Transposition of the great arteries (TGA), also called dextro-transposition of the great arteries (or d-TGA), occurs when the two main arteries leaving the heart are reversed (transposed). A rarer type of this condition is called levo-transposition of the great arteries or corrected transposition of the great arteries.
What is transposition of the great arteries?
TGA occurs when the aorta, which normally comes off the left ventricle and pumps red blood to the body, arises from the right ventricle (1) and pumps blue blood returning from the body back to the body bypassing the lungs completely. The pulmonary artery, which normally arises from the right ventricle and pumps blue blood to the lungs, arises from the left ventricle (2) and sends red blood returning from the lungs right back to the lungs. Essentially, the great arteries are reversed from their normal connections.
What causes transposition of the great arteries?
The cause of the problem is not understood. It is the most common form of cyanotic congenital heart disease which presents in the newborn period. It is more common in males and the babies are usually normal birth weight and size. TOGA accounts for 5 to 7% of all congenital heart defects.
There are several other heart abnormalities that may occur along with TOGA. The most common associated problem is a ventricular septal defect (3). This is a defect or hole in the wall that separates the lower two chambers of the heart, the ventricles. There may be narrowing of the area of the heart where blood flows out to the pulmonary artery. This is called left ventricular outflow tract obstruction.
Many of these babies have an atrial septal defect (4) (a hole in the wall that separates the top two chambers of the heart) and/or a patent ductus arteriosus (5). This is normal birth channel between the aorta and pulmonary artery present at birth that may fail to close in the presence of other heart problems.
What are the effects of this defect on my child's health?
When a baby has TGA, there are two separate circuits of blood flow instead of a connected one. Blue blood returning from the body is pumped right back out to the body and red blood returning from the lungs is pumped right back to the lungs. As a result, the baby develops a blue color, called cyanosis, shortly after birth. The blue color can best be noticed in the lips or under the fingernails. In a baby with heart related cyanosis, the blue color does not improve with the use of oxygen.
If this situation were to continue the baby could soon die from lack of oxygen delivery to the body. The only way a baby with TGA can survive after birth is if there is a way for the red and blue blood to mix together within the heart so that some red blood gets pumped out to the body. An atrial septal defect and/or a patent ductus arteriosus will usually permit enough oxygen to allow the baby to survive until a more definitive intervention can be performed.
Some babies with TGA also have a hole between the heart's lower chambers called a ventricular septal defect. If this is present, enough mixing of blood may occur that the baby may not appear cyanotic at all and may actually become ill with symptoms of heart failure because of the extra blood flow going to the lungs. Then the baby will have symptoms of poor feeding, poor weight gain, sweating, and fast or labored breathing.
Finally, there may be narrowing of the area leading out the left ventricle to the pulmonary artery called left ventricle outflow tract obstruction. In this situation even though there is the hole for the blood to mix, the total amount of blood flow going into the lungs is reduced. The degree of narrowing varies and can be mild at first but can get worse with time. As the narrowing increases the baby's coloring will become more cyanotic (blue).
The severity of symptoms is dependent on how much red and blue blood mix together and the presence or absence of obstruction to blood flow out the left ventricle. The type and timing of operation depend on the combination of defects that accompany the primary problem of TGA.
Babies with TGA may develop early pulmonary vascular disease. This is an increase in the pressure in the lung blood vessels that cause changes that make it hard for them to accept low-pressure blood flow. These changes can occur as early as a few weeks of life and tend to occur more frequently in babies who have ventricular septal defects in addition to TGA. Early corrective surgery minimizes the chances of development of elevated pulmonary vascular resistance in these babies.
How is this defect diagnosed?
Clinical features: As described above, babies with complete TOGA have lower blood oxygen levels from the time of birth. The blue color is seen in the lips and under the fingernail beds and can be quite hard to detect just by looking at the baby. Signs of heart failure including symptoms of congestive heart failure develop including excessive sweating (a cold, clammy sweat often noted during feeding); poor feeding, slow weight gain, irritability or lethargy, and/or rapid breathing usually develop during the newborn period.
Physical findings: TGA is usually diagnosed with 24 to 48 hours of birth due to the presence of cyanosis which is moderate or severe in most cases. The second heart sound is loud and single. There may or may not be a murmur depending on the presence of a ventricular septal defect. If the baby is in congestive heart failure, the breathing rate will be fast and the liver will be enlarged.
