Donor-Recipient Matching in Heart Transplantation
Is there survival benefit of heart transplantation when compared to waiting (while accounting for the estimated risk of a given donor-recipient match)?
The study cohort was comprised of 28,548 heart transplant candidates in the Organ Procurement and Transplant Network between July 2006 and December 2015. The study investigators estimated donor-recipient match quality from the donor risk index (DRI). The outcome of interest for the waiting group was death while waiting or delisting as too ill for transplant. The outcome of interest for the transplanted group was graft failure. DRI scores were divided into quartiles to create groups of ascending risk for time-dependent covariate analysis. The DRI score was calculated from the variables of ischemic time (<2 hours = 1 point; 2-3.9 hours = 2 points; 4-5.9 hours = 3 points; 6-7.9 hours = 4 points; ≥8 hours = 5 points), donor age (<40 years = 0 points; 40-49 years = 3 points; ≥50 years = 5 points), race mismatch between donor and recipient (2 points if true), and the ratio of the blood urea nitrogen/creatinine ratio of the donor (3 points if >30). The maximum score possible is 15 points. The study authors used a time-dependent covariate Cox model to determine the effect of donor-recipient match quality on the likelihood of a composite outcome while waiting for transplant or after transplant.
Over the 10-year time period, the study cohort included 17,949 heart transplant recipients. Of this group, 4,325 candidates died or were delisted for being too ill for transplant while waiting, and 3,504 transplant recipients had graft failure. The investigators found that donor/recipient risk estimates were inversely related to candidate urgency, and that the net benefit from transplant was evident across all estimates of donor-recipient status 1A and 1B candidates: status 1A (lowest risk quartile hazard ratio [HR], 0.37; 95% confidence interval [CI], 0.31-0.43; highest risk quartile HR, 0.52; 95% CI, 0.44-0.61) and status 1B candidates (lowest risk quartile HR, 0.41; 95% CI, 0.36-0.47; highest risk quartile HR, 0.66; 95% CI, 0.58-0.74). Status 2 candidates showed a benefit from transplant; however, survival benefit was delayed. On average, status 2 recipients had a net survival benefit of heart transplantation after 13 months for the low-risk group and after 39 months for the high-risk group. Only low-risk donor hearts offer status 2 candidates a survival benefit over continued waiting. For the highest-risk donor-recipient matches, a net benefit of transplant occurred immediately for status 1A, after 12 months for status 1B, and after 3 years for status 2 candidates.
The study authors found a survival benefit of heart transplant across all ranges of estimated donor-recipient match risk for status 1A and status 1B candidates. They opined that donor heart acceptance should be the favored strategy for such candidates. For status 2 candidates, the benefit of heart transplant was less apparent and dependent on estimated donor-recipient match risk. They opined that a measure of donor-recipient match quality may be useful when considering the immediate benefit of heart transplantation for stable status 2 candidates.
Although this is a retrospective study, the findings are important because they suggest that allocation of organs will benefit from good estimates of risk. Prospective studies estimating risk are the next step, particularly because the current allocation system is relatively new.
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