With increasing emphasis on readmissions as an important quality metric, there is an interest in regionalization of care to high-volume centers. As a result, care of readmitted cardiac surgery patients may be fragmented if readmission occurs at a nonindex hospital. This study characterizes the frequency, risk factors, and outcomes of nonindex hospital readmission after cardiac surgery.

In this multicenter, population-based, nationally representative sample, we used weighted 2010-2015 National Readmission Database claims to identify all US adult patients who underwent 2 of the major cardiac surgeries, isolated coronary artery bypass grafting (CABG) or isolated surgical aortic valve replacement (SAVR), during their initial hospitalization. We examined characteristics, predictors, and outcomes after nonindex readmission.

Overall, 1,070,073 procedures were included (844,206 CABG and 225,866 SAVR). Readmission at 30 days was 12.8% for CABG and 14.5% for SAVR. Nonindex readmissions accounted for 23% and 26% at 30 days; these were primarily noncardiac in etiology. The proportion of nonindex readmissions did not change significantly from 2010 to 2015. For CABG and SAVR, in-hospital mortality (adjusted odds ratios of 1.26 and 1.37, respectively) and major complications (odds ratios of 1.17 and 1.25, respectively) were significantly higher during nonindex versus index readmission, even after adjusting for patient risk profile, case mix, and hospital characteristics. Older age, higher income, and increased comorbidity burden were all independent predictors of nonindex readmission.

A considerable proportion of patients readmitted after cardiac surgery are readmitted to nonindex hospitals. This fragmentation of care may account for worse outcomes associated with nonindex readmissions in this complex population.