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 oxygen blood to the body 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 severe cyanosis (blueness) unless the obstruction gets worse with time, which it usually does.
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 increased blood flow from the right to the left ventricle. They can be dangerous and, if they occur, the pediatric cardiologist needs to be notified immediately. 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 — the size of the pulmonary arteries, the amount of narrowing or obstruction below the pulmonary valve and other factors.