Platelet activation induced by shear stresses and non-physiological flow field generated by bileaflet mechanical heart valves (BMHVs) leads to thromboembolism, which can cause fatal consequences. One of the causes of platelet activation could be intermittent regurgitation, which arises due to asynchronous movement and rebound of BMHV leaflets during the valve closing phase. In this numerical study, the effect of intermittent regurgitation on the platelet activation potential of BMHVs was quantified by modeling a BMHV in the straight and anatomic aorta at implantation tilt angles 0°, 5°, 10°, and 20°. A fully implicit Arbitrary Lagrangian-Eulerian-based Fluid-Structure Interaction formulation was adopted with blood modeled as a multiphase, non-Newtonian fluid. Results showed that the intermittent regurgitation and consequently the platelet activation level increases with the increasing implantation tilt of BMHV. For the straight aorta, the leaflet of the 20° tilted BMHV underwent a rebound of approximately 20° after initially closing, whereas the leaflet of the 10°, 5°, and 0° tilted BMHVs underwent a rebound of 8.5°, 3°, and 0°, respectively. For the anatomic aorta, the leaflet of the 20° tilted BMHV underwent a rebound of approximately 24° after initially closing, whereas the leaflet of the 10°, 5°, and 0° tilted BMHVs underwent a rebound of 14°, 10°, and 7°, respectively. For all the implantation orientations of BMHVs, intermittent regurgitation and platelet activation were always higher in the anatomic aorta than in the straight aorta. The study concludes that the pivot axis of BMHV must be implanted parallel to the aortic root's curvature to minimize intermittent regurgitation and platelet activation. K E Y W O R D Saortic root geometry, bileaflet mechanical heart valve, implantation tilting angle, intermittent regurgitation, platelet activation

No abstract

No abstract

No abstract

Abstract. Flow induced structural stresses can cause mechanical prosthetic aortic valve to fail due to yielding. In this study, we have performed the structural analysis, especially the effect of leaflet thickness on equivalent stresses developed in a Bileaflet mechanical heart valve (BMHV) due to blood flow through it has been investigated. The leaflet thickness varies from 0.5mm to 0.7mm, by 0.1mm. A fluid-structure interaction approach based on Arbitrary Lagrangian Eulerian (ALE) technique has been employed with the aid of an user defined function (UDF). Results of the analysis show that high von Mises stresses are developed in BMHV with leaflet thickness of 0.5mm and 0.6mm, being 75% and 13% higher than allowable equivalent stress respectively. Such thinner leaflets are therefore, not sustainable to be replaced with diseased aortic valve.

Numerical fluid–structure interaction (FSI) methods have been widely used to predict the cardiac mechanics and associated hemodynamics of native and artificial heart valves (AHVs). Offering a high degree of spatial and temporal resolution, these methods circumvent the need for cardiac surgery to assess the performance of heart valves. Assessment of these FSI methods in terms of accuracy, realistic modeling, and numerical stability is required, which is the objective of this paper. FSI methods could be classified based on how the computational domain is discretized, and on the coupling techniques employed between fluid and structure domains. The grid-based FSI methods could be further classified based on the kinematical description of the computational fluid (blood) grid, being either fixed grid, moving grid, or combined fixed–moving grid methods. The review reveals that fixed grid methods mostly cause imprecise calculations of flow parameters near the blood–leaflet interface. Moving grid methods are more accurate, however they require cumbersome remeshing and smoothing. The combined fixed–moving grid methods overcome the shortcomings of fixed and moving grid methods, but they are computationally expensive. The mesh-free methods have been able to encounter the problems faced by grid-based methods; however, they have been only limitedly applied to heart valve simulations. Among the coupling techniques, explicit partitioned coupling is mostly unstable, however the implicit partitioned coupling not only has the potential to be stable but is also comparatively cheaper. This in-depth review is expected to be helpful for the readers to evaluate the pros and cons of FSI methods for heart valve simulations.

Thromboembolism remains a major concern associated with the use of BMHVs, and one of its leading causes could be cavitation, which has been reported to occur due to rapid closing of BMHV leaflets and consequent pressure drop. The aortic root geometry and the implantation rotation of BMHV significantly affect the leaflet kinematics and associated hemodynamics of BMHV and, consequently, may also initiate cavitation which has been investigated in this study. Two aortic roots, straight and bulged, were modelled, while three implantation rotation angles of BMHV were modelled, differing by 45°. ALE was employed as the FSI method, and blood was modelled as non-Newtonian. The results show that the closing velocity of one of the leaflets of a 0° rotated BMHV was 15% higher in bulged aorta as compared to straight aorta. The maximum closing velocity of fast closing leaflet was found to increase with the increasing implantation rotation of BMHV in bulged aorta, being, respectively, 8% and 19% higher for 45° and 90° rotated BMHV as compared to a 0° rotated BMHV. Consequently, it was observed that the pressure dropped below the vapour pressure for all the modelled implantation rotation angles of BMHV in bulged aorta near the leaflet tip. The maximum pressure drop across BMHV also increased with the increasing implantation rotation of BMHV in bulged aorta, being, respectively, 20% and 44% higher for 45° and 90° rotated BMHV as compared to a 0° rotated BMHV. The leaflet kinematics have been found liable to initiate cavitation.

No abstract