Reappraisal of the Impact of Institutional Volume on Outcomes After Heart Transplantation

Institutional volume influences heart transplant outcomes, although this relationship has not been studied following the 2018 allocation change. This study reappraises the volume-outcomes relationship in the modern era.

The United Network for Organ Sharing registry was used to identify adult patients ≥18 years undergoing isolated heart transplant from October 18, 2018-December 31, 2023. Patient-level tertiles were created based on transplant center volume. Center volume was presented as continuous and categorical variables for univariable and multivariable Cox regression analyses assessed survival, Kaplan-Meier analyses compared survival. Sequential receiver operating characteristics and loess smoothing plot explore an estimated annual volume threshold.

A total of 139 centers were evaluated: 92 low-volume, 31 moderate-volume, and 16 high-volume. Across volume categories, 90-day (94.3% vs 95.9%, p=.0005), 1-year (90.5% vs 93.3%, p<.0001) and 3-year survival (86.5% vs 89.5%, p<.0001) were higher in high-volume centers. After risk adjustment, heart transplant at low-volume centers was predictive of 90-day (hazard ratio (HR) 1.48, 95% confidence interval (CI) [1.23-1.78], p<.001) and 1-year mortality (HR 1.51, 95% CI [1.30-1.74], p<.001). When modeled continuously, there was an association of lower mortality with increasing center volume (HR .995, 95% CI [.992-.998], p=.001). The inflection point for improved 90-day and 1-year survival was 31 heart transplants annually.

The volume-outcomes relationship remains important in the current era. The threshold for improved survival has increased compared to historical thresholds. Although it should be interpreted cautiously as a reference point and not a discrete optimal threshold due to the continuous association.