Abstract

Question Does the current national six-status heart allocation system rank waitlisted transplant patients based on medical urgency? Can this heart allocation system’s prognostic performance be improved?

Findings The six-status system is poorly calibrated, lacks sufficient statistical discrimination, and underestimates risk in the highest-risk patients, or those with an observed six-month mortality probability greater than 2%. By combining the current status system with six additional patient characteristics (previous transplant, ventilation, mean pulmonary capillary wedge pressure, willingness to accept a donor after cardiac death, diabetes status, and most recent creatinine), we correctly predicted greater than 80% of six-month waitlist mortalities in 7,706 study participants.

Meaning This study challenges the safety and efficacy of the current national heart allocation system.

Importance In December 2016, the Organ Procurement and Transplantation Network (OPTN) approved a bylaw that restructured the national heart allocation policy from a three-status to a six-status system. This new allocation system, which aimed to assign the highest priority to the patients with the highest mortality risk, went into effect on October 18, 2018. Since then, studies have identified limitations with the current system. However, no changes have been made to improve the national heart allocation system.

Objective Given the clear importance and impact of ranking patients based on medical urgency, we carefully evaluated the six-status heart allocation system to determine its correlation with observed mortality, or calibration, and its ability to predict six-month patient mortality risk and waitlist survival. We identified six additional patient characteristics associated with waitlist mortality and combined them with the six-status score to significantly improve the current allocation system’s ability to predict six-month waitlist mortality.

Design A retrospective, secondary analysis of the Scientific Registry of Transplant Recipients (SRTR) database of heart transplant candidates and recipients waitlisted from October 18, 2018, to December 31, 2024.

Setting The United States

Participants Single-organ heart transplant candidates, 18 years of age and older who were placed on the waitlist (N = 19,275). Patients listed multi-organ transplantation were excluded.

Exposures All-cause waitlist mortality

Main Outcomes and Measures The primary outcome of this study was the validation of the calibration and prognostic performance of the current heart allocation system. The secondary outcome is a simple model that greatly improves upon the current system’s ability to accurately (>80%) predict waitlisted patient mortality.

Results With a mean calibration slope of 0.94 (0.66, 1.21) and an area under the receiver operating curve of 0.71 (0.47, 0.87), the current allocation system is poorly calibrated, has only moderate statistical discrimination, and underestimates patient risk in the most critically ill patients. Hazard and time-series regression analysis confirmed that the six-status system does not adequately rank patients based on medical urgency. Our combined model demonstrates that the national allocation system can be improved.

Conclusions and Relevance While the current heart distribution system accounts for some patient risk factors, a more objective and accurate model is needed to achieve the OPTN’s strategic objective to more reliably model and predict patient risk and survival likelihood. Our model more accurately predicts patient waitlist mortality and will better inform waitlist management and improve waitlist survival by prioritizing medical urgency.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

No funding was using in this research

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The Colorado Multiple Institutional Review Board (COMIRB) approved all research

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

Data Availability

All data are publically available

ABBREVIATIONSAUCArea under the curveANOVAAnalysis of varianceCIConfidence intervalCHARMColorado Heart Failure Acuity Risk ModelCPHRCox proportional-hazard regressionECMOExtracorporeal membrane oxygenationHFHeart failureHRHazard ratioIABPIntra-aortic balloon pumpICDImplantable cardiac defibrillatorsMAGGICMeta-Analysis global group in chronic heart failureMELDThe model for end-stage liver diseaseOPTNOrgan procurement and transplantation networkPCWPPulmonary capillary wedge pressureROCReceiver operating characteristicSRTRScientific registry of transplant recipientsSDStandard deviationLVADLeft ventricular assist devices