Tetralogy of Fallot (TOF)

What is tetralogy of Fallot?

Tetralogy of Fallot (TOF) is a serious, congenital heart defect, affecting about two in 10,000 babies. In TOF, the abnormal connections prevent enough oxygen-poor (blue) blood from flowing to the lungs as it should. As a result, a person with TOF has a lower-than-normal amount of oxygen in the blood and typically, surgical correction is necessary. Historically, children with TOF were called “blue babies.”

In a normal heart, oxygen-poor blood returns to the right atrium from the body and travels to the right ventricle. Then, it is pumped through the pulmonary artery into the lungs, where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle and then is pumped through the aorta out to the body.

Children born with TOF have a combination of four cardiac anatomic characteristics:

  1. Ventricular septal defect: There is a hole between the right and left pumping chambers (ventricles) of the heart.
  2. Right ventricular outflow tract obstruction: The connection between the right ventricle and lung (pulmonary) artery is narrowed, and blood flow to the lungs is blocked. This is what causes babies to be blue.
  3. Overriding aorta: The artery that connects the left ventricle to the body is positioned too far to the right.
  4. Right ventricular hypertrophy: The right ventricle is thicker than normal, because it’s pumping against a blockage. It’s working too hard.

Tetralogy of Fallot heart illustration

As a result of these defects, blood flow to the lungs is limited. The degree of blockage generally worsens with time. Sometimes, the pulmonary valve is completely obstructed — a more severe form of TOF called tetralogy of Fallot with pulmonary atresia.

What are the symptoms of tetralogy of Fallot?

Cyanosis, which is a blue color of the skin, is often the first sign of tetralogy of Fallot (TOF). This happens when the amount of oxygen in the blood is lower than normal. In other cases, a heart murmur is the first sign.

Even after a baby is diagnosed with TOF, there may be no symptoms for weeks or even months. Some babies will show signs of failure to thrive — becoming tired with feeding, poor weight gain — if the amount of lung blockage is mild. Typically, babies start with mild symptoms that worsen over time.

Tet spells

Tet spells, also known as hypercyanotic episodes, are a more severe symptom of TOT. These spells can occur after feeding, bathing, or crying. They result from a further decrease in blood flow to the lungs, making the baby more blue.

What causes tetralogy of Fallot?

Most cases of TOF have no genetic association; however, there are some cases with a genetic link. Parents who already have a child with a congenital heart defect are more likely to have a second child with a heart defect.

How we care for tetralogy of Fallot

Our team at the Boston Children’s Hospital Benderson Family Heart Center treats some of the most complex pediatric heart conditions in the world, with excellent results. Adults who were treated for congenital heart disease as children will need to be followed by a cardiologist because complications from early heart disease can arise in adulthood. The Boston Adult Congenital Heart Program (BACH) is a world leader in the care of this unique patient population.