Factors Affecting the Displacement Force Exerted on a Stent Graft after AAA Repair—An In vitro Study

OBJECTIVES: To investigate the distraction forces affecting grafts used to treat abdominal aortic aneurysms in an in vitro model. METHOD: Using a standard cardiac pump and a rigid plastic circulation system, distraction forces were measured with a gramometer attached to a PTFE graft while the pressure inside a rigid aortic sac was varied. RESULTS: If the pressure in the 'aneurysm sac' is maintained at the same level as the systemic pressure, the displacement force is zero. The displacement force is affected adversely by the level of systemic pressure, as this rises the displacement forces rise in an almost linear fashion. CONCLUSIONS: These observations may have important consequences for stent graft design and use in vivo pressurisation of a sealed sac may therefore not necessarily be an adverse event. Systemic hypertension is obviously important and its control may be necessary to prevent graft migration.