The most commonly seen defects at birth are congenital heart defects (CHD). These anomalies arise when there is a failure of the heart or its major blood vessels to form properly during embryonic and/or fetal growth and development.
They may range from simple holes in the cardiac septum, or narrow valves, to more complex defects like tetralogy of Fallot (ToF), which is a combination of four distinct defects. In the United States, CHD affects about 1% of the infants born per year, and roughly 25% of these babies will have a serious CHD.
There are at least 18 different types of CHD recognized as of now. Of these, ventricular septal defects (VSDs) are the most common. Most infant deaths from CHD occur within the neonatal period. In fact, one study found that CHD account for 4.2% of all deaths in neonates.
An infant’s chances of survival are dependent on the severity of the CHD, the time before it is diagnosed, and the success of treatment. Approximately 95% of children with a non-critical CHD will survive past their eighteenth birthday. This number is significantly reduced to around 70% in those with a critical CHD.
Among the simple CHD are septal defects. These arise due to holes in the walls of the heart that create communications, which cause oxygen-rich and oxygen-poor blood to mix. Atrial septal defects (ASD) and VSD are the two main types of septal defects.
ASD occur in approximately 2 in every 1000 infants and are found between the two upper chambers of the heart, namely, the right and left atria. Many children with ASD often do not have many symptoms, if any at all, and about half of these children will have the ASD close over time on its own.
VSD occur in the two lower chambers of the heart ( the ventricles) and also allow the mixing of oxygen-deficient and oxygen-rich blood. There is normally a difference in pressures between the left and right ventricles of the heart, with the left being under higher pressure than the right.
This is because the left ventricle has to pump blood to the entire body, while the right ventricle only pumps blood to the lungs and does not require as much force to do so.
When there is a hole in the ventricles, not only is the body being robbed of the full load of oxygen-rich blood being pumped from the left ventricle, but the higher pressure from the left ventricle is also transmitted to the right ventricle. This can cause pathological enlargement of the right ventricle as well as higher pressure in the lungs, sufficient to cause damage to the pulmonary vasculature.
Smaller VSD, like ASD, may close on their own, but larger ones need to be closed surgically. Untreated symptomatic VSD can eventually lead to heart failure and death.
Another example of a simple CHD is patent ductus arteriosus (PDA). This condition is rather common and occurs when there is an abnormally persisting communication between the pulmonary artery and the aorta. These two vessels physiologically communicate in utero via the ductus arteriosus, which is vital in the fetal circulation to allow the nonfunctioning lungs to develop.
The communication closes within three days after birth, but may remain patent in some babies. This again allows oxygen-rich and oxygen-poor blood to mix, and an increase in pulmonary pressure.
In addition to holes in the cardiac wall and vessels, valves may also be abnormal in simple CHD. Valves are important for preventing the backflow of blood. Those that do not close tightly enough cause a condition that is referred to as regurgitation. In contrast, stenosis occurs when valves are not able to open fully. It is as a result of valves leaflets fusing together, stiffening, thickening, or narrowing.
Pulmonary stenosis is the most common valvular defect. Another type of valve defect is atresia, which is more complex than simple and occurs due to malformation or the valve lacking an opening for the passage of blood.
Of the complex CHD, ToF is the most common. It consists of a combination of four major defects, namely, a VSD, pulmonary stenosis, overriding aorta and hypertrophy of the right ventricle. The latter refers to an abnormal increase in the muscle mass of the right ventricle, because it has to work much harder than it physiologically should. Overriding aorta is when the aorta originates at the VSD between the right and left ventricles.
ToF disrupts the normal oxygenation of blood in the lungs, and it causes oxygen-deficient blood to be pumped to the rest of the body.
Infants may also have another CHD, which is known as complete atrioventricular canal defect. Here there is a hole spanning all of the heart’s four chambers. Just as serious, children may be born with transposition of the great arteries, which is the reversal of the normal anatomical position of the aorta and pulmonary artery.
This leads to an interruption in blood flow to the lungs or body. Ebstein’s anomaly, a failure in the tricuspid valve that is usually accompanied by an ASD, is yet another complex CHD.
Other types of complex CHD include coarctation of the aorta, truncus arteriosus and anomalous pulmonary venous connection (APVC). Infants with coarctation of the aorta have a narrowing of this great vessel, and there is a disruption in the free flow of blood to the body.
Truncus arteriosus occurs when there is one common great arterial trunk as opposed to two separate arteries supplying blood to the body and lungs. APVC causes oxygen-rich blood to enter the wrong chamber, because the veins from the lungs are incorrectly connected. Surgery is required to correct all complex CHD.