Evaluating the effectiveness of a rapidly adopted cardiovascular technology with administrative data: The case of drug-eluting stents for acute coronary syndromes

Background Instrumental variable (IV) methods can correct for unmeasured confounding when using administrative (claims) data for cardiovascular outcomes research, but difficulties identifying valid IVs have limited their use. We evaluated the safety and efficacy of drug-eluting coronary stents (DES) compared with bare-metal stents (BMS) for Medicare beneficiaries with acute coronary syndromes using the rapid uptake of DES in clinical practice as an instrument. We compared results from IV with those from propensity score matching (PSM) and multivariable regression models. Methods This is a retrospective cohort study involving 62,309 fee-for-service beneficiaries 66 years and older treated with coronary stenting between May 2003 and February 2004. Outcomes were measured for 46 months after revascularization using claims data. Results Recipients of DES were younger, had a lower prevalence of myocardial infarction, and had fewer comorbidities compared with BMS recipients. Use of DES was associated with lower rates of mortality by PSM (hazard ratio [HR] 0.80, CI 0.77-0.83) but not by IV (HR 0.99, CI 0.87-1.11). Instrumental variable models estimated a larger reduction in repeat revascularization (HR 0.76, CI 0.63-0.89) than did PSM (HR 0.90, CI 0.87-0.93). Conclusions Based on IV analysis, the increased utilization of DES relative to BMS among Medicare beneficiaries with acute coronary syndrome is associated with reduced rates of repeat revascularization and no difference in mortality. Instrumental variable approaches provide a useful complement to conventional approaches to cardiovascular outcomes research with administrative data.