Comparison of two biological aortic valve prostheses inside patient-specific aorta model by bi-directional fluid-structure interaction

Abstract

In Germany in 2016 17,085 patients received TAVI operations and 9,579 had conventional aortic valve surgery. The 'Heart Team' uses established scoring systems (EuroSCORE, STS, German AV Score) to evaluate operation risks and which technique to use. However, such risk grading fails to consider patient morphology and possible long-term behavior of the replacement valve chosen. Therefore, pre-operative simulation of the dynamic loading on the valve leaflets after TAVR provides information vital for the selection of the appropriate aortic valve therapy - interventional versus conventional. Individual aorta used in this study was captured by MRI. Segmentation and data processing were done with Mimic In-novation Suite. The available biological aortic valves prostheses were reverse engineered to create a 3D CAD model. Simulations combined bi-directional fluid structure interaction (FSI) with a first order Ogden model of the hyperelastic behavior of aortic leaflets from bovine pericardium. Movements induced by flow and the resultant tension on the biological leaflets were computed with developed simulation model. Stress analyses of the leaflets showed behavior attributable to their particular structure. Both valves showed two stress peaks within the initial 0.3 s. Maximum stress occurred, however, at other time points. Furthermore, the initial increase in stress showed a delayed onset. The patterns of movement were also significantly different. So, at opening of the valve, the freely perfused area of the valve, the freedom of leaflet movement and symmetry at closure were different in the two valves. Simulated movement of valve leaflets corresponds well with reality. The estimated stresses clearly lie below thresholds published in the literature for bovine pericardium. It is planned to further develop the current workflow to increase stability and optimize processing time, with the intention of providing the 'Heart Team' with a tool for incorporating individual anatomy when selecting the aortic valves.