What is congenital heart disease?

Causes and Symptoms

Congenital heart disease
includes various structural and functional defects of the heart and blood vessels resulting from errors that occur during
embryonic development. The defects may cause heart murmurs, high or low blood pressure, congestive heart failure, cyanosis (blue skin), abnormal heart rhythms and rates, and incidences of low oxygen (hypoxia). Congenital heart disease is detected in about 0.7 percent of live births and more than 10 percent of stillbirths. Some babies born with congenital heart disease have difficulty during the first few weeks of life. Some problems, however, are not easily detected at the time of birth and are discovered at various stages of life. Heart defects may be inherited from parents, induced by environmental agents such as drugs, or caused by an interaction of genetic and environmental factors. Defects are more common in children with genetic disorders such as Down syndrome. With intensive treatment, including surgery, many forms of congenital heart disease can be corrected, allowing those affected to lead normal lives.

Knowledge of normal heart development will help in understanding how congenital heart disease occurs and will provide a means for categorizing these defects. Near the end of the third week of embryonic development, the heart begins to form from two cords of tissue that hollow out and fuse to form a primitive heart tube. This tube undergoes some constrictions and dilations to form the early divisions of the heart, including a receiving chamber, the atrium, and a pumping chamber, the ventricle, which exits into a muscular tube called the truncus arteriosus. At about twenty-two days, the heart begins to contract and pump blood. A day later, it bends or loops upon itself to form an S shape, with the atrium on one side, the truncus arteriosus on the other side, and the ventricle in the middle. If it bends to the left instead of to the right, a rare heart defect called dextrocardia results. The heart will be displaced to the right side of the body and may have some accompanying abnormalities.

During the fourth and fifth week of development, the heart begins to divide into four chambers by first forming a septum (dividing membrane) in the canal between the atrium and the ventricle. This septum is formed by heart tissue called the endocardial cushions. Failure of this septum to form properly causes atrioventricular canal defects. These are often associated with Down syndrome. During the fifth week of development, a spiral septum forms in the truncus arteriosus that divides it into two vessels: the
pulmonary artery, which connects to the right ventricle, and the aorta, which connects to the left ventricle. The formation of this septum and the ventricular connections are subject to error and may result in a group of anomalies called conotruncal defects.

As these large arteries are forming, a shunt (bypass) develops between them called the ductus arteriosus. This short vessel allows the blood to be diverted away from the nonfunctional fetal lungs into the aorta and on to the placenta, where it will receive oxygen and nutrients. Persistence of this shunt after birth is responsible for a defect called patent ductus. A septum dividing the atrium into right and left halves also forms during the fourth and fifth weeks of development; however, blood is allowed to pass from the right atrium to the left atrium through a small hole in this septum called the foramen ovale. This hole normally closes after birth but is necessary during fetal life to shunt blood away from the fetal lungs and toward the placenta in a manner similar to that of the ductus arteriosus. At about the same time, a septum forms from the floor of the ventricle and divides it into right and left halves. Failure of the atrial and ventricular septa to form properly and to close at the time of birth results in septal defects.

After the appearance of the four chambers, two pairs of valves form in the heart to prevent the backflow of blood and to ensure greater efficiency in pumping. The semilunar valves (also called the pulmonary and aortic valves) form between the ventricles and their respective outlet arteries (pulmonary artery and aorta), and the atrioventricular valves (bicuspid or mitral on the left and tricuspid on the right) form between the atria and the ventricles. Improperly formed valves can lead to flow defects. During development, the heart also makes connections with veins returning from the general
circulation and the lungs. Errors in these connections and other structural errors cause several other less common congenital heart defects.

The most common congenital heart defects are the septal defects and patent ductus, which together account for about 37 percent of all heart defects. After birth, because the pressure becomes higher in the left side of the heart, blood moves from left to right through the openings in the heart that come with such defects, causing too much to flow to the lungs and a mixing of systemic and pulmonary blood. The child’s lungs will be congested, causing difficulty in breathing and eventually heart failure.

About 29 percent of congenital heart defects are categorized as right-heart and left-heart flow defects. These defects impede the flow of blood from either the right or the left side of the heart to its normal destination. Right-heart flow defects include bicuspid pulmonary valve (a valve with two cusps instead of three), pulmonary valve
stenosis (a narrowing of the valve), dysplastic pulmonary valve (a malformed valve), peripheral pulmonary stenosis (a narrowing of the walls of the pulmonary artery), infundibular pulmonary stenosis (a narrowing below the valve), and hypoplastic right ventricle (incomplete formation of the valve). These defects impede blood flow to the lungs, which results in poor oxygenation of the blood (cyanosis). Left-heart flow defects include bicuspid aortic valve, aortic valve stenosis, coarctation of the aorta (narrowing), aortic atresia (a blocked aorta), and hypoplastic left ventricle. These defects impede blood flow to the body and often result in altered blood pressure, hypoxia of body tissues, and congestive heart failure.

