What Is Tetralogy of Fallot?
Tetralogy of Fallot (teh-TRAL-uh-jee of fuh-LOW) — or TOF — is a combination of congenital heart defects. It has four components:
- A ventricular septal defect (VSD)
- Pulmonary stenosis : This may be narrowing of the valve itself, or narrowing above or below the valve. Often, it is below the valve (known as infundibular narrowing or sub-PS) and at the valve level
- Thickening of the right ventricle called right ventricular hypertrophy (RVH)
- Overriding or straddling of the aorta over the wall (septum) between the right and left ventricles
To understand TOF, frequently called “tet,” you must understand two main abnormalities:
- A large hole, or ventricular septal defect (VSD)
- A narrowing (stenosis) (sten-O'-sis) at or just beneath the pulmonary valve
This narrowing partially blocks/obstructs the blood flow from the heart's right side to the lungs. If there were no hole between the ventricles, the right ventricle would have to increase the pressure to overcome this narrowing or obstruction.
However, since there is a VSD, blood can flow from the right ventricle to the left ventricle without going through the lungs. Therefore, blue blood (blood with less oxygen) goes to the body and the patient may appear more blue or “cyanotic.” The more obstruction there is, the less blood can get to the lungs to become oxygenated and the bluer (more cyanotic) the patient becomes.
In some patients, there is complete obstruction to blood flow to the lungs (known as pulmonary atresia), in which case, all the blue blood goes from the right to the left ventricle. The only way to get blood to the lungs is if the ductus arteriosus remains open by giving a medication called prostaglandin.
In less severe forms of tetralogy of Fallot, there is only mild obstruction to blood flow to the lungs. These patients may not have cyanosis (blueness) unless the obstruction gets worse with time, which it often does. Some patients with tetralogy of Fallot have normal saturations and are referred to as having “pink” tetralogy.
What Are Tet Spells?
Some babies with tetralogy of Fallot have “spells” where they suddenly become very blue (cyanotic) and breathe rapidly. They may become irritable or even become unconscious. These “spells” are caused by a decrease in blood flow to the lungs and increased blue blood flow from the right to the left ventricle, then to the body. They can be dangerous and, if they occur, the pediatric cardiologist needs to be notified and patients require urgent/emergent evaluation.
Usually, in the United States, surgery is performed early in life so that these “spells” do not occur. The type of surgery depends in part on the anatomy of the heart and vessels, specifically the size of the pulmonary arteries, the amount of narrowing or obstruction below the pulmonary valve, the pulmonary valve size and several other factors.