Medical tests: Blood oxygen levels can be measured by an oxygen saturation test or by a blood test. Sometimes the baby will be placed in an oxygen tent and given 100% oxygen to breathe in order to see if the blood oxygen levels increase. If the oxygen levels do increase significantly, it suggests that the low level of oxygen if from a lung problem instead of a heart problem.
An electrocardiogram and chest x-ray is also usually done. The defect is diagnosed by a heart test called an echocardiogram or heart ultrasound. The echocardiogram uses sound waves to form an image of the valves and chambers inside the heart. It is safe and painless and test results are available right away. In some cases, the diagnosis is made before birth during a fetal ultrasound. The earliest time the test can be used to diagnose this problem is when the mother is 18 weeks into her pregnancy.
Another heart test called a heart catheterization will be necessary if the echocardiogram is not completely clear about the heart problem or if additional abnormalities are present that may affect how the surgeon would fix the defect. During this procedure, catheters (thin plastic tubes) are placed into the large blood vessels located in the groin area and gently guided into the heart. Contrast or "dye" is then put into the heart so x-ray pictures can be taken. Pressure measurements and oxygen levels are also obtained. It is more involved then the echocardiogram but is considered very safe. The babies are sedated and given pain medicines during the test. The results are most often available on the same day.
Care and services for patients with TGA are provided in the Congenital Heart and Cardiovascular Surgery clinics at the University of Michigan Health C.S. Mott Children’s Hospital. For more information on our programs and services, or to make an appointment, please call 734-764-5176.
How is TGA treated?
A heart operation will be necessary to correct the defect. While waiting for surgery, a medicine called prostaglandin may be used to keep the ductus arteriosus open and allow for better mixing of red and blue blood. A procedure called a balloon atrial septostomy may be needed to increase mixing of red and blue blood inside the heart and prevent complications of severe cyanosis. This procedure is done during a heart catheterization. A thin plastic tube or catheter is placed into a large vein in the baby's groin. This catheter is then passed into the right atrium and across the small hole in the wall between the right and left atrium. Once the catheter is in the left atrium a balloon is expanded and pulled back through the hole into the right atrium making the hole bigger. This allows more mixing of the red and blue blood and higher oxygen levels while the baby awaits surgery.
The age of the child at operation and the kind of operation will depend on the child's symptoms and the precise anatomy of the defect. The surgery most frequently performed for TGA with or without a ventricular septal defect is called an arterial switch operation. In this operation the two blood vessels which are reversed are "switched" back to the correct location. This operation must be done within the first few weeks of the infant's life when both the right and left ventricle are used to pumping blood against the higher pressures found in the fetal circulation.
When a surgeon fixes this defect, an incision is made down the center of the breastbone and the heart is stopped for a short period of time while the body is supported with a heart/lung bypass machine. The aorta and pulmonary artery are divided and reconnected so that the pulmonary artery is connected to the right ventricle (1) and supplies blue blood to the lungs. The aorta is connected to the left ventricle and supplies red blood to the body (2). The coronary arteries are also relocated so that they will receive red blood from the aorta for the heart muscle itself. If there are any septal defects, either in the atrium or the ventricle, these holes are also closed.
At the end of the operation the baby's heart is completely normal both in its connections (anatomy) and in the way the blood flows (physiology). In addition, this operation provides the advantage of keeping the left ventricle on the side of the heart that pumps blood to the body.
If the baby is older at the time of diagnosis or there is an unusual location of one of the coronary arteries, the surgeon may choose to perform an atrial switch operation called a Mustard or Senning operation. For this operation, now rarely used, the incision is made as it is with the arterial switch and the heart/lung bypass machine is used. The venous drainage of blood coming into the heart is rerouted rather switching the arteries that carry blood out of the heart. In this case the blue blood returning to the right atrium is redirected to the left atrium (1), flows to the left ventricle (2) where it is pumped through the pulmonary arteries to the lungs. Red blood returning from the lungs is baffled to the right atrium (3), flows to the right ventricle (4) where it is pumped through the aorta and out to the body. Even though the blood goes to the right location, the heart remains configured so the right ventricle pumps blood to the body and the left ventricle pumps blood to the lungs.
