What is tricuspid atresia?
Tricuspid atresia is an abnormality of the tricuspid valve in which the valve fails to develop normally. Typically there is simply a plate of tissue where the normal valve should be. This results in no direct communication between the right atrium and right ventricle. Tricuspid atresia is almost invariably associated with some sort of hypoplasia, or underdevelopment of the right ventricle, due to the lack of adequate blood flow through the valve and into the ventricle. Different types of tricuspid atresia are classified based on the relationship of the two great arteries, the aorta and pulmonary artery. Type I describes patients with normally related great arteries (the most common type, accounting for 70-80% of cases), and Type II refers to patients with transposition of the great arteries (12-25%). Type III, an uncommon type of tricuspid valve atresia (3-6%), usually is associated with more complex abnormalities and malpositions.
Tricuspid atresia is classified as a ccongenital heart defect, and specifically as a cyanotic heart defect. Cyanotic heart defects refers to those heart defects that result in decreased or inadequate blood flow to the lungs. The term cyanosis refers to the blue discoloration of the skin that these infants and children typically have to due to low blood oxygen levels. In tricuspid atresia, because blood cannot pass from the right atrium to the right ventricle, it must flow across a hole between the two atria (termed a foramen ovale or atrial septal defect), where it then enters the left atrium and left ventricle. From here, some blood may be pumped out to the lungs through a hole between the ventricles (ventricular septal defect), but the majority usually is returned to the body. The amount of blood flow to the lungs is typically determined by factors such as the size of the VSD, the presence of any pulmonary stenosis, or the presence of transposition of the great arteries.
Incidence
The incidence of tricuspid atresia is approximately 5-6 per 100,000 births. As many as 20% of those affected also have other heart defects.
Cause
The cause of tricuspid atresia, as with many congenital heart defects, remains unknown. Certainly genetic factors may play a role. Many infants born with tricuspid atresia have no other apparent abnormalities.
Signs and symptoms
Tricuspid atresia is a cyanotic heart defect. The term cyanosis means a bluish discoloration of the skin. The cause of cyanosis is a lower than normal blood oxygen level. Children with tricuspid atresia are at risk for cyanosis because of decreased blood flow to the lungsdue to the absence of normal flow through the right atrium and right ventricle. The presence of a VSD allows blood to pass to the lungs; infants with large VSD's and no significant pulmonary stenosis may have a decent amount of blood flow and therefore appear relatively in color. The severity of cyanosis, and therefore the severity of symptoms, is determined by the severity of pulmonary stenosis and the size of the VSD.
Diagnosis
Diagnosis may be suspected by the presence of a heart murmur as well as the presence of cyanosis. The definitive diagnosis is typically made by an echocardiogram. Once the diagnosis is made, infants with tricuspid atresia usually require a medication called prostaglandin E1 (PGE-1) in order to maintain circulation of blood to the lungs. PGE-1 allows for a normal fetal structure, the patent ductus arteriosus, to remain open. This acts as a source for blood to enter the lungs to receive oxygen.
Treatment
Tricuspid atresia always requires surgical repair. In order to re-route the deoxygenated blood to the lungs, multiple stages of surgical palliation are necessary. The first stage involves placing an artificial shunt (a modified Blalock-Taussig shunt) in order to maintain blood flow to the lungs. Following this surgery, the baby can usually go home, with close follow up by a pediatric cardiologist.
The second stage, known as the Glenn procedure, is performed between 4-6 months of age. During this surgery, the superior vena cava, the main vein carrying deoxygenated (blue) blood from the upper half of the body is disconnected from the heart and directly connected to the pulmonary artery. In addition, the previously placed modified Blalock-Taussig shunt is removed.
The final stage, usually performed around 3 years of age, is known as the Fontan procedure. This involves connecting the inferior vena cava, the vein draining blood from the lower part of the body back to the heart, directly to the pulmonary artery as well. Following this procedure, all deoxygenated blood flows passively back to the lungs, while the heart focuses solely on pumping oxygenated blood returning from the lungs back to the body.
Prognosis
Tricuspid atresia is one of the great success stories of the last 30 years in the treatment of congenital heart disease. Currently survival to one year of age is in excess of 90% with survival at 5 to 10 years of age in excess of 85%. As recently as the 1980s, many children born with tricuspida atresia did not survive infancy. Long-term complications associated with the Fontan procedure include issues such as blood clots, infections, and electrical disorders of the heart. Other issues for families may include questions regarding participation in athletics, and considerations related to pregnancy in women who have survived into adulthood. While the data on these issues is continually being revised, optimism is growing that more and more patients will be able to live relatively normal lives in the setting of major congenital heart defects such as tricuspid atresia.