Tetralogy of Fallot (TOF) is a combination of four congenital (present at birth) heart defects that affect infants and children. The defects occur together and change the way blood flows through the heart and lungs. TOF occurs in about 1 out of every 2,518 babies born in the U.S. each year.

Pediatric cardiologist Rukmalee Vithana of the Blalock-Taussig-Thomas Pediatric and Congenital Heart Center explains what you should know about TOF.

What is tetralogy of Fallot?

In a healthy heart, blood travels through the heart to the lungs, where it picks up oxygen. Then oxygen-rich blood leaves the lungs, travels back to the heart, and then courses throughout the body. Infants with TOF have trouble getting enough blood to their lungs, so the body gets too much oxygen-poor blood.

The four heart defects of tetralogy of Fallot include:

1. Pulmonary stenosis: A narrowed or stiffened pulmonary valve means the pulmonary artery has trouble sending enough blood from the heart to the lungs.
2. Ventricular septal defect (VSD): VSD is a hole between the two lower chambers (ventricles) of the heart. The hole allows oxygen-rich blood and oxygen-poor blood to mix, so the body does not receive enough oxygen-rich blood.
3. Overriding aorta: The aorta, which is the artery that carries oxygen-rich blood to the body, is out of place and rises above both ventricles. As a result, the body gets too much oxygen-poor blood.
4. Hypertrophy (enlargement) of the right ventricle: The right lower chamber of the heart is bigger or thicker than normal, making it harder for blood to go through the pulmonary valve.

Tetralogy of Fallot Causes

Tetralogy of Fallot occurs when a baby’s heart does not form correctly in the womb. Experts aren’t sure exactly what causes the defects. TOF might be the result of changes to genes or chromosomes. Children with certain genetic syndromes, such as Down syndrome or DiGeorge syndrome, may be at higher risk of developing TOF.

The risk of congenital heart defects like TOF may also increase due to:

• Environmental factors, such as smoking or taking certain medications during pregnancy
• Family history
• Having certain medical conditions during pregnancy, such as diabetes or rubella

Tetralogy of Fallot Symptoms

The most common symptom of TOF is cyanosis, which is when the skin, lips and nail beds are blueish in color. Cyanosis is the result of too much oxygen-poor blood being pumped through the body.

Cyanosis may come in sudden spells, called tet spells, when a baby is crying or feeding. It happens when a baby's blood oxygen level drops quickly. During the spell, babies may have a hard time breathing. In the most extreme circumstances, they may go limp or lose consciousness.

Other symptoms of tetralogy of Fallot at birth may include:

• Difficult or rapid breathing
• Fatigue
• Fussiness
• Heart murmur
• Trouble feeding or gaining weight

Tetralogy of Fallot Diagnosis

Some babies are diagnosed with tetralogy of Fallot before birth. The heart conditions may be seen and heard on prenatal ultrasounds, while the baby is still in the womb.

After birth, tests for TOF may include:

• Cardiac catheterization
• Chest X-ray
• Echocardiogram (echo)
• Electrocardiogram (ECG)
• Cardiac CT
• MRI

Tetralogy of Fallot Treatment

All children with tetralogy of Fallot need surgery. Most children have surgery when they’re about six months old. Your doctor will determine which surgery is most appropriate.

Temporary Shunt Operation

Babies who are not strong enough for a full repair surgery or who have other health problems may have a shunt operation. A shunt is a tube that is sewn into place between the aorta and the pulmonary artery. It helps blood flow to the lungs. A shunt operation is not permanent; babies with a shunt still need a full repair surgery later.

Full Repair Surgery

A full tetralogy of Fallot repair surgery involves:

• Placing a patch over the ventricular septal defect
• Removing thickened tissue from the right ventricle
• Widening the pulmonary valve

Tetralogy of Fallot Complications

Potential complications of TOF include:

• Abnormal heart rhythm (arrhythmia)
• Blood clots
• Death
• Heart failure
• Infection in the lining of the heart and heart valves (bacterial endocarditis)
• Leakage (regurgitation) from the repaired pulmonary valve

Living with Tetralogy of Fallot

Most children go on to lead active, healthy lives after TOF treatment. They will need ongoing care and monitoring from a pediatric cardiologist. People who had TOF repair surgery as children may need continuing TOF treatment into adulthood, such as a second surgery or cardiac catheterization to replace their pulmonary valve. They should seek care from an adult congenital heart specialist.