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Transposition of the Great Arteries

Definition :
Transposition of the great arteries is a heart defect present at birth (congenital), in which the two main arteries leaving the heart are reversed (transposed). In transposition of the great arteries, these two arteries — the aorta and the pulmonary artery — are connected to the wrong chambers of the heart.

In a normal circulatory system, oxygen-depleted blood returns from your body to the right side of your heart and is pumped through the pulmonary arteries to your lungs. In your lungs, your blood receives oxygen, is returned to the left side of your heart and is pumped back to the rest of your body.

In transposition of the great arteries, the systems of blood circulation are reversed. Oxygen-poor blood circulates through the right side of the heart and then is pumped to the aorta instead of the pulmonary artery. This "blue blood" is circulated throughout the body and gives a bluish cast to the skin. Oxygen-rich blood circulates through the left side of the heart and back into the lungs without going to the rest of the body.

All babies born with transposition of the great arteries must have some type of connection (shunt) between the two circulatory systems to survive. Surgery within the first several weeks of life is usually necessary to correct transposition of the great arteries. With corrective surgery and ongoing care, most children born with transposition of the great arteries survive to adulthood.

Causes :
Your heart has four chambers. Normally, the pulmonary artery is attached to the lower right chamber (right ventricle). The pulmonary artery carries oxygen-poor blood from your heart to be enriched with oxygen in your lungs. From your lungs, the oxygen-rich blood goes to the heart's upper left chamber (left atrium), through the mitral valve into the lower left chamber (left ventricle). The aorta is normally attached to the left ventricle. It carries oxygen-rich blood out of your heart back to the rest of
your body.

In transposition of the great arteries, the aorta is connected to the right ventricle and the pulmonary artery is connected to the left ventricle. Transposition of the great arteries results in oxygen-poor blood circulating through the right side of the heart and back to the body without passing through the lungs. Oxygen-rich blood circulates through the left side of the heart and back into the lungs without going to the rest of the body.

Oxygen-poor blood circulating to the body causes the skin to have a blue tint (cyanosis). Because of this, transposition of the great arteries is called a congenital cyanotic heart defect. Transposition of the great arteries is the most common cyanotic heart defect, accounting for about 10 percent of all cases of congenital heart defects.

One or more connections needed
In order to survive, infants with transposition of the great arteries must have an additional heart defect — such as a hole in the wall between the chambers of the heart (ventricular septal defect or atrial septal defect) or a connection between the aorta and the pulmonary artery (patent ductus arteriosus) — that allows some mixing of oxygen-rich blood with the oxygen-poor blood. Some babies will need medications to keep these connections open or a procedure to create or enlarge an atrial septal defect to increase the amount of oxygen delivered to the body.

Transposition of the great arteries occurs during fetal growth when the baby's heart is developing. Although some factors, such as rubella or other viral illnesses during pregnancy, maternal age over 40 or diabetes, may increase the risk of this condition, in most cases the cause is unknown.

Risk Factor :
Although the exact cause of transposition of the great arteries is unknown, several factors may increase the risk of a baby being born with this condition. These include :

  • A mother who had rubella (German measles) or another viral illness during pregnancy
  • A parent who had transposition of the great arteries or another congenital heart defect
  • Poor nutrition during pregnancy
  • Excessive alcohol consumption during pregnancy
  • A mother older than 40
  • A mother who has diabetes

Children born with Down syndrome, a genetic condition resulting from an extra 21st chromosome, also are at increased risk of having transposition of the great arteries and other congenital heart defects.

When to seek medical advice :
Seek medical help if you notice that your baby has the following Symptoms:

  • Blue coloration of the skin
  • Shortness of breath
  • Lack of appetite
  • Poor weight gain

Symptoms :
Typical signs and symptoms of transposition of the great arteries include :

  • Blue color of the skin
  • Shortness of breath
  • Lack of appetite
  • Poor weight gain

Diagnosis :
After your baby is born, his or her doctor may immediately suspect a heart defect such as transposition of the great arteries if your baby has blue-tinged skin or if your baby is having trouble breathing. If your baby has a large atrial or ventricular septal defect, the blood may have enough oxygen initially that the bluish skin color won't be very noticeable. But, as your baby becomes more active, eventually the cyanosis will become obvious. Your baby's doctor may also suspect a heart defect if he or she hears a heart murmur — an abnormal whooshing sound caused by turbulent blood flow.

