Transposition of the great arteries (TGA) is a type of congenital heart defect in which the two great arteries (the pulmonary artery and the aorta) are in reversed (transposed) locations. This reverses circulation in the heart. Normally, oxygen-rich blood travels through the aorta to nourish the cells and tissues, while oxygen-poor blood travels through the pulmonary artery on its way to the lungs for fresh oxygen.
By contrast, TGA results in two kinds of parallel circulation. Oxygen-poor blood from the body is pumped back out to the body through the aorta, while oxygen-rich blood is pumped back to the lungs through the pulmonary artery.
Survival depends on the presence of other heart defects that allow some mixing of oxygen-rich and oxygen poor blood. Even with other defects, however, the baby will likely not be getting sufficient oxygen from the blood. As a result, the infant will often be born with a bluish tone (cyanosis) to the skin, lips, nails and other parts of the body (blue baby).
The other defects that might be present with TGA include a hole in the muscular wall between the heart’s upper chambers (an atrial septal defect) or a hole in the wall between the lower chambers (a ventricular septal defect). Alternatively, the young patient may be born with a patent ductus arteriosus – a condition in which the prenatal channel between the aorta and the pulmonary artery (ductus arteriosus) remains open (patent) at birth. Typically, newborn babies with TGA are given a drug that keeps the ductus arteriosus open to encourage the flow of oxygen-rich blood to the body.
To correct any heart-associated defects, surgery is generally performed in the early days following birth. Anyone who has TGA must have heart surgery early in life to survive, according to the American Heart Association.
About TGA
Transposition of the great arteries (TGA) is a type of congenital heart defect in which the two great arteries (the pulmonary artery and the aorta) are in reversed (transposed) locations. This reverses circulation in the heart. Normally, oxygen-rich blood travels from the left ventricle through the aorta to nourish the cells and tissues, while oxygen-poor blood travels from the right ventricle through the pulmonary artery on its way to the lungs for fresh oxygen.
By contrast, TGA results in two kinds of parallel circulation. Oxygen-poor blood from the body is pumped back out to the body through the aorta, which is connected to the right ventricle.
Meanwhile, oxygen-rich blood is pumped back to the lungs through the pulmonary artery, which is connected to the left ventricle. Early survival depends on the presence of other heart defects that allow some mixing of oxygen-rich and oxygen poor blood.
Even with other defects, however, the baby will likely not be getting sufficient oxygen from the blood. As a result, the infant will often be born with cyanosis, a bluish tone to the skin, lips, nails and other parts of the body (blue baby).
In an effort to compensate for the lack of oxygen-rich blood reaching the body, the heart will overwork itself. Untreated, this added strain could eventually lead to heart failure, a serious condition in which the heart is not pumping efficiently enough to meet the body’s demand for oxygen.
The other defects that may occur with TGA include:
Atrial septal defect. A hole in the septum between the heart's two upper chambers (atria).
Ventricular septal defect. A hole in the muscular wall (septum) between the heart’s two lower chambers (ventricles). About 20 percent of children born with TGA will also have a ventricular septal defect.
Patent ductus arteriosus. A heart defect that occurs when a blood vessel called the ductus arteriosus fails to close after birth, as it normally should. The ductus arteriosus is an open channel in every fetus that allows blood to bypass the lungs, which are not used until the baby takes the first breath after birth. Shortly after the baby’s first breath, the ductus arteriosus should close permanently. If it does not, it is known as a patent ductus arteriosus (PDA). Among babies with TGA, a drug called prostaglandin E1 will often be administered to ensure that the ductus arteriosus stays open instead of closing within a few days of birth.
The presence of one of these defects actually enables a TGA baby to survive the first few days of life. Without some mixing of oxygen-rich and oxygen-poor blood, the tissues of the body and organs would rapidly die. TGA accounts for 5 to 7 percent of all congenital heart defects, affecting approximately 40 out of every 100,000 babies. If left untreated, only about 10 percent of TGA babies will live for more than a year.
Risk factors and causes of TGA
Like some other congenital heart defects, the cause of TGA is unknown. However, there are a number of factors that have been associated with an increased risk of TGA, although they have not been shown to actually cause the defect. They include the following:
Rubella (German measles) infection in the mother during pregnancy
Other viral illnesses during pregnancy
Poor prenatal nutrition
Maternal alcoholism
Maternal diabetes
Maternal age over 40
Studies have found that maternal exposure during pregnancy to lawn and garden weed killers and rat poisons increases the risk of TGA to the developing fetus.
Signs and symptoms of TGA
Transposition of the great arteries (TGA) is the most common of the cyanotic congenital heart defects, or defects that cause newborn babies to have a bluish tint to the skin, lips, fingernails and other areas of the body. This cyanosis will usually appear in the first hours of life. Other signs and symptoms include:
Weakness and fatigue. Feeding time can be especially difficult.
Failure to thrive. This sign is generally apparent to the trained eye of a physician.
