Transposition of the Great Arteries (TGA)

What is transposition of the great arteries?

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Transposition of the great arteries is a congenital (present at birth) heart defect. Due to abnormal development of the fetal heart during the first 8 weeks of pregnancy, the large vessels that take blood away from the heart to the lungs, or to the body, are improperly connected.

Normally, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped through the aorta out to the 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 - the exact opposite of a normal heart's anatomy.

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• Oxygen-poor (blue) blood returns to the right atrium from the body, passes through the right atrium and ventricle, then goes into the misconnected aorta back to the body.
  
  
• Oxygen-rich (red) blood returns to the left atrium from the lungs, passes through the left atrium and ventricle, then goes into the pulmonary artery and back to the lungs.

Two separate circuits are formed - one that circulates oxygen-poor (blue) blood from the lungs back to the lungs, and another that recirculates oxygen-rich (red) blood from the body back to the body.

Other heart defects are often associated with TGA, and they actually may be necessary in order for an infant with transposition of the great arteries to live. An opening in the atrial or ventricular septum will allow blood from one side to mix with blood from another, creating "purple" blood with an oxygen level somewhere in-between that of the oxygen-poor (blue) and the oxygen-rich (red) blood. Patent ductus arteriosus (another type of congenital heart defect) will also allow mixing of oxygen-poor (blue) and oxygen-rich (red) blood through the connection between the aorta and pulmonary artery. The "purple" blood that results from this mixing is beneficial, providing at least smaller amounts of oxygen to the body, if not a normal amount of oxygen.

Because of the low amount of oxygen provided to the body, TGA is a heart problem that is labeled "blue-baby syndrome."

Transposition of the great arteries is the second most common congenital heart defect that causes problems in early infancy. TGA occurs in 5 to 7 percent of all congenital heart defects. Sixty to 70 percent of the infants born with the defect are boys.

What causes transposition of the great arteries?

Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality, or environmental exposure, causing heart problems to occur more often in certain families. Most of the time this heart defect occurs sporadically (by chance), with no clear reason for its development.

Why is transposition of the great arteries a concern?

Even when a good bit of mixing of oxygen-poor (blue) and oxygen-rich (red) blood can occur, other problems are present. The left ventricle, which in TGA is connected to the pulmonary artery, is the stronger of the two ventricles since it normally has to generate a lot of force to pump blood to the body. The right ventricle, connected to the aorta in TGA, is the weaker of the two ventricles. Because the right ventricle is weaker, it may not be able to pump blood efficiently to the body, and it will enlarge under the strain of the job. The left ventricle may pump blood into the lungs more vigorously than needed, leading to strain in the blood vessels in the lungs.

What are the symptoms of transposition of the great arteries?

The following are the other most common symptoms of TGA. However, each child may experience symptoms differently. Symptoms may include:

• rapid breathing
• labored breathing
• rapid heart rate
• cool, clammy skin

The symptoms of TGA may resemble other medical conditions or heart problems. Always consult your child's physician for a diagnosis.

How is transposition of the great arteries diagnosed?

Cyanosis is the major indication that there is a problem with your newborn. Your child's physician may have also heard a heart murmur during a physical examination. A heart murmur is simply a noise caused by the turbulence of blood flowing through the openings that allow the blood to mix.

Other diagnostic tests are needed to help with the diagnosis, and may include the following:

• chest x-ray - a diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
  
  
• electrocardiogram (ECG or EKG) - a test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle stress.
  
  
• echocardiogram (echo) - a procedure that evaluates the structure and function of the heart by using sound waves recorded on an electronic sensor that produce a moving picture of the heart and heart valves.
  
  
• cardiac catheterization - a cardiac catheterization is an invasive procedure that gives very detailed information about the structures inside the heart. Under sedation, a small, thin, flexible tube (catheter) is inserted into a blood vessel in the groin, and guided to the inside of the heart. Blood pressure and oxygen measurements are taken in the four chambers of the heart, as well as the pulmonary artery and aorta. Contrast dye is also injected to more clearly visualize the structures inside the heart.

Treatment for transposition of the great arteries:

• your child's age, overall health, and medical history
• extent of the disease
• your child's tolerance for specific medications, procedures, or therapies
• expectations for the course of the disease
• your opinion or preference

Your child will most likely be admitted to the intensive care unit (ICU) or special care nursery once symptoms are noted. Initially, your child may be placed on oxygen, and possibly even on a ventilator, to assist his/her breathing. Intravenous (IV) medications may be given to help the heart and lungs function more efficiently.

Other important aspects of initial treatment include the following:

• A cardiac catheterization procedure can be used as a diagnostic procedure, as well as initial treatment procedure for some heart defects. A cardiac catheterization procedure will usually be performed to evaluate the defect(s) and the amount of blood that is mixing.
  
