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Congenital Heart Defects
More than 32,000 infants (one out of every 125 to 150) are born with heart defects each year in the United States. The defect may be so slight that the baby appears healthy for many years after birth, or so severe that its life is in immediate danger.
Heart defects are among the most common birth defects, and are the leading cause of birth defect-related deaths. However, advances in diagnosis and surgical treatment over the past 40 years have led to dramatic increases in survival for children with serious heart defects. Between 1987 and 1997, the death rates from congenital heart defects dropped 23 percent.
What is a congenital heart defect?
A condition is called congenital when it is present at birth. Heart defects originate in the early part of pregnancy when the heart is forming. Congenital heart defects can affect any of the different parts or functions of the heart.
How does the heart work?
The heart is a muscle that pumps blood to the body. It is divided into four hollow parts called chambers. Two chambers are located on the right side of the heart, and two are on the left.
Within the heart are four valves (one-way openings) that let the blood go forward and keep it from going back. Blood goes from the heart to the lungs where it picks up oxygen. The blood carrying oxygen, which appears bright red, goes back to the heart. The heart then pumps the oxygen-rich blood through the body by way of arteries. As the oxygen is used up by the body's tissues and organs, the blood becomes dark and returns by way of veins to the heart, where the process starts over again.
How do heart defects affect a child?
Some babies and children with heart defects experience no symptoms. The heart defect may be diagnosed if the doctor hears an abnormal sound, referred to as a murmur. Children with normal hearts also can have heart murmurs. These are called "innocent" or "functional" murmurs. A physician may suggest tests to rule out a heart defect.
Certain heart defects prevent the heart from pumping adequate blood to the lungs or other parts of the body. This can cause congestive heart failure. An affected child may experience a rapid heartbeat and breathing difficulties, especially during exercise (or in infants, during feeding—sometimes resulting in inadequate weight gain). Swelling of the legs or abdomen or around the eyes also may occur.
Some heart defects result in a pale grayish or bluish coloring of the skin (called cyanosis), usually appearing soon after birth or during infancy. On occasion, it may be delayed until later in childhood. It is a sign of defects that prevent the blood from getting enough oxygen. Children with cyanosis may tire easily. Symptoms such as shortness of breath and fainting often worsen when the child exerts himself. Some youngsters may squat frequently to ease their shortness of breath.
What causes congenital heart defects?
In most cases, scientists do not know what makes a baby's heart develop abnormally. Both genetic and environmental factors appear to play roles.
Among the few environmental factors known to contribute to congenital heart defects are a virus and certain drugs. Women who contract rubella (German measles) during the first three months of pregnancy have a high risk of having a baby with a heart defect. Other viral infections also may contribute.
Certain medications also increase the risk. These include the acne medication Accutane, lithium (used to treat certain forms of mental illness) and, possibly, certain anti-seizure medications. Drinking alcohol in pregnancy also can increase the risk of heart defects—babies with fetal alcohol syndrome (FAS) often have them. Studies also suggest that use of cocaine in pregnancy increases the risk of these birth defects.
Certain chronic illnesses in the mother also can increase the risk of heart defects. For example, women with diabetes are at increased risk of having a baby with a heart defect, although this risk can be reduced or eliminated if the diabetes is closely controlled, starting before pregnancy. Women with an inborn error of body chemistry called phenylketonuria (PKU) also are at high risk of having a baby with a heart defect, unless they follow a special diet before pregnancy and during the first trimester. Several studies suggest that women who do not consume enough of the B vitamin folic acid before and during the early weeks of pregnancy are at increased risk of having a baby with a heart defect.
While most families have no more than one child with a heart defect, these malformations are more likely to occur in siblings or offspring of people who have heart defects than in unaffected families. This fact has long suggested that genetics plays a role in heart defects, at least in those families. In fact, scientists have recently discovered more than 100 mutations (changes) in more than a dozen genes that directly impair the heart. Many of these mutations cause cardiomyopathy (enlargement of the heart) or heart rhythm disturbances that can be fatal in childhood, adolescence or adulthood.
However, scientists also have pinpointed several mutations that affect the formation of the heart, leading to congenital heart malformations. For example, in 1999 a March of Dimes grantee at the University of Texas Southwestern Medical Center in Dallas discovered a gene that appears to contribute to a common, important group of malformations affecting the heart’s outflow tract and the blood vessels arising from it. Researchers at Harvard Medical School identified a gene responsible for the heart defect called atrial septal defect (a hole between the upper chambers of the heart) in four families with multiple members affected by heart disease. The same researchers also identified another gene mutation that causes atrial septal defects accompanied by arm and hand malformations (Holt-Oram syndrome).
Researchers appear to be on the brink of discovering the genes that underlie numerous heart defects. They have recently identified several genes that direct development of the embryonic heart in mice. This should greatly improve our understanding of these genes’ human counterparts—and possibly lead to ways to prevent the various heart defects that mutations of those genes may cause.
Heart defects also can be part of a wider pattern of birth defects. For example, more than one-third of children with the chromosomal abnormality Down syndrome (characterized by mental retardation and physical birth defects) have heart defects, as do about a quarter of girls with another chromosomal abnormality called Turner syndrome (short stature, lack of sexual development and other problems). In fact, approximately 10 percent of children with heart defects have a chromosomal abnormality. Children with Down, Turner and certain other chromosomal abnormalities should be routinely evaluated for heart defects. Heart defects also are common in children with a variety of inherited disorders, including: Noonan (short stature, learning disabilities), Alagille (liver and other problems), Marfan (skeletal and eye defects) and Williams (mental retardation) syndromes.
