title: Heart valve replacement: a statistical review of 35 years' results.
abstract: OBJECTIVE
  Having performed our first heart valve replacement in 1960, we began a prospective lifetime follow up service for all patients, contacting them at least annually to determine survivorship and heart valve complications.
  
  
  METHODS
  We reviewed isolated aortic (AVR) and mitral (MVR) valve replacements from 1960 to 1993, with follow up to 1998. In total, 2,942 AVR and 1,579 MVR were performed, with 21,742 and 12,142 patient-years of follow up, respectively. Analysis of the results affords an opportunity to demonstrate the usefulness and necessity of certain statistical methods, including multivariable event-free analyses and cumulative incidence functions.
  
  
  RESULTS
  The survival rate was 8% at 30 years for both valve positions. However, an overall survival curve is an artificial composite of patients of increasingly higher risk being served during increasingly safer years of calendar time. One result is that, for AVR, age is not a significant univariate risk factor for operative mortality, but is highly significant after accounting for date of surgery using logistic regression. Long-term mortality is higher for tissue valves than for mechanical valves; but mean age is greater (74 versus 57 years), and after accounting for age using Cox regression, mortality is similar for both valve types. Kaplan-Meier analysis estimates thromboembolism occurrences of 85% for AVR and 95% for MVR at 35 and 34 years, respectively, but the cumulative incidence estimates are only 32% and 41%, respectively.
  
  
  CONCLUSIONS
  Prospective follow up for over 35 years has provided an opportunity to illustrate important statistical issues: Multivariate analyses are essential to avoid being misled by excluding important risk factors or including artifactual ones, and the cumulative incidence estimates the percentage of patients who will actually experience a complication.
authors.affiliation: Providence Health System, Portland, Oregon, USA.
authors.forename: G L
authors.initials: GL
authors.lastname: Grunkemeier
authors.forename: H H
authors.initials: HH
authors.lastname: Li
authors.forename: A
authors.initials: A
authors.lastname: Starr
mesh_terms: D000328:Adult; D000368:Aged; D001021:Aortic Valve / Q000601:surgery; D005260:Female; D005500:Follow-Up Studies; D019918:Heart Valve Prosthesis Implantation / Q000401:mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D008943:Mitral Valve / Q000601:surgery; D015999:Multivariate Analysis; D011446:Prospective Studies; D012307:Risk Factors; D015996:Survival Rate