Transposition of the great arteries

Definition

Transposition of the great arteries (TGA) is a birth defect causing a fatal condition in which there is a reversal, or switch, in the primary connections of the two main (great) blood vessels to the heart, the aorta and pulmonary artery.

Description

There are two great arteries that transport blood away from the heart, the pulmonary artery and the aorta. Normally, the pulmonary artery carries blood from the right ventricle to the lungs. The aorta carries blood from the left ventricle to the vessels of the rest of the body.

Ordinarily, blood returning to the heart is depleted in oxygen. It goes first to the right atrium of the heart and then to the right ventricle where it is pumped to the lungs. While in the lungs, the blood picks up more oxygen. After the lungs, the blood flows to the left atrium, then the left ventricle pumps the blood out through the aorta to the rest of the body, thereby supplying the body with oxygenated blood.

In children with transposition of the great arteries, the connection of the two great arteries is reversed. This condition causes oxygen depleted blood to be circulated to the body because the aorta is connected to the right ventricle. Blood returning to the heart goes to the right atrium and ventricle, and then it goes into the aorta for distribution throughout the body instead of to the lungs to be oxygenated. At the same time, blood in the lungs goes to the left atrium, the left ventricle, but then back to the lungs rather than going to the body because the pulmonary artery is connected to the left ventricle. The result is that highly oxygenated blood keeps recycling through the lungs, while oxygen-depleted blood recycles through the body without going through the lungs to reoxygenate. The body cannot survive without oxygenated blood.

This condition occurs during the fetal development and must be treated promptly after birth if the newborn is to survive. The newborn can survive for a few days while the foramen ovale, a small hole in the septum that separates the two atria, is open, allowing some oxygenated blood to escape and mix into the blood that is being pumped throughout the body. However, within a few days after birth, the foramen ovale normally closes, and no oxygenated blood is available for the body.

Demographics

Transposition of the great arteries affects 20 to 30 of every 100,000 live births each year. It is the most common reason for cyanotic heart disease in newborns accounting for 5 to 7 percent of all infants with congenital heart disease . Transposition of the great arteries is most often an isolated defect and is not associated with other congenital syndromes. It affects males more than females with 60 to 70 percent of all cases occurring in males. It does not affect any race or nationality more than another.

Causes and symptoms

Transposition of the great arteries is a birth defect that occurs during fetal development. There is no identifiable disease or cause. The main symptom is a cyanotic or blue baby appearance, caused by a general lack of oxygen in the body's tissues.

Diagnosis

Diagnosis is made immediately after birth, when it is observed that the newborn has a bluish color. A definite diagnosis is made by x ray, electrocardiography (ECG), and echocardiography.

Treatment

Transposition of the great arteries may be treated by the use of medications called prostaglandins which keep the ductus arteriousus open. A procedure called a cardiac catheterization can then be performed during which a small thin tube (catheter) with a balloon tip, may be used to enlarge the opening between the two atria until surgery can be performed. However, both procedures are temporary treatments that help prolong the infant's life, in some cases allowing him or her to gain strength, until surgery can be performed. The only permanent solution for this condition is open-heart surgery. In transposition of the great arteries repair surgery, the infant's heart is stopped, and blood is circulated through the body using a mechanical heart-lung machine. The two great arteries are reconnected to their proper destination. This correction restores the normal blood flow pattern. The coronary arteries are also reconnected, so that they can supply blood to the heart itself.

Prognosis

Left untreated, this disease is fatal within the first weeks of life. After surgical repair, the survival rate is 90 percent, and most individuals grow and develop normally.

Prevention

Because there is no identifiable cause, there is no way to prevent this condition.

KEY TERMS

Aorta —The main artery located above the heart that pumps oxygenated blood out into the body. The aorta is the largest artery in the body.

Atrial —Referring to the upper chambers of the heart.

Cyanosis —A bluish tinge to the skin that can occur when the blood oxygen level drops too low.

Echocardiography —A non-invasive technique, using ultrasound waves, used to look at the various structures and functions of the heart.

Electrocardiagram (ECG, EKG) —A record of the electrical activity of the heart, with each wave being labeled as P, Q, R, S, and T waves. It is often used in the diagnosis of cases of abnormal cardiac rhythm and myocardial damage.

Foramen ovale —The foramen ovale is a fetal cardiac structure that allows the blood in both upper chambers (atria) of the heart to mix. After birth, the pressure rises in the left atrium pushing this opening closed, allowing the heart to function in a two-sided fashion: the right side carries the unoxygenated blood to the lungs, and the left side pumps the oxygenated blood out into the body.

Oxygenate —To supply with oxygen.

Pulmonary artery —An artery that carries blood from the heart to the lungs.

Ventricles —The lower pumping chambers of the heart. The ventricles push blood to the lungs and the rest of the body.

Parental concerns

Transposition of the great arteries is a complex congenital malformation; however, open heart surgery is highly effective in correcting it. Most children have an excellent outcome and a normal healthy life. For most children, activity level, appetite, and growth eventually return to normal. Open heart surgery to repair transposition of the great arteries is usually performed within the first days or weeks of life.

After the child's heart surgery parents should follow all instructions given by the healthcare team. Most children continue to be seen by a team of doctors including the pediatrician, cardiologist, and pediatric cardiac surgeon.

When to call the doctor

Following open heart surgery, parents should call the doctor if any of the following occurs:

fever of 101.5 (38.6°C) or higher
swelling or puffiness around the child's eyes, arms, or legs
redness or swelling, cloudy yellow drainage, or an opening at the incision site
rapid breathing
increased fatigue or tiredness
dry cough that was not present before surgery
decreased appetite or refusal to eat
increased pain

Resources

WEB SITES

Charpie, John R. "Transposition of the great arteries." eMedicine , October 27, 2004. Available online at http://www.emedicine.com/ped/topic2548.htm (accessed November 7, 2004).

"Transposition of the Great Arteries." Children's Hospital Boston. Available online at http://www.childrenshospital.org/cfapps/A2ZtopicDisplay.cfm?Topic=Transposition+of+the+Great+Arteries (accessed November 7, 2004).

John T. Lohr, PhD Deborah L. Nurmi, MS