Tetralogy of Fallot
What is Tetralogy of Fallot?
Tetralogy of Fallot (ToF) is a rare birth defect that affects the normal flow of blood through a baby’s heart, caused by abnormal development of the heart during pregnancy. There are a group of rare congenital heart defects that cause a bluish discoloration of the skin due to low oxygen levels in the blood (cyanosis), and of these diseases Tetralogy of Fallot is the most common. During pregnancy, the normal development of the baby’s heart starts around the 20th day, with the growth and fusion of tubes to form the different valves and ventricles of the heart. A baby’s right ventricle is the dominant chamber while growing in the uterus, receiving blood from the mother and contributing to later development of other components of the heart. Thus, abnormal development of this component can affect many characteristics of the heart, leading to Tetralogy of Fallot.
The name Tetralogy of Fallot comes from a 19th century physician in France, Etienne Louis Arthur Fallot, who was the first to describe the symptoms, and the fact that there are 4 different heart defects that make up this rare disease. In order to be qualified as Tetralogy of Fallot, an infant must have all 4 of the following heart defects:
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A hole between the two lower chambers/ventricles of the heart (ventricular septal defect) which allows oxygen-enriched and oxygen-poor blood to mix
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Narrow pulmonary valve into the main pulmonary artery (pulmonary stenosis) that reduces the flow of oxygen-poor blood into the lungs. This can also be due to an absent or abnormally formed pulmonary valve (see Absent pulmonary valve syndrome)
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Enlarged aorta with access to both ventricles instead of just the left ventricle, allowing oxygen-poor blood to flow throughout the body and causing a bluish color to appear in the skin (cyanosis)
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Thickened muscular wall of the right ventricle (ventricular hypertrophy) because more blood is being pumped from the body into the right ventricle than from the lungs into the left ventricle
Some babies born with Tetralogy of Fallot may have other rare heart defects such as ventricular or atrial septal defects, or abnormal branching of valves in the heart that allow for the proper flow of blood (see related absent pulmonary valve syndrome). All of these heart abnormalities reduce the flow of oxygen into the bloodstream and can cause a baby’s skin to turn blue during fits of crying or while eating (tet spell).
Synonyms
- Steno-Fallot tetralogy
- Pulmonic stenosis-ventricular septal defect
Tetralogy of Fallot (ToF) is a rare birth defect that affects the normal flow of blood through a baby’s heart, caused by abnormal development of the heart during pregnancy. There are a group of rare congenital heart defects that cause a bluish discoloration of the skin due to low oxygen levels in the blood (cyanosis), and of these diseases Tetralogy of Fallot is the most common. During pregnancy, the normal development of the baby’s heart starts around the 20th day, with the growth and fusion of tubes to form the different valves and ventricles of the heart. A baby’s right ventricle is the dominant chamber while growing in the uterus, receiving blood from the mother and contributing to later development of other components of the heart. Thus, abnormal development of this component can affect many characteristics of the heart, leading to Tetralogy of Fallot.
The name Tetralogy of Fallot comes from a 19th century physician in France, Etienne Louis Arthur Fallot, who was the first to describe the symptoms, and the fact that there are 4 different heart defects that make up this rare disease. In order to be qualified as Tetralogy of Fallot, an infant must have all 4 of the following heart defects:
-
A hole between the two lower chambers/ventricles of the heart (ventricular septal defect) which allows oxygen-enriched and oxygen-poor blood to mix
-
Narrow pulmonary valve into the main pulmonary artery (pulmonary stenosis) that reduces the flow of oxygen-poor blood into the lungs. This can also be due to an absent or abnormally formed pulmonary valve (see Absent pulmonary valve syndrome)
-
Enlarged aorta with access to both ventricles instead of just the left ventricle, allowing oxygen-poor blood to flow throughout the body and causing a bluish color to appear in the skin (cyanosis)
-
Thickened muscular wall of the right ventricle (ventricular hypertrophy) because more blood is being pumped from the body into the right ventricle than from the lungs into the left ventricle
Some babies born with Tetralogy of Fallot may have other rare heart defects such as ventricular or atrial septal defects, or abnormal branching of valves in the heart that allow for the proper flow of blood (see related absent pulmonary valve syndrome). All of these heart abnormalities reduce the flow of oxygen into the bloodstream and can cause a baby’s skin to turn blue during fits of crying or while eating (tet spell).
Tetralogy of Fallot is the most common heart defect diagnosed in infants born with critical heart conditions: 1% of infants are born with congenital heart defects and 10% of these cases are caused by Tetralogy of Fallot. This disease affects male and female children equally and occurs in 3-5 out of every 10,000 children. This equates to about 1,660 babies in the U.S being born with ToF every year.
| Name | Abbreviation |
|---|---|
| Steno-Fallot tetralogy | |
| Pulmonic stenosis-ventricular septal defect |
The exact cause of Tetralogy of Fallot is unknown. Since it is a congenital heart disorder that is the result of abnormal development of a baby’s heart, it may be related to complications during pregnancy due to exposure to environmental hazards. These could include conditions that affect the health of the mother, such as untreated maternal diabetes, maternal consumption of alcohol, or phenylalanine buildup in the body (phenylketonuria). Tetralogy of Fallot may also be linked to a genetic mutation, as many cases of children diagnosed with ToF also have chromosomal abnormalities such as trisomies 21, 18, and 13 (three chromosome copies instead of two), microdeletions of chromosome 22q11.2, and Alagille syndrome with JAG1/NOTCH2 mutations. Other genetic abnormalities that are found in children with tetralogy of Fallot include mutations in transcription factor NKX2.5, methylenetetrahydrofolate reductase polymorphism, and mutations in TBX1 and ZFPM2. About 25% of children born with Tetralogy of Fallot have other birth defects that are unrelated to heart conditions, which indicates that more research is needed to understand the underlying causes of this rare disease.
