A congenital defect is one that is present from birth, and there are a variety of defects that can occur in the heart tissue or heart valves due to improper fetal growth, as well as problems with the closure of fetal vessels after birth. Congenital heart defects are usually recognized in infants shortly after birth because of the importance of circulation in sustaining life, and the change in palor that presents with cyanotic (lack of oxygen) defects. The Merck Manual for Healthcare Professionals reports that 1 of every 120 live births has a congenital heart defect, and they tend to form in the first 10 weeks of fetal life. Some of the more common congenital heart defects are discussed below.
Left-to-Right Shunt
A left-to-right shunt allows blood inside the heart to bypass being pumped through the aorta (to the body), but instead returns to the right side of the heart. This causes some of the oxygenated blood to continue circulating in the heart and pulmonary vessels instead of the body. The most common type of congenital heart disease is a left-to-right shunt caused by holes in the ventricular septum (the tissue between the left and right ventricles) due to defects in the membrane along the intraventricular ridge. The holes are sometimes asymptomatic and usually close spontaneously throughout childhood.
Another left-to-right shunt is the improper closing of the foramen ovale. The fetal heart is not identical to the heart of a child or adult. Because a fetus receives oxygen from the mother's circulation and does not use its lungs, the fetal circulation does not pass through the pulmonary vessels. Instead, a hole in the atrial septum, the wall between the right and left atria, allows blood to pass directly from the right side of the heart to the left side of the heart - the hole is called the foramen ovale. When a baby takes its first breath of air outside the womb, the pressure causes a flap to close over the foramen ovale. If this closure does not occur, or if it is incomplete, blood is able to seep through the atrial septal defect, resulting in a shunt.
The size of the shunt will determine if, and to what extent, symptoms occur. The pressure within the pulmonary artery or ventricle may increase, depending on the type of left-to-right shunt. High pressure in the ventricle could result in ventricular hypertrophy. High pressure in the pulmonary vessels can affect lung function.
Right-to-Left Shunt
A right-to-left shunt bypasses the pulmonary circulation and results in what is referred to as a "blue baby," that is, a lack of oxygen to the body results in cyanosis and the pink tinge is lost from the baby's complexion. The shunt occurs as either a transposition of the great vessels (aorta and pulmonary artery) or the Tetralogy of Fallot (see below), which is the most common cyanotic congenital heart defect. A hole in the heart (discussed above) results in a left-to-right shunt because the pressure in the left side of the heart is usually greater than the pressure in the right side of the heart.
Transposition of the great vessels occurs when the aorta and pulmonary artery end up being attached to the wrong side of the heart because they do not align (or twist, as they are in an arched formation) properly during growth. Deoxygenated blood is then pumped out through the aorta without making it through the pulmonary circulation or left ventricle.
The Tetralogy of Fallot
This disorder is so-named because it consists of four things: a ventricular septal defect; a septal defect with a dextraposed aorta overriding the ventricular septal defect, so the blood is pumped directly out of the heart from the right side; right ventricular hypertrophy, which is an enlarged right ventricle, often caused by increased workload; and a narrowed, and thus obstructed, pulmonary artery or valve, which would impair deoxygenated blood from getting to the lungs. These characteristics result in a cyanotic condition because blood cannot get to the lungs and is still pumped out to the body.
Other Defects of the Great Vessels
Another different between the fetal heart and the heart after birth is an extra vessel alongside the great vessels. The aorta and pulmonary artery align and twist around each other during gestation. The additional vessel is called the ductus arteriosus, and it usually constricts after birth in response to increased arterial oxygen. In healthy infants, the vessel is nonfunctional within 1 to 2 days of birth. Infants who experience hypoxia (a lack of oxygen) may have delayed closure, resulting in blood being shunted from the pulmonary artery to the aorta, exacerbating cyanosis and hypoxia. This is called patent ductus arteriosus, meaning that the vessel is persistent.
Another type of congenital defect is coarctation of the aorta, a narrowing of the vessel. The narrowing can also occur in adults, but the coarctation is preductal in infants, whereas, in adults, it is postductal. The narrowing of the vessel prevents the heart from properly pumping blood out to the body. There are also potential obstructions of the heart valves or vessels (called stenosis) that can prevent appropriate flow through, or out of, the heart.
Treatment of Congenital Heart Defects
Some congenital heart lesions, such as ventricular septal defects, heal on their own in the absence of other defects or disease. Other congenital lesions, and more severe cases, may require surgical intervention to correct the defect and restore proper circulation through the heart and lungs. A lack of blood oxygenation can lead to brain damage, other organ damage, and eventually death. The heart may attempt to compensate and be damaged if defects are not corrected in a timely manner. Sometimes the defects are obvious, like cyanosis, sometimes there are audible heart murmurs to clue doctors into the potential problem within the baby's chest. There may also be irregular rhythms or pain as the condition affects the heart over time. However, it is not always easy to know for sure that there is a problem with a baby's heart until it has advanced, so once identified by a doctor congenital heart defects are usually treated immediately,