|Abstract:|| Purpose. To examine intra heartbeat displacements (IHD) and geometrical changes over years, defined as follow-up displacements (FUD), of the endograft for abdominal aortic aneurysm repair, and to correlate them with computational fluid dynamics (CFD). Despite the widespread diffusion of endovascular aneurysm repair (EVAR) we still do not know very much about endograft behavior after deployment.
Methods. Two cases, treated with expanded polytetrafluoroethylene (PTFE) on nitinol stent frame (PI) and with woven polyester fabric sutured to stainless steel Z-stent skeleton (PII), respectively, were submitted to dynamic computed tomography angiography (CTA) at 1, 12 and 60 months. After segmentation, IHD were computed as displacements of the reconstructed surface with respect to the diastolic instant. Similarly, FUD were studied using imaging techniques that align temporal successive segmentations. At last, numerical simulations for blood dynamics were performed to compute viscous forces i.e. Wall Shear Stress (WSS) and Time Average WSS (TAWSS).
Results. IHD analysis showed slight translations without deformation for PI endograft with respect to the stiffer stainless steel endograft behaviour of PII. FUD showed in PI motion of the metallic struts mainly focused in the distal main body and in overlapping zone with iliac branches while in PII we observed a huge FUD in the middle and inferior-anterior regions of the main body. CFD analysis revealed changes of velocity patterns associated to remodelling of the iliac zone for PI and of the main body region for PII, where flow impinges the lumen wall and progressively provokes deformation of the endograft wires. TAWSS exhibits flow disturbances in the enlarged region coherently with displacements analysis.
Conclusion. Image-based displacements analysis associated to CFD allow to perform very subtle evaluations of endograft behaviour on different temporal scales. This kind of study could be helpful both for physicians, forecasting evolution during the life span of the endograft, and for manufacturers, giving them useful indication about endograft implant and design.