Interaction between ischemic time and donor age under the new donor heart allocation system: Effect on post-transplant survival

Background Ischemic time (IT) under the new heart transplant (HTx) allocation system has increased compared to the old system. We investigated the effect of IT and donor age on post-HTx survival. Methods The United Network for Organ Sharing (UNOS) database was analyzed to identify adult HTx between October 2015 and August 2020. Recipients were stratified by donor age, transplantation era, and IT. Kaplan-Meier and log-rank tests were used to compare 180-day post-HTx mortality. Cox proportional hazards modeling and propensity score matching were performed to adjust for confounders. Results Under the new system (N = 3654), IT >= 4 h led to decreased survival compared to IT < 4 h (91.4% vs. 93.7%; P = .02), although this decrease was undetectable among those with donors >= 39 years old (90.4% vs. 91.1%; P = .73). IT >= 4 h led to decreased survival with donors < 39 years old (91.7% vs. 94.6%; P < .01). Under the old system (N = 5987), IT >= 4 h resulted in decreased survival (89.8% vs. 93.9%; P < .01), including with donors >= 39 years old (86.9% vs. 92.4%; P < .01). Conclusions IT >= 4 h remains a risk for post-HTx mortality under the new system. However, the magnitude of this effect is blunted when donor age is >= 39 years, likely secondary to increased allocation of these organs to lower status, more stable recipients.