An in vitro evaluation of turbulence after transcatheter aortic valve implantation

Abstract

Background: This study aimed at assessment of post-transcatheter aortic valve (TAV) replacement hemodynamics and turbulence when a same-size SAPIEN 3 (Edwards Lifesciences Corp, Irvine, Calif) and Medtronic Evolut (Minneapolis, Minn) were implanted in a rigid aortic root with physiological dimensions and in a representative root with calcific leaflets obtained from patient computed tomography scans.

Methods: TAV hemodynamics were studied by placing a SAPIEN 3 26-mm and an Evolut 26-mm in rigid aortic roots and representative root with calcific leaflets under physiological conditions. Hemodynamics were assessed using high-fidelity particle image velocimetry and high-speed imaging. Transvalvular pressure gradients (PGs), pinwheeling indices, and Reynolds shear stress (RSS) were calculated.

Results: (1) PGs obtained with the Evolut and the SAPIEN 3 were comparable among the different models (10.5 ± 0.15 mm Hg vs 7.76 ± 0.083 mm Hg in the rigid model along with 13.9 ± 0.19 mm Hg vs 5.0 ± 0.09 mm Hg in representative root with calcific leaflets obtained from patient computed tomography scans respectively); (2) more pinwheeling was found in the SAPIEN 3 than the Evolut (0.231 ± 0.057 vs 0.201 ± 0.05 in the representative root with calcific leaflets and 0.366 ± 0.067 vs 0.122 ± 0.045 in the rigid model); (3) higher rates of RSS were found in the Evolut (161.27 ± 3.45 vs 122.84 ± 1.76 Pa in representative root with calcific leaflets and 337.22 ± 7.05 vs 157.91 ± 1.80 Pa in rigid models). More lateral fluctuations were found in representative root with calcific leaflets.

Conclusions: (1) Comparable PGs were found among the TAVs in different models; (2) pinwheeling indices were found to be different between both TAVs; (3) turbulence patterns among both TAVs translated according to RSS were different. Rigid aortic models yield more conservative estimates of turbulence; (4) both TAVs exhibit peak maximal RSS that exceeds platelet activation 100 Pa threshold limit.

Keywords: hemodynamics; platelet activation; transcatheter aortic valve; turbulence.

Figure 1

(a) Rigid aortic valve chamber with sinuses (b) Patient-specific aortic root models with end extensions and (c) Aortic side view of the 3D printed leaflet calcifications in the patient-specific models.

Figure 2

En-face imaging of the valves at different phases in the cardiac cycle.

Figure 3

Phase averaged velocity vectors and vorticity contours at different phases in the cardiac cycle.

Figure 4

Principal Reynolds shear stresses at different phases in the cardiac cycle.

Figure 5

Turbulent kinetic energy at different phases in the cardiac cycle.

Figure 6

Standard deviation contour plots of the random velocity fluctuations U′ and V′ for the different valve models at peak systole.

Figure 7

(a, c) Instantaneous velocity in the x direction (U) and (c, d) Instantaneous velocity in the y direction (V) plots of the different valve combinations through the cardiac cycle at points A and B respectively in the shear layers.

Video 1

En-face imaging views of the valves throughout the cardiac cycle.

Video 2

Ensemble averaged velocity vectors and vorticity contours for the valves.

Video 3

Main flow streak visualization of the different valves.