In transposition of the great arteries, the two major arteries leaving the heart are connected to the wrong ventricles, the two lower chambers of the heart. The result is that blood containing oxygen from the lungs is pumped back into the lungs, while blood that lacks oxygen, which is necessary to nourish the body, is pumped throughout the body.
To understand transposition of the great arteries, it helps to understand the healthy heart and how it functions. The heart consists of four chambers: the two upper chambers, called atria, where blood enters the heart, and the two lower chambers, called ventricles, where blood is pumped out of the heart. The flow between the chambers is controlled by a set of valves that act as one-way doors.
Normally blood is pumped from the right side of the heart through the pulmonary valve and the pulmonary artery to the lungs, where the blood is filled with oxygen. From the lungs, the blood travels back down to the left atrium and left ventricle. The newly oxygenated blood then is pumped through another big blood vessel, called the aorta, to the rest of the body.
A baby with transposed arteries is cyanotic - the medical term for bluish discoloration of the skin because of deficient oxygenation of the blood - shortly after birth. The blueness doesn't go away even if the baby is given extra oxygen. For a baby with transposed arteries to survive, blood flow between the right and left sides of the heart must be increased.
Sometimes, other heart abnormalities may temporarily minimize the problem caused by this condition. For example, an atrial septal defect (ASD), an abnormal hole between the two atrial chambers, or a ventricular septal defect (VSD), an abnormal hole between the two ventricles, will allow blood to circulate between the two sides of the heart.
If the VSD is an alternate route for blood flow, the baby may actually get too much blood in the lungs. The baby won't be blue but may begin to suffer from congestive heart failure and show symptoms of rapid breathing, poor feeding and sweating.
Another abnormality that could provide some short-term relief is a patent ductus arteriosus (PDA) that doesn't close normally after birth. The PDA is a connection between the aorta and pulmonary arteries that exists while a baby is in the womb and doesn't use its lungs. The PDA usually closes shortly after birth.
Permanent treatment requires a surgical procedure to switch the arteries to their proper places.
Symptoms of transposition of the great arteries include:
- Bluish colored skin (cyanosis)
- Shortness of breath
- Poor weight gain
- Poor feeding
A complete transposition usually is diagnosed shortly after birth due to the baby's increasing blue coloration or cyanosis. There may or may not be a heart murmur or extra sound in the heartbeat.
Tests used to make a diagnosis may include:
'Early treatment is aimed at maintaining blood circulation. A medication called prostaglandin may be used to keep the ductus arteriosus - the connection between the aorta and pulmonary arteries that normally closes after birth - open.
Another procedure, called an atrial septostomy, may be used to enlarge an atrial septal defect. In this procedure, performed in our Cardiac Catheterization Laboratory, a thin plastic tube called a catheter is inserted into a blood vessel in the groin and then directed to the heart and the site of the foramen ovale. A balloon on the tip of the catheter is inflated and then pulled back to enlarge the hole.
Permanent treatment requires a surgical procedure to switch the arteries to their proper places. This operation, called an arterial switch operation, is done within the first few weeks of life. It is an open-heart procedure that requires a temporary stopping of the baby's heart while a heart-lung machine handles respiration and blood circulation. Any abnormal holes between the ventricles or atria also are closed.
As part of the procedure, the coronary arteries - the arteries that supply blood to the heart - have to be taken off their normal position on the aorta and transplanted into the new "aorta" that now carries oxygenated blood from the left ventricle around the body. Rarely, this may be lead to problems that require further procedures.