title: Instrumental variable analysis to compare effectiveness of stents in the extremely elderly.
abstract: BACKGROUND
  Evaluating novel therapies is challenging in the extremely elderly. Instrumental variable methods identify variables associated with treatment allocation to perform adjusted comparisons that may overcome limitations of more traditional approaches.
  
  
  RESULTS
  Among all patients aged ≥85 years undergoing percutaneous coronary intervention in nonfederal hospitals in Massachusetts between 2003 and 2009 (n=2690), we identified quarterly drug-eluting stent (DES) use rates as an instrumental variable. We estimated risk-adjusted differences in outcomes for DES versus bare metal stents using a 2-stage least squares instrumental variable analysis method. Quarterly DES use ranged from 15% to 88%. Unadjusted 1-year mortality rates were 14.5% for DES versus 23.0% for bare metal stents (risk difference, -8.5%; P<0.001), an implausible finding compared with randomized trial results. Using instrumental variable analysis, DES were associated with no difference in 1-year mortality (risk difference, -0.8%; P=0.76) or bleeding (risk difference, 2.3%; P=0.33) and with significant reduction in target vessel revascularization (risk difference, -8.3%; P<0.0001).
  
  
  CONCLUSIONS
  Using an instrumental variable analysis, DES were associated with similar mortality and bleeding and a significant reduction in target vessel revascularization compared with bare metal stents in the extremely elderly. Variation in use rates may be useful as an instrumental variable to facilitate comparative effectiveness in groups underrepresented in randomized trials.
authors.affiliation: Cardiology Division, Department of Medicine, Massachusetts General Hospital, Boston, MA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Yeh
authors.forename: Samip
authors.initials: S
authors.lastname: Vasaiwala
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Forman
authors.forename: Treacy S
authors.initials: TS
authors.lastname: Silbaugh
authors.forename: Katya
authors.initials: K
authors.lastname: Zelevinski
authors.forename: Ann
authors.initials: A
authors.lastname: Lovett
authors.forename: Sharon-Lise T
authors.initials: SL
authors.lastname: Normand
authors.forename: Laura
authors.initials: L
authors.lastname: Mauri
mesh_terms: D054058:Acute Coronary Syndrome / Q000453:epidemiology / Q000401:mortality / Q000628:therapy*; D000369:Aged, 80 and over; D003627:Data Interpretation, Statistical; D054855:Drug-Eluting Stents; D005260:Female; D006470:Hemorrhage / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D008404:Massachusetts / Q000453:epidemiology; D008670:Metals; D062645:Percutaneous Coronary Intervention / Q000295:instrumentation* / Q000379:methods; D012189:Retrospective Studies; D015607:Stents; D015996:Survival Rate; D016896:Treatment Outcome
chemical_list: D008670:Metals
keywords: aged; drug-eluting stents; percutaneous coronary intervention; stents