Patient-specific computational fluid dynamic simulation for assessing hemodynamic changes following branched endovascular aneurysm repair: A pilot study

Abstract

Abstract Objective This pilot study assessed the hypothesis that patient-specific computational fluid dynamic (CFD) modelling can detect aortic branch hemodynamic changes following branched endovascular aneurysm repair (bEVAR). Methods Patients who underwent bEVAR with the Jotec E-xtra Design for thoracoabdominal aortic aneurysms were retrospectively selected. Using open-source SimVascular software, pre- and post-operative aortic finite element volume meshes were constructed from CT imaging. Pulsatile in-flow conditions were derived and adjusted for patient-specific clinical variables. Outlet boundary conditions consisted of Windkessel models approximated from physiologic flow splits. Rigid wall flow simulations were then performed on pre- and post-operative models with equivalent boundary conditions. Computations were performed with an incompressible Navier-Stokes flow solver on a 72-core cluster. Results Pre- and post-operative flow simulations were performed on 10 patients undergoing bEVAR with a total of 40 target vessels (10 celiac, 20 superior mesenteric, 20 renal stents). Compared to pre-operative values, bEVAR was associated with a decrease in peak renal artery pressure (116.8 ± 11.5 vs 112.8 ± 11.6 mmHg, p<.001) and flow rate (13.7 ± 2.3 vs 12.9 ± 2.4 ml/s, p<.001). No post-operative differences were observed in pressure or flow rates in the celiac or mesenteric arteries (p=.10-.55). Representative perfusion waveforms from a single patient are shown in Figure 1. bEVAR resulted in a significant increase in aortic (1.4 ± 0.5 vs 4.3 ± 2.9 dynes/cm2, p=.009) and renal artery (24.3 ± 7.1 vs 35.4 ± 12.4 dynes/cm2, p=.23) wall shear stress; however, these values remained within the physiologic range. In certain graft configurations, 3D visualization of blood flow streamlines revealed areas of turbulent flow at the origin of external branches which were associated with decreased target artery perfusion (Figure 2). Conclusion Changes in para-visceral aortic geometry after bEVAR is associated with a decrease in computationally estimated renal perfusion, without significant changes to celiac or mesenteric hemodynamics. Further CFD simulation-based studies are needed to assess whether changes in branch configuration or hemodynamics after bEVAR can predict loss of branch patency.