A multiscale model for hemodynamic properties ’ prediction after fenestrated endovascular aneurysm repair . A pilot study

Aim: Fenestrated endovascular abdominal aortic aneurysm repair (FEVAR) has been increasingly applied for the treatment of anatomically suitable short-necked, juxtarenal, and suprarenal abdominal aortic aneurysms (AAA). Blood flow in the visceral vessels is maintained after FEVAR, but deployment of both the device and bridging covered stents might give rise to hemodynamic conditions that could impair the long-term success of the treatment. The aim of the present study is the development of a multiscale model that can reproduce hemodynamic flow in endograft models after FEVAR. Methods: We reconstructed preand post-operative computed tomography scans of two patients treated with a custom-made fenestrated endograft. Blood flow properties were obtained by computational fluid dynamics (CFD) simulations for the post-FEVAR cases. Specifically, pressure drop, velocity, wall shear stress and mean helicity were measured during the cardiac cycle. Results: No hemodynamic extremities with respect to the specialized wall shear stress (WSS) and helicity, based indexes were observed. A coherent helical field characterized blood flow topology during the cardiac cycle, with two counter-rotating helical structures. Regions of lowest time averaged WSS (TAWSS) in combination with high oscillatory shear index (OSI) are the areas after the splanchnic vessels at the aortic wall. Flow in the superior mesenteric and renal arteries remains almost unaffected after FEVAR. Important indices such as TAWSS, OSI and helicity are retained to almost normal levels. Low WSS values followed by high OSI values suggest that specific regions are sensitive to flow separation and probably to thrombus formation. Conclusion: This pilot study shows the possibility of predicting non-invasively the hemodynamic performance of FEVAR utilizing CFD. FEVAR does not seem to alter target vessel and aorta perfusion significantly allowing good perfusion of visceral arteries. 74 Hellenic Journal of Vascular and Endovascular Surgery | Volume 1 Issue 2 2019 The modeling of such hemodynamic flows requires specialized multiscale models due to the complexity of physiology. There have been proposed holistic models of the arterial system10,11. Detailed three-dimensional time-dependent models have been developed, describing a particular part of the cardiovascular system. In these models the waveforms obtained from 1D / 0D models, used as boundary conditions for the 3D simulations12,13. The aim of the present study is the development of a multiscale model that can reproduce hemodynamic flow in endograft models after FEVAR. MATERIAL AND METHODS In this study, a multiscale model, composed of 1D and 3D parts that can reproduce hemodynamic flow in endograft models after FEVAR is presented. Through computational simulations, the blood flow in an indicative FEVAR case is characterized, drawing attention to the arteries that are supplied with blood through the fenestrations in the splanchnic vessels. The model provides high-resolution hemodynamic analytics, such as, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and local normalized helicity (LNH). We studied the computed tomography (CT) scans, preoperatively and 1 month after FEVAR of 2 patients with a para-renal AAA treated electively by FEVAR. The patients underwent implantation of a custom-made fenestrated device at the Department of Vascular Surgery, Paracelsus Medical University, Nuremberg, Germany. Both patients gave written consent for utilization of the imaging data. The first patient underwent a double FEVAR (two fenestrations for the renal arteries and one scallop for the superior mesenteric artery, SMA). The second patient underwent FEVAR with three fenestrations (two for the renals and one for the SMA) and one scallop for the celiac axis, as depicted in Figure 1. Both patients received balloon expandable bridging stent-grafts in all target vessels.