Association of Volume and Outcomes in 234,556 Patients Undergoing Surgical Aortic Valve Replacement

Abstract

Background The relationship between institutional volume and operative mortality following SAVR remains unclear.
Methods From 1/2013 to 6/2018, 234,556 patients underwent isolated SAVR (n=144,177) or SAVR+CABG (n=90,379) within the STS ACSD. The association between annualized SAVR volume [Group 1 (1-25 SAVR), Group 2 (26-50 SAVR), Group 3 (51-100 SAVR), and Group 4 (>100 SAVR)] and operative mortality and composite major morbidity/mortality was assessed. Random effects models were used to evaluate whether historic (2013-2015) SAVR volume or risk-adjusted outcomes explained future (2016-2018) risk-adjusted outcomes.
Results The annualized median number of SAVRs per site was 35 [IQR: 22-59, isolated AVR: 20, AVR+CABG: 13]. Among isolated SAVR cases, the mean operative mortality and composite morbidity/mortality were 1.5% and 9.7%, respectively, at the highest volume sites (Group 4); with significantly higher rates among progressively lower volume groups (p-trend<0.001). After adjustment, lower volume centers experienced increased odds of operative mortality [Group 1 vs. 4 (Ref): AOR (SAVR), 2.24 (1.91-2.64); AOR (SAVR+CABG), 1.96 (1.67-2.30)] and major morbidity/mortality [AOR (SAVR), 1.53 (1.39-1.69); AOR (SAVR+CABG), 1.46 (1.32-1.61)] compared to the highest volume institutions. Substantial variation in outcomes was observed across hospitals within each volume category and prior outcomes explained a greater proportion of hospital operative outcomes than prior volume.
Conclusions Operative outcomes following SAVR±CABG is inversely associated with institutional procedure volumes; however, prior outcomes are more predictive than prior volume of future outcomes. Given excellent outcomes observed at many lower volume hospitals, procedural outcomes may be preferable to procedural volumes as a quality metric.