title: Factors and forces influencing stent-graft migration after endovascular aortic aneurysm repair.
abstract: OBJECTIVE
  To assess and validate the clinical features predisposing to stent-graft migration and to calculate the distal displacement forces exerted at the proximal fixation site following endovascular aortic aneurysm repair (EVAR).
  
  
  METHODS
  Demographic, anatomical, and graft-related features from 2862 patients were analyzed in a regression model to identify variables associated with stent-graft migration, which was defined as device movement >5 mm or considered significant by the investigator. Using the principles of continuity and momentum, a mathematical model of blood flow was created. The pulse pressure, proximal aortic and distal iliac diameters, and the degree of iliac angulation were varied in the calculations, and the distal displacement force exerted at the proximal fixation site was calculated.
  
  
  RESULTS
  Ninety-nine patients developed stent-graft migration, which was clinically relevant in 85 (3.0%). Hypertension (p=0.015), smoking (p=0.009), maximal aortic diameter (p=0.004), and distal transverse aortic diameter (p=0.03) correlated with migration in the univariate analysis, but iliac angulation did not quite achieve significance (p=0.06). On multivariate analysis, current smoking, hypertension, distal transverse aortic diameter, maximum common iliac diameter, and increasing proximal graft size were significantly associated with stent-graft migration. The mathematical model calculated the distal displacement force exerted on the proximal fixation site of the stent-graft and validated the clinical findings. The ratio of graft-diameter change from proximal aorta to distal iliac influenced the greatest increase in the displacement force.
  
  
  CONCLUSIONS
  The mathematical model validated hypertension, aneurysm morphology, and endograft size as clinical factors significantly associated with stent-graft migration. These findings may have important implications for the choice and design of future stent-grafts.
authors.affiliation: Royal Liverpool University Hospital, University of Liverpool, England, UK.
authors.forename: Irwin V
authors.initials: IV
authors.lastname: Mohan
authors.forename: Peter L
authors.initials: PL
authors.lastname: Harris
authors.forename: Corine J
authors.initials: CJ
authors.lastname: Van Marrewijk
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Laheij
authors.forename: Thien V
authors.initials: TV
authors.lastname: How
mesh_terms: D017544:Aortic Aneurysm, Abdominal / Q000150:complications / Q000453:epidemiology / Q000601:surgery*; D001794:Blood Pressure / Q000502:physiology; D001807:Blood Vessel Prosthesis / Q000009:adverse effects*; D004868:Equipment Failure; D005260:Female; D005500:Follow-Up Studies; D005548:Foreign-Body Migration / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D015999:Multivariate Analysis; D011183:Postoperative Complications / Q000453:epidemiology / Q000209:etiology; D011474:Prosthesis Design; D012307:Risk Factors; D015607:Stents / Q000009:adverse effects*; D014654:Vascular Patency / Q000502:physiology; D014656:Vascular Surgical Procedures / Q000295:instrumentation*