Computational Fluid Dynamics Modelling of the Effect of Outflow Graft Flow on Vessel Wall Deformation: Possible Implications for Aortic Regurgitation Development in Patients with Continuous-Flow LVAD

Purpose: Aortic regurgitation (AR), the diastolic reverse flow of blood from the ascending aorta into the left ventricle, is a common condition in patients with a left ventricular assist device (LVAD) that is associated with increased morbidity and mortality. We investigated the effect of the outflow graft (OG) flow on the aortic vessel wall and AR development in patients with LVAD.
Methods: We retrospectively analysed the data of 152 patients with LVAD at Wythenshawe Hospital (Manchester, UK) between 2015 and 2023. Three-dimensional models of the aorta with the OG were created using the CT data of 50 patients (median age 50; 26% women, 74% men) with a HeartMate III LVAD. Computational fluid dynamics (CFD) simulations were performed to quantify the flow patterns and aortic wall shear stresses for patients with different levels of aortic regurgitation (none, trivial, mild, moderate, and severe).
Results: 36% of the patients in the sample were diagnosed with AR (14% trivial or mild, 12% moderate or severe) and the severity of the condition increased over time. The CFD results show that, during instant systolic peak, the device induces continuous turbulent flows which create a high concentration of stresses in the vessel wall in sections of the ascending aorta located directly across from the OG and low wall shear stress around the aortic root. During diastole, retrograde flows can be observed, which increase in line with the severity of AR.
Conclusion: The hemodynamics produced by the LVAD OG may influence the progressive deformation of the vessel wall, along with patient-specific factors including the morphology of the aorta and pre-existing conditions such as hypertension. Optimised positioning of the OG may help to decelerate the degenerative processes associated with AR such as vessel wall deformation, thrombus formation, and leaflet deterioration.