  
• As part of the cardiac catheterization, a procedure called a balloon atrial septostomy may be performed to improve mixing of oxygen-rich (red) and oxygen-poor (blue) blood.
  
  
  • A special catheter with a balloon in the tip is used to create an opening in the atrial septum (wall between the left and right atria).
    
    
  • The catheter is guided through the foramen ovale (a small opening present in the atrial septum that closes shortly after birth) and into the left atrium.
    
    
  • The balloon is inflated.
    
    
  • The catheter is quickly pulled back through the hole, into the right atrium, enlarging the hole, allowing blood to mix between the atria.
    
    
• An intravenous medication called prostaglandin E1 is given to keep the ductus arteriosus from closing.

Within the first 1 to 2 weeks of age, transposition of the great arteries is surgically repaired. The procedure that accomplishes this is called a "switch," which roughly describes the surgical process.

The operation is performed under general anesthesia, and involves the following:

• The aorta is moved from the right ventricle to its normal position over the left ventricle.
  
  
• The pulmonary artery is moved from the left ventricle to its normal position over the right ventricle.
  
  
• The coronary arteries are moved so they will originate from the aorta and take oxygen-rich (red) blood to the heart muscle.
  
  
• Other defects, such as atrial or ventricular septal defects or a patent ductus arteriosus, are commonly closed.

Postoperative care for your child:

While your child is in the ICU, special equipment will be used to help him/her recover, and may include the following:

• ventilator - a machine that helps your child breathe while he/she is under anesthesia during the operation. A small, plastic tube is guided into the windpipe and attached to the ventilator, which breathes for your child while he/she is too sleepy to breathe effectively on his/her own. After a transposition of the great arteries, children will benefit from remaining on the ventilator overnight or even longer so they can rest.
  
  
• intravenous (IV) catheters - small, plastic tubes inserted through the skin into blood vessels to provide IV fluids and important medicines that help your child recover from the operation.
  
  
• arterial line - a specialized IV line is placed in the wrist or other area of the body where a pulse can be felt, that measures blood pressure continuously during surgery and while your child is in the ICU.
  
  
• nasogastric (NG) tube - a small, flexible tube that keeps the stomach drained of acid and gas bubbles that may build up during surgery.
  
  
• urinary catheter - a small, flexible tube that allows urine to drain out of the bladder and accurately measures how much urine the body makes, which helps determine how well the heart is functioning. After surgery, the heart will be a little weaker than it was before, and, therefore, the body may start to hold onto fluid, causing swelling and puffiness. Diuretics may be given to help the kidneys to remove excess fluid from the body.
  
  
• chest tube - a drainage tube may be inserted to keep the chest free of blood that would otherwise accumulate after the incision is closed. Bleeding may occur for several hours, or even a few days after surgery.
  
  
• heart monitor - a machine that constantly displays a picture of your child's heart rhythm, and monitors heart rate, arterial blood pressure, and other values.

Your child may need other equipment not mentioned here to provide support while in the ICU, or afterwards. The hospital staff will explain all of the necessary equipment to you.

Your child will be kept as comfortable as possible with several different medications; some which relieve pain, and some which relieve anxiety. The staff will also be asking for your input as to how best to soothe and comfort your child.

After discharged from the ICU, your child will recuperate on another hospital unit for a few days before going home. You will learn how to care for your child at home before your child is discharged. Your child may need to take medications for a while, and these will be explained to you. The staff will give you written instructions regarding medications, activity limitations, and follow-up appointments before your child is discharged.

Infants who spent a lot of time on a ventilator, or who were fairly ill while in the ICU, may have trouble feeding initially. These babies may have an oral aversion; they might equate something placed in the mouth, such as a pacifier or bottle, with a less pleasant sensation such as being on the ventilator. Some infants are just tired, and need to build their strength up before they will be able to learn to bottle feed. Strategies used to help infants with nutrition include the following:

• high-calorie formula or breast milk
  Special nutritional supplements may be added to formula or pumped breast milk that increase the number of calories in each ounce, thereby allowing your baby to drink less and still consume enough calories to grow properly.
  
  
• supplemental tube feedings
  Feedings given through a small, flexible tube that passes through the nose, down the esophagus, and into the stomach, that can either supplement or take the place of bottle-feedings. Infants who can drink part of their bottle, but not all, may be fed the remainder through the feeding tube. Infants who are too tired to bottle-feed at all may receive their formula or breast milk through the feeding tube alone.

Caring for your child at home following a TGA surgical repair:

If any special treatments are to be given at home, the nursing staff will ensure that you are able to provide them, or a home health agency may assist you.

You may receive additional instructions from your child's physicians and the hospital staff.

Long-term outlook after TGA surgical repair:

• fast, slow, or irregular heart rhythms
• leaky heart valves
• narrowing of one or both of the great arteries at the switch connection site(s)
• narrowing of the coronary arteries at their switch connection site

Consult your child's physician regarding the specific outlook for your child.

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