A physical exam alone isn't enough to diagnose transposition of the great arteries, however. One or more of the following tests are necessary for an accurate Diagnosis:

  • Echocardiography. Echocardiograms use sound waves that bounce off your baby's heart and produce moving images that can be viewed on a video screen. Doctors use this test to diagnose transposition of the great arteries by assessing the position of the aorta and the pulmonary artery. Echocardiograms can also identify associated heart defects, such as a ventricular septal defect or an atrial septal defect.
  • Chest X-ray. X-rays produce pictures by passing an X-ray beam through a structure of the body. The beam is absorbed in different amounts by body structures. Although a chest X-ray doesn't provide a definitive diagnosis of transposition of the great arteries, it does allow the doctor to assess your baby's heart size and see the position of the aorta and pulmonary artery.
  • Electrocardiogram. An electrocardiogram records the electrical activity in the heart each time it contracts. During this procedure, patches with wires (electrodes) are placed on your baby's chest, wrists and ankles. The electrodes measure electrical activity, which is recorded on paper.
  • Cardiac catheterization. During this procedure, the doctor inserts a thin flexible tube (catheter) into an artery or vein in your baby's groin and weaves it up to his or her heart. A dye is injected through the catheter to make your baby's heart structures visible on X-ray pictures. The catheter also measures pressure in the chambers of the heart and in the blood vessels.

Complications :
Potential complications of transposition of the great arteries include :

  • Lack of oxygen to tissues. Your baby's tissues may be getting too little oxygen (hypoxia).
  • Congestive heart failure. Unless there's some mixing of oxygen-rich blood and oxygen-poor blood within the body, congestive heart failure — a condition in which the heart can't pump enough blood to meet the body's needs — will develop.
  • Pulmonary vascular obstructive disease. This condition causes damage to the lungs, making breathing difficult.

Without corrective surgery, transposition of the great arteries is fatal in most cases within the first six months of life.

Babies who have surgery to correct transposition of the great arteries sometimes have the following associated conditions later in life :

  • Leaky heart valves
  • Problems with the arteries that supply the heart muscle with blood (coronary arteries)
  • Heart rhythm abnormalities (arrhythmias)
  • Decline in function of the heart muscle or heart valves

Treatment:
All infants with transposition of the great arteries require surgery to correct the defect.

Before surgery
Your baby's doctor may recommend several options to help manage the condition before corrective surgery. They include :

  • Medication. The medication prostaglandin E1 helps keep open the ductus arteriosus — a connection between the aorta and pulmonary artery — to increase blood flow and improve mixing of oxygen-poor and oxygen-rich blood.
  • Atrial septostomy. This procedure — usually done using cardiac catheterization rather than surgery — makes bigger a natural connection between the heart's atria. It allows for the oxygen-rich and oxygen-poor blood to mix and results in improved oxygen delivery to the body.

Surgery
Surgical options include :

  • Arterial switch operation. This is the surgery that doctors most often use to correct transposition of the great arteries. Doctors usually perform this surgery within the first month of life.

    During an arterial switch operation, the pulmonary artery and the aorta are moved to their normal positions: the pulmonary artery connected to the right ventricle and the aorta connected to the left ventricle. The coronary arteries also are reattached to the aorta.

    If your baby has a ventricular septal defect or an atrial septal defect, those holes usually are closed during surgery. In some cases, however, the doctor may leave small ventricular septal defects to close on their own.

  • Atrial switch operation (Mustard or Senning operation). In this surgery, the surgeon makes a tunnel (baffle) between the heart's two upper chambers (atria). This diverts the oxygen-poor blood to the left ventricle and the pulmonary artery and the oxygen-rich blood to the right ventricle and the aorta. With this procedure, the right ventricle must pump blood to the entire body, instead of just to the lungs as it would do in a normal heart.

    The atrial switch was used frequently beginning in the 1960s. Since the 1980s, however, it has been largely replaced by the arterial switch operation because the latter is not associated with many of the long-term complications of the atrial switch, such as arrhythmias, baffle obstructions or leaks, and problems with right ventricle function.

After surgery
After corrective surgery, your baby will need lifelong follow-up care with a heart doctor (cardiologist) who specializes in congenital heart disease to monitor his or her heart health. The cardiologist may recommend that your child limit physical activity. Your child will need to take antibiotics before dental procedures and other surgical procedures to prevent infections.

Many people who undergo the arterial switch operation don't need additional surgery. However, some complications, such as arrhythmias, heart valve leaks or problems with the heart's pumping, may require treatment.

Prevention:
In most cases, transposition of the great arteries cannot be prevented. If you have a family history of heart defects or if you already have a child with a congenital heart defect, before getting pregnant consider talking with a genetic counselor and a cardiologist experienced in congenital heart defects.

 
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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