# Stents in Congenital Heart Disease: State of the Art and Future Scenarios
## 5 Vision and Future Perspectives  
Despite great advancements in the field of transcatheter stenting procedures for CHD treatment being made since their introduction, some issues are still to be solved, and open questions guide ongoing research studies. Even if the definition of a unique ideal stent for each specific malformation seems to be quite hard given the high morphological variability, it is possible to outline the optimal characteristics that an ad hoc designed device should pursue. For what concerns ductal stenting, an optimal device should be characterized by:  
* High conformability to well adapt to duct geometry and shape;
* High radial force to counteract duct constriction keeping duct patency;
* Low profile for implantation at birth through small delivery sheaths;* Good longitudinal flexibility to allow for delivery and maneuverability in/through torturous vessels during implantation;
* Minimal foreshortening for precise positioning in the duct, avoiding portions of the conduit being left uncovered after stent expansion;
* Minimal recoil to maintain duct patency after expansion. Since implantation is only temporary and the device will be removed 4-6 months after birth during the next surgery step, accommodation of somatic growth is not generally perceived as an issue. For the same reason, fatigue testing should be adapted to this reduced lifetime. Following the most recent innovations in the market of devices for hybrid palliation of HLHS, a self-expandable stent with an optimized design to guarantee sufficient radial force and flexibility for delivery would be the best option. An increased oversize of the device with respect to the vessel might improve the radial expansion force, helping in counteracting ductal constriction. Another possibility might be the design of variable strut thickness along the device length to increase the radial strength in those areas of the ductus having remarkable power to restrict. Specifically for HLHS treatment, ad hoc geometries with lateral protrusions in the pulmonary conduits might be investigated to achieve both pulmonary artery flow reduction (as with the surgical banding) and stenting with a single device, in a unique procedure. Conversely, for what concerns ductal stenting in pulmonary atresia, the complex geometry of the tortuous ductus paves the way toward less traditional manufacturing technologies. As an emerging example, additive manufacturing techniques are quite attractive for realizing personalized stents to target specific lesions in patients with complex cardiac anatomy [26]. Moving to great vessel stenting, the characteristic features of an optimal device should include:  
* Adaptable dimensions to accommodate vessel somatic growth;
* High radial strength to resist external radial forces applied by the stenotic vessel wall;
* Low profile for implantation in small children through small delivery sheaths;
* High longitudinal flexibility to allow for delivery in/through torturous vessels and maneuverability during deployment;
* Minimal foreshortening at maximal expansion for precise positioning in the vessel, to better match the length of the stenotic lesion;
* Excellent durability to withstand long-term working conditions;
* Open-cell configuration to ensure blood flow in side branches. Following the trend of medical industries, the best option for great vessel stenting is represented by devices with great expansion potential, characterized by a low profile and small minimum diameter for implantation in newborns. Optimized designs allow for further balloon expansion up to adult size (above 20 mm) without neither stent uncontrolled fracture nor in-stent re-stenting. Of course, a long-term fatigue assessment of these devices is needed to evaluate their durability, since they are expected to have a longer working life than standard adult stenting. Within this context, it is also worth mentioning that some authors advocate the use of bioresorbable stents to overcome the issue of somatic growth accommodation [67; 105; 114].