How is this defect treated? (continued)
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 does not require the heart/lung bypass machine. The incision is made on the side of the chest under the arm between the ribs. 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 out the ventricle bypassed 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 this diagnosis?
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. Life long 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.