Complete transposition of the great arteries (TOGA) 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.
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 ducts 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.
When a baby has TOGA, 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 TOGA 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 ducts 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 congestive 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.
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 congestive 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: Complete TOGA 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 this problem are provided in the Congenital Heart and Cardiovascular Surgery clinics at the University of Michigan Medical Center in Ann Arbor.
Lupinetti FM, Bove EL, Snider AR, Callow LB, Meliones JN, Crowley DC, Beekman RH, Minich LL, Rosenthal A: Intermediate-term survival and functional results after arterial repair for transposition of the great arteries. J Thorac Cardiovasc Surg 1992;103:421-7.
Bove EL, Beekman RH, Snider AR, Rocchini AP, Dick M, Crowley DC, Serwer GS, Rosenthal A: Arterial repair for transposition and large ventricular septal defect in early infancy. Circulation l988;78 (Suppl III):III-26-III-3l.
Written by: Louise Callow RN, MSN (12/99)
Reviewed January, 2010