Widening volume and persistent outcome disparity in valve operations: New York statewide analysis, 2005-2016.

Objectives: Volume concentration of complex noncardiac operations to high-volume centers has been observed, but whether this is also occurring in cardiac surgery is unknown. We examined the relationship between volume concentration and mortality rates for valve surgery and coronary artery bypass grafting (CABG) between 2005 and 2016 in New York State.

Methods: We analyzed publicly available, hospital-level case volume and risk-adjusted mortality rates (RAMRs) from 2005 to 2016 for isolated CABG and isolated or concomitant valve operations performed in New York. We identified hospitals in the top- and bottom-volume quartiles for each procedure type and compared changes in percent market share and outcomes. Bivariate and univariate longitudinal analysis was used to evaluate the statistical significance of the temporal trend.

Results: Among 36 centers, percent market share of the top-volume quartile increased for valve cases from 54.4% to 59.4%, whereas CABG share increased from 41.4% to 44.3%. No significant changes were noted in market share for the bottom quartile. The top-volume quartile demonstrated significant trends in improving outcomes over the study period for both valve procedures (RAMR: -0.261%/year, P < .001) and CABG (RAMR: -0.071%/year, P = .018). No significant trends were noted in the bottom quartile for either procedure.

Conclusions: In New York, over the last decade, highest-volume hospitals increased their market share for valve operations while maintaining lower mortality rates than lowest-volume hospitals. Valve volume is regionalizing in the setting of a persistent outcome gap between the highest- and lowest-volume hospitals, suggesting that volume-based referrals for specialized cardiac procedures may improve surgical mortality.