How Should We Interpret Worsening Outcomes in Heart-Kidney Transplantation, and What Can Be Done About Them?

Changes in allocation policy are ultimately designed to benefit transplant candidates and may address disparities in access based on geography, demographics, or medical criteria such as urgency, or optimize waitlist or posttransplant outcomes. For nonrenal transplant candidates with advanced renal dysfunction who may benefit from concomitant kidney transplants, optimizing allocation is complex and puts established principles governing allocation policy in conflict. Intuitively, individual patients are more likely to benefit from a combined transplant compared with an extrarenal transplant alone, and some evidence points to better outcomes in these recipients. In contrast, due to imprecise renal recovery predictions in this population, many patients receive no incremental benefit, and such transplants draw deceased donor kidneys from kidney-alone candidates, which impacts optimal utilization. In this issue of Transplantation, Ariyamuthu et al1 reported on outcomes of simultaneous heart-kidney transplant (SHKT) recipients following the implementation of heart allocation changes in 2018. Using Organ Procurement and Transplantation Network data from simultaneous SHKT recipients, outcomes were compared before and after the adult Heart Allocation Policy (aHAP) implementation. The authors demonstrated a significant increase in mortality and all-cause heart and kidney graft failure and worse overall 1-y kidney graft function following policy implementation. These findings raise concerns about the impact of the revised policy on both SHKT and kidney-alone waitlist candidates. Although the study did not compare outcomes to heart-alone recipients, the authors suggest that a sicker waitlist and transplant population may have contributed, as the policy increased prioritization of higher acuity patients on temporary mechanical circulatory support devices, who may be more likely to have renal dysfunction and receive SHKT, and indeed SHKT significantly increased following policy implementation. The increase in primary nonfunction of transplanted kidneys and an increase in post-SHKT dialysis support requirements also point to an increase in patients with a higher likelihood of mortality and posttransplant kidney transplant dysfunction. The association of kidney cold ischemia time with mortality warrants further study. This may be significant in light of trends in travel distance and machine perfusion but may also reflect selection bias, as the trend in practice to delay kidney transplant contingent on recipient stability after the heart transplant may result in longer kidney cold ischemia time for recipients already on the path to a poor outcome. Regardless, the increase in mortality and poor kidney outcomes in these recipients adds to the debate as to whether these transplants constitute the best use of deceased donor kidneys. Similar findings of inferior kidney outcomes have been reported in Europe.2 Aside from the obvious implications for potential SHKT recipients, it is important to interpret these findings in the broader context of the overall heart transplant population. As the authors point out, the implementation of the aHAP has also resulted in lower waitlist mortality rates and faster times to transplant without the adverse impact on posttransplant mortality observed in SHKT recipients.3 These findings may be the tradeoff for enhanced access to transplants for the highest-risk recipients. Thus, the question is not whether the aHAP has achieved its overarching goals but how to mitigate these adverse outcomes in SHKT recipients. In addition to refinements in candidate selection and perioperative management, additional constraints on or modifications to allocation for SHKT candidates have been implemented. In this regard, the discourse and subsequent policy modifications parallel those of simultaneous liver-kidney transplantation (SLKT), with the establishment of listing criteria to address increasing transplant numbers and reduce inappropriate kidney transplants and the incorporation of safety net provisions.4 It is noteworthy that in this study, survival rates only worsened following policy implementation in SHKT recipients with an estimated glomerular filtration rate of <30 mL/min who were not on dialysis. As with SLKT, these recipients constitute the exact population for which the incremental benefit of kidney transplant has not been definitively established and for which outcome analyses are limited by diverse patient populations, varying patterns of disease etiology and progression, and differences in selection practices. The safety net is particularly relevant considering the high rate of poor kidney outcomes. As with liver transplant recipients, kidney wastage on recipients destined for mortality, graft failure, or other poor outcome by virtue of adverse perioperative events would be eliminated by use of the safety net; in liver transplantation, deceased donor kidney utilization decreased as measured by either SLKT or a combination of SLKT and kidney after liver transplant under the safety net, without adverse impact on posttransplant outcomes.5,6 The potential value of the safety net in SHKT candidates is complicated by the unknown benefit of normal postoperative kidney function and uncertainty about whether the liver transplant experience can be replicated in a different transplant population. In this regard, ongoing evaluation of the appropriateness of SHKT eligibility criteria and the impact of the safety net is warranted. The anticipated implementation of continuous distribution may also inform this evaluation. The authors describe additional approaches to balance access and outcomes among the broader population of deceased donor kidney candidates and recipients. These include stricter chronic kidney disease eligibility criteria, incorporation of multiorgan transplant (MOT) candidates into broader kidney allocation with prioritization based on urgency and outcomes, dynamic modifications of allocation policy based on an upper limit of MOTs, increased transplant program accountability, and more robust data collection to inform outcomes analyses. These approaches are worthy of consideration, but some may best be deferred until the effects of recent changes are assessed, as many are reliant on an imperfect evidence base, the need for broad agreement on metrics, and/or additional demands on transplant centers and the Organ Procurement and Transplantation Network to support these efforts. The most fundamental challenge remains where to set the bar on distributing deceased donor kidneys among MOT and kidney-alone recipients. The general paradigm has been to incentivize the responsible use of MOT but, lacking evidence disproving the benefit of a kidney transplant, errs on the side of optimizing outcomes for the highest urgency candidates. It remains to be seen whether the use of selection criteria and the safety net will be sufficient to address calls from the kidney transplant community to rethink this paradigm.