Institutional Volume and the Effect of Recipient Risk on Short-Term Mortality After Orthotopic Heart Transplant
What are the predictors of short-term mortality after cardiac transplant?
This was an analysis of 18,226 patients who underwent transplant within the United States between January 2000-April 2010. Data were compiled in the United Network of Organ Sharing (UNOS) database. Transplant center volume was defined as low- (<7 transplants/year), medium- (7-15 transplants/year), and high-volume (>15 transplants per year), and patients were stratified into one of these three groups. IMPACT risk scores were calculated on all patients to estimate survival based on 12 preoperative risk factors. The primary outcome of interest was survival at 1 year, based on transplant center volume.
Over a median 45 months of follow-up, there were 4,892 deaths. One-year survival was 13.6%. The median center volume was 10 transplants per year (range 0.2-76 per year) with 6.4% of transplants occurring at low-volume centers, 29% at medium-volume centers, and 64% at high-volume centers. Center volume was a significant predictor of survival, with unadjusted mortalities of 11.6%, 13.5%, and 18.1% in high-, medium-, and low-volume centers at 1 year (p < 0.01). Compared with high-volume centers, patient survival at low- and medium-volume centers was 58% (odds ratio [OR], 1.58 [1.30-1.92]) and 20% lower (OR, 1.20 [1.09-1.33]) at 1 year. The interaction between center volume and outcome in high-risk patients by (Index for Mortality Prediction After Cardiac Transplantation) IMPACT score was significant (p = 0.02; OR, 1.04 per point increase in IMPACT score), suggesting that higher-risk patients do even worse at lower-volume centers.
Center volume is an effect modifier for outcome after transplant. High-risk patients have worse outcome at low-volume centers. The authors suggest that high-risk patients should be transplanted at high-volume centers.
This is a large analysis of mandatory data collected on all cardiac transplants that take place within the United States. As with other cardiac interventions, center experience appears to impact patient outcome within 1 year of cardiac transplant, especially in those patients who are high risk. The curves separate early (within 90 days), suggesting that patient selection, operative experience, and perioperative management strategies may differ by center experience. In a field where the actual intervention is rare (~3,500 per year in the United States) due to donor scarcity, ensuring favorable outcomes is key for both patients and the field of cardiac transplant. Center volume, however, is not only limited by the density of transplant centers (organ donor or patient competition) within a state, but also by the population density and/or radius of available donors. Donor ischemic time cannot be compromised by consolidation of transplant centers, and patients need center proximity to ensure follow-up of biopsies and other post-transplant testing. Higher-risk patients may benefit from referral to larger-volume centers. The use (or reasons for disuse) of left ventricular assist devices in these higher-risk patients should also be investigated.
Keywords: Heart Diseases, Follow-Up Studies, Liver Transplantation, Graft Rejection, Tissue Donors, Cardiology, Pancreas Transplantation, Heart Failure, Risk Factors, United States, Heart Transplantation
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