Tricuspid Atresia

Tricuspid atresia is a cyanotic congenital heart defect characterized by complete absence or agenesis of the tricuspid valve, resulting in no direct communication between the right atrium and right ventricle. The right ventricle is consequently hypoplastic. Systemic venous blood cannot travel through the usual right-sided pathway, so it must cross an atrial septal defect or patent foramen ovale into the left atrium. That atrial communication is not an incidental finding. It is obligatory: without it, systemic venous return has nowhere to go. Blood entering the left atrium mixes with pulmonary venous blood, so systemic oxygen saturation falls. Pulmonary blood flow requires another route. A ventricular septal defect may allow blood to pass from the left ventricle toward the pulmonary arteries through the small right ventricle, or a patent ductus arteriosus may carry blood from the aorta to the pulmonary arteries. The size of the VSD, pulmonary stenosis or atresia, and the great-artery relationship determine whether pulmonary flow is inadequate, excessive, or relatively balanced. This is why a closing ductus can turn a previously stable neonate into an emergency. If the...