Transposition of great vessels

Definition

Congenital heart disease includes a variety of malformations of the heart or its major blood vessels that are present at the birth of a child.

Description

Congenital heart disease occurs when the heart or blood vessels near the heart do not develop properly before birth. About eight out of every 1,000 newborns have congenital heart disease, which is the most frequent congenital malformation. About half of these cases require medical treatment. More than 500,000 patients with congenital heart disease in the United States have reached adulthood. Some of these had mild types of congenital heart disease, but most needed surgery in order to survive. Patients who had surgery are likely to experience other cardiac problems later in life. Congenital heart disease is also called congenital heart defect.

Most types of congenital heart disease obstruct the flow of blood in the heart or the vessels near it, or cause an abnormal flow of blood through the heart. Rarer types of congenital heart disease occur when the newborn has only one ventricle, when the pulmonary artery and the aorta come out of the same ventricle, or when one side of the heart is not completely formed.

Patent ductus arteriosus

When the temporary blood vessel connecting the left pulmonary artery to the aorta in the fetus does not close in the newborn, some of the blood that should flow through the aorta returns to the lungs. Patent ductus arteriosus is common in premature babies, but rare in full-term babies. It has also been associated with mothers who had German measles (rubella) while pregnant.

Hypoplastic left heart syndrome

Hypoplastic left heart syndrome, where the left side of the heart is underdeveloped, is rare, but it is the most serious type of congenital heart disease. In this situation, blood reaches the aorta, which pumps blood to the entire body, only from the ductus, which then normally closes within a few days of birth. In hypoplastic left heart syndrome, the baby seems normal at birth, but as the ductus closes, blood cannot reach the aorta and circulation fails.

Obstruction defects

When heart valves, arteries, or veins are narrowed, they partly or completely block the flow of blood. The most common obstruction defects are pulmonary valve stenosis, aortic valve stenosis, and coarctation of the aorta. Bicuspid aortic valve and subaortic stenosis are less common.

Stenosis is a narrowing of the valves or arteries. In pulmonary stenosis, the pulmonary valve does not open properly, forcing the right ventricle to work harder. In aortic stenosis, the improperly formed aortic valve is narrowed. As the left ventricle works harder to pump blood through the body, it becomes enlarged. In coarctation of the aorta, the aorta is constricted, reducing the flow of blood to the lower part of the body and increasing blood pressure in the upper body.

A bicuspid aortic valve has only two flaps, instead of three, which can lead to stenosis in adulthood. Subaortic stenosis is a narrowing of the left ventricle below the aortic valve, which limits the flow of blood from the left ventricle.

Septal defects

When a baby is born with a hole in the septum (the wall separating the right and left sides of the heart), blood leaks from the left side of the heart to the right. A major leakage can lead to enlargement of the heart and failing circulation. The most common types of septal defects are atrial septal defect, an opening between the two upper heart chambers, and ventricular septal defect, an opening between the two lower heart chambers.

Cyanotic defects

Heart disorders that cause a decreased, inadequate amount of oxygen in blood pumped to the body are called cyanotic defects. Cyanotic defects, including tetralogy of Fallot, transposition of the great arteries, and tricuspid atresia, result in a blue discoloration of the skin due to low oxygen levels. About 10% of cases of congenital heart disease in the United States are tetralogy of Fallot, which includes four defects. The major defects are a large hole between the ventricles, which allows oxygen-poor blood to mix with oxygen-rich blood, and narrowing at or beneath the pulmonary valve. The other defects are an overly muscular right ventricle and an aorta that lies over the ventricular hole.

In transposition (reversal of position) of the great arteries, the pulmonary artery and the aorta are reversed, causing oxygen-rich blood to re-circulate to the lungs while oxygen-poor blood goes to the rest of the body. In tricuspid atresia, the baby lacks a triscupid valve and blood cannot flow properly from the right atrium to the right ventricle.

Causes & symptoms

In most cases, the causes of congenital heart disease cannot be identified. Genetic and environmental factors, and lifestyle habits can all be involved. The likelihood of having a child with a congenital heart disease increases if the mother or father, another child, or another relative had congenital heart disease. Viral infections, such as German measles, can produce congenital heart disease. Many cases of congenital heart disease result from the mother's excessive use of alcohol or taking illegal drugs, such as cocaine, while pregnant. The mother's exposure to certain anticonvulsant and dermatologic drugs during pregnancy can also cause congenital heart disease. There are some genetic conditions, such as Down's syndrome, which affect multiple organs and can cause congenital heart disease.

Symptoms of congenital heart disease in general include: shortness of breath, cyanosis (bluish discoloration of the skin), heart murmur, respiratory infections that recur excessively, stunted growth, and limbs and muscles that are underdeveloped.

Symptoms of specific types of congenital heart disease are as follows:

• Patent ductus arteriosus: quick tiring, slow growth, susceptibility to pneumonia, rapid breathing. If the ductus is small, there are no symptoms.
• Hypoplastic left heart syndrome: ashen color, rapid and difficult breathing, inability to eat.
• Obstruction defects: cyanosis (skin that is discolored blue), chest pain, tiring easily, dizziness or fainting, congestive heart failure, and high blood pressure.
• Septal defects: difficulty breathing, stunted growth. Sometimes there are no symptoms.
• Cyanotic defects: cyanosis, sudden rapid breathing or unconsciousness, and shortness of breath and fainting during exercise.

