Significant Association of Annual Hospital Volume with the Risk of Inhospital Stroke or Death Following Carotid Endarterectomy but Likely Not after Carotid Stenting: Secondary Data Analysis of the Statutory German Carotid Quality Assurance Database

Background-Associations between hospital volume and the risk of stroke or death following carotid endarterectomy (CEA) and carotid artery stenting (CAS) on a national level in Germany were analyzed. Methods and Results-Secondary data analysis using microdata from the nationwide statutory German quality assurance database on all surgical or endovascular carotid interventions on the extracranial carotid artery between 2009 and 2014. Hospitals were categorized into empirically determined quintiles according to the annual case volume. The resulting volume thresholds were 10, 25, 46, and 79 for CEA and 2, 6, 12, and 26 for CAS procedures. The primary outcome was any stroke or death before hospital discharge. For risk-adjusted analyses, a multilevel regression model was applied. The analysis included 161 448 CEA and 17 575 CAS procedures. In CEA patients, the crude risk of stroke or death decreased monotonically from 4.2% (95% confidence interval, 3.6%-4.9%) in low-volume hospitals (first quintile 1-10 CEA per year) to 2.1% (2.0%-2.2%) in hospitals providing ≥80 CEA per year (fifth quintile; P<0.001 for trend). The overall risk of any stroke or death in CAS patients was 3.7% (3.5%-4.0%), but no trend on annual volume was seen (P=0.304). Risk-adjusted analyses confirmed a significant inverse relationship between hospital volume (categorized or continuous) and the risk of stroke or death after CEA but not CAS procedures. Conclusions-An inverse volume-outcome relationship in CEA-treated patients was demonstrated. No significant association between hospital volume and the risk of stroke or death was found for CAS.