How are congenital heart defects treated?
The outlook has never been brighter for babies and children with congenital heart defects. Today, most heart defects can be corrected, or at least helped, by surgery, medicine or devices such as artificial valves and pacemakers.
In the last 30 years, advances in treatment of heart defects have enabled nearly 1 million U.S. children with significant heart defects to survive into adulthood. Half the children who require surgical repair of a heart defect now undergo surgery before age two. Until fairly recently, it was often necessary to make temporary repairs and postpone corrective surgery until later in childhood. Early corrective surgery often prevents development of additional complications and allows the child to live a more normal life sooner. Some of the most common defects include:
- Patent ductus arteriosus. Before birth, much of a fetus’s blood goes through a passageway (ductus arteriosus) from one blood vessel to another instead of through the lungs, because the lungs are not yet in use. The passageway should close soon after birth, so the blood can take the normal route from heart to lungs and back. If it doesn't close, blood doesn't flow correctly. This problem occurs most frequently in premature babies. In some cases, drug treatment can help close the passageway. If that doesn't work, surgery can close it.
- Septal defects. If the defect is a hole in the wall (septum) that divides the two upper or two lower chambers, the blood can't circulate as it should and the heart has to work too hard. A surgeon can close the hole by sewing or patching it. Small holes may heal by themselves or not need repair at all.
- Coarctation of the aorta. Part of the aorta, the large artery that sends blood from the heart to the rest of the body, may be too narrow for the blood to flow evenly. A surgeon can cut away the narrow part and sew the open ends together, replace the constricted section with man-made material, or patch it with part of a blood vessel taken from elsewhere in the body. Sometimes, this narrowed area can be widened by inflating a balloon on the tip of a catheter inserted through an artery.
- Heart valve abnormalities. Some babies are born with heart valves that do not close normally or are narrowed, closed or blocked and prevent blood from flowing smoothly. Surgeons usually can repair the valves or replace them with man-made ones. Balloons on catheters also are frequently used to fix faulty valves.
- Tetralogy of Fallot. A combination of four heart defects keeps some blood from getting to the lungs, so that a baby has episodes of cyanosis and may grow poorly. New surgical techniques allow early repair of this complex heart defect, so that most affected children live normal or near-normal lives.
- Transposition of the great arteries. Here, the positions of the two major arteries leaving the heart are reversed, so that each arises from the wrong pumping chamber. Recent surgical advances have enabled correction of this otherwise lethal defect in the early newborn period.
- Hypoplastic left heart syndrome. A combination of defects results in a left ventricle (the heart’s main pumping chamber) that is too small to support life. This defect is the most common cause of death from congenital heart disease. New surgical procedures and heart transplants have begun to save some of these babies, but the long-term outlook for these babies remains uncertain.
Children and adults with certain heart defects, even after surgical repair, remain at increased risk of infection involving the heart and its valves. Parents of children with heart defects and adults with repaired heart defects should discuss with their doctor whether they need to take antibiotics before certain dental and surgical procedures in order to prevent these infections.
Is there a prenatal test for congenital heart defects?
A special form of sonography (looking at the fetus by means of sound waves) called echocardiography can accurately identify many heart defects. If certain heart problems, such as a heart that is beating too fast or too slowly, are diagnosed before birth, medications may restore a normal heart rhythm before the fetal heart starts to fail. In other cases, where the heart defect can't be treated before birth, knowing that it exists enables doctors to be ready to give the baby the treatment it needs as soon as it is born.
Can congenital heart defects be prevented?
While most congenital heart defects cannot yet be prevented, there are some steps a woman can take that may help reduce her risk of having a baby with a heart defect. A woman should be tested prior to pregnancy for immunity to rubella, and vaccinated if she is not immune. Pregnant women should avoid alcohol and unprescribed drugs. Those with chronic health conditions such as diabetes, seizure disorders and PKU should consult their doctors before they attempt to conceive so that their medications and/or diets can be adjusted. Any woman who could become pregnant should take a multivitamin containing 400 micrograms of folic acid daily to reduce the risk of serious birth defects of the brain and spinal cord and, possibly, other birth defects including heart defects.
Genetic counselors can tell parents of affected children roughly what the chances are that any future child of theirs will have a heart defect. Siblings of an affected child are slightly more likely than other children to have the same kind of heart defect as their brother or sister. In some cases, if the affected child's heart defect is part of a syndrome of other defects, the recurrence risk may be higher. Parents who themselves have a heart defect also are at increased risk of having a child with a heart defect.
What research is under way on congenital heart defects?
Scientists funded by the March of Dimes are among many who are trying to learn more about the causes of heart defects, so that they can develop better ways of preventing and treating them. For example, several March of Dimes grantees are studying genes that may underlie specific heart defects. While nearly all heart defects are attributed to interactions of unknown genes with usually unknown environmental factors, few causal genes have yet been linked with specific heart defects. Grantees also are seeking to develop better ways to treat babies with serious heart defects.
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