Tetralogy of Fallot
Tetralogy of Fallot (TOF or "TET") is a complex condition involving several associated congenital (present at birth) heart defects that occur due to abnormal development of the fetal heart. These problems include the following:
Ventricular Septal Defect (VSD) - A hole in the ventricular septum, or dividing muscular wall between the two lower pumping chambers of the heart known as the right and left ventricles.
Pulmonary (or right ventricular outflow tract) Obstruction - A muscular obstruction in the right ventricle, just below the pulmonary valve, that decreases the normal flow of blood. The pulmonary valve also may be small, and the pulmonary arteries in the lungs can be affected.
Overriding Aorta - An aorta that is shifted toward the right side of the heart so that it sits over the ventricular septal defect.
Tetralogy" refers to four heart problems. The fourth problem is that the right ventricle becomes enlarged as it tries to pump blood past the obstruction into the pulmonary artery. This is known as "hypertrophy."
Normally, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it picks up oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, then is pumped through the aorta out to the body.
In Tetralogy of Fallot, blood flow within the heart varies and is largely dependent on how severe the obstruction from the right ventricle to the lungs is. Tetralogy of Fallot encompasses a family, or spectrum of diseases, from nearly no obstruction to severe obstruction or, in some cases, atresia of the pulmonary valve.
With mild right ventricle obstruction, the pressure in the right ventricle can be slightly higher than the left. Some of the oxygen-poor (blue) blood in the right ventricle will pass through the VSD to the left ventricle, mix with the oxygen-rich (red) blood there, and then flow into the aorta. The rest of the oxygen-poor (blue) blood will go its normal route to the lungs. These children may have slightly lower oxygen levels than usual, but may not appear blue. Oxygen, or saturation levels, can be checked with a skin sensor ("sat" probe), and normally are 99 percent.
With more serious obstruction in the right ventricle, it is harder for oxygen-poor (blue) blood to flow into the pulmonary artery, so more of it passes through the VSD into the left ventricle, mixing with oxygen-rich (red) blood, and then moving out to the body. These children will have lower than normal oxygen levels in the bloodstream, and may appear blue, especially whenever the pressure in the right ventricle is very high and large amounts of oxygen-poor (blue) blood pass through the VSD to the left side of the heart. These children can have skin blood saturations as low as 80 percent, and sometimes even lower.
Tetralogy of Fallot occurs in about two out of every 10,000 live births. It makes up about 8 percent of all cases of congenital heart disease. Tetralogy of Fallot occurs equally in boys and in girls.
What causes Tetralogy of Fallot?
Tetralogy of Fallot occurs due to improper development of the heart in the first eight weeks of fetal growth.
Most of the time, this heart defect occurs sporadically (by chance), with no clear reason evident for its development. Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality or environmental exposure, causing heart problems to occur more often in certain families.
One genetic link that has been associated with Tetralogy of Fallot is a deletion, or tiny missing piece, of chromosone 22q11. This is present in a minority of patients but is thought to be more common in those with a severe form of Tetralogy of Fallot, with pulmonary atresia. The condition is known as the 22q11 deletion, and blood tests are available to detect it.
Environmental exposures, such as maternal abuse of alcohol during pregnancy leading to fetal alcohol syndrome (FAS), are linked to Tetralogy of Fallot. Mothers who take medications to control seizures and mothers with phenylketonuria (PKU) also are more likely to have a baby with Tetralogy of Fallot.
Why is Tetralogy of Fallot a concern?
The amount of oxygen-poor (blue) blood that passes through the VSD to the left side of the heart varies. If the right ventricle obstruction is severe, or if the pressure in the lungs is high, a large amount of oxygen-poor (blue) blood passes through the VSD, mixes with the oxygen-rich (red) blood in the left ventricle, and is pumped to the body. The more blood that goes through the VSD, the less blood that goes through the pulmonary artery to the lungs, and the less oxygen-rich (red) blood that returns to the right side of the heart. Soon, nearly all the blood in the left ventricle is oxygen-poor (blue). This is an emergency situation, as the body will not have enough oxygen to meet its needs.
Some situations, such as crying, increase the pressure in the lungs temporarily, and increasing blueness might be noted as a baby with Tetralogy of Fallot cries. In other situations, the pathway from the right ventricle to the pulmonary artery becomes tighter, preventing much blood from passing that way, and allowing oxygen-poor (blue) blood to flow through the VSD into the left heart circulation. Both of these situations are nicknamed "TET spells." Sometimes, steps can be taken to lessen the pressure or the obstruction, allowing more blood to flow into the lungs and less through the VSD. These steps, however, are not always effective.
