Pediatric Heart Disease Great Arteries Transposition

Transposition of the great arteries is a congenital heart defect that affects four out of every 10,000 births. If a child is born with transposition of the great arteries, the two main blood vessels leading out of the heart have switched positions.

Without treatment, 50 percent of infants with transposition of the great arteries will die within the first month of life. Ninety percent of untreated cases prove fatal within a year.

Overview of Transposition of the Great Arteries

The heart pumps blood into two major arteries, the aorta and the pulmonary arteries. In healthy hearts, the left ventricle pumps oxygen-rich blood into the aorta that carries oxygenated blood to the body. Simultaneously, the right ventricle pumps venous (unoxygenated) blood into the pulmonary artery to return oxygen-poor blood to the lungs.

When transposition of the great arteries occurs, the aorta is attached to the right ventricle, and the pulmonary artery is attached to the left ventricle. Transposition of the great arteries creates two closed circulation systems, dangerously impeding blood flow. Instead of being returned to the lungs, oxygen-depleted blood is returned to the body through the aorta while oxygen-rich blood is pumped back to the lungs through the pulmonary artery.

Transposition of the Great Arteries: The Figure Eight

To understand the effect of transposition of the great arteries, imagine a figure eight. As long as the two loops of the figure eight are connected, passage from one loop to the other is possible. However, if the two loops are separated, the process is reduced to two circles that are each completely self-contained.

Simply speaking, this is what transposition of the great arteries does to blood circulation: It divides the circulatory system into two separate units.

Transposition of the Great Arteries in Newborns

If transposition of the great arteries results in two separate blood systems, how can an infant live long enough to undergo treatment?

Fortunately, elements of the newborn heart do allow some mixing of oxygen-rich and oxygen-poor blood. If sufficient mixing occurs, the child’s body receives enough oxygen to survive temporarily. Possible avenues for the mixing of oxygenated and unoxygenated blood include:

  • Heart Defects: Congenital heart defects, such as atrial septal defect and ventricular septal defect, may allow some mixing of oxygenated and unoxygenated blood. Such heart defects can co-exist with transposition of the great arteries. For example, ventricular septal defect causes a hole in the wall between the right and left ventricle where blood from one ventricle can mix with blood from the other. Ventricular septal defect occurs in approximately a quarter of all transposition of the great arteries cases.
  • The Ductus Arteriosus: Babies are born with an extra blood vessel, the ductus arteriosus, which connects the pulmonary artery and the aorta. The ductus arteriosus allows some mixing of oxygenated and unoxygenated blood in the event of transposition of the great arteries. However, within two to three days of birth, the ductus arteriosus usually closes, cutting off this passage as a possible way for oxygenated and unoxygenated blood to mix.

Transposition of the Great Arteries Symptoms

Symptoms of transposition of the great arteries are usually apparent within hours of birth. Along with rapid breathing due to low levels of blood oxygen, babies will display symptoms of severe cyanosis, a condition in which the skin appears blue due to insufficient oxygenation.

In some cases, cyanosis may not develop until the ductus arteriosus closes. Once this happens, cyanotic symptoms appear quickly.

Ironically, the presence of other heart defects may allow for safe oxygen levels in the blood despite the presence of transposition of the great arteries. If this occurs, symptoms may appear for months until congestive heart failure becomes severe enough to cause symptoms.

Diagnosing Transposition of the Great Arteries

Newborns with severe cyanosis routinely receive supplemental oxygen, as cyanosis is often caused by lung disorders. However, supplemental oxygen will not improve cyanosis caused by transposition of the great arteries. Continued cyanosis in spite of supplemental oxygen suggests this condition is the result of an underlying heart defect.

An echocardiogram is the most common tool used to confirm transposition of the great arteries. Echocardiograms, tests that use sound waves to construct an image of the heart and arteries, detect transposition of the great arteries. They can also be used to confirm co-morbid (simultaneously existing) heart defects, such as ventricular septal defect.

Treatments for Transposition of the Great Arteries

Surgical correction of transposition of the great arteries is essential for survival. Yet, before surgery, blood oxygen levels must be stabilized. Treatment will include intravenous administration of prostaglandin to prevent the ductus arteriosus from closing.

Remember, initial surgery is usually a temporary solution: Permanent surgical correction can wait until the child is slightly older and stronger.

Initial treatment sometimes begins by creating an artificial heart defect. All babies are born with a hole in the wall separating the left and right atrium, called the foramen ovale. As part of transposition of the great arteries treatment, the foramen ovale can be enlarged to promote circulation of oxygen-rich blood.

A procedure called balloon atrial septostomy enlarges the foramen ovale, creating an atrial septal defect. The balloon atrial septostomy positions a small balloon in the foramen ovale by means of a catheter. The balloon is then inflated, expanding the foramen ovale to encourage blood flow between the two atria. Balloon atrial septostomy has the potential to restore oxygen levels to 80 percent of normal levels.

After temporary treatments restore near normal oxygen levels, permanent surgical correction should occur as soon as possible, often within a week of the initial treatment. An atrial switch is a serious procedure that severs the two great arteries to reattach them to the correct ventricles.

Transposition of the Great Arteries Treatment Outcomes

Transposition of the great arteries treatment has over a 95 percent success rate, barring secondary health conditions. In a few cases, pulmonary stenosis (a narrowing of the pulmonary artery) may develop after surgery, requiring additional surgical treatment.

While the long-term outcomes of treatment are generally positive, long-term care by a pediatric cardiologist is essential for children who have undergone successful transposition of the great arteries treatment. Periodic physical exams and tests increase the chance of identifying any heart condition before it becomes serious.

Resources

American Heart Association (n.d.). Transposition of the great arteries (TGA). Retrieved September 17, 2007, from the AHA Web site: www.americanheart.org/presenter.jhtml?identifier=1682.

Cincinnati Children’s’ Hospital Medical Center (n.d.). Transposition of the great arteries. Retrieved September 17, 2007, from the Cincinnati Children’s’ Hospital Medical Center Web site: www.cincinnatichildrens.org/health/heart-encyclopedia/anomalies/transposition.htm.

MedlinePlus Medical Encyclopedia (2004). Transposition of the great vessels. Retrieved September 17, 2007, from the U.S. National Library of Medicine Web site: www.nlm.nih.gov/medlineplus/ency/article/001568.htm.