Tetralogy of Fallot is a rare congenital disorder that affects the structure of the heart. It is most commonly diagnosed in babies and infants or even prenatally. It consists of a combination of four heart defects.
One of these defects is pulmonary valve stenosis which involves the narrowing of the passage between the right ventricle and pulmonary artery. This narrowing means that it is harder for the deoxygenated blood to flow out of the right ventricle to the lungs where it would be oxygenated.
Pulmonary valve stenosis leads to the second abnormality which is right ventricle hypertrophy. As the myocardium is working harder to push blood through the pulmonary valve, the wall of the right ventricle thickens. This hypertrophy can eventually lead to the heart stiffening, and consequently failing.
The third heart abnormality is a ventricular septal defect which is a hole in the septum between the right and left ventricles. The septum is important for dividing the heart into the right and left side as they have different functions. The right side of the heart is involved in pulmonary circulation, bringing deoxygenated blood from the body to the lungs where it can be oxygenated. While the left side of the heart takes that oxygenated blood and distributes it to the rest of the body in systematic circulation. The ventricular septal defect usually means that deoxygenated blood from the right ventricle is pushed into the left ventricle, disrupting the normal flow of blood.
The final heart defect involves the shifting of the aorta, called an overriding aorta. This can be variable but often the aorta will be moved to lie directly above the ventricular septal defect. This means that the aorta can pump out a mix of oxygenated blood from the left ventricle and deoxygenated blood from the right ventricle.
Essentially, all these four heart abnormalities contribute to the movement of deoxygenated blood from the right ventricle to the left ventricle, and subsequent distribution around the body in the systemic circulation. This causes low blood oxygen levels in the body which can produce a blue discolouration of the skin, known as cyanosis.
Other symptoms of tetralogy of Fallot include shortness of breath, fainting, heart murmur, failure to gain weight, tiring easily, irritability and excessive crying. Patients can also develop clubbing which is the rounding of the nail beds in the fingers and toes.
The cause of tetralogy of Fallot is unknown but some risk factors include having Down syndrome or DiGeorge syndrome. In addition, drinking alcohol, poor nutrition and viral illness during pregnancy can lead to the development of tetralogy of Fallot in the baby.
Open-heart surgery is needed to treat tetralogy of Fallot, and careful observation and care throughout life is required.