Distinct pressure half-time values by transthoracic echocardiography for grading of paravalvular regurgitation after transcatheter aortic valve replacement.

Postprocedural aortic regurgitation (AR) has negative impact on patient outcome after transcatheter aortic valve replacement (TAVR). Standard assessment of AR severity by echocardiography is hampered after TAVR. Measurement of pressure half-time (PHT) by echocardiography is not limited in these patients but it may be affected by concomitant left ventricular hypertrophy (LVH). This study sought to evaluate distinct cut-off values of PHT differentiating between patients without and with more than mild LVH for grading of AR after TAVR with cardiac magnetic resonance (CMR) as the reference method for comparison. 71 patients (age 81 ± 6 years) with severe aortic stenosis undergoing TAVR were included into the study. Transthoracic echocardiography (TTE) and CMR were performed after TAVR. Left ventricular mass index was calculated by TTE. PHT was measured by continuous-wave Doppler echocardiography of aortic regurgitation jet. In 18 patients (25%) PHT could not be obtained due to no or very faint Doppler signal. Aortic regurgitant volume and regurgitant fraction were calculated by CMR by flow analysis of the ascending aorta. In 14 of 53 patients (26%) AR after TAVR was moderate or severe as categorized by CMR analysis. More than mild LVH was present in 27 of 53 patients (51%). PHT correlated inversely less to regurgitant fraction by CMR analysis in patients with LVH (r = -0.293; p = 0.138) than in patients without LVH (r = -0.455; p = 0.020). In patients without relevant LVH accuracy of PHT to predict moderate or severe paravalvular regurgitation AUC was 0.813 using a cut-off value of 347 ms and AUC was 0.729 in patients with more than mild LVH using a cut-off value of 420 ms. Analysis of PHT by TTE with distinct cut-off values for patients without and with more than mild LVH allows detection of moderate or severe AR after TAVR as defined by CMR. In none of the patients in which PHT could not be measured AR was categorized as more than trace by CMR analysis.

Numerical modeling of fluid-structure interaction in arteries with anisotropic polyconvex hyperelastic and anisotropic viscoelastic material models at finite strains.

The accurate prediction of transmural stresses in arterial walls requires on the one hand robust and efficient numerical schemes for the solution of boundary value problems including fluid-structure interactions and on the other hand the use of a material model for the vessel wall that is able to capture the relevant features of the material behavior. One of the main contributions of this paper is the application of a highly nonlinear, polyconvex anisotropic structural model for the solid in the context of fluid-structure interaction, together with a suitable discretization. Additionally, the influence of viscoelasticity is investigated. The fluid-structure interaction problem is solved using a monolithic approach; that is, the nonlinear system is solved (after time and space discretizations) as a whole without splitting among its components. The linearized block systems are solved iteratively using parallel domain decomposition preconditioners. A simple - but nonsymmetric - curved geometry is proposed that is demonstrated to be suitable as a benchmark testbed for fluid-structure interaction simulations in biomechanics where nonlinear structural models are used. Based on the curved benchmark geometry, the influence of different material models, spatial discretizations, and meshes of varying refinement is investigated. It turns out that often-used standard displacement elements with linear shape functions are not sufficient to provide good approximations of the arterial wall stresses, whereas for standard displacement elements or F-bar formulations with quadratic shape functions, suitable results are obtained. For the time discretization, a second-order backward differentiation formula scheme is used. It is shown that the curved geometry enables the analysis of non-rotationally symmetric distributions of the mechanical fields. For instance, the maximal shear stresses in the fluid-structure interface are found to be higher in the inner curve that corresponds to clinical observations indicating a high plaque nucleation probability at such locations. Copyright © 2015 John Wiley & Sons, Ltd.