The principal conotruncal defects, which account for about 17 percent of heart defects, are tetralogy of Fallot and transposition of the great arteries. Tetralogy of Fallot includes four defects that result in cyanosis: pulmonary stenosis, a ventricular septal defect, an overriding or displaced aorta, and hypertrophy or enlargement of the right ventricle. With transposition of the great arteries, the aorta connects to the right ventricle and the pulmonary artery to the left ventricle, the opposite of the normal formation. The blood is not properly oxygenated, and survival is not possible without medical intervention or a natural shunt such as patent ductus. Other rare conotruncal defects include double outlet right ventricle (the aorta and the pulmonary artery attached to right ventricle), truncus
arteriosus (failure of the truncus to separate into the aorta and the pulmonary artery), and aortopulmonary window (an opening between the aorta and the pulmonary artery).

Defects resulting from improper fusion of the endocardial cushions and surrounding tissues cause atrioventricular defects, which affect about 9 percent of congenital heart disease cases. Complete atrioventricular canal defect occurs in about 20 percent of Down syndrome cases, but it is rare outside this group. The defect produces a large open space in the center of the heart, allowing blood to intermix freely between the right and left sides of the heart. The defect is sometimes accompanied by hypoplastic ventricle. If the condition is not treated, the heart will fail. Patent foramen primum or ostium primum is a milder form of atrioventricular canal defect in which the atrial septum fails to fuse with the endocardial cushions, resulting in a problem similar to atrial septal defect. In addition, the mitral valve is usually deformed.

Other less common defects include looping defects such as dextrocardia, in which the apex of the heart points to the right instead of to the left. This change in symmetry normally does not affect heart function, but some looping defects are associated with other problems such as transposition of the great arteries. Another less common defect is anomalous venous return, in which the veins returning blood to the heart from the lungs attach to the right atrium or return to the right atrium by attaching to other large veins rather than to the left atrium. Errors in the coronary artery connections may also occur, causing poor circulation of blood to the heart muscles. Very rarely, the heart may protrude through the chest wall at birth, causing a difficult-to-treat problem called ectopia cordis.

Treatment and Therapy

Congenital heart disease can often be diagnosed shortly after birth, especially if the baby experiences certain symptoms such as cyanosis, shortness of breath, fatigue and sweating while eating, and inability to gain weight. A physical examination by a physician will include checking the heart and breathing rates for abnormalities and listening to the heart for possible murmurs. Heart murmurs are whooshing sounds caused by turbulent movement of blood that may indicate faulty valves, patent ductus, and other heart defects. A cardiologist will make the definitive diagnosis by administering such tests as the electrocardiogram, the Doppler-echocardiogram, and the cardiac catheterization. The electrocardiogram measures the rhythmic electrical signal that passes through the heart with each beat. An abnormal signal will often indicate problems with a particular region of the heart and is especially useful in identifying rhythm disorders. The echocardiogram produces visual images of the heart by sending out ultrasound waves that bounce off and return to a receiving device. Most structural heart defects can be detected with this technique, and many are discovered prenatally with routine fetal ultrasound monitoring. At the same time, a second receiving device (the Doppler) analyzes ultrasound signals from blood moving through the heart and is able to provide information about the speed and direction of blood flow within the heart. This helps detect abnormal functions such as reverse blood flow. The Doppler-echocardiogram has revolutionized congenital heart disease diagnosis and, in most cases, provides enough information to define the patient’s problem accurately.

If the cardiologist believes it to be necessary, then further tests can be done. A chest X-ray may be taken to determine if there is any lung involvement in the disorder. Cardiac catheterization can add information about the internal heart blood pressures and blood oxygen levels and can help visualize some defects better with the administration of contrast dyes in combination with X-ray analysis. Special monitors can be used to record the electrocardiogram for one or two days to check for intermittent rhythm irregularities, and older children can be monitored while exercising to see how the heart performs under stress. These and other tests allow physicians to assess the seriousness of the problem and to recommend timely and appropriate treatment.

Serious heart malformations need to be treated immediately upon diagnosis. Often these include defects that cause cyanosis, including transposition of the great arteries, left-heart flow defects such as coarctation of the aorta, and defects that cause heart failure, such as truncus arteriosus. Immediate emergency surgery may be needed to save the life of the newborn infant. Additional follow-up surgeries may also be required to correct the defect completely. For example, one way of correcting transposition of the great arteries is by performing an atrial switch operation in which systemic blood returning from the body is diverted to the left side of the heart (so it can be pumped to the lungs) and pulmonary blood from the lungs is diverted to the right side of the heart (so it can be pumped to the body). This is accomplished by first enlarging the foramen ovale with a balloon catheter, a procedure called Rashkind balloon atrial septostomy. A second operation several months later enlarges the opening between the two atria further and installs a flap to enhance the cross flow of blood. This is known as a Mustard or Senning atrial switch operation. A more recently developed procedure for correcting this defect requires only one operation. The
misplaced aorta and pulmonary artery are both cut and then reattached to the correct heart chamber; this is called a Jatene arterial switch operation. At the same time, the coronary arteries are moved to the new aorta.

