Patient–Specific Immersed Finite Element–Difference Model of Transcatheter Aortic Valve Replacement

Figures

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  FIGURE 1.. Patient-specific three-dimensional aortic root geometry from computed tomography (CT) image data. (a) Identification of patient-specific aortic root geometry through semi-automated Ct image segmentation in iTk-sNaP. (b) Reconstructed aortic root geometry. The aortic root measures 26 mm in diameter, 7.68 cm in length, and 1.0 mm in thickness. (c) Native aortic valve geometry. The idealized volumetric native aortic valve leaflets are constructed from measurements by Sahasakul et al.33 and trimmed to fit within the reconstructed aortic root. The thickness of the leaflets is 0.4 mm in the belly regions and 0.92 mm in the nodules of Arantius. (d) Native aortic valve model fiber architecture. The mean fiber orientation runs from commissure to commissure; however, two fiber directions (shown separately in red and blue) are used in each leaflet to account for fiber angle dispersion and are fit to tensile test data from Pham et al.31

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  FIGURE 2.. CoreValve Evolut R model geometry. (a) Evolut R Nitinol stent frame model geometry reconstructed from a computed tomography (CT) scan of a 26 mm Medtronic CoreValve Evolut R device. (b) Evolut R glutaraldehyde-fixed porcine pericardial sealing skirt geometry with a thickness of 0.34 mm. (c) Evolut R glutaraldehyde-fixed porcine pericardial leaflets geometry with a thickness of 0.34 mm. (d) Rendering of one vertical curve of stent points connected by a series of beams and springs. (e) Evolut R glutaraldehyde-fixed porcine pericardial sealing skirt fiber architecture. The mean fiber direction is 45°; however, two fiber directions (shown separately in red and blue) are used in each leaflet to account for fiber angle dispersion. (f) Evolut R glutaraldehyde-fixed porcine pericardial leaflets fiber architecture. The mean fiber direction is parallel to the direction of flow; however, two fiber directions (shown separately in red and blue) are used to account for fiber angle dispersion

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  FIGURE 3.. Evolut R crimping and deployment. (a) Side view of the uncrimped Evolut R model. (b) Side view of the Evolut R with model crimping device. (c) Top views of the crimping process. The model crimping device applies radial force to the stent frame to crimp the Evolut R. Contact is handled implicitly via the immersed finite element-difference (IFED) method. (d) Side view of the crimped Evolut R model. The final crimped diameter is approximately 17.25 Fr. (e) Expansion of the Evolut R within the stenotic native valve. The top row gives a cross-sectional view of the native valve and Evolut R model kinematics during expansion, and the bottom row provides a top view of the valve at coinciding times

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  FIGURE 4.. Diastolic pressure loading of the deployed Evolut R, shown at the time of peak transvalvular pressure difference. (a) Cross-sectional view of detailed diastolic pressure pattern for the deployed Evolut R model at the time of peak transvalvular pressure difference. The color indicates the pressure at the center plane of the valve, with cooler colors indicating lower pressures and warmer colors indicating higher pressures. (b) Top view of the pressure-loaded Evolut R model at the time of peak transvalvular pressure difference. The transvalvular pressure difference at this time is approximately 72 mmHg, but the Evolut R remains in place within the stenotic native aortic valve. (c) Detailed von Mises stress distribution for the porcine pericardial leaflets and sealing skirt of the deployed Evolut R model at the time of peak transvalvular pressure difference. The color indicates the von Mises stress, with cooler colors indicating lower stresses and warmer colors indicating higher stresses

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  FIGURE 5.. Cross-sectional view of detailed flow patterns for the Evolut R model using driving conditions based on the time-dependent elastance-based left heart model, as given by (7), (8), (9), and (10). The color indicates the magnitude of the velocity through the aortic root at the center plane of the valve, with cooler colors indicating lower velocities and warmer colors indicating higher velocities. The time increment between frames is 0.1 s. The first row shows the velocity magnitude at each location in the plane, while the second row displays a sampling of normalized velocity vectors

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  FIGURE 6.. (a) Leaflet kinematics and von Mises stress distributions of the Evolut R model during valve opening. The color in the second row indicates the von Mises stress, with cooler colors indicating lower stresses and warmer colors indicating higher stresses. The time increment between frames is 25 ms. (b) Leaflet kinematics and von Mises stress distributions of the Evolut R model during valve closing. The color in the second row indicates the von Mises stress, with cooler colors indicating lower stresses and warmer colors indicating higher stresses. The time increment between frames is 25 ms

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  FIGURE 7.. Leaflet tip displacement, pressure, and flow rate waveforms for the Evolut R model using driving conditions based on the time-dependent elastance-based left heart model, as given by (7), (8), (9), and (10). (a) Leaflet tip displacement during systole for the Evolut R’s porcine pericardial leaflets. (b) Left atrial (LA), left ventricular (LV), left ventricular outflow tract (LVOT), and aortic pressure waveforms with the implanted Evolut R. The mean systolic transvalvular pressure difference is 9.62 mmHg, and the effective orifice area (EOA) is 1.50 cm2. (c) Transvalvular flow rate for the implanted Evolut R. The stroke volume is 84.27 mL, yielding a cardiac output of 5.91 L/min

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  FIGURE 8.. Comparison of systolic transvalvular pressure difference waveforms for the Evolut R model, the stenotic native valve model, and the healthy native valve model, while prescribing a flow rate waveform measured by Garcia et al.9 for a patient with severe aortic valve stenosis. (a) Simulated systolic transvalvular pressure differences for the Evolut R, the stenotic native valve, and the healthy native valve. The mean systolic transvalvular pressure differences in the simulated results are: 6.84 mmHg for the Evolut R, 41.42 mmHg for the stenotic native valve, and 0.47 mmHg for the healthy native valve. (b) Prescribed transvalvular flow rate measured by Garcia et al. for a patient with severe aortic valve stenosis. The stroke volume is 45.32 mL, yielding a cardiac output of 3.47 L/min