Effect of percutaneous aortic valve position on stress map in ascending aorta: A fluid‐structure interaction analysis

Abstract

Transcatheter aortic valve implantation (TAVI) is an increasingly widespread procedure. Although this intervention is indicated for high and low surgical risk patients, some issues still remain, such as prosthesis positioning optimization in the aortic annulus. Coaxial positioning of the percutaneous prosthesis influences directly on the aortic wall stress map. The determination of the mechanical stress that acts on the vascular endothelium resulting from blood flow can be considered an important task, since TAVI positioning can lead to unfavorable hemodynamic patterns, resulting in changes in parietal stress, such as those found in post‐stenotic dilatation region. This research aims to investigate the influence of the prosthetic valve inclination angle in the mechanical stresses acting in the ascending aortic wall. Aortic compliance and blood flow during cardiac cycle were numerically obtained using fluid structure interaction. The aortic model was developed through segmentation of a computed tomography image of a specific patient submitted to TAVI. When compared to standard position (coaxiality match between the prosthesis and the aortic annulus), the inclination of 4° directed to the left main coronary artery decreased the aortic wall area with high values of wall shear stress and pressure. Coaxial positioning optimization of percutaneous aortic prosthesis may decrease the high mechanical stress area. These changes may be important to reduce the aortic remodeling process, vascular calcification or even the prosthesis half‐life. Computational fluid dynamics makes room for personalized medicine, with manufactured prosthesis tailored to each patient.

Stress Load and Ascending Aortic Aneurysms: An Observational, Longitudinal, Single-Center Study Using Computational Fluid Dynamics

“…To determine blood flow, a constitutive model of blood rheology is necessary. In the present study, blood was modeled as a Newtonian fluid (dynamic viscosity = 3.5 cP [ 26 , 32 ]) since inside vessels with a large diameter such as the aorta, during the systolic peak, the deformation rate is higher than 50 , and the blood behaves like a Newtonian fluid [ 32 , 33 , 34 ]. A comparison of the flow prediction at the systolic peak inside aortas with aneurysms, employing Newtonian and non-Newtonian viscosity models [ 35 ], revealed similar flow patterns and wall tension distributions, corroborating the small impact of viscoelasticity on these large vessels.…”

“…Although the physiological flow is pulsatile, as a first approximation, it can be represented by a succession of stationary states. This is a convenient approximation since it substantially reduces the computing effort while maintaining the major flow characteristics [ 32 , 33 , 34 , 35 ]. Furthermore, as shown in Perocco [ 36 ], the critical condition with respect to high pressure and high WSS actually occurs at the systolic peak, indicating that this is a good approach for examining the worst scenario.…”

“…At each outflow, diffusion flux was neglected and the flow rate percentage distribution, based on a typical physiological condition as proposed by Alastruey et al [ 47 ] was prescribed: descending aorta, 69.1%; brachiocephalic trunk, 19.3%; left carotid artery, 5.2%; and left subclavian artery, 6.4% ( Figure 2 e). A no-slip condition was imposed at the aortic wall, which was considered rigid, due to the small compliance that exists when its maximum diameter is reached during the systolic peak [ 32 , 48 ].…”

“…To correlate the data between the two groups of patients (with and without aneurysm growth), we determined the mean and maximum relative pressure values in the area with pressure equal to or above the critical value of 100 Pa. This is a conservative threshold, selected based on the study of a healthy patient by Ibanez et al [ 32 ], who found a pressure difference between the aortic valve and the ascending aortic wall of approximately 1 mmHg (133 Pa). According to Simão et al [ 25 ], the critical WSS is 5 Pa, while Etli et al [ 51 ] consider 9 Pa to be the critical WSS.…”

“…To determine blood flow, a constitutive model of blood rheology is necessary. In th present study, blood was modeled as a Newtonian fluid (dynamic viscosity 𝜇 = 3.5 c [26,32]) since inside vessels with a large diameter such as the aorta, during the systol peak, the deformation rate is higher than 50 s , and the blood behaves like a Newtonia Although the physiological flow is pulsatile, as a first approximation, it can be represented by a succession of stationary states. This is a convenient approximation since it substantially reduces the computing effort while maintaining the major flow characteristics [32][33][34][35].…”