into the right ventricle, it will be hypoplastic. In most cases, there will also be a ventricular septal defect allowing some blood into the pulmonary circulation. Due to the lack of blood flow into the pulmonary circulation, there is poor oxygenation of blood, leading to progressively worsening cyanosis. Diagnosis The majority of cases can be diagnosed prenatally during a routine anomaly scan. If evidence of a congenital heart disease is found, the diagnosis can be confirmed by a foetal echocardiogram. If it is not diagnosed prenatally, it may be diagnosed shortly after birth with physical examination, which would reveal cyanosis and murmur. Further evidence for the diagnosis can be obtained with an electrocardiogram and a chest radiograph. ECG will typically show a left axis deviation, while the chest X-ray may show pulmonary oligaemia or hyperaemia. The definitive investigation is, as in all congenital heart diseases, an echocardiogram, although the aforementioned tests along with clinical features might be sufficient for most cases. Treatment Treatment is based on: PGE1 to maintain patent ductus arteriosus. First operation: modified Blalock-Taussig shunt to maintain pulmonary blood flow by placing a Gore-Tex conduit between the subclavian artery and the pulmonary artery. See also Norwood procedure. Where too much flow to the lungs is present, a pulmonary band may be placed in a first operation. Second operation: cavopulmonary anastomosis (hemi-Fontan or bidirectional Glenn) to provide stable pulmonary flow Final operation: Fontan procedure to redirect inferior vena cava and hepatic vein flow into the pulmonary circulation. Epidemiology Tricuspid atresia is the third most common critical congenital heart defect. It is estimated to cause between 1% and 3% of all congenital heart defects. References External links Congenital heart defects