In silico mechanical standard tests of a transcatheter aortic valve with anti-embolic filter

Aortic stenosis is a narrowing of the aortic valve opening caused by calcium formation on the native leaflets of the valve, which alter the normal blood circulation. This pathology is one of the most common cardiovascular diseases in North America and Europe. Currently, there is no pharmacological treatment that inhibits the progress of the pathology and usually the stenotic native valve is surgically replaced with a biological or mechanical prosthesis. Transcatheter aortic valve (TAV) implantation is a minimally invasive alternative to open-heart surgical valve replacement. This technique represents the only possibility for about a third of patients with severe aortic stenosis in advanced age that are not eligible for surgical treatment. However, TAV implantation is still associated to several problems related to post-operative recovery that limit its effectiveness, including an increased risk of stroke. In this regard, an innovative TAV with anti-embolic filter with Nitinol frame has been recently developed to limit the risk of stroke. This device is for temporary use and the filter of the device aims to capture calcium debris during the replacement of the aortic valve, overcoming some of the limitations of TAV implantation. Computational modelling has a fundamental role in supporting the design and testing of endovascular devices. Comparing to an experimental approach, it allows optimizing the device mechanical performance with reduced time and costs in the product development cycle. In this context, here the finite element method was used to perform in silico two typical tests for the evaluation of the mechanical performance of the TAV with antiembolic filter according to the standard ISO 5840-3 for heart valve substitutes, namely the crush and crimping tests. Particular attention was dedicated to the verification phase of the models. Three different types of meshes of the TAV model, namely a tetrahedral, hexahedral, and one-dimensional mesh, were compared by quantifying the stress and strain on the device, the computed forces on the testing equipment and the final deformed TAV geometry, for both the crush and crimping test. The element size for each mesh type was chosen after a mesh independence study. The findings of the study showed that the choice of the element type depends on the testing needs. For instance, one-dimensional elements are the most suitable to compute the forces generated between the device and the testing equipment, in terms of excellent compromise between precison and computational cost. Moreover, the conducted in silico tests allowed observing that the device could support the conditions of load without deforming in a permanent way, suggesting that the current design of the TAV could satisfy the requirements of the standard ISO 5840-3 related to the crush and crimping tests. In conclusion, this study presented an in silico replica of the crush and crimping standard tests for the characterization of a TAV with antiembolic filter. Once validated, the two models may substitute the corresponding experimental tests during the certification stage of the device, helping to reduce the time and costs associated with the development of this endovascular device.