Transposition of the Great Arteries (TGA)

What is transposition of the great arteries?

Transposition of the great arteries is a congenital (present at birth) heart defect. Due to abnormal development of the fetal heart during the first 8 weeks of pregnancy, the large vessels that take blood away from the heart to the lungs, or to the body, are improperly connected.

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 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.

In transposition of the great arteries, 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.

  • 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 lungs back to the lungs, and another that recirculates oxygen-rich (red) blood from the body back to the body.

Other heart defects are often associated with TGA, and they actually may be necessary in order for an infant with transposition of the great arteries to live. An opening in the atrial or ventricular septum will allow blood from one side to mix with blood from another, creating "purple" blood with an oxygen level somewhere in-between that of the oxygen-poor (blue) and the oxygen-rich (red) blood. Patent ductus arteriosus (another type of congenital heart defect) will also allow 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 to the body, if not a normal amount of oxygen.

Because of the low amount of oxygen provided to the body, TGA is a heart problem that is labeled "blue-baby syndrome."

Transposition of the great arteries is the second most common congenital heart defect that causes problems in early infancy. TGA occurs in 5 to 7 percent of all congenital heart defects. Sixty to 70 percent of the infants born with the defect are boys.

What causes transposition of the great arteries?

The heart is forming during the first 8 weeks of fetal development. The problem occurs in the middle of these weeks, allowing the aorta and pulmonary artery to be attached to the incorrect chamber.

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. Most of the time this heart defect occurs sporadically (by chance), with no clear reason for its development.

Why is transposition of the great arteries a concern?

Babies with TGA have two separate circuits - one that circulates oxygen-poor (blue) blood from the lungs back to the lungs, and another that recirculates oxygen-rich (red) blood from the body back to the body. 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 will have oxygen-poor (blue) blood circulating through the body - a situation that is fatal. Even with an additional defect present that allows mixing, babies with transposition of the great arteries will not have enough oxygen in the bloodstream to meet the body's demands.

Even when a good bit of mixing of oxygen-poor (blue) and oxygen-rich (red) blood can occur, other problems are present. The left ventricle, which in TGA is connected to the pulmonary artery, is the stronger of the two ventricles since it normally has to generate a lot of force to pump blood to the body. The right ventricle, connected to the aorta in TGA, is the weaker of the two ventricles. Because the right ventricle is weaker, it may not be able to pump blood efficiently to the body, and it will enlarge under the strain of the job. The left ventricle may pump blood into the lungs more vigorously than needed, leading to strain in the blood vessels in the lungs.

What are the symptoms of transposition of the great arteries?

The obvious indication of TGA is a newborn who becomes cyanotic (blue) in the transitional first day of life when the maternal source of oxygen (from the placenta) is removed. Cyanosis is noted in the first hours of life in about half of the 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, including a patent ductus arteriosus - a fetal connection between the aorta and the pulmonary artery present in the newborn, which usually closes in the first few days after birth.

The following are the other most common symptoms of TGA. However, each child may experience symptoms differently. Symptoms may include:

  • rapid breathing
  • labored breathing
  • rapid heart rate
  • cool, clammy skin

The symptoms of TGA may resemble other medical conditions or heart problems. Always consult your child's physician for a diagnosis.

How is transposition of the great arteries diagnosed?

A pediatric cardiologist and/or a neonatologist may be involved in your child's care. 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. A neonatologist specializes in illnesses affecting newborns, both premature and full-term.

Cyanosis is the major indication that there is a problem with your newborn. Your child's physician may have also heard a heart murmur during a physical examination. A heart murmur is simply a noise caused by the turbulence of blood flowing through the openings that allow the blood to mix.

Other diagnostic tests are needed to help with the diagnosis, and may include the following:

  • chest x-ray - a diagnostic test which 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.

  • cardiac catheterization - a cardiac catheterization is an invasive 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 the pulmonary artery and aorta. Contrast dye is also injected to more clearly visualize the structures inside the heart.

Treatment for transposition of the great arteries:

Specific treatment for transposition of the great arteries will be determined by your child's physician based on:
  • your child's age, overall health, and medical history
  • extent of the disease
  • your child's tolerance for specific medications, procedures, or therapies
  • expectations for the course of the disease
  • your opinion or preference

Your child will most likely be admitted to the intensive care unit (ICU) or special care nursery once symptoms are noted. Initially, your child may be placed on oxygen, and possibly even on a ventilator, to assist his/her breathing. Intravenous (IV) medications may be given to help the heart and lungs function more efficiently.

Other important aspects of initial treatment include the following:

  • A cardiac catheterization procedure can be used as a diagnostic procedure, as well as initial treatment procedure for some heart defects. A cardiac catheterization procedure will usually be performed to evaluate the defect(s) and the amount of blood that is mixing.

  • As part of the cardiac catheterization, a procedure called a balloon atrial septostomy may be performed to improve mixing of oxygen-rich (red) and oxygen-poor (blue) blood.

    • A special catheter with a balloon in the tip is used to create an opening in the atrial septum (wall between the left and right atria).

    • The catheter is guided through the foramen ovale (a small opening present 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, allowing blood to mix between the atria.

  • An intravenous medication called prostaglandin E1 is given to keep the ductus arteriosus from closing.

Within the first 1 to 2 weeks of age, transposition of the great arteries is surgically repaired. The procedure that accomplishes this is called a "switch," which roughly describes the surgical process.

The operation is performed under general anesthesia, and involves the following:

  • 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.