Tetralogy of Fallot (fah-LO) is a combination of problems caused by a birth defect in the structure of the heart that changes the way blood flows through the heart.
Each year, 4 out of every 10,000 babies born in the United States have the condition, which was named after the French doctor who first described it in the late 1800s, Étienne Fallot. About 10% of all babies born with a heart problem have tetralogy of Fallot (TOF).
The four related problems that together make up tetralogy of Fallot are:
Ventricular septal defect (VSD), which is a hole in the septum, or wall, separating the two lower chambers, or ventricles, of the heart. The septum acts as a barrier that prevents blood from both sides of the heart from mixing together. But when there is a VSD, blood high in oxygen from the left ventricle can mix with blood low in oxygen from the right ventricle. VSD is the defect that can lead to the other problems associated with TOF.
Pulmonary stenosis, a narrowing or thickening of the valve that connects the right ventricle to the pulmonary artery, a blood vessel that carries low-oxygen blood from the heart to the lungs, where the blood receives more oxygen and then returns to the heart. With pulmonary stenosis, the heart has to work harder than normal to pump blood to the lungs. Often, the amount of blood reaching the lungs is below normal.
Right ventricular hypertrophy (hi-PER-truh-fee), which is a thickening of the muscular wall of the right ventricle. The thickened wall can block the flow of blood through the pulmonary valve, which allows blood from the heart to flow into the lungs.
An "overriding aorta," which means the artery that carries high-oxygen blood to the body is out of place and arises above both ventricles, instead of just the left ventricle, as in a healthy heart. This allows some blood that is low in oxygen to flow into the aorta and out to the body, instead of to the pulmonary artery, which would normally take it to the lungs to pick up oxygen.
As a result of these defects, too little blood goes to the lungs. The low-oxygen blood then circulates to the rest of the body and too little oxygen reaches the body tissues.
If tetralogy of Fallot goes untreated, a child may have:
dizziness, fainting, or seizures
a higher risk of developing endocarditis, an infection of the inner layer of the heart
high pressure in the right side of the heart that can cause an irregular heartbeat, called an arrhythmia
A child whose TOF is not repaired might need to limit participation in competitive sports and other physical activities. Many infants who have surgery to correct the defect do very well, participate in normal kid activities, and live to adulthood.
Scientists have not yet identified a specific cause for tetralogy of Fallot in all cases, but they believe genetics play a role. Someone born with TOF is more likely to have a child or sibling with it.
Mothers who get rubella (German measles) or other viral illnesses during their pregnancies are at a higher risk of giving birth to babies with TOF. Other risk factors and conditions include poor nutrition, alcohol abuse, uncontrolled diabetes, and the mother's age (over 40).
Most of the time, a child with TOF does not have any other birth defects. But children who have certain genetic disorders, such as Down syndrome, often have congenital heart defects, including TOF.
Certain environmental factors, such as air pollution, also may increase a mother's chances of having a baby with TOF.
One of the most common signs of tetralogy of Fallot is cyanosis (a blue or purple tint to the baby's skin, lips, and fingernails). Healthy babies can sometimes also have a bluish skin tone around the mouth or around the eyes from prominent veins under the skin. This is perfectly normal. If a baby's lips and tongue look pink, you generally don't have to be concerned because babies who have low oxygen levels in the blood usually have blue lips and tongues in addition to bluish skin.
A child with TOF might have sudden episodes of deep cyanosis, called "Tet spells," during crying or feeding. Older children who have Tet spells will often instinctively squat down, which helps to stop the spell.
Other signs include:
easy tiring with exertion
rapid heartbeat (palpitations)
"clubbing," where the skin or bones around the tips of fingers are widened or rounded
echocardiogram, or "echo": an ultrasound picture of the heart structures (chambers, walls, and valves). It records the motion of the blood through the heart and can measure the direction and speed of blood flow within the heart structures.
cardiac catheterization: a thin, flexible tube called a catheter is inserted into the heart, usually through a vein in the leg or arm, and provides information about the heart structures as well as blood pressure and blood oxygen levels within the heart chambers. Sometimes a device will be inserted into the heart or blood vessels through the heart catheter.
Tetralogy of Fallot is repaired through open-heart surgery soon after birth or later in infancy, depending on the baby's health and weight and severity of defects and symptoms.
The two surgical options are:
Complete repair: the surgeon widens the passageway between the right ventricle and the pulmonary artery to improve blood flow to the lungs. The ventricular septal defect is patched to stop the mixing of high-oxygen blood with low-oxygen blood between the ventricles.
These repairs also fix the two remaining defects (overriding aorta and right ventricular hypertrophy). Because the right ventricle doesn't have to work as hard to pump blood into the lungs, the thickness of the ventricle wall will decrease. And the patched VSD prevents blood with low oxygen from flowing into the aorta.
Temporary or palliative surgery: minor repairs are made to improve blood flow to the lungs. This usually only occurs when the baby is too weak or small to undergo full surgery. In the temporary surgery, the surgeon creates a secondary route for blood to travel to the lungs for oxygen. This is done by placing a small tube, called a shunt, between a large artery branching off the aorta and the pulmonary artery.
Later when the baby grows stronger, the full repair is performed.
Most babies born with tetralogy of Fallot do very well and survive to adulthood, but require regular follow-up with a heart specialist.