The impact of hospital cardiac specialization on outcomes after coronary artery bypass graft surgery: Analysis of Medicare claims data

Background: Hospital volume has been widely embraced as a proxy measure for hospital quality; little attention has been focused on an alternative quality measure-hospital specialization. Even though specialization occurs on a continuum, previous studies have only focused on a small number of highly specialized hospitals (single-specialty hospitals). Studies on the broad relationship between hospital specialization and outcomes after coronary artery bypass grafting (CABG) are limited. Methods and Results: We conducted a retrospective cohort study of 705 084 Medicare patients (1130 hospitals) who underwent CABG during 2001 to 2005. We stratified hospitals into quintiles, based on their degree of cardiac specialization (proportion of a hospital's Medicare discharges classified as Major Diagnostic Category 5-cardiovascular diseases). We compared patient and hospital characteristics and outcomes across quintiles of cardiac specialization. Patient characteristics were generally similar across quintiles, but mean annual CABG volume increased progressively from quintile 1 (least specialized) to quintile 5 (most specialized). Unadjusted 30-day mortality was similar at hospitals in quintiles 1 to 4 (4.8%), except quintile 5, where mortality was lower (4.3%). A strong inverse association was seen between hospital cardiac specialization and 30-day mortality after adjustment for patient characteristics (P_trend=0.001). However, this was no longer significant after additional adjustment for CABG volume (P _trend=0.65). Results were similar for other mortality outcomes and length of stay. Conclusions: After accounting for patient characteristics and CABG volume, greater cardiac specialization was not associated with clinically significant improvement in patient outcomes. This study calls into question the benefit of cardiac specialization for the vast majority of CABG-performing US hospitals.