In situations where there is obstruction of blood flow out the left ventricle and into the pulmonary artery two operations are usually required to fix the heart. This type of TGA, known as transposition with left ventricular outflow tract obstruction, cannot usually be repaired by an arterial switch operation because of the narrowing out of the left ventricle, although in some cases the narrowing can be removed. The first operation may be required when the baby is a newborn if the level of oxygen saturation in the blood is too low, lower than in the mid 70's%. This operation is called a shunt operation and is done to increase blood flow to the lungs and provide the baby with the oxygen necessary to grow and develop until they get to a size and age where complete repair is safe and low risk. This is usually about 6 months of age. In some babies the shunt operation is not necessary because even though the baby has blue coloring, the level of oxygen in the blood is satisfactory because the narrowing is not too severe.
The shunt operation may or may not require the heart/lung bypass machine. The incision is made either on the side of the chest under the arm between the ribs or across the breastbone. A tube of Gore-Tex is placed between the pulmonary artery and a blood vessel branching off the aorta. Therefore, when blood goes out the right ventricle and aorta (transposition) some will go through the shunt into the pulmonary artery and to the lungs to get oxygen. This protects blood flow to the lungs even if the narrowing out the left ventricle is really severe. Eventually the shunt will be taken out when the full repair is done.
In order to fully correct transposition with left ventricular outflow tract obstruction, the ventricular septal defect must be closed, the narrowing of the ventricle by-passed, and the blood flow redirected such that red blood exits to the body via the left ventricle and blue blood exits the right ventricle to the lungs. This operation is called a Rastelli operation.
When the surgeon fixes the heart with this operation an incision is made down the center of the breastbone and the heart is stopped for a short period of time while the body is supported with a heart/lung bypass machine. The ventricular septal defect is closed in such a way that the left ventricle is connected to the aorta and the right ventricle is connected to the lungs using a tube or conduit with a valve in it (1). One end of the conduit is connected to the right ventricle where blood exits into the pulmonary artery and the other end is attached to the pulmonary artery (2). It acts as a "bypass" for blood to flow around the naturally occurring narrowing. This particular tube or conduit will need to be replaced as the child grows. Usually this is not necessary for 3 to 5 years after the original operation if done in infancy and then 1 to 2 more times throughout the child's life.
In extremely rare cases, TGA may not be diagnosed until the baby is over a month of age. It is too late at this time to perform an arterial switch operation since the left ventricle is no longer strong enough to pump blood to the body. In this situation there are two options for repair. The first is the venous or atrial switch operation as discussed previously. The second option is to do an operation to make the left ventricle stronger again and able to pump blood to the body. In order to do that a band is placed around the pulmonary artery and tightened causing the left ventricle to push against higher pressure. This acts to strengthen the muscle of the left ventricle. In addition, a shunt is placed which provides extra blood volume to the left ventricle. This also acts to increase the work of the left ventricle and make it ready to handle the work of pumping blood to the body. The optimal time to wait between this operation and the arterial switch depends on the baby's age and the response of the left ventricle but is generally only a few days to weeks. This procedure is referred to as a staged arterial switch.
What is the outlook for children with TGA?
The surgical repair for complete TGA is generally very safe and both early and late outcomes are excellent. The risk for the arterial switch operation is less than 3 to 5% when TGA exists alone or with an associated VSD. The Rastelli operation carries a slightly higher risk, approximately 5 to 10%. Further surgery is usually not required, but about 5% of children will need additional surgery to repair a narrow connection later in life. When necessary, this almost always involves the connection into the lungs (pulmonary artery). The presence of certain unusual coronary artery variants may also increase the risk of an arterial switch operation, but in experienced centers, this increase is minimal, if at all. If a conduit is required, replacement will be necessary as indicated above. The risk for replacement is very low.
The majority of children lead normal, active lives after repair of TGA. Lifelong follow-up is required to assess for the possible development of late problems, including narrowing of a connection into the lungs, valve leakage, coronary artery narrowing, and heart muscle function.
Take the next step
Care and services for patients with TGA are provided in the Congenital Heart Center and cardiovascular surgery clinics at the University of Michigan Health C.S. Mott Children’s Hospital. For more information on our programs and services, or to make an appointment, please call 734-764-5176.