Bioengineering Case Study to Evaluate Complications of Adverse Anatomy of Aortic Root in Transcatheter Aortic Valve Replacement: Combining Biomechanical Modelling with CT Imaging

Figures

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  Figure 1. FEA may predict possible TAVR complications.

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  Figure 2. Nine-month follow-up gated CT scan demonstrating bioprosthesis malposition in respect to left main coronary. 3D reconstructions in longitudinal and cross-section before (A) and after the procedure (B,C). Please note coronary ostia proximity with calcifications and ostial stenosis due to partial obstruction by a portion of the THV frame (C).

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  Figure 3. Nine-month follow-up gated CT scan demonstrating bioprosthesis malposition in respect to right coronary. 3D reconstructions in longitudinal and cross-section before (A) and after the procedure (B,C). Please note ostia proximity with calcifications and ostial stenosis due to partial obstruction by a portion of the bioprosthesis frame (C).

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  Figure 4. CT scan before TAVR shows: (1) RCA ostium calcification (yellow arrow); (2) calcification near ostium of the Left Main (blue arrow) and (3) calcified native valve under left coronary ostium (red arrow).

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  Figure 5. Using Rhinoceros 3D (McNeel & associates, Seattle, WA, USA) and Simulia Abaqus we performed an isogeometric analysis interfacing between computer aided design (CAD) and finite element analysis. (A,B) Pre-processing of aortic root model through the extraction of patient specific aortic valve geometry from medical CT images using VMTK (Vascular Modeling Toolkit, http://www.vmtk.org/) and MATLAB code (v.R2018b, Mathworks Inc-Natick, MA, USA). (C,D) Pre-processing of patient specific aortic valve. The modelling of leaflets was obtained using Rhinoceros 3D to Abaqus. (E) Generation of CAD model of the aortic wall (blue areas) with calcifications (yellow blocks). (F) Mapping of calcific leaflets from patient’s CT images. (G) Apposition of leaflets in patient’s aortic root model.

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  Figure 6. Main steps of simulation of TAVR using finite element analysis investigation. Catheter model has rigid material properties. (A) stent crimping; (B) catheter removing; (C) stent self-expansion.

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  Figure 7. (A,B) Stent-root interaction area shows regions of aortic root elements with a contact pressure higher than zero. Quantitative measure of the device footprint onto the inner wall of the aortic root after expansion is shown. The evaluation of stent adhesion and anchoring to the aortic wall allows to reveal areas with inadequate stress and contact potentially leading to device migration. (C,D) Von Mises average stress measures the forces induced by the device expansion onto the inner wall of the aortic root and the quantitative and qualitative evaluation of their locations with higher peak stress. Higher values of stress also mean higher global anchoring force.

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  Figure 8. (A, top and bottom) Ideal CoreValve expansion with stent shape implantation; (B, top and bottom) Real deformation of the stent shape after implantation in the investigated patient’s root. Top: not complete expansion of the device; Bottom: asymmetric stent expansion.

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  Figure 9. Areas of paravalvular leak can be measured as area of the orifices generated between the inner aortic wall and the device, after its expansion. The amount of blood flow regurgitation could be also quantitatively and indirectly evaluated from the dimension of paravalvular orifice. (A) cutting plane Ω correspondent to sino-tubular junction (STJ) of the model with incomplete expansion of the inferior part of the device (blue arrow). (B) Mismatch between expanded stent and inner aortic root wall is indicative of the development of paravalvular leakage (PVL) (red area).