Paradoxical outcome of heart transplantation associated with institutional case volume

Background: Previous studies in heart transplantation have shown an association between institutional case volume and outcomes. We aim to determine the case volume associated with optimal 1-year survival after transplantation. Methods and results: The United Network for Organ Sharing (UNOS) national database was analyzed for adult patients who underwent orthotopic heart transplantation between January 2013 and December 2017. A total of 11,196 cases at 128 transplant centers were included. Risk-adjusted restricted cubic splines revealed a non-linear association between institutional case volume and 1-year post-transplant survival. In the risk-adjusted, random-effect Cox model with segmented linear splines, higher heart transplant volume up to 24 cases per year was associated with better 1-year survival (HR =.978 every additional case, 95% CI.963–.993), and optimal survival was maintained between 24 and 38 cases per year. However, further increase in volume above 38 transplants per year was associated with mildly decreased 1-year survival (HR = 1.007 every additional case, 95% CI 1.002–1.013). Conclusions: The relationship between institutional case volume and heart transplant 1-year survival is non-linear, with optimal survival observed at institutional case volume of 24–38 cases per year.