A review of state-of-the-art numerical methods for simulating flow through mechanical heart valves

Abstract

In nearly half of the heart valve replacement surgeries performed annually, surgeons prefer to implant bileaflet mechanical heart valves (BMHV) because of their durability and long life span. All current BMHV designs, however, are prone to thromboembolic complications and implant recipients need to be on a life-long anticoagulant medication regiment. Non-physiologic flow patterns and turbulence generated by the valve leaflets are believed to be the major culprit for the increased risk of thromboembolism in BMHV implant recipients. In this paper, we review recent advances in developing predictive fluid-structure interaction (FSI) algorithms that can simulate BMHV flows at physiologic conditions and at resolution sufficiently fine to start probing the links between hemodynamics and blood-cell damage. Numerical simulations have provided the first glimpse into the complex hemodynamic environment experienced by blood cells downstream of the valve leaflets and successfully resolved for the first time the experimentally observed explosive transition to a turbulent-like state at the start of the decelerating flow phase. The simulations have also resolved a number of subtle features of experimentally observed valve kinematics, such as the asymmetric opening and closing of the leaflets and the leaflet rebound during closing. The paper also discusses a future research agenda toward developing a powerful patient-specific computational framework for optimizing valve design and implantation in a virtual surgery environment.

Fig. 1

A typical clinical quality bi-leaflet mechanical heart valve (St. Jude Regent)

Fig. 2

The 3D BMHV geometry (23 mm St. Jude Regent) including the housing and the leaflets in a straight aorta (left) and the definition of leaflet angle (right). Taken from [4]

Fig. 3

BMHV simulation [4]. Physiologic inflow waveform (dashed line) and comparison of the calculated leaflet kinematics (solid line) with experimental observations [10] (circles). Adopted from [4]

Fig. 4

BMHV simulation [4] compared with the PIV measurements of Dasi et al. [10]. Instantaneous out-of-plane vorticity contours on the mid-plane