CONGENITAL HEART DISEASE: CYANOTIC CHDs AND OTHERS
The heart is composed of specialized muscles that pump blood between the lungs and the rest of the body (through blood vessels). This allows for a proper flow of oxygen, nutrients, and waste products. Other than four chambers, the heart also has four valves separating its four chambers and connections with the pulmonary artery and the aorta.
In the United States, nearly one fourth of all cases of congenital defects involve the heart. The exact cause of congenital heart defects (CHDs) is unknown, as these develop before a child is born. Some CHDs are benign and usually diagnosed late in childhood or even at adulthood, while serious and severe forms exhibit symptoms within the first few months of life.
For an in-depth introduction to congenital heart defects, please see (CHD article #1).
For information on diagnosis of CHDs and on acyanotic defects, please see (CHD article #2).
Cyanotic CHDs
Congenital heart defects are categorized mainly by the presence of a bluish discoloration over the skin and mucous membranes, called cyanosis. This discoloration is due to insufficient amounts of oxygen circulating around the body. Not all CHDs cause cyanosis, but severe congenital heart defects may still be seen in both cyanotic and acyanotic heart disease.
Tetralogy of Fallot
Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect in newborns who survive beyond the first month of life. It is unique in the sense that it is a combination of four specific defects. It is one of critical CHDs that will need surgical management.
In TOF, first defect is a hole between the left and right ventricles, called a ventricular septal defect. The second defect is a narrowing of either the pulmonary valve or the pulmonary artery. The pulmonary valve allows unoxygenated blood to flow from the right ventricle to the pulmonary artery. In the third defect, the aorta communicates with not just the left ventricle, but the right ventricle as well. Typically, the aorta receives oxygenated blood from the left ventricle. This mixing of blood from both ventricles causes an overall decrease in oxygen that circulates around the body. Lastly, the fourth defect is partly caused by the first three defects: because of additional strain on the right ventricle, its muscular wall becomes thicker to accommodate the extra volume and pressure.
Newborns with TOF may also have a patent ductus arteriosus (PDA) to help with handling blood flow. In addition, mild cases of TOF may not have as much trouble with blood flow coming from the right ventricle. As a result, some newborns may not have cyanosis at birth, and are diagnosed weeks to months later.
Besides cyanosis, children may have difficulty breathing when actively playing or in exercise, clubbed toes and fingers and dusky skin. Within the first few years of life, these infants and toddlers are prone to hypoxic spells (“blue” or “tet” spells) that are usually triggered by dehydration or agitation: episodes of cyanosis and severely decreased oxygen levels that leads to deep breathing and gasping, restlessness, and eventually loss of consciousness (also known as syncope). Although very rare, severe spells can cause convulsions or death. These episodes consume much energy, leaving affected individuals weak and sleepy afterwards.
Tet spells may be halted with the help of medical treatment. The following three steps may be done in order:
1. place the child in a knee-chest position and help them calm down
2. provide oxygen support
3. administer morphine via injection
Fluids given through an intravenous (IV) line and other medications may also help in terminating a tet spell. Healthcare providers may decide if these are still needed on a case-to-case basis.
In babies who are diagnosed with TOF within the first few days of life, prostaglandin may be given before they undergo surgical treatment. Depending on the extent of the defects, surgery may be extended in to a two-stage repair. Because of the nature of the defects involved, there is also a chance that reoperation will be needed within the next 3 to 5 years after surgery.
Pulmonary Atresia
In pulmonary atresia, the valve that separates the right ventricle from the pulmonary artery (called the pulmonary valve) does not develop. The normal flow of unoxygenated blood from the right side of the heart to the lungs does not occur. For the baby to survive, blood passes through a small opening between the left and right atrium. As blood flows to the left side of the heart and into the aorta, a special duct called the ductus arteriosus remains open (PDA) to allow the unoxygenated blood to pass from the aorta into the pulmonary artery, and into the lungs to receive much-needed oxygen.
Pulmonary atresia is usually a critical condition diagnosed either prenatally through a fetal ultrasound, or within the first few hours of birth. This condition affects roughly one for every 7,000 newborns each year in the United States. Babies appear cyanotic, with difficulty breathing, difficulty in feeding, looking very weak or sleepy. A pulse oximetry test will show low oxygen levels in the blood. Heart murmurs may or may not be present.
Because affected children survive birth and delivery with the help of heart structures that typically close after delivery, medications are needed to keep these open. Depending on the extent of the defect, treatment can involve cardiac catheterization or surgery.
Tricuspid Atresia
Similar to pulmonary atresia, there is underdevelopment of the tricuspid valve in tricuspid atresia. Unoxygenated blood cannot pass from the right atrium to the right ventricle. Babies with this condition survive by means of other heart defects: either an incomplete closure in the wall separating the atria or the ventricles, or a PDA. A narrow pulmonary artery may also be noted.
