the arterial oxygen level since more oxygen poor blood is shunting from the right ventricle to the aorta.
Diagnosis of TOF
The newborn baby with symptoms of cyanosis is placed in supplemental oxygen. The but that causes very little effect in the levels of oxygen in the child with TOF.
This hyperoxia test is often the first clue to suspect the cyanotic cardia defect. If the pulmonary stenosis is mild also referred as Pink TOF, the first clue is the detection of murmur sound from the heart on hearing from stethoscope
Once these few test are done, next step is echocardiography that can accurately demonstrate the presence of four related defects characteristics of TOF
For evaluating the size and distribution of the pulmonary arteries to clarify the branching pattern of the coronary arteries, a cardiologist might suggest cardia catheterization (right heart catheterization). It allows a doctor to know the abnormality of the blood vessel from the aorta.
Treatment of TOF in Children
Once the diagnosis is completed it is determined whether the child’s oxygen level is in safe range or not. If it is too low, a prostaglandin infusion is usually initiated to keep the ductus arteriosus open which will provide additional pulmonary blood flow and increase in the oxygen levels.
These infants will require to undergo a surgical procedure in neonatal period. In fact, with normal oxygen level or mild cyanosis can go home within the first week of life.
Once the child is 6 months old, the baby can now undergo a full-repair procedure as long as the oxygen levels are adequate to proceed. If the child faces sudden decrease in oxygen of progressive decline in health a Palliative BT Shunt repair procedure is suggested by the cardiologist.
Surgical Correction of the defect is always necessary, as patient might require palliative procedure prior to the final correction. Corrective Repair of TOF includes closure of the ventricular septal defects with the synthetic dacron patch and resection of hypertrophied muscle so that blood can flow normally from the left ventricle to the aorta.
For treating the narrowing of the pulmonary and right ventricular outflow of the tract, the surgeon will use advance methods to cut away the obstructive muscle tissues in the right ventricles and then enlarge the outflow pathway with a patch.
In rare condition the coronary arteries are branched across the right ventricular outflow tract where the patch would normally be placed. In these babies the incision in this area to place the patch would damage the coronary artery, which cannot be safely done. In this case, a hole in the front surface of the right ventricle is made and a conduit is sewed from the right ventricle to the bifurcation of the pulmonary arteries to provide unobstructed blood flow from the right ventricle to the lung.