Additionally, lack of infrastructure to track prevalence, fragmented care systems, loss to follow-up, and changes in treatment strategies over time all contribute to the challenges of developing Comprehensive multicenter and pop- ulation registries and databases are needed to have adequate numbers of patients to address clinical questions. Novel study methodologies are needed to ascertain effectiveness of diagnostic and therapeutic options when each disease is sufficiently rare and e- vents occur over sufficiently long periods that RCTs are impractical. Although there are data that patients with complex CHD have improved survival when cared for at an ACHD center, how can networks of care be developed that ensure patients get the ex- pert care needed when there are inadequate number of ACHD cardiologists and ACHD centers? How do we ensure that patients are not lost to care as they transition from pediatric to adult cardiology? How do we ensure that patients with ACHD who would ben- efit from heart transplantation receive accurate listing priority? See Table 35 for a collection of high-impact research questions in ACHD. 