title: Risk factors for early failure after peripheral endovascular intervention: application of a reliability engineering approach.
abstract: BACKGROUND
  We apply an innovative and novel analytic approach, based on reliability engineering (RE) principles frequently used to characterize the behavior of manufactured products, to examine outcomes after peripheral endovascular intervention. We hypothesized that this would allow for improved prediction of outcome after peripheral endovascular intervention, specifically with regard to identification of risk factors for early failure.
  
  
  METHODS
  Patients undergoing infrainguinal endovascular intervention for chronic lower-extremity ischemia from 2005 to 2010 were identified in a prospectively maintained database. The primary outcome of failure was defined as patency loss detected by duplex ultrasonography, with or without clinical failure. Analysis included univariate and multivariate Cox regression models, as well as RE-based analysis including product life-cycle models and Weibull failure plots. Early failures were distinguished using the RE principle of "basic rating life," and multivariate models identified independent risk factors for early failure.
  
  
  RESULTS
  From 2005 to 2010, 434 primary endovascular peripheral interventions were performed for claudication (51.8%), rest pain (16.8%), or tissue loss (31.3%). Fifty-five percent of patients were aged ≥75 years; 57% were men. Failure was noted after 159 (36.6%) interventions during a mean follow-up of 18 months (range, 0-71 months). Using multivariate (Cox) regression analysis, rest pain and tissue loss were independent predictors of patency loss, with hazard ratios of 2.5 (95% confidence interval, 1.6-4.1; P < 0.001) and 3.2 (95% confidence interval, 2.0-5.2, P < 0.001), respectively. The distribution of failure times for both claudication and critical limb ischemia fit distinct Weibull plots, with different characteristics: interventions for claudication demonstrated an increasing failure rate (β = 1.22, θ = 13.46, mean time to failure = 12.603 months, index of fit = 0.99037, R(2) = 0.98084), whereas interventions for critical limb ischemia demonstrated a decreasing failure rate, suggesting the predominance of early failures (β = 0.7395, θ = 6.8, mean time to failure = 8.2, index of fit = 0.99391, R(2) = 0.98786). By 3.1 months, 10% of interventions failed. This point (90% reliability) was identified as the basic rating life. Using multivariate analysis of failure data, independent predictors of early failure (before 3.1 months) included tissue loss, long lesion length, chronic total occlusions, heart failure, and end-stage renal disease.
  
  
  CONCLUSIONS
  Application of a RE framework to the assessment of clinical outcomes after peripheral interventions is feasible, and potentially more informative than traditional techniques. Conceptualization of interventions as "products" permits application of product life-cycle models that allow for empiric definition of "early failure" may facilitate comparative effectiveness analysis and enable the development of individualized surveillance programs after endovascular interventions.
authors.affiliation: Division of Vascular and Endovascular Surgery, Weill Cornell Medical College, New York-Presbyterian Hospital, New York, NY 10065, USA. ajm9007@med.cornell.edu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Meltzer
authors.forename: Ashley
authors.initials: A
authors.lastname: Graham
authors.forename: Peter H
authors.initials: PH
authors.lastname: Connolly
authors.forename: John K
authors.initials: JK
authors.lastname: Karwowski
authors.forename: Harry L
authors.initials: HL
authors.lastname: Bush
authors.forename: Peter I
authors.initials: PI
authors.lastname: Frazier
authors.forename: Darren B
authors.initials: DB
authors.lastname: Schneider
mesh_terms: D000368:Aged; D016009:Chi-Square Distribution; D057510:Endovascular Procedures / Q000009:adverse effects*; D004738:Engineering / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007383:Intermittent Claudication / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D007511:Ischemia / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D053208:Kaplan-Meier Estimate; D035002:Lower Extremity / Q000098:blood supply*; D008297:Male; D015233:Models, Statistical; D015999:Multivariate Analysis; D016491:Peripheral Vascular Diseases / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D013997:Time Factors; D017211:Treatment Failure; D018616:Ultrasonography, Doppler, Duplex; D014654:Vascular Patency