The effects of positioning of transcatheter aortic valves on fluid dynamics of the aortic root

Abstract

Transcatheter aortic valve implantation is a novel treatment for severe aortic valve stenosis. Due to the recent use of this technology and the procedural variability, there is very little data that quantify the hemodynamic consequences of variations in valve placement. Changes in aortic wall stresses and fluid retention in the sinuses of Valsalva can have a significant effect on the clinical response a patient has to the procedure. By comprehensively characterizing complex flow in the sinuses of Valsalva using digital particle image velocimetry and an advanced heart-flow simulator, various positions of a deployed transcatheter valve with respect to a bioprosthetic aortic valve (valve-in-valve) were tested in vitro. Displacements of the transcatheter valve were axial and directed below the simulated native valve annulus. It was determined that for both blood residence time and aortic Reynolds stresses, it is optimal to have the annulus of the transcatheter valve deployed as close to the aortic valve annulus as possible.

Figure 1

The heart-flow simulator schematic is illustrated, all components are included and their function is discussed in the text.

Figure 2

(A) Geometry of the aortic model (side and top view). (B) The aortic model with the presence of PIV particles during the experimental analysis. The region of interest used for calculating particle residence time, is highlighted by a red box.

Figure 3

Graph of Valve Position with reference to the native annulus versus Particle Residence time for the two distinct states of cardiac output.

Figure 4

Representation of particle residence time at 4 L/min of cardiac output based on the percentage of particles washed out of sinus of Valsalva (region of interest) at each distinct time interval. For each time interval a certain portion of particles are washed out. (A) is for a 5mm displacement, (B) is for 10mm, (C) for 15mm and (D) for 20mm. It can be observed that a far greater percentage of the particles remain in the sinus past 0.2s in the 5mm displacement than the 20mm displacement.

Figure 5

Reynolds’ shear stress at 2L/min of cardiac output. Magnitude of the shear stress in indicated in a color scale with blue being low values, green, yellow, orange and red indicating an increasing value. (A) is for 5mm of displacement, (B) 10mm, (C) 15mm and (D) 20mm. For all values other than 10mm the stress distribution is relatively low and symmetric.

Figure 6

Reynolds’ shear stress at 4L/min of cardiac output. Magnitude of the shear stress in indicated in a color scale with blue being low values, green, yellow, orange and red indicating an increasing value. (A) is for 5mm of displacement, (B) 10mm, (C) 15mm and (D) for 20mm. For increasing displacement the shear stress increases dramatically and becomes more unstable and asymmetric.