Flow patterns in an endovascular stent-graft for abdominal aortic aneurysm repair.

Endovascular exclusion of the abdominal aortic aneurysm (AAA) has been carried out in selected patients during the past decade. The deployment of a complex multicomponent endovascular device in an aneurysmal aorta may alter the local haemodynamics and lead to thrombosis and intimal hyperplasia development. The aim of this in vitro study was to investigate the flow patterns using flow visualisation and laser Doppler anemometry in a commercial bifurcated stent-graft. Two configurations of the stent-graft, endo-stent and exo-stent, were investigated in an idealised planar AAA model. The flow structures in the main trunk in both configurations of the stent-graft are three-dimensional with complex secondary structures. However, these flow structures were not entirely caused by the stent-graft. The stent struts in the endo-stent configuration cause localised alteration in the flow pattern but the overall flow structures were not significantly affected. Low velocity regions in the main trunk and flow separation in the stump region and the curved segment of the iliac limbs were observed. These areas are associated with thrombosis in the clinical situation. Improvements in the design of endovascular devices may remove these areas of unfavourable flow patterns and lead to better clinical performance.