Pediatric risk to orthotopic heart transplant (PRO) score: Insights from United Network for Organ Sharing (UNOS) waitlist mortality findings

Abstract

Background: Pediatric heart transplant candidates on the waitlist have the highest mortality rate among all solid organ transplants. A risk score incorporating a candidate's individual risk factors may better predict mortality on the waitlist and optimize organ allocation to the sickest of those awaiting transplant.

Methods: Using the United Network for Organ Sharing (UNOS) database, we evaluated a total of 5542 patients aged 0-18 years old on the waitlist for a single, first time, heart transplant from January 2010 to June 2019. We performed a univariate analysis on two-thirds (N = 3705) of these patients to derive the factors most associated with waitlist mortality or delisting secondary to deterioration within 1 year. Those with a p <0.2 underwent a multivariate analysis and the resulting factors were used to build a prediction model using the Fine-Grey model analysis. This predictive scoring model was then validated on the remaining one-third of the patients (N = 1852).

Results: The Pediatric Risk to OHT (PRO) scoring model utilizes the following unique patient variables: blood type, diagnosis of congenital heart disease, weight, presence of ventilator support, presence of inotropic support, extracorporeal membrane oxygenation (ecmo) status, creatinine level, and region. A higher score indicates an increased risk of mortality. The PRO score had a predictive strength of 0.762 as measured by area under the ROC curve at 1 year.

Conclusion: The PRO score is an improved predictive model with the potential to better assess mortality for patients awaiting heart transplant.

Keywords: pediatric heart transplant; pediatric transplantation; risk factors; solid organ transplantation.

Figure 1:

Nomogram incorporating the variables of the final PRO score- a higher score indicates an increased 1 year waitlist mortality probability (Diagnosis: C= congenital, O= other, H= hypertrophic cardiomyopathy, R= restrictive cardiomyopathy, M= myocarditis, D= dilated cardiomyopathy). The ruler length for each clinical factor is a scaled version of the proportion of that factor’s contribution (range of possible values times coefficient) divided by the maximum predictor contribution. The total points are mapped to the one-year mortality probably while on the waitlist. For example, a 15 kg patient with congenital heart disease listed for heart transplant in Region 5 with AB blood type on ventilator support but no ecmo support and a most recent creatinine of 1.77 would result in a PRO score of 125 which corresponds to a waitlist mortality of approximately 0.25

Figure 2:

Area under the curve for derivation (training) cohort and validation cohort showing the PRO score with a predictive strength of 0.762.

Figure 3:

PRO score distribution of the derivation (training) group and the validation group demonstrating a similar bell curve characteristic.

Figure 4:

PRO Score distribution within each listing status: 1A, 1B, and 2. Variation of scores within each status conveys the heterogeneity of the patients within that group. As expected, there is a greater distribution of higher scores within Status 1A compared to Status 1B and Status 2.