Tricuspid atresia

Tricuspid atresia is a form of congenital heart disease whereby there is a complete absence of the tricuspid valve. Therefore, there is an absence of right atrioventricular connection. This leads to a hypoplastic (undersized) or absent right ventricle. This defect occurs during prenatal development, when the heart does not finish developing. It causes the systemic circulation to be filled with relatively deoxygenated blood. The causes of tricuspid atresia are unknown.

In most cases of tricuspid atresia, additional defects exist to allow exchange of blood between the loops of systematic circulation and pulmonary circulation, filling in the role of the missing atrioventricular connection. An atrial septal defect (ASD) must be present to fill the left atrium and the left ventricle with blood. Since there is a lack of connection to the right ventricle, there must also be a way to pump blood into the pulmonary artery. This can be accomplished by a ventricular septal defect (VSD) connecting the left ventricle to the pulmonary artery or by a patent ductus arteriosus (PDA) connecting the aorta to the pulmonary artery. In the latter case, prostaglandin E1 is used to maintain the PDA connection until emergency corrective surgery can be completed. As oxygenated blood is mixed with deoxygenated blood in both cases, there is a reduction in the oxygen-carrying capacity.

It is also possible for tricuspid atresia to appear without the life-saving defects. In this case, the systemic and pulmonary circulations would be cut off from each other and no useful breathing can occur. An experimental procedure called fetal balloon atrial septostomy can be used to artificially create the required defect in utero.