pulmonary atresia
Pulmonary atresia is a defect in which the normal doorway from the right ventricle into the lung artery is sealed shut: the pulmonary valve is absent or imperforate, blocking the path blood should take to the lungs. Atresia means a passage that should be open but is closed off, like a sealed-over exit door.
With no forward route to the lungs, blood must reach them by some other channel. In the newborn period that channel is usually the ductus arteriosus, which carries blood from the aorta backward into the lung circulation. As long as the duct stays open the baby can oxygenate; when it closes, oxygen levels plummet and the infant becomes deeply cyanotic.
Pulmonary atresia therefore behaves as duct-dependent cyanotic heart disease. Initial treatment keeps the ductus open with medication, and definitive care depends on the anatomy, ranging from opening or bypassing the blocked valve to staged single-ventricle reconstruction when the right ventricle is too small.
A deeply cyanotic newborn is found to have pulmonary atresia; prostaglandin is started to keep the ductus arteriosus open until a procedure can establish reliable flow to the lungs.
Pulmonary atresia is duct-dependent: closing the ductus removes the only path to the lungs.
Pulmonary atresia often coexists with other defects, such as a ventricular septal defect; the size and health of the right ventricle largely determine whether a two-ventricle repair is possible.