Tetralogy of Fallot occurs when the right side of the heart does not develop properly while a baby is in the mother's womb. A French physician, Etienne Fallot first described it, in 1888. The cause of the problem is not understood. The parts of the heart affected are the pulmonary valve, right ventricle and the ventricular septum. It is the most common form of cyanotic congenital heart disease and is slightly more common in males. It affects one out of every 1000 babies born with congenital heart disease. This heart problem is known to be associated with other congenital problems including Goldenhar syndrome, velo-cardio-facial syndrome, and DiGeorge syndrome.
In tetralogy of Fallot, the area of the right ventricle that leads to the pulmonary artery is narrow (1) . In addition, the pulmonary valve itself is often small causing further obstruction of blood flow to the lungs. These areas of narrowing make the right ventricle work harder to get blood past the blockage and results in thickening of the muscle of the right ventricle. This thickening of the muscle is called right ventricular hypertrophy (2). Another part of this heart defect is a hole in the wall of the heart (called the septum) that separates the right and left ventricle (3). This hole, called a ventricular septal defect, allows blue blood from the thick, narrow, high-pressure right ventricle to cross over to the lower pressure left ventricle where it mixes with red blood. The mixing of red blood with blue blood before the blood is sent out to the body is what causes the baby to appear blue. This blue color which is seen in the lips and under the fingernails is called cyanosis. The degree of cyanosis is dependent on the severity of the narrowing in the right ventricle. The fourth part of the defect as originally described by Dr. Fallot is the altered position of the aorta called aortic override (4).
Tetralogy of Fallot is a serious heart problem because it obstructs blood from reaching the lungs. Usually, the baby will have a bluish color called cyanosis. Although this may not be very severe at first, it generally increases over time. In some babies, the obstruction is severe causing significant cyanosis and very low oxygen levels soon after birth.
Usually the child's growth and development is not significantly affected.
Some babies with tetralogy of Fallot have periods where the cyanosis becomes very severe and the baby looks very blue. The baby may be upset at the time, and may actually pass out or even have a seizure. These periods are called "tetralogy spells" or hypoxic spells. The precise cause is not known but during a spell there is very little blood flow to the lungs. Hypoxic spells are more likely to happen when the baby is a little "dry" or dehydrated and may be prevented by careful attention to hydration particularly if the baby is having problems with vomiting or diarrhea. Spells are also more likely if the baby is anemic (low blood) so if this is noted the doctor may order an iron supplement.
During a spell, the baby turns very blue even though he or she is breathing rapidly. If a spells occurs, the baby should be placed in a knee-chest position (draw the baby’s knees up to their chest and hug them close to your body), attempt to calm the baby, and call the pediatric cardiologist or pediatrician. If a baby has even one spell, surgery will need to be scheduled to try to avoid another one that could possibly result in harm to the baby. Sometimes medicine is used to relax the right ventricle and hopefully prevent additional spells while the child is awaiting surgery.
Clinical features: As described above, most babies with tetralogy of Fallot are "blue" which means that they have lower blood oxygen levels than normal. The medical term for low blood oxygen levels is cyanosis. The blue color is best seen in the lips and under the fingernail beds but can be quite hard to detect just by looking at the baby. Most babies are otherwise healthy and grow normally although some have other health problems.
Physical findings: Most babies with TOF have a heart murmur and look a little blue. The examination is otherwise usually normal.
Medical tests: Blood oxygen levels are measured by an oxygen saturation test or by a blood test. An electrocardiogram and chest x-ray. The defect is diagnosed by a heart test called an echocardiogram or heart ultrasound. The echocardiogram uses sound waves to form an image of the valves and chambers inside the heart. It is safe and painless and test results are available right away.
Another heart test called a heart catheterization is needed if the echocardiogram is not completely clear about the heart problem or additional abnormalities are present that may affect how the surgeon would go about fixing the defect. During a heart catheterization catheters (thin plastic tubes) are placed into a large blood vessel in the child's groin and dye is put into the blood stream. Ray type pictures are then used to follow the blood through the heart chambers, valves and arteries to see the areas of narrowing or other abnormal places of blood flow. It is more involved then the echocardiogram but is considered very safe. The babies are sedated and treated for pain during the test. The results of the test are most often available on the same day.