What are the symptoms of Tetralogy of Fallot?
The following are the most common symptoms of tetralogy of Fallot. Each child may experience symptoms differently. Symptoms may include:
Because large amounts of oxygen-poor (blue) blood can flow to the body under certain circumstances, one of the indications of Tetralogy of Fallot is cyanosis (blue color of the skin, lips and nailbeds) that occurs with such activities as crying or feeding, and quickly becomes more obvious.
Some babies do not have noticeable cyanosis (blue color of the skin, lips and nailbeds), but instead may be very irritable or lethargic due to a decreasing amount of oxygen available in the bloodstream.
Some children become pale or ashen in color, and may have cool, clammy skin.
Any of these can be symptoms of Tetralogy of Fallot. The symptoms of Tetralogy of Fallot may resemble other medical conditions or heart problems. Always consult your child's physician for a diagnosis.
How is Tetralogy of Fallot diagnosed?
Your child's physician may have heard a heart murmur during a physical examination, and referred your child to a pediatric cardiologist for a diagnosis. A heart murmur is simply a noise, heard with a stethoscope, caused by the turbulence of blood flowing through the obstruction from the right ventricle to the pulmonary artery. Symptoms your child exhibits will help with the diagnosis.
A pediatric cardiologist specializes in the diagnosis and medical management of congenital heart defects, as well as heart problems that may develop later in childhood. The cardiologist will perform a physical examination, listening to the heart and lungs, and make other observations that help in the diagnosis. The location within the chest that the murmur is heard best, as well as the loudness and quality of the murmur (harsh, blowing, etc.), will give the cardiologist an initial idea of which heart problem your child may have. Other tests are needed to help with the diagnosis, and may include the following:
Chest X-ray — A diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones and organs onto film.
Electrocardiogram (ECG or EKG) — A test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias) and detects heart muscle stress.
Echocardiogram (echo) — A procedure that evaluates the structure and function of the heart by using sound waves, recorded on an electronic sensor, that produce a moving picture of the heart and heart valves. This is a type of ultrasound.
Cardiac Catheterization — A procedure that gives very detailed information about the structures inside the heart. Under sedation, a small, thin, flexible tube (catheter) is inserted into a blood vessel in the groin and guided to the inside of the heart. Blood pressure and oxygen measurements are taken in the four chambers of the heart, as well as in the pulmonary artery and aorta. Contrast dye is injected to more clearly visualize the structures inside the heart.
Cardiac Magnetic Resonance Imaging (MRI) — A non-invasive test that uses three-dimensional imaging technology produced by magnets to accurately determine blood flow and functioning of the heart as it is working.
What are the treatments for Tetralogy of Fallot?
Specific treatment for Tetralogy of Fallot will be determined by your child's physician based on:
your child's age, overall health and medical history
extent of the condition
your child's tolerance for specific medications, procedures or therapies
how your child's doctor expects the condition may progress
your opinion or preference
The surgical correction of TOF is typically carried out through an incision in the middle of the chest. The incision is continued through the breastbone, or sternum, which is spread apart to expose the heart. A heart-lung machine is used to do the work of the heart while the heart is cooled, stopped, emptied and opened, through the right atrium or ventricle. The hole in the wall between the right and left ventricles, or VSD, is closed with a patch of Dacron cloth or a patch of thin leather-like material called pericardium. The muscle bundles and the narrowed pulmonary valve blocking the right ventricle are divided, and the passage out of the right ventricle toward the lungs is widened, usually by applying a patch to this area. The heart is then closed and begins pumping as the heart-lung machine is withdrawn. There are many variations of this surgery, each of which is tailored for the specific needs of a particular child's anatomy.
What is the long-term outlook after Tetralogy of Fallot surgical repair?
Most children who have had a Tetralogy of Fallot surgical repair will live healthy lives. Activity levels, appetite and growth will eventually return to normal in most children. Your child's cardiologist will recommend that antibiotics be given to prevent bacterial endocarditis after discharge from the hospital.
Consult your child's physicians regarding the specific outlook for your child.
What is the latest research on Tetralogy of Fallot?
Complementing the Cardiovascular Program Children's Hospital Boston is the nation's most intensive clinical and basic research program focused on pediatric heart disease. Children's is a world leader in opening new avenues of "translational research," bringing laboratory advances to the bedside and doctor's office as quickly as possible. All senior medical staff members of the Cardiovascular Program participate in clinical research activities.
