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Response to Letter to the Editor

We would like to offer a response to the criticism generated by Powel and deFreitas from East Carolina Heart Institute of our recent publication entitled ‘‘Carotid Artery Stenting in the Nation: The Influence of Hospital and Physician Volume on Outcomes.’’ The relationship between volume and outcomes is a well-established paradigm, so much so that it is the basis of the current leapfrog criteria used to evaluate hospital quality. It has been stated that, ‘‘If the Leapfrog volume standards are successfully implemented, employers and health-care purchasers could prevent many surgical deaths by requiring hospital volume standards for high-risk procedures’’. High surgeon volume has been associated with a reduction in surgical complications in a veritable plethora of procedures ranging from coronary artery bypass graft (CABG) to colon cancer to abdominal aortic aneurysm (AAA) to carotid endarterectomy (CEA). Why Powel and deFreitas disagree with this finding with regard to carotid artery stenting (CAS) lacks substance, as the volume to outcome relationship prevails throughout the surgical literature across a myriad of varied disciplines. With regard to the methodology used for this analysis, it follows the methodology used by Birkmeyer et al and others in defining the relationship of hospital and physician volume to outcomes. The volume criteria defined by quartiles are similar to previously published procedure requirements contained within the experience from the lead-in phase of CREST. As well, these data were adjusted as we have stated in the manuscript, ‘‘To compare risk-adjusted estimates for stroke between hospital and providers with different volume, we used a logistic regression model with stroke as an outcome and patient’s age, gender, comorbidities, and dichotomous variables for hospital and provider volume (low/high) as predictors.’’ After adjustment, this analysis demonstrated that patients of low-volume providers were 1.4 times as likely to have a stroke as patients of high-volume providers (95% CI1⁄4 1.01-1.97) and patients in low-volume hospitals were 1.2 times (95% CI1⁄4 1.02-1.41) as likely to have a stroke as patients in high-volume hospitals. With regard to the criticism of arch anatomy, degree of calcification, and so on, these anatomic elements are not contained within the data set, but we evaluated 18 599 cases of elective stenting of CAS across the nation. One could suggest that these variants are likely distributed similarly across such a large population in so many facilities. As well, an analysis of patient sociodemographic characteristics and comorbidities did not vary by hospital or physician volume, supporting the likelihood that these patient populations are in fact quite similar. To quote Holt et al, ‘‘There is clear evidence that many centers and individual clinicians are currently undertaking an insufficient number of cases to provide the best achievable outcomes for major vascular surgical procedures.’’ Suggestions for the association between increasing hospital volume and postoperative mortality may derive from a full spectrum of clinical services at high-volume centers that may facilitate the prompt recognition and treatment of complications. Unfortunate or not, the association of volume to outcomes exists for many complex procedures and CAS is no different.