Transposition of the Great Arteries (TGA)

What is transposition of the great arteries?

Anatomy of the heart, normal

Transposition of the great arteries is a congenital (present at birth) heart defect. Due to abnormal development of the fetal heart during the first eight 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 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.

Anatomy of a heart with transposition of the great arteries

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 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 one of the heart problems 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 about 3 percent of all congenital heart defects. About two-thirds of the infants born with the defect are boys.

Prevention & Risk Treatment

Prevention & Risk Treatment

What causes transposition of the great arteries?

The heart is forming during the first eight 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 body back to the body, and another that recirculates oxygen-rich (red) blood from the lungs back to the lungs. 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 or a patent ductus arteriosus, 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 for long.

What are the symptoms of transposition of the great arteries?

The obvious indication of TGA is a newborn who becomes cyanotic (blue) in the 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 most 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 doctor for a diagnosis.

Diagnosis

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 doctor may have also heard a heart murmur during a physical examination. In this case, a heart murmur is a noise caused by the turbulence of blood flowing through the openings that allow the blood to mix, such as the ventricular septal defect or patent ductus arteriosus. 

Diagnostic testing for congenital heart disease varies by the child's age, clinical condition, and institutional preferences.  Some tests that may be recommended include the following:

  • Chest X-ray. A diagnostic test that uses invisible X-ray 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), 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.
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Washington Adult Congenital Heart Program (WACH)

The Washington Adult Congenital Heart Program meets the unique needs of adult patients with congenital heart disease by providing all the necessary resources and highly sophisticated care in a central location.

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Children’s National Heart Institute, an international leader in comprehensive cardiac care for infants, children, and adults.

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Learn more about the advanced cardiac imaging procedures we use to diagnose infants and children in our Heart Institute.

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When your baby needs the most advanced cardiac care, Children’s National Heart Institute is the preeminent provider of fetal cardiac services in the Washington, DC, metropolitan area.

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