Pulmonary atresia is the third most common critical congenital heart disease. In the United States, this is diagnosed in one newborn for every 10,000 babies. Signs and symptoms other than cyanosis include difficulty breathing, difficulty in feeding, and falling asleep easily. Pulse oximetry test will reveal low oxygen levels, while murmurs may or may not be heard.
Again, as in pulmonary atresia, medications are needed to keep the ductus arteriosus open to allow for blood to be oxygenated in the lungs. More than one type of surgery may be needed to improve oxygenation of blood and overall function of the heart.
Transposition of the Great Arteries
The normal circuitry of the heart is as follows: blood from the body (that is low in oxygen) drains into the right atrium, through the tricuspid valve, and into the right ventricle, before passing through the pulmonary valve and into the pulmonary artery. This vessel brings blood to the lungs for oxygenation. After the blood receives oxygen, it proceeds toward the left atrium, through the mitral valve and into left ventricle, where it is pumped through the aortic valve, into the aorta, and the rest of the body.
In transposition of the great arteries (TGA), the main arteries are switched. The right ventricle is attached to the aorta, while the left ventricle is connected to the pulmonary artery. Blood that is unoxygenated only flows through the body, while oxygenated blood flows only within the lungs and the heart. A baby with this critical congenital heart defect cannot survive without additional heart defects that allow mixing of the oxygenated and unoxygenated blood. In fact, nearly 90% of babies with TGA who are not treated may die before they turn one year of age.
Other heart defects are associated with TGA, such as ventricular septal defects (VSDs) and unusual anatomy of the coronary arteries, which supply blood to the heart muscle itself.
Babies with TGA present with cyanosis and difficulty breathing, while a physical exam may reveal a murmur. The heart may be enlarged in a chest x-ray or in an electrocardiogram (EKG). In a pulse oximetry test, there are significant differences in the oxygen levels of the arms and legs.
Medical treatment with prostaglandin is usually given, while a special procedure called an atrial septostomy can be done if prostaglandin therapy isn’t enough to resolve the cyanosis. Eventually, the patient will need to undergo surgery to correct the connections between the heart and the major blood vessels involved.
Truncus Arteriosus
Truncus arteriosus is another cyanotic CHD involving the major arteries of the heart. During development of the heart, the aorta and pulmonary artery both come from one blood vessel and are later separated as the fetus grows. In truncus arteriosus, they fail to separate, leading to one large vessel that simultaneously connects both ventricles to both the lungs and the major blood vessels supplying the body. This defect leads to mixing of both oxygenated and unoxygenated blood.
Truncus arteriosus may be rare at only 4% of CHDs, but about 70% of all truncus arteriosus cases may succumb to death before one year of age. Newborns commonly present with cyanosis and are diagnosed within the first few days of life. Symptoms progress to difficulty breathing, difficulty gaining weight, and excessive sweating. Murmurs, erratic heart pulses, and an enlarged liver may also be seen. Like most cases of congenital heart disease, truncus arteriosus is managed with surgery.
Other CHDs
Vascular Rings
As oxygenated blood flows through the left side of the heart, it is distributed throughout the body by first passing through the aorta. This large artery forms an arch above the heart, connected to major blood vessels from the upper areas of the body, before it continues downward to supply the middle and lower parts of the body.
Vascular rings pertain to anomalies in the formation of the aortic arch. Some arteries may develop in the wrong area of the aortic arch, or certain areas of the aorta become too narrow that it affects the amount of blood the body receives.
This condition is very rare, at only 0.1%. Some kids may not have any symptoms at all, while others may have difficulty breathing or feeding, or both. They may experience constant “seal-like, barking cough”, repeated respiratory infections, and momentary lapses of apnea (a condition where a child suddenly stops breathing).
This rare disease is usually diagnosed through advanced imaging studies, such as a CT scan or an MRI. A special procedure called bronchoscopy may also be done. This involves the use of a small camera in a thin tube to visualize the air passages (trachea) and rule out other unusual anatomical structures. Surgical repair is needed to correct the anatomical defects.
Ectopia Cordis
A very rare defect called ectopia cordis (EC) literally shows the heart outside the chest. Diagnosed through fetal ultrasound or immediately after birth, this condition is life-threatening. There are only about 5 to 7 cases for every million babies, and only 10% survive.
The heart is one of the first few organs to form. As the fetus grows inside the mother’s womb, part of the future chest and abdominal wall grow towards the front of the heart and fuse together. In EC, these tissues do not completely fuse together, allowing part of the heart (and sometimes other abdominal organs) to develop outside the body.
Surgery is started promptly after birth to move the heart back within the chest wall, followed by subsequent surgeries to completely close the sternum.
Summary
This article is the third in a small series on congenital heart defects, focusing on heart conditions that cause cyanosis, as well as other CHDs that do not fall under acyanotic and cyanotic categories. Most CHDs need surgical management. CHDs that require a PDA to remain open will need medical management as well.
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