What are Congenital Heart Defects?

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 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 body's tissues and organs use up the oxygen, 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 health care provider 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 provider 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 (inability of the heart to pump out all the blood that returns to it, leading to fluid build-up in the heart, lungs and other parts of the body). An affected child may experience a rapid heartbeat and breathing difficulties, especially during exercise. Infants may experience these difficulties during feeding, sometimes resulting in inadequate weight gain. Affected infants and children also may have swelling of the legs or abdomen or around the eyes.

Some heart defects result in a pale grayish or bluish coloring of the skin called cyanosis. This usually appears soon after birth or during infancy. On occasion, cyanosis 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 tests are used to diagnose heart defects?

Babies and children who are suspected of having a heart defect are usually referred to a pediatric cardiologist (children's heart disease specialist). This doctor will do a physical examination and often recommend one or more tests. These tests often include a chest X-ray, an electrocardiogram (which records heart rate patterns) and an echocardiogram (a special form of ultrasound that uses sound waves to take pictures of the heart). All of these tests are painless and non-invasive (nothing enters the child's body). Some children with heart disease also may need to undergo a procedure called cardiac catheterization. In this procedure, a thin, flexible tube is inserted into the heart after the child is given medications to make him sleepy. This test provides detailed information about the heart and how it is working.

What causes congenital heart defects?

In most cases, scientists do not know what makes a baby's heart develop abnormally. Both environmental and genetic factors appear to play roles.

A few environmental factors are known to contribute to congenital heart defects. 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, as may exposure to certain industrial chemicals (solvents) (1, 3). Drinking alcohol in pregnancy also can increase the risk of heart defects, as may cocaine (3).

Certain medications increase the risk. These include the acne medication isotretinoin (Accutane and other brand names), lithium (used to treat certain forms of mental illness) and certain anti-seizure medications (3).

Certain chronic illnesses in the mother may contribute to the risk. For example, women with diabetes are at increased risk of having a baby with a heart defect (3). However, women with diabetes can reduce their risk by seeing their health care provider before pregnancy to make sure their blood sugar levels are well controlled. Women with an inherited error of body chemistry called phenylketonuria (PKU) also are at high risk of having an affected baby, unless they follow a special diet before and during pregnancy (4). Some studies suggest that women who do not consume enough of the B vitamin folic acid before and during the early weeks of pregnancy may be at increased risk of having a baby with a heart defect (3).

Scientists are making progress in understanding the genetics of heart defects. Since the 1990s, they have identified several gene mutations (changes) that can cause heart defects. For example, a March of Dimes grantee discovered a series of genetic steps that appears to contribute to a common, important group of malformations affecting the heart's outflow tract (5). He also identified a gene that can cause a heart defect called an atrial septal defect (a hole between the upper chambers of the heart) and one that may contribute to hypoplastic left heart syndrome (underdevelopment of the heart's main pumping chamber) (6, 7).

Heart defects also can be part of a wider pattern of birth defects. For example, about one-half of children with the chromosomal abnormalities Down syndrome (mental retardation and physical birth defects) and Turner syndrome (short stature and lack of sexual development) have heart defects (8). Children with Down syndrome, Turner syndrome 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), velocardiofacial (craniofacial defects and immune deficiencies), and Holt-Oram (limb defects) syndromes (9).