Tetralogy of Fallot (TOF) is a congenital disorder of the heart. It is made up of four anatomical malformations, hence the prefix tetra, which denotes a four part event. The anomalies are ventricular septal defect (VSD), pulmonary infundibular stenosis, right ventricular hypertrophy and overriding aorta.
One of the commonest presenting complain is failure to thrive and this results from difficulty in feeding due to dyspnea. Infants typically develop cyanosis and the severity is related to the degree of stenosis . Sometimes these infants only develop these signs when they cry or feed in a phenomenon known as Tet spells. Older children with this condition squat a lot as squatting increases pulmonary blood flow by increasing peripheral vascular resistance. Dyspnea on exertion worsens with age and older children may rupture some bronchial collaterals which will cause hemoptysis .
Physical exam will reveal a small for age baby, cyanosis, finger clubbing in older children, heart murmurs typically a systolic ejection murmur, scoliosis, bulging left hemithorax, palpable right ventricle and retinal engorgement.
Radiologic studies include chest X-rays which shows a characteristic boot shaped heart, signifying right ventricular hypertrophy. MRI is also valuable as it shows vessels in addition to the heart. An echocardiogram is the mainstay in diagnosis as it demonstrates the four anatomical defects. Electrocardiograms can also be done to examine the electrical activity of the heart .
The definitive treatment of this condition is surgical correction and this is best done in the first year of life. The surgery aims to close the ventricular septal defect with the use of a patch or homograft, resect the infundibular stenosis and relieve right ventricular outflow tract obstruction. These procedures are usually done under cardiopulmonary bypass.
The two common surgical procedures are Blalock-Taussig shunt which is palliative and intracardiac repair which is definitive.
Before surgery however, medications like prostaglandins may be necessary to keep the ductus arteriosus patent. Other associated acute complications are also managed like diuretics and digitalis for heart failure .
The prognosis is favorable for patients who undergo surgical repair with over 90% of 20-year survival rate. The advancement of surgical techniques has seen a drastic reduction in the number of deaths. There is however a high mortality rate in those who do not undergo surgical repair. It is estimated that 50% of them would have died by the age of 6 years. Less than 20% of them reach the age of 10 years and less than half of those live beyond 20 years. Patients who survive beyond this point develop congestive cardiac failure .
The cause of tetralogy of Fallot, like most congenital heart diseases, is unknown. Studies however suggest a multifactorial etiology. There are prenatal factors that have been associated with an increased risk of developing tetralogy of Fallot. These include viral illnesses during pregnancy e.g rubella, mothers age greater than 40 years, maternal alcohol use, diabetes, and poor prenatal nutrition. Children born with Down syndrome and fetal hydantoin syndrome also have an increased risk of suffering from tetralogy of Fallot .
It is estimated that tetralogy of Fallot is responsible for 10% of all cases of congenital heart disease. It has an incidence of up to 6 in 100,000 live births and it is the most common cause of cyanotic congenital heart disease. It is responsible for approximately 33% of all congenital heart diseases in patients younger than 15 years .
It affects males more than females and the cases are usually sporadic with no familial association. It is associated with other extracardiac defects like hypospadias, cleft lip and palate, and craniofacial and skeletal anomalies.
The initial defect is pulmonary infundibular stenosis which causes narrowing of the outflow tract, which limits the amount of deoxygenated blood that goes into pulmonary circulation. In response to this, the right ventricle increases the pressure with which it pumps blood into the lungs. This increased workload will lead to hypertrophy of the muscles of the right ventricle. There is also a ventricular septal defect which allows shunting of blood between both ventricles. In VSD, due to the hypertrophy of the right ventricle, the shunting is from right to left i.e. deoxygenated to oxygenated. This blood which is part deoxygenated is then pumped though the overriding aorta to the systemic circulation leading to the cyanosis that is manifested .
In different individuals, there is slight anatomical variation in the degree of anomalies. The severity of the outflow tract varies between patients and is responsible for severity of symptoms. In patients with smaller obstructions, as in patients with isolated VSD, the shunt is left to right and this allows the blood to go into the lungs where it can get reoxygenated .
Tetralogy of Fallot is a common congenital heart disorder. It is a cyanotic heart disease and is the most common cause of blue baby syndrome, a common name for methemoglobinemia in newborns. Although it comprises of four main anomalies, there could be other defects and they are all together responsible for the myriad of symptoms seen in patients with tetralogy of Fallot .
Definition: Tetralogy of Fallot (TOF) is a congenital heart defect, the baby is born with it. It is made up of 4 different defects and the severity of these defects determine the severity of the symptoms in the child.
Cause: There is no known cause. However, some maternal factors have been associated with an increased risk of the child developing TOF. They include, viral infections in pregnancy, maternal diabetes, maternal age over 40, maternal alcohol use, and poor prenatal nutrition.
Symptoms: The most common symptom us the child’s inability to feed. The growth will also be stunted as a result. There might also be blue discoloration especially of the lips and mouth (blue baby syndrome) and sometimes, this discoloration is only noticed when the child feeds or cries. Older children tend to squat a lot. There may be also be difficulty in breathing after a little exercise and coughing up blood.
Diagnosis: A series of blood tests will be required to check the blood levels including its gases. Some imaging tests like X-rays and echocardiograms will also be done to look at the size of the heart and the direction of blood flow within it.
Treatment: The main treatment is corrective surgery. This is preferably done in the first year of life and ideally not later than 2 years. Medications are given before surgery to manage circulation and also treat acute attacks.