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Carotid artery stenting and CABANA: implications for credentialing

In this issue of Catheterization and Cardiovascular Intervention, Hopkins et al. report the outcomes of high-risk patients treated with carotid artery stenting (CAS) in the Carotid Stenting Boston Scientific Surveillance Program (CABANA), using the carotid WALLSTENT and FilterWire EZ Embolic Protection System (Boston Scientific, Natick, MA) [1]. CABANA enrolled 1,097 patients from 99 institutions in the United States between 2008 and 2010, including 34% with anatomical high-risk criteria, 50% with clinical high-risk criteria, and 15% with both anatomical and clinical high-risk criteria. Enrolled patients included 67% who were asymptomatic and 18% who were older than 80 years; technical success (delivery of WALLSTENT; delivery and retrieval of FilterWire EZ) was achieved in over 97% of patients. The primary endpoint was the composite of independently adjudicated major adverse events (MAEs) at 30-days (which was reported in 1,025 patients). The rate of MAE at 30days was 4.6%, including death in 1.3%, stroke in 3.3%, and myocardial infarction in 0.5%. As stated in the discussion, CABANA outcomes are generally similar to those reported by many high-risk CAS registries, even though the WALLSTENT and the FilterWire EZ represent early CAS technology and the rate of stroke (including major stroke) is a bit higher than those reported in the most contemporary CAS registries. However, another interesting observation from CABANA is lack of statistical relationship between hospital or operator CAS experience and MAE, as reported by other high-risk CAS registries [2,3]. This observation is interesting for several reasons: first, >90% of CABANA patients were treated in the most experienced hospitals by the most experienced operators (Tiers 1 and 2), so the study may have been underpowered to identify statistical significance. Second, the MAE rate was actually higher in Tier 1 and 2 institutions than in the lowest tier of hospital and operator experience (Tier 3), although the differences were not statistically significant. The likely explanation is that CAS patients were highly selected, and more experienced operators probably assisted less experienced Tier 3 operators. Finally, the principle investigators at Tier 3 institutions had performed 25–40 CAS procedures, so even though these sites were considered the least experienced, the operators actually had reasonable CAS expertise. It seems that the apparent lack of relationship between CAS experience and outcome defies what most would believe is common sense. There are a number of signals that suggest that there is a relationship between CAS experience and outcome (or at least that many prominent investigators believe that a relationship exists): first, in the Carotid Revascularization Endarterectomy and Stent Trial (CREST), potential CAS operators required preapproval based on documentation of at least 30 CAS procedures and attainment of satisfactory in-hospital and 30-day outcomes. Second, in CREST-2, CAS operators require preapproval based on documentation of at least 100 CAS procedures in the last 2 years. Third, several professional societies, including cardiovascular, vascular surgical, and radiological societies have published formal training guidelines for CAS, including documentation of requisite cognitive and technical skills, as well as the number of CAS procedures required to acquire and maintain CAS privileges [4,5]. Nevertheless, all of us recognize that operator volume per se should not be the only measure of operator experience; some may argue that arbitrary volume requirements may actually incent operators to do unnecessary procedures just to maintain their privileges. I believe there is a common sense approach to credentialing institutions and physicians for CAS,