Étude biomécanique personnalisée du traitement endovasculaire de l'aorte thoracique (TEVAR)

Endovascular treatment of the thoracic aorta (TEVAR) has become the gold standard treatment for most pathologies of the descending thoracic aorta, including aneurysms, aortic dissections and blunt trauma. Despite very good clinical results, recent studies suggest that the presence of the endograft may alter the aorta's biomechanical properties, cardiac function and ventricular-aortic coupling. To date, data confirming these findings remain scarce. Four-dimensional flow magnetic resonance imaging (4D flow MRI) is a recent imaging modality enabling high-resolution in vivo imaging of the three-dimensional flow field in blood vessels over time. Through a prospective clinical study 4D flow MRI of patients with a history of aneurysm and/or dissection were performed before and after stenting. We complemented in vivo flow measurements with patient-specific computational fluid dynamics (CFD) simulations in which aortic geometry and flow boundary conditions were derived from the 4D MRI data. Our study on pulse wave velocity and aortic radial compliance showed an increased stiffness at the level of the endograft but an increased elasticity upstream of the endoprosthesis, in the native ascending aorta. The study of cardiac function revealed no significant difference in either left (LV) or right ventricular (RV) function at 6 months post-stenting. However, an increase in LV mass index, a decrease in RV ejection fraction and an increase in cardiac biomarkers (NT-proBNP) suggest the development of bi-ventricular adaptation mechanisms raising the risk of deterioration in cardiac function over the longer term. Flow analyses showed a significant reduction in retrograde flow in the ascending aorta, suggesting a reduction in turbulence upstream of the graft, probably in connection with the exclusion of underlying aortic pathology. These data are being confirmed by the quantification of vortical flow through the development of an in-house flow analysis pipeline. We also present the development of a patient-specific CFD model whose initial results, particularly in terms of shear stress distribution on the aortic wall, promise to improve our understanding of how TEVAR affects flow patterns and to provide a tool for optimizing the design of customized stents.