Transposition of the Great Arteries (d-TGA)
Transposition of the great arteries is a cyanotic congenital heart defect (blue baby), in which the two main arteries of the heart and are transposed (reversed). There are different types of TGA. This section deals with d-TGA, in which the aorta and the pulmonary artery are connected to the wrong ventricles of the heart. Normally, the aorta is attached to the left ventricle, and in TGA it is attached to the right ventricle. In a normal heart, the pulmonary artery is connected to the right ventricle, but in TGA, it is connected to the left ventricle instead.
In d-TGA, the oxygen-poor blood, in the right ventricle is pumped to the aorta instead of the pulmonary artery. This “blue blood” is circulated throughout the body and gives the baby a dark bluish color to the skin. The red blood (oxygen-rich) is pumped by the left ventricle to the lungs instead of the aorta. The end result is two separate circuits of blood circulation. The pulmonary circulation consists of red blood circulating over and over from the lungs to the left heart.
The systemic circulation carrying blue blood (oxygen-poor blood) is circulating throughout the body and then returning to the right side of the heart and then pumped back again into the body. The oxygen-poor blood circulates through the right side of the heart and back to the body without passing through the lungs to get oxygenated. Therefore, all babies born with d-TGA must have some type of connection between the two circulatory systems so that they can survive.
When babies are born they usually have a communication (opening) in the middle wall of the right and left atrium. This is called a patent foramen ovale. This opening helps get some of the oxygen-rich blood to the body unless it becomes obstructed or closes spontaneously. In addition, most babies have a patent ductus arteriosus, PDA, (open communication between the two main arteries of the heart), which may help raise the poor oxygen levels in these babies.
Babies with poor mixing of the two circulations usually become very ill and blue and may require immediate intervention and transfer to a surgical center. Some blue babies may benefit from medication to keep the PDA open. In addition, they may require balloon atrial septostomy to enlarge the patent foramen ovale and increase the amount of oxygen-rich blood delivery to the body.
Transposition of the great arteries may exist alone or in association with other heart defects such as a hole in the middle wall between the right and left chambers of the heart (ventricular septal defect or atrial septal defect), pulmonary stenosis, subaortic stenosis, Ebstein’s anomaly of the tricuspid valve, and others.
Transposition of the great arteries occurs during pregnancy while the baby’s heart is developing. In most cases, the cause is unknown. Some factors such as diabetes, maternal age over 40, alcohol consumption, poor nutrition, some illnesses, and in parents with a congenital heart defect may increase the risk of this condition.
A child born with Down syndrome also has an increased risk of having transposition of the great arteries (or other congenital heart defects).
Cyanosis (bluish skin)
Rapid and difficult breathing
Poor weight gain
Shortness of breath
Infants with simple TGA usually become critically ill and acidotic as the baby’s body is getting too little oxygen (hypoxia). Babies with TGA and large holes in the heart may develop heart failure.
Cardiovascular Tests and Diagnosis:
This heart defect may be missed by a screening fetal echocardiogram. Mothers with high risk factors such as diabetes may be referred to a high-risk obstetrician (perinatologist) for a more comprehensive fetal echocardiogram. Transposition of the great arteries may be detected by a more comprehensive fetal echocardiogram, which includes additional views of the heart and its major arteries.
After the baby is born, we may immediately suspect a heart defect such as this one if the baby is blue and having trouble breathing. A heart murmur may or may not be present. The cyanosis may become more obvious as the baby becomes more active or if the patent ductus arteriosus or patent foramen ovale becomes obstructed.
A physical examination is not enough to diagnose TGA. The following tests are helpful in the diagnosis of TGA:
Blood gases and pulse oximetry. These tests help us check the low levels of oxygen in the baby’s body.
Chest x-ray. Although a chest x-ray does not provide a definite diagnosis of TGA, it does help us to assess the heart’s shape and size as well as the lung fields and the position of the aorta and pulmonary artery.
Electrocardiogram (ECG). The ECG may not provide a definite diagnosis of TGA but allows us to assess the baby’s electrical activity in the heart each time it contracts.
Echocardiogram. The echocardiogram helps establish the diagnosis and identify associated heart defects, such as a hole in the heart, obstructions in the heart or the main arteries leaving the heart. In addition, it helps assess heart function and the size of the patent foramen ovale and patent ductus arteriosus.
Cardiac catheterization may be performed for complex cases of TGA or if a balloon atrial septostomy is required.
All infants with TGA will require some type of surgery. A medication called prostaglandin may be given prior to surgery to help keep open the patent ductus arteriosus. In some centers, an atrial septostomy is performed prior to surgery. This may help allow for the oxygen-rich blood to mix with the oxygen-poor blood and stabilize the baby.
Patients with TGA will benefit from surgery. There are several surgical options including the arterial switch operation or an atrial switch operation. An arterial switch operation is the surgery that surgeons most often use. The surgery is usually performed during the first two weeks of life. During the operation, the aorta and pulmonary arteries are moved to their normal positions: the aorta is connected to the left ventricle and the pulmonary artery is connected to the right ventricle. In addition, the coronary arteries are also reattached to the aorta. If the baby has a ventricular or atrial septal defect, those holes are usually closed during heart surgery. In some cases, the surgeon may choose not to close a small hole.
Some patients may benefit from a different type of surgery. A conduit may be inserted in more complex cases to redirect the blood flow or bypass an obstruction inside the heart.
Although the surgery may correct the main problem, the baby will need lifelong follow-up care with a cardiologist such as Dr. Villafañe who specializes in congenital heart defects. Patients may develop complications such as leaky valves, obstructions inside the heart or in the main arteries, irregular heartbeats, and, quite infrequently, a heart attack. Most patients require serial echocardiograms. In selected cases, a cardiac catheterization may be indicated. Patients with cyanotic congenital heart defects (blue babies) may eventually develop attention deficit disorder as well as behavioral problems and academic problems.
Most patients will lead a normal life, with limited or no restrictions to sports. A complete evaluation is usually performed on a case-by-case basis prior to cardiovascular clearance for participation in competitive sports.
The risks of pregnancy are usually low, but it depends on the type of surgery and any residual abnormalities. A cardiovascular assessment is recommended prior to any pregnancy. It should be kept in mind that babies born to parents with congenital heart defects might have a greater incidence of similar or other types of congenital heart defects as well. The risk of a miscarriage is about 25%. There is also a risk for delayed fetal growth.