Transposition of the Great Arteries in Children
Basics of the Transposition of the Great Arteries
Transposition of the great arteries (TGA) is a heart defect that occurs from birth (“congenital”). The two major vessels that carry blood away from the heart — the aorta and pulmonary artery — are switched (transposed).
In a normal heart, 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 receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped through the aorta out to the body.
However, in TGA the aorta is connected to the right ventricle, and the pulmonary artery is connected to the left ventricle—the exact opposite of a normal heart's anatomy. As a result:
- Oxygen-poor (blue) blood returns to the right atrium from the body, passes through the right atrium and ventricle, then goes into the misconnected aorta back to the body.
- Oxygen-rich (red) blood returns to the left atrium from the lungs, passes through the left atrium and ventricle, then goes into the pulmonary artery and back to the lungs.
Two separate circuits are formed—one that circulates oxygen-poor (blue) blood from the body back to the body, and another that recirculates oxygen-rich (red) blood from the lungs back to the lungs.
Other heart defects are often associated with TGA and actually help an infant with TGA survive. For example, a type of congenital heart defect known as “patent ductus arteriosus” allows mixing of oxygen-poor (blue) and oxygen-rich (red) blood through the connection between the aorta and pulmonary artery. The "purple" blood that results from this mixing is beneficial, providing at least smaller amounts of oxygen, if not normal amounts, to the body.
Because of the low level of oxygen delivered to the body, TGA is a heart problem that is known as "blue-baby syndrome."
Fast Facts of the Transposition of the Great Arteries
- Transposition of the great arteries is the second most common congenital heart defect that causes problems in early infancy.
- TGA occurs in 5 percent to 7 percent of all congenital heart defects.
- Sixty percent to 70 percent of infants born with the defect are boys.
Causes of the Transposition of the Great Arteries
The cause of most congenital heart defects remains unknown. However, five factors in the mother that may increase the risk of this condition include:
- Age over 40
- Poor nutrition during pregnancy
- Rubella or other viral illness during pregnancy
Symptoms of the Transposition of the Great Arteries
The obvious sign of TGA is when the infant turns blue (or becomes “cyanotic”) in the transitional first day of life, when the maternal source of oxygen (from the placenta) is removed. Cyanosis appears in the first hours of life in about half of infants with TGA, and within the first days of life in 90 percent of them. The degree of cyanosis is related to the presence of other defects that allow blood to mix. One such defect is patent ductus arteriosus, a fetal connection between the aorta and pulmonary artery that usually closes in the first few days after birth.
Each child may experience symptoms of TGA differently, but common symptoms include:
- Rapid breathing
- Labored breathing
- Rapid heart rate
- Cool, clammy skin
Because symptoms of TGA may resemble other medical conditions or heart problems, it’s important to consult with a child's physician for a diagnosis.
Health Problems Associated with the Transposition of the Great Arteries
Without an additional heart defect that allows mixing of oxygen-poor (blue) and oxygen-rich (red) blood, such as an atrial or ventricular septal defect, infants with TGA have oxygen-poor (blue) blood circulating through the body—a situation that is fatal.
Even with an additional heart defect that allows mixing, babies with TGA do not have enough oxygen in the bloodstream to meet the body's needs, which causes other problems that strain the lungs.
Tests, Procedures and Diagnosis of the Transposition of the Great Arteries
Cyanosis is a major sign that a newborn has a heart problem. A newborn’s physician may also hear a heart murmur during a physical examination. Diagnostic testing for congenital heart disease varies by a child's age and clinical condition and may include:
- Chest X-ray. This diagnostic test uses X-ray beams to produce images onto film of internal tissues, bones and organs.
- Electrocardiogram (ECG or EKG). This procedure records the electrical activity of the heart, showing abnormal rhythms (arrhythmias or dysrhythmias) and detecting heart muscle stress.
- Echocardiogram (“echo”). This procedure 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 its valves.
- Cardiac catheterization. This invasive procedure 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 gently guided to the inside of the heart. Blood pressure and oxygen measurements are taken in the four chambers of the heart, pulmonary artery and aorta. In addition, contrast dye is injected to more clearly visualize the structures inside the heart.
Treatment for the Transposition of the Great Arteries
A child’s physician determines the specific treatment for transposition of the great arteries, based on:
- A child's age, overall health and medical history
- Severity of the disease
- A child's tolerance for specific medications, procedures or therapies
- Expectations for the course of the disease
- Parents’ opinions or preferences
In most cases, children are admitted to the intensive care unit (ICU) or special care nursery once symptoms are noted. Initially a child may be placed on oxygen, and possibly even on a ventilator, to assist with breathing. A child may also receive intravenous (IV) to help the heart and lungs function more efficiently.
Other important aspects of initial treatment include:
- A cardiac catheterization procedure can be used as both a diagnostic procedure and initial treatment for some heart defects. A cardiac catheterization procedure can evaluate the defect(s) and amount of blood that is mixing.
- During cardiac catheterization, a procedure called a balloon atrial septostomy may be performed to improve mixing of oxygen-rich (red) and oxygen-poor (blue) blood. During this procedure:
- A special catheter with a balloon in the tip is used to create an opening in the wall between the left and right atria known as the atrial septum.
- The catheter is guided through the foramen ovale (a small opening in the atrial septum that closes shortly after birth) and into the left atrium.
- The balloon is inflated.
- The catheter is quickly pulled back through the hole, into the right atrium, enlarging the hole and allowing blood to mix between the atria.
- An intravenous medication called prostaglandin E1 is given to keep the ductus arteriosus from closing.
TGA is surgically repaired within the first 1 to 2 weeks of age using a procedure called a "switch," which roughly describes the process. The child is sedated before the “switch,” which involves the following steps:
- The aorta is moved from the right ventricle to its normal position over the left ventricle.
- The pulmonary artery is moved from the left ventricle to its normal position over the right ventricle.
- The coronary arteries are moved so they will originate from the aorta and take oxygen-rich (red) blood to the heart muscle.
- Other defects, such as atrial or ventricular septal defects or a patent ductus arteriosus, are commonly closed.