Some defects require no surgery but can be treated with drugs and other less traumatic procedures, such as the
balloon catheter. Drugs are also used to help improve heart performance before and after surgery. When fluid accumulates in the lungs or other body tissues, the heart has problems pumping all the blood that returns to it because of the congestion. The overworked heart suffers under this stress, and thus the condition is called congestive heart failure. Diuretics such as Lasix (furosemide) improve the kidneys’ ability to remove the excess fluid and relieve the congestion. Another drug, digitalis, can be helpful in treating congestive heart failure by slowing the heart rate and causing the heart to beat more forcefully. An open ductus is beneficial to children born with cyanotic heart defects because it allows a more even distribution of oxygenated blood. Treatment with prostaglandin E1 helps to keep the ductus open until corrective surgery can be performed. Indomethacin has the opposite effect and is often used to promote closing of a patent ductus in premature babies. As in adults, drugs such as digitalis, beta-blockers, and calcium channel blockers can be used to treat abnormal heart rhythms (arrhythmia) in children with congenital heart disease. The
balloon catheter is used to enlarge narrow vessels and passages and has been used successfully to treat pulmonary and aortic valve stenosis in a technique called balloon valvuloplasty.

Types of surgery done later in infancy or childhood include closed-heart operations such as repair of a patent ductus and partial treatment of some types of cyanosis with a Blalock-Taussig shunt (connecting the subclavian artery to the pulmonary artery to bring more blood to the lungs).
Open-heart surgery is used to repair defects inside the heart such as septal defects. A heart-lung machine is used to bypass the heart and lungs while the operation is under way, and the body is cooled so that the brain and other tissues require less oxygen. Children with very serious heart defects such as hypoplastic right or left ventricles may require a series of corrective surgical operations, and for some the only hope is a heart transplant. For example, children with hypoplastic right ventricle are given a Blalock-Taussig shunt shortly after birth to improve blood flow to their lungs and then are later given the Fontan operation, which involves closing off the Blalock-Taussig shunt and connecting the pulmonary artery to the right atrium so that blood returning from the body will flow directly to the lungs, completely bypassing the defective right ventricle.

Some heart defects require no treatment. For example, most small septal defects close on their own during the first one or two years of life. Also, mild disorders such as benign valve defects usually require no treatment, and many children with heart murmurs have no detectable problems.

Perspective and Prospects

In the late nineteenth and early twentieth centuries, physicians were beginning to understand that certain congenital heart defects such as patent ductus could be diagnosed by listening to the heart. Treatment, however, was not possible at that time. The Atlas of Congenital Cardiac Disease was published in 1936 by Maude Abbot of McGill University. This manual greatly assisted physicians in recognizing and diagnosing congenital heart disease. In 1939, Robert Gross of Boston repaired a patent ductus, and in 1944, Alfred Blalock and Helen Taussig developed and performed their shunt operation in order to treat children with tetralogy of Fallot. Open-heart surgery was not performed until the mid-1950s, when the heart-lung machine was perfected. Even then, open-heart surgery could be performed only on older children. These operations were pioneered by Walton Lillehei of the University of Minnesota and John Kirlin of the Mayo Clinic. Open-heart surgery on newborn infants was developed in the 1970s by Brian Barratt-Boyes of New Zealand.

During the period while heart surgery was being developed, cardiac catheterization was also advancing. It was used primarily for diagnosis, but in 1966, William Rashkind of Philadelphia began to use the balloon catheter to enlarge openings in the atrial septum in order to treat transposition of the great arteries. Microsurgical catheters are currently being developed to repair patent ductus and other heart defects without the need for major surgery. The echocardiogram was pioneered by Inge Edler in the 1950s, and the Doppler-echocardiogram came into widespread use as a diagnostic tool in the 1980s. This instrument has greatly reduced the need for other diagnostic tests that were used in the past.

The modern strategy for treatment of congenital heart defects is to perform the corrective surgery as early in infancy as possible. This eliminates the need for numerous hospitalizations and diagnostic tests and reduces the need for extensive drug treatment. Children with multiple defects may still need more than one surgery. Modern treatment also emphasizes the roles of the child, the family, and health care personnel in fostering an understanding of the condition, treatment, and outcome. Even children who have been successfully treated will sometimes have physical limitations. These children need to be encouraged and supported by their families and allowed to pursue their goals to the fullest extent possible. Overcoming congenital heart disease is now possible for the vast majority of those who are afflicted.

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