Institutional volume and the effect of recipient risk on short-term mortality after orthotopic heart transplant

Objective: We developed a validated 50-point recipient risk index predicting short-term mortality after orthotopic heart transplant (OHT). This study examined the relationship between institutional volume and recipient risk on post-OHT mortality. Methods: We used United Network for Organ Sharing (UNOS) data to identify primary OHT recipients between January 2000 and April 2010. Centers were stratified by mean annual volume. Preoperative Index for Mortality Prediction After Cardiac Transplantation risk scores were calculated for each patient with our validated 50-point system. Primary outcomes were 30-day and 1-year survivals. Multivariable logistic regression analysis included interaction terms to examine effect modification of risk and volume on mortality. Results: In all, 18,226 patients underwent transplant at 141 centers: 1173 (6.4%) recipients at low-volume centers (<7 procedures/y), 5353 (29.4%) at medium-volume centers (7-15 procedures/y), and 11,700 (64.2%) at high-volume centers (>15 procedures/y). Low center volume was associated with worse 1-year mortality (odds ratio, 1.58; 95% confidence interval, 1.30-1.92; P < .001). For 1-year survival, there was significant positive interaction between center volume and recipient risk score (odds ratio, 1.04; 95% confidence interval, 1.01-1.07; P = .02), indicating effect of risk on mortality at low-volume centers greater than from either variable analyzed individually. Among high-risk recipients (score >= 10), 1-year survival was improved at high-volume centers (high, 79%; medium, 75%; low, 64%). Conclusions: In analysis of UNOS data with our validated recipient risk index, institutional volume acted as an effect modifier on association between risk and mortality. High-risk patients had higher mortality at low-volume centers; differences dissipated among lower-risk recipients. These data support a mandate for high-risk transplants at higher-volume centers. (J Thorac Cardiovasc Surg 2012;143:157-67)