Blood Type O Heart Transplant Candidates Have Longer Waitlist Times But Comparable Post-transplant Outcomes Under The Revised UNOS Organ Allocation Criteria

Abstract

In October 2018 the United Network for Organ Sharing (UNOS) updated the heart allocation criteria aiming to improve mortality and reduce waitlist time. Although blood type (BT) O candidates had longer waitlist times and lower heart transplant (HT) rates under the prior guidelines, BT remains absent from the revised criteria. Accordingly, we evaluated the impact of the revised UNOS criteria on bridging strategies and waitlist and transplant outcomes based on candidate BT. Using UNOS registry data, we retrospectively evaluated 4,132 HT candidates and 2,727 recipients between Nov. 18, 2018 and Mar. 20, 2020. Statistical significance was defined as p<0.001. BT O was the most common blood type at time of HT listing: A 1,550 (38%), AB 182 (4%), B 593 (14%) and O 1,807 (44%). At listing there was no difference in the use of temporary mechanical support (TMCS) including intra-aortic balloon pump (IABP) (p=0.11) and extracorporeal mechanical oxygenation (ECMO) (p=0.16), nor listing status, though BT O were more frequently listed as status 4 (p=0.006). There was a trend towards less frequent LVAD use in BT O at listing: A 1,078 (70%), AB 132 (73%), B 418 (71%) and O 1,213 (67%) (p=0.19). Fewer BT O candidates underwent HT (A 1,020 (93%), AB 147 (94%), B 411 (92%) and O 889 (86%); p<0.001) and were more frequently listed as status 1 or 2: A 626 (56%), AB 70 (41%), B 262 (58%) and O 717 (73%) (p<0.001). At transplant, BT O were more likely to be in the ICU (A 52%, AB 44%, B 53% and O 61%; p<0.001) and require IABP support (A 30%, AB 18.3%, B 31% and O 36%; p<0.001). BT O also trended towards increased use of inotropes (A 37%, AB 36%, B 41% and O 42%; p <0.05) and ECMO (A 5.3%, AB 4.7%, B 4.8% and O 6.6%; p=0.41). There was no significant difference in LVAD use at the time of HT (p=0.63). BT O had significantly longer median time to transplantation (A 17 [IQR 6-61], AB 14 [IQR 6-47], B 20 [IQR 7-63] and O 23 [IQR 8-77] days; p<0.001) and a trend towards increased risk for waitlist mortality (p=0.2). Kaplan-Meier analysis showed no significant difference in post-transplant survival at one year (p=0.3) or outcomes including renal failure, stroke, pacemaker use, hospital length of stay and acute rejection at one year (p=0.2). Under the new UNOS allocation criteria BTO candidates continue to be transplanted at significantly lower rates. With longer waitlist times, there was a trend to list BT O at lower status and with less frequent LVAD use. At the time of transplantation significantly more BTO candidates were transplanted at higher status and with increased use of ICU care, inotropes and TMCS. This shift in bridging strategies may suggest BT O clinical deterioration, also reflected by the increased risk in waitlist mortality. However, post-transplant mortality and outcomes were not adversely affected, possibly mitigated by advancements in post-HT care. Long-term outcomes remain to be seen.