Patients supported by VA-ECMO are prioritized for heart transplantation under the new United States donor allocation system, which is intended to decrease their waitlist mortality. The use of VA-ECMO as a bridge to transplant (BTT) has increased under the new system, which may lead to shifts in the characteristics of the VA-ECMO BTT population. We hypothesize that 1) the rate of waitlist death or delisting for VA-ECMO BTT is lower under the new allocation system and 2) this improvement is mediated by a shorter waitlist duration.
Using the United Network for Organ Sharing database, we analyzed all adult patients listed for heart transplant between 1/1/2014 and 6/12/2020 who were on VA-ECMO at listing. Waitlist entry after October 18, 2018 defined the new allocation system. We used Fine-Gray competing risk models to analyze the subdistribution relative hazard (sdRH) of death or delisting while accounting for the competing risk of successful transplant, with adjustment for baseline characteristics. Risk of death may increase with additional waitlist duration, so we compared separate models conditional on survival (without transplant) to days 7 and 14.
VA-ECMO was present at listing in 238 patients in the old system and 163 in the new system, with comparable baseline characteristics. Under the old system, waitlist death or delisting occurred in 125 patients (53%), with 108 (45%) transplanted and median time to transplant 51 days (IQR 11 to 228). In the new system, death or delisting occurred in 29 patients (18%), with 125 (77%) transplants and median time to transplant 4 days (IQR 2 to 7). The adjusted risk of death or delisting decreased by 73% in the new system (sdRH 0.27, 95%CI 0.17-0.42, P<0.001) (Figure). In time-updated models, this improvement was mediated entirely by a shorter time to transplant.
For patients bridged to heart transplant with VA-ECMO, the risk of waitlist death or delisting is significantly lower in the new allocation system. This improvement is mediated by a shorter time to transplant.
© 2021 Published by Elsevier Inc.