Comparing the Effectiveness of Carotid Stent Systems versus Endarterectomy

1. Comparing the Effectiveness of Carotid Stent Systems versus Endarterectomy Peter W. Groeneveld, MD, MS Assistant Professor of Medicine Philadelphia Veterans Affairs Medical Center University of Pennsylvania School of Medicine

2. Acknowledgements • Feifei Yang, MS • Alexis Greenhut, MPH • Christine Camacho, BA • Janell Olah, MFA

3. Carotid Stent Systems • Catheter-based treatment of carotid stenosis • Distal embolic protection to prevent stroke during procedure • Alternative to vascular surgical procedure (carotid endarterectomy)

4. Carotid Stent System

5. Carotid Stent Systems: Recent Events • FDA approved first CSS in 2004 • CMS covered CSS in March, 2005 • Clinical trials have reported conflicting results about the efficacy of CSS compared to CE • CREST trial (2011?) … pending

6. Research objective • Leveraging the limited clinical availability of CSS (n=951 hospitals) compared to endarterectomy (n=2229 hospitals): What were the observed differences in outcomes between CSS recipients vs. endarterectomy patients in the year after the 2005 coverage decision?

7. Methods/1 • Fee-for-service Medicare inpatient claims from 2005-2006 (MEDPAR) • Patients over age 65 • Identified all recipients of CSS or endarterectomy • Fit propensity score model predicting receipt of CSS, using patient-level demographic, clinical variables, and hospital-level variables, as predictors

8. Methods/2 • CSS patients matched to CE patients during same time period (4/05-3/06: “contemporary controls”) • Separately fit PS model and matched “historical” CE patients (Apr 2004-Mar 2005) to CSS recipients • Fit proportional hazards and logistic regression models for mortality and combined death/stroke/AMI

9. Methods/3 • Outcomes determined via death indicators in the Medicare enrollment database (Denominator) and/or by view of subsequent hospitalization records in the 270 days following the carotid procedure

11. Alternative Approach • HRR strongly correlated with CSS receipt, but weakly correlated with other factors influencing mortality • Used Hospital Referral Region as instrumental variable for CSS receipt • Fit probit models where mortality or mortality/stroke/AMI at 90/270 days were the outcomes • Implemented with STATA’s ivprobit

12. Study Cohorts • 8,306 CSS recipients matched to 8,306 “contemporary” and 8,306 “historical” endarterectomy controls • 66,457 endarterectomy patients and 8,306 CSS patients included in instrumental variables analysis

13. Match quality/1

14. Match quality/2

20. Conclusions • Propensity-score matched comparisons of CSS and endarterectomy patients suggest CSS associated with worse outcomes • However these findings were not duplicated in the IV analysis, suggesting unobserved heterogeneity among patient populations

21. Conclusions/2 • Although inferiority of CSS cannot be disproved by these results, we did not find a clear case supporting the superiority of endarterectomy • Confidence boundaries suggest differences in 270-day mortality rates are less than 3.3 percentage points

22. Impact on Future Research • If the difference in outcomes were only 2%, 3,202 patients would be needed in a clinical trial to detect it with 80% power • Unlikely that the ongoing CREST trial (goal enrollment=1200-1600 patients, anticipated completion date=2011) will be able to definitively determine superiority of one therapy versus the other

23. Impact on Policy • Our study provides evidence that in the carefully selected clinical settings at which Medicare beneficiaries can receive CSS, outcomes of care for CSS patients are comparable to those achieved by patients receiving endarterectomy