Tetralogy of Fallot affects the flow of blood and the availability of oxygen, causing symptoms such as difficulty breathing, fatigue, headaches, and other related ailments. There are differences in severity of disease symptoms depending on the degree of obstruction to the flow of blood, especially into the lungs causing bluish discoloration (cyanosis). Blood that lacks oxygen is darker and has a bluish color (lacking iron) and thus babies with ToF will have bluer skin than red, usually in their lips and skin of their fingers and toes. Infants with Tetralogy of Fallot may experience periods of lower than average blood flow, causing severe cyanosis and/or breathing difficulties, which can cause gasping for air and loss of consciousness in some cases. This has become known as “tet spells” and can last from a few minutes to a few hours and are a critical sign of congenital heart problems. Infants with Tetralogy of Fallot may also have an increased risk of the following conditions due to abnormal heart physiology:
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A higher risk of getting an infection of the layers of the heart, called endocarditis.
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A higher risk of having irregular heart rhythms, called arrhythmia.
Tetralogy of Fallot can also cause delayed growth and development. Infants may also be predisposed to blood disorders such as abnormal increase in red blood cells or the formation of blood clots, which can affect the delivery of blood to the brain. All of these symptoms support the importance of surgical repair of the heart in infants diagnosed with Tetralogy of Fallot.
In order to provide the necessary surgery to correct congenital heart failure, infants born with Tetralogy of Fallot must be diagnosed during pregnancy or soon after birth, often within the first year of life. ToF is a critical congenital heart defect (CHD) that requires corrective surgery once a baby is born with it.
Testing for Tetralogy of Fallot is conducted differently depending on the period of development.
Before Birth:
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Ultrasound - imaging test that uses sound waves to produce a picture and structure of the body’s major organs, including those of a fetus during pregnancy
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Fetal echocardiogram - an ultrasound of just the heart of the fetus to detect abnormal development or features; can show problems with the heart
After Birth:
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Physical exam - a physical exam of the infant following birth is conducted to ensure that the heart is functioning properly and there is no evidence of bluish extremities or a heart murmur
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Newborn Echocardiogram
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Pulse oximetry - test for the levels of oxygen in a newborn’s blood
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Electrocardiogram - measurement of the electrical activity of the heart
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Chest x-ray
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Cardiac MRI - produces a 3D image of the heart for analysis
About 25% of infants with Tetralogy of Fallot also have one of the following congenital birth conditions: DiGeorge syndrome, Trisomy 21 (Down syndrome), Alagille syndrome or chromosome 22q11.2 deletion syndrome. Genetic testing can be conducted if these rare diseases are suspected in combination with Tetralogy of Fallot.
Treatment for Tetralogy of Fallot requires surgery after birth or within the first year of life. This depends on the severity of symptoms, status of diagnosis, and whether the child is strong enough to undergo open heart surgery. If the newborn or infant is experiencing difficulty breathing and multiple “tet spells”, emergency oxygen and opening of the airway should be provided. In such cases, a drug capable of expanding the blood vessels and increasing blood flow called prostaglandin is administered to keep key vessels in the heart open, such as the ductus arteriosus. Surgery is often required to repair the heart defects, or to work around any obstructions or abnormal openings that change the normal flow of blood from the heart into the lungs and then into the rest of the body. Some of the surgical methods that may be required include:
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Closing the hole between the two lower chambers of the heart (ventricular septal defect) by applying a Dacron patch
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Enlarge the pulmonary valve to increase the flow of blood out of the heart and into the lungs
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Temporarily connecting the pulmonary arteries to the larger arteries of the heart until the infant is old/developed enough for the full open heart surgery
Additionally, infants diagnosed with Tetralogy of Fallot may be prescribed antibiotics while being treated in the hospital to prevent infections in the lungs that would add to breathing difficulties.
The development and improvement of surgeries for congenital heart disorders have increased the life expectancy of infants with Tetralogy of Fallot in recent years. In fact, 95% of infants born with Tetralogy of Fallot and treated with surgery within the first year of life survive the procedure and continue to lead healthy lives. Some children may require medication following surgery if their heart rate continues to be irregular (arrhythmia) or if they have trouble breathing, but this is uncommon.
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Diaz-Frias J, Guillaume M. Tetralogy of Fallot. [Updated 2022 Jan 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513288/
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https://www.cdc.gov/ncbddd/heartdefects/tetralogyoffallot.html#:~:text=Tetralogy%20of%20Fallot%20(pronounced%20te,the%20mother's%20womb%20during%20pregnancy.
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https://www.mayoclinic.org/diseases-conditions/tetralogy-of-fallot/symptoms-causes/syc-20353477
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