Creation of a quantitative recipient risk index for mortality prediction after cardiac transplantation (IMPACT)

Background: No recipient risk index exists predicting short-term mortality after orthotopic heart transplantation (OHT). We utilized United Network for Organ Sharing (UNOS) data to develop a novel quantitative recipient risk score for use in OHT. Methods: A prospectively collected open cohort of 21,378 primary OHT patients (1997 to 2008) was randomly divided into subgroups. The training cohort (n = 17,079) was used for score derivation and the test cohort (n = 4,299) was used for independent validation. Recipient specific variables associated with 1-year mortality (exploratory p value < 0.2) were incorporated stepwise into a multivariable logistic regression model. The final model contained variables which maximized explanatory power (assessed by pseudo R2, area under the curve, and likelihood-ratio test). A risk index was created by apportioning points approximating the relative impact of variables on 1-year mortality. The Kaplan-Meier method was used to assess impact of risk score on short-term survival. Results: The 50-point scoring system incorporated 12 recipient specific variables. Derivation and validation cohort scores ranged from 0 to 33 and 0 to 27, respectively (mean 6.1 ± 3.7 and 6.1 ± 3.7). Each point increased the odds of 1-year death by 14% in the derivation cohort (odds ratio 1.14 [1.13 to 1.15], p < 0.001) and 15% in the validation cohort (odds ratio 1.15 [1.12 to 1.17], p < 0001). One-year survivals in the validation cohort (by increments of 3 points) were the following: 0 to 2 (92.5%); 3 to 5 (89.9%); 7 to 9 (86.3%); and 10 or greater (74.9%); p < 0.001. Patients transplanted with risk scores of 20 or higher had 1-year mortality rates greater than 50%. Conclusions: We present a novel internally validated OHT recipient risk score, which is highly predictive of 1-year mortality. This risk index may prove valuable for patient prognosis, organ allocation, and research stratification in OHT.