# Stents in Congenital Heart Disease: State of the Art and Future Scenarios
## 3 Congenital Heart Disease
### Defects Amenable to Stenting
#### 3.2.2 Pulmonary Atresia  
Pulmonary atresia is a defect of the pulmonary valve regulating the blood flow from the right ventricle to the pulmonary artery, which lacks continuity with the ventricular chamber or does not form at all during development. Since blood flow toward the lungs is strongly impaired, this malformation is commonly classified as a cyanotic disease [45; 46; 47]. Two variants of the pathology can be recognized according to the presence of a ventricular septal defect separating the two ventricular chambers. In particular, the most critical condition is considered in this review, characterized by an intact ventricular septum, which leads to a very small amount of blood flowing to the right ventricle. As a direct consequence, the right side of the heart develops hypoplasia involving both the right ventricle and the pulmonary artery (Figure 3b), which assumes a severe degree in 35% of the patients [48]. This disease is retained as a quite rare form of CHD. It occurs in approximately 3% of all CHD malformations [45]. During in utero life, the presence of the foramen ovale allows the blood flow from the inferior and superior vena cava to move from the right atrium to the left atrium under a pressure gradient. The blood is pumped into the aorta from the left ventricle and it perfuses the systemic circulation. Just a small amount of blood (10%) flows through a narrowed ductus arteriosus in a reversed direction with respect to physiological conditions, feeding the pulmonary circulation. With duct-dependent pulmonary blood flow, the ductus arteriosus is typically long, curved, and tortuous [49]. After birth, medical intervention is required within the first weeks of life in most cases due to the spontaneous closure of the ductus arteriosus, being blood circulation in the lungs duct-dependent [45]. Given the high morphologic variability of the pathology, the most appropriate surgical and/or transcatheter treatment is planned in each case according to the specific morphologic features and classification. Various management strategies for pulmonary atresia with intact ventricular septum have been established by different centers [45; 47; 48]. Medical treatment is always preceded by transthoracic echocardiography to assess the size of the pulmonary valve annulus, the size and functionality of the tricuspid valve and the right ventricle, and the morphology of the ductus arteriosus. In any case, the goal of the treatment is to provide adequate pulmonary blood flow, favoring at the same time the growth of the right ventricle. In the less critical patients having a normal or mildly hypoplastic right ventricle, a biventricular approach is preferred, aiming to establish a separate biventricular circulation by creating a patent right ventricular outflow tract (RVOT). This allows for the decompressing of the right ventricle and guarantees an anterograde pulmonary blood flow. This procedure can be performed either percutaneousally, through transcatheter pulmonary valve perforation followed by balloon dilation, or surgically, performing pulmonary valvotomy and RVOT reconstruction, and it may result in right ventricle growth [50; 51]. Additionally, a hybrid technique that combines surgical access with a transcatheter intervention has been proposed, having the advantage of avoiding cardiopulmonary bypass and sternotomy in the neonatal period but reducing at the same time the procedural complication and failure rates of the purely percutaneous route [52]. In the most critical patients characterized by severe right ventricle hypoplasia, a universentricular approach is followed, requiring the creation of a systemic-to-pulmonary communication as initial palliation in the neonatal period. Stenting of the ductus arteriosus is generally preferred as a less invasive alternative to the conventional placement of a shunt between the subclavian and the pulmonary artery, allowing for a reduction in post-procedure morbidity and hospital stay [47].