Abstract
Abstract Although the development of the transcatheter aortic valve (TAV) has saved many lives of inoperable patients and has a very good clinical outcome, concerns about valve thrombosis are increasing. Due to the potential risk of late clinically relevant events, the US Food and Drug Administration (FDA) suggests a careful systematic investigation of thrombosis and reduced leaflet motion related to hemodynamic changes induced by TAV implantation. Furthermore, recently published position papers of the ISO working group address numerical and experimental flow field assessment of TAV. In particular, pathologically high shear rates and a reduced washout of the sinuses may increase the risk of valve thrombosis and should therefore be investigated. By means of fluid-structure interaction (FSI) as a powerful in silico tool, the transient flow field in an aortic valve was analyzed. A linear elastic behavior was assumed for leaflet material properties (Young modulus: 10 MPa, Poisson ratio: 0.46 and leaflet material density: 1000 kg/m3) and blood was specified as a homogeneous, Newtonian and incompressible fluid (fluid density: 1060 kg/m3 and a dynamic viscosity: 0.0035 Pa s). In this numerical study we present a Eulerian approach, which is based on transport equation of the residence time (RT) as a passively transported scalar. It can be clearly seen that the RT is significantly higher in the sinus referred to the main flow. At time step t = 0.25 s, the average residence time in the main flow is RTavg ≈ 0.05 s, whereas RT ≈ 0.25 s in the sinus. In particular, RT is a valuable hemodynamic metric to quantify the washout of the sinus in order to evaluate the thrombogenic potential of TAV devices. Further studies will concentrate on particle image velocimetry measurements for validation purposes. In particular the velocity in the sinus and therefore the washout is one important hemodynamic key feature that has to be improved for future TAV designs.
Highlights
Today, surgical aortic valve replacement (SAVR) is the gold standard of treatment for patients with aortic stenosis
At time step t = 0.25 s, the average residence time in the main flow is RTavg ≈ 0.05 s, whereas RT ≈ 0.25 s in the sinus
The hemodynamic situation in the sinuses of the valve prosthesis, which is characterized by recirculation, low fluid velocity and high residence time (RT), is a critical factor in the development of valve thrombosis [9]
Summary
Surgical aortic valve replacement (SAVR) is the gold standard of treatment for patients with aortic stenosis. Patients with an increased surgical risk are preferably treated by transcatheter aortic valve implantation (TAVI) [1,2]. In Germany the number of TAVI is twice as high as SAVR [3]. The occurrence of valve thrombosis is associated with reduced leaflet motion and flow stagnation in the sinuses [6-8]. These findings trigger concerns regarding an increased risk of stroke and the limitation of long-term valve durability [9]. The mechanisms leading to thrombosis in the cardiovascular system are traditionally described by means of Virchow’s triad [10]: hemodynamic factor (fluid stasis and/or high shear stresses), surface factor (endothelial injury, leaflet damage), and hemostatic factor (hypercoagulability, significant tissue injury) [7,11]
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