Validation of the United States-derived Index for Mortality Prediction After Cardiac Transplantation (IMPACT) using international registry data.

BACKGROUND: We previously derived and validated the Index for Mortality Prediction After Cardiac Transplantation (IMPACT) using United Network for Organ Sharing (UNOS) data. This study aimed to validate the IMPACT score using international data. METHODS: International Society for Heart and Lung Transplantation (ISHLT) data were used to identify orthotopic heart transplantation (OHT) patients between 2001 and 2010. The primary outcome was all-cause 1-year post-OHT mortality. Secondary outcomes included 30-day and 5-year mortality. Logistic regression, weighted regression, and Kaplan-Meier analyses evaluated the predictive accuracy of the IMPACT score. A sub-analysis of OHTs performed from 2009 to 2010 examined patients completely external to the original UNOS derivation cohort. RESULTS: We identified 29,242 OHT recipients. Their mean IMPACT score was 5.1 ± 3.6. The IMPACT score was highly predictive of 1-year mortality (odds ratio [OR], 1.14, p < 0.001), a finding that persisted after adjusting for donor age and ischemic time (OR, 1.13; p < 0.001). A significant correlation was found between the expected 1-year mortality rates for each IMPACT score based on the original derivation cohort and the actual 1-year mortality rates in the ISHLT cohort (r = 0.87, p < 0.001). Kaplan-Meier 1-year survival by IMPACT score was 92.3% for a score < 5, 88.5% for scores of 5 to 10, and 75.1% for scores > 10 (p < 0.001). The IMPACT score also accurately predicted 30-day and 5-year mortality (each p < 0.001). These results were confirmed in the sub-analysis. CONCLUSIONS: This study validates the use of the IMPACT score as a predictor of short- and long-term mortality after OHT. Strong consideration should be given to broadly implementing and prospectively using the IMPACT score to predict mortality after OHT.