The Colorado Heart Failure Acuity Risk Model: A Mortality Model for Waitlisted Cardiac Transplant Patients

Background: Currently, there is no mathematical model used nationally to determine the medical urgency of patients on the heart transplant waitlist in the United States. While the current organ distribution system accounts for many patient factors, a truly objective model is needed to more reliably stratify patients by their medical acuity.

Objectives: The aim of the study was to develop risk scores (Colorado Heart failure Acuity Risk Model [CHARM] score) to predict mortality in adults waitlisted for heart transplant.

Methods: Risk scores were based on multivariable logistic regression models with mortality endpoints at 90 days, 180 days, 1 year, and 2 years. The models included serology data and patient history variables from waitlisted patients (N = 4,176) within the Scientific Registry of Transplant Recipients database from January 1, 2017, to September 2, 2023.

Results: The CHARM score included serum markers (brain natriuretic peptide, creatinine, sodium, aspartate aminotransferase, albumin, total bilirubin) and clinical variables (history of cardiac surgery, prior transplant, willingness to accept an hepatitis C virus positive heart, use of extracorporeal membrane oxygenation, use of mechanical life support, implantation of a cardiac defibrillator, and ventilator support prior to transplant). Sample holdout-validation for the models yielded average area under the curves of 0.825 (90-day), 0.805 (180-day), 0.779 (1-year), and 0.766 (2-year). Risk indices for all models were 99% correlated with observed mortality rates.

Conclusions: The CHARM score provides reliable calibration and prediction, offering an objective system for identifying critically ill patients on the heart transplant waitlist. The CHARM score will be useful in the era of continuous distribution to standardize organ allocation.