Diagnosis

Echocardiography and cardiac magnetic resonance imaging are used to confirm congenital heart disease when it is suggested by the symptoms and physical examination. An echocardiograph will display an image of the heart that is formed by sound waves. It detects valve and other heart problems. Fetal echocardiography is used to diagnose congenital heart disease in utero. Cardiac magnetic resonance imaging, a scanning method which uses magnetic fields and radio waves, can help physicians evaluate congenital heart disease, but is not always necessary.

Treatment

Congenital heart disease is treated with drugs and/or surgery. Drugs used include diuretics, which aid the baby in excreting water and salts, and digoxin, which strengthens the contraction of the heart, slows the heartbeat, and removes fluid from tissues. Surgical procedures seek to repair the defect as much as possible and restore circulation to as close to normal as possible. Sometimes, multiple surgical procedures are necessary. Surgical procedures include: arterial switch, balloon atrial septostomy, balloon valvuloplasty, Damus-Kaye-Stansel procedure, Fontan procedure, pulmonary artery banding, Ross procedure, shunt procedure, and venous switch or intra-atrial baffle. Children with congenital heart disease require lifelong monitoring, even after successful surgery.

Arterial switch, to correct transposition of the great arteries, involves connecting the aorta to the left ventricle and connecting the pulmonary artery to the right ventricle. Balloon atrial septostomy, also done to correct transposition of the great arteries, enlarges the atrial opening during heart catheterization. Balloon valvuloplasty uses a balloon-tipped catheter to open a narrowed heart valve, improving the flow of blood in pulmonary stenosis. It is sometimes used in aortic stenosis. Transposition of the great arteries can also be corrected by the Damus-Kaye-Stansel procedure, in which the pulmonary artery is cut in two and connected to the ascending aorta and the farthest section of the right ventricle. For tricuspid atresia and pulmonary atresia, the Fontan procedure connects the right atrium to the pulmonary artery directly or with a conduit, and the atrial defect is closed. Pulmonary artery banding, narrowing the pulmonary artery with a band to reduce blood flow and pressure in the lungs, is used for ventricular septal defect, atrioventricular canal defect, and tricuspid atresia. Later, the band can be removed and the defect corrected with open-heart surgery. To correct aortic stenosis, the Ross procedure grafts the pulmonary artery to the aorta. For tetralogy of Fallot, tricuspid atresia, or pulmonary atresia, the shunt procedure creates a passage between blood vessels, sending blood into parts of the body that need it. For transposition of the great arteries, venous switch creates a tunnel inside the atria to re-direct oxygen-rich blood to the right ventricle and aorta and venous blood to the left ventricle and pulmonary artery.

Prognosis

The outlook for children with congenital heart disease has improved markedly in the past two decades. Many types of congenital heart disease that would have been fatal can now be treated successfully. Research on diagnosing heart defects when the fetus is in the womb may lead to future treatment to correct defects before the baby is born.

Prevention

Congenital heart disease cannot be predicted and most types cannot be prevented. General measures to ensure the birth of a healthy baby, such as avoiding excess alcohol, not taking drugs, and avoiding exposure to rubella and environmental toxins, will help prevent some cases.

Key Terms

Aorta

The main artery which pumps blood through the body. Many congenital heart defects affect the aorta.

Congenital

Refers to physically abnormal conditions that are present at birth. Congenital heart disease includes a variety of defects that babies are born with.

Cyanotic

Marked by bluish discoloration of the skin due to a lack of oxygen in the blood. It is one of the types of congenital heart disease.

Ductus

The blood vessel that joins the pulmonary artery and the aorta. When the ductus does not close at birth, it causes a type of congenital heart disease called patent ductus arteriosus.

Hypoplastic

Incomplete development or underdevelopment of the heart. Hypoplastic left heart syndrome is the most serious type of congenital heart disease.

Septal

Relating to the septum, the thin muscle wall dividing the right and left sides of the heart. Holes in the septum are called septal defects.

Stenosis

A narrowing or constriction--in this case, of various heart valves. Stenosis reduces or cuts off the flow of blood. It is one of the types of congenital heart disease.

Further Reading

For Your Information

Books

• DeBakey Michael E, and Antonio Gotto, Jr. "Congenital Abnormalities of the Heart." In The New Living Heart. Holbrook, MA: Adams Media Corporation, 1997.
• Texas Heart Institute. "Congenital Heart Disease." In Texas Heart Institute Heart Owner's Handbook. New York: John Wiley & Sons, 1996.
• Warnes, Carole A. "Congenital Heart Disease: The Scope of the Problem." In Mayo Clinic Practice of Cardiology, Third Edition. St. Louis: Mosby, 1996.

  Periodicals

• "Congenital Heart Defects." USA Today Magazine 125(February 1997): 13.
• Kleinert, Sabine. "Routine Prenatal Screening for Congenital Heart Disease." Lancet 348(September 28, 1996): 836.

  Organizations

• American Heart Association. National Center. 7272 Greenville Avenue, Dallas, TX 75231-4596. (214) 373-6300. http://www.medsearch.com/pf/profiles/amerh/.
• Congenital Heart Anomalies Support, Education & Resources, Inc. 2112 North Wilkins Road, Swanton, OH 43558. (419) 825-5575. http://www.csun.edu/~hfmth006/chaser/.
• Congenital Heart Disease Information and Resources. 1561 Clark Drive, Yardley, PA 19067. http://www.tchin.org/.
• Texas Heart Institute Heart Information Service. P.O. Box 20345, Houston, TX 77225-0345. 800-292-2221. Http://www.tmc.edu/thi/his.html.

Gale Encyclopedia of Medicine. Gale Research, 1999.