Tetralogy of Fallot (TOF) is a congenital (present at birth) heart problem made up of four heart defects that occur together.
TOF is caused by the combination of four heart defects that occur during the growth of the fetus:
- Ventricular septal defect (VSD)
—A hole in the wall of the heart separates the right and left ventricles (lower chambers), allowing blood to bypass the lungs. Oxygen-poor blood returning to the heart from the body abnormally mixes with oxygen-rich blood. The result is a low level of oxygen in the blood leaving the heart and returning to the body tissues.
- Pulmonary stenosis—This involves narrowing at or around the valve that leads from the right side of the heart to the lungs. This obstructs blood flow and increases the pressure in the right side of the heart, forcing more blood from right to left through the VSD.
- Placement of the aorta shifted toward the right (transposition)—This shift makes the aorta (the major artery from the heart to the body) open to the right and left ventricle, rather than just to the left ventricle. This misplacement allows oxygen-poor and oxygen-rich blood to mix before going out to the body.
- Right ventricular hypertrophy—The right ventricle becomes larger due to thickening of its muscle wall. This thickening occurs because the right ventricle has to work harder to push blood through the narrowed artery to the lungs. As a result, the heart may develop irregular rhythms and not work as well.
Risk Factors
Some factors can increase the risk of TOF, including:
- Maternal exposure to thalidomide
- Maternal alcohol use
- Maternal infection with rubella
Some people who have TOF also have a chromosomal disorder, such as
Down syndrome.
Symptoms
Symptoms may include:
-
Loud
heart murmur
—a sound caused by turbulent blood flow through the heart, which can be heard through a stethoscope
- Cyanosis—blue coloring of the skin and lips caused by a low oxygen level in the blood
- Shortness of breath and rapid breathing—caused by a low oxygen level in the blood
These symptoms usually appear during the first few weeks of life. In mild TOF cases, symptoms may not appear until much later when the child or young adult becomes more active, placing more demand on the heart. Without treatment, symptoms will persist.
In severe cases, a “tetralogy spell” may occur if the oxygen level in the blood drops suddenly. The lips and skin become much more blue. The baby becomes breathless and irritable. If the very low oxygen level persists, the baby may become sleepy or unconscious.
Older children may have shortness of breath and fainting spells when they exercise. When they have a tetralogy spell, they may squat with their knees on their chest to help recover from the breathlessness.
Diagnosis
A diagnosis of TOF is often made very soon after birth. The doctor will ask about symptoms and perform a physical exam. A newborn with significant bluish coloring of the skin (cyanosis) is often given extra oxygen. If this does not increase the baby’s oxygen level, a heart defect is suspected. If a baby with TOF does not have blue skin, the first clue is a loud heart murmur.
If a heart defect is suspected, tests may include:
- Chest x-ray
—a test that uses radiation to take a picture of structures inside the chest
- Echocardiogram
—a test that uses high-frequency sound waves (ultrasound) to examine the size, shape, and motion of the heart
- Cardiac catheterization
—a tube-like instrument is inserted into the heart through a vein or artery (usually in the arm or leg) to detect problems with the heart and its blood supply
Treatment
Various medications are often given to relieve symptoms and prevent complications. The underlying heart problem of TOF is primarily treated surgically. Surgical options include:
Temporary Operation
Small infants with severe TOF may need a temporary operation to provide enough blood flow to their lungs. A passage is made between the aorta, or another major artery, and the pulmonary artery. This increases the amount of oxygen in the blood and allows the child to grow large enough to have a complete repair.
Complete Repair
Most children with TOF have open-heart surgery within the first few years of life. The operation involves:
- Closing the hole in the heart with a patch
-
Opening the outflow pathway from the right ventricle of the heart by one or more of the following procedures:
- Taking out some of the thickened muscle below the pulmonary valve
- Repairing or replacing the pulmonary valve
- Enlarging the pulmonary arteries that carry blood to both lungs
In some cases, a passageway is created between the right ventricle and pulmonary artery.
In many cases, the surgery is successful. However, in some cases further surgery is needed. Long-term follow-up is always needed to detect recurring or new problems.
Prevention
There are no guidelines for preventing TOF.
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