Fainting (syncope).
Clubbing of the fingers or toes.
Diagnosis methods for TGA
A physical examination in the baby’s first few days of life will usually indicate to a physician that the baby is not thriving and something is wrong. The physician may order one of the following tests to screen for a problem with the heart or lungs:
Chest x-ray. A painless radiation-based imaging test that offers the physician a picture of the general size, shape, and structure of the heart and lungs.
Electrocardiogram (EKG or ECG). A painless recording of the heart’s electrical activity as a graph on a moving strip of paper or video monitor. The highly sensitive electrocardiograph machine helps detect heart irregularities, disease and damage by measuring the heart’s rhythms and electrical impulses.
Cardiac catheterization. This test allows the physician to delineate the anatomy of the heart and large vessels, coronary arteries and oxygen saturation in different heart chambers.
Echocardiogram. This painless test uses sound waves to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage (regurgitation) or narrowing (stenosis). During this test, a Doppler ultrasound may be done to evaluate cardiac blood flow. Prenatal echocardiograms, or ultrasounds, are often used to diagnose the condition while the baby is still in utero. This allows the physicians and parents to prepare a treatment plan for immediately after birth.
Treatment options for TGA
The treatment of transposition of the great arteries (TGA) involves repair of the defect(s) as quickly as possible, coupled with preventive steps to keep the baby alive until surgery. To keep the ductus arteriosus open (which helps by mixing oxygen-rich and oxygen-poor blood) physicians may give the baby infusions of a drug called prostaglandin.
A physician may also perform a procedure called a balloon atrial septostomy. During this catheter-based procedure, a balloon-tipped catheter is guided into one of the atria (upper chambers of the heart) where it is used to either expand or create a hole in the wall of muscle separating the atria (septum). This aids in the mixture of oxygen-rich and oxygen-poor blood. It is a palliative procedure, or temporary procedure designed only to relieve the worst of the defect until corrective surgery can be performed.
Another such palliative procedure is known as pulmonary artery banding. During this procedure, a band is placed around the pulmonary artery to reduce the pressure of blood flowing to and from the lungs. This reduces the likelihood of high blood pressure developing in the lungs (pulmonary hypertension), which can cause permanent damage to the blood vessels of the lungs. Palliative techniques such as these improve the baby’s condition by alleviating some of the heart’s workload and helping to prevent heart failure. However, corrective surgery is necessary to correct TGA as soon as possible.
To correct TGA, the surgeon will perform an arterial switch operation. During this procedure, the aorta and pulmonary artery are returned to their normal positions. The end of the pulmonary artery is carefully cut from the left ventricle (lower chamber of the heart) and sewn to the right ventricle, and the end of the aorta is carefully cut from the right ventricle and sewn to the left ventricle. At the same time, any associated defects, such as ventricular septal defects, are repaired. Also, the surgeon will repair or move any defects in the coronary arteries, which should normally connect to the aorta and supply the heart itself with oxygen-rich blood. There is a range of coronary artery abnormalities associated with TGA.
After surgery and recovery, lifelong medical management will be necessary. Additional surgeries may be necessary, such as to repair valves or improve the heart’s pumping ability. Also, the patient may need to take antibiotics before dental procedures or other surgeries to prevent infection of the heart walls or valves (bacterial endocarditis).
According to the American Heart Association, people with TGA can expect:
Probable restrictions on physical activity, as recommended by their cardiologist (e.g., no competitive sports)
An increased risk of developing abnormal heartbeat (arrhythmias), which may require periodic monitoring with cardiac catheterization
An increased risk to female TGA patients during pregnancy if there are serious problems with heart muscle or arrhythmias, though women with repaired TGA can have successful pregnancies
Research has shown that many adults with congenital heart defects such as TGA do not receive regular cardiac care. The U.S. National Institutes of Health (NIH) is considering requests from cardiologists to establish a national registry of such patients to improve care.
Questions for your doctor regarding TGA
Preparing questions in advance can help patients (and parents) have more meaningful discussions with their physicians regarding their conditions. Parents may wish to ask their doctor the following questions about transposition of the great arteries (TGA):
How is TGA diagnosed?
Are any other heart defects present?
What treatments are needed, and when?
What are my baby’s chances for recovery?
What precautions will my child have to observe later in life?
If I have other children, will they be at increased risk of TGA? If so, is there anything I can do to decrease the risk?
After successful treatment of TGA, patients may face increased risk for other heart-related problems. The following questions may help adult patients address their concerns with their physicians:
Do I need cardiac catheterization or other tests to check for arrhythmias or other heart problems?
What condition is my heart in? What is my long-term prognosis?
What types of exercise are best for me? Should I avoid certain activities and sports?
Would I have increased health risks if I become pregnant?
If I have children, will they be at increased risk of TGA? If so, is there anything I can do to decrease the risk?
Atrial septal defect. A hole in the septum between the heart's two upper chambers (atria). 