Since the defect causes cyanosis and overwork for the heart, a corrective operation during early childhood is needed. Sometimes medicines are used to prevent spells while surgery is being planned.
The age of the child at operation and the kind of operation will depend on the child’s symptoms and the precise anatomy of the defect. Generally, repair is performed on babies with tetralogy of Fallot around 4 to 6 months of life or sooner if spells occur. If the baby is has a spell, repair is then done at that time no matter the baby's age.
When the surgeon fixes this defect an incision is made down the center of the breast bone and the heart is stopped for a brief period of time while the body is supported with a heart lung bypass machine. The defect is then fixed by patching the hole in the wall between the two ventricles such that blue blood goes out the right ventricle to the pulmonary artery and lungs and the red blood goes out the left ventricle to the aorta and to the body. Dividing thickened strands of muscle tissue that cross over the area where the blood exits the right ventricle relieves the area of narrowing out the right ventricle. Sometimes a small amount of excess muscle needs to be removed.
The area of narrowing at the pulmonary valve is treated differently depending on the actual size of the valve itself. Sometimes the surgeon opens the valve with an instrument called a dilator that allows blood to go across the valve without a problem. Unfortunately, this is not always sufficient to open the valve enough because the whole valve area is too small. In this case the surgeon will sew a patch across the area of the pulmonary valve to enlarge the area and allow blood to cross into the pulmonary artery without narrowing. Most of the surgery is done through an incision in the right atrium and if a patch is needed to open the valve area only a tiny ventricular incision is needed.
If the baby has other health concerns or there is an unusual location of one of the heart arteries the surgeon may choose to delay the total repair and do a shunt operation. This operation will give the baby adequate blood flow to the lungs and provide protection from the dangers of hypoxic spells until other concerns can be fixed or the baby is older. A shunt operation does not require the heart lung bypass machine. The incision is on the side of the chest under the arm between the ribs. A tube of Gore-Tex is placed between the pulmonary artery and a blood vessel branching off the aorta. Some blood in the aorta will go through the shunt into the pulmonary artery and to the lungs to get oxygen. This protects blood flow to the lungs even if the narrowing out the right ventricle is really severe. The shunt will be taken out when the full repair is done.
Care and services for patients with this problem are provided in the Congenital Heart and Cardiovascular Surgery clinics at the University of Michigan Medical Center in Ann Arbor.
The operative risk is approximately 3% and is unaffected by age at repair. The late outcome following repair of tetralogy of Fallot is excellent and many long-term studies document excellent results with normal exercise capabilities well into adult life.
There are certain associated conditions that will, however, alter the nature of the surgical repair and increase the likelihood that additional surgery will be required in the future. One such condition is the presence of pulmonary atresia (absence of the pulmonary valve) which requires the placement of a conduit, or tube, to establish a connection between the right ventricle and the pulmonary artery. Most conduits will require replacement in later life because of growth or malfunction. Reoperation for a conduit change can be done at very low risk.
Regardless of the presence or absence of associated conditions, all children require lifetime follow-up to check for the development of other conditions that may require treatment. These include rhythm disturbances, valve regurgitation, and decreased heart function.
Atallah-Yunes NH, Kavey RW, Bove EL, Smith FC, Byrum CJ, Kveselis DA, Gaum WE: Postoperative assessment of a modified surgical approach to repair of tetralogy of Fallot: Long term follow up. Circulation 1996;94[suppl II]:II-22-II-26.
Hennein HA, Mosca RS, Urcelay G, Crowley DC, Bove EL: Intermediate results following complete repair of tetralogy of Fallot in neonates. J Thorac Cardiovasc Surg 1995;109:332-44.
Bove EL, Lupinetti FL: Tetralogy of Fallot. In Pediatric Cardiac Surgery, Ed C. Mavroudis and C. Backer, Mosby, 276-291.
Written by: L. Callow RN, MSN, CPNP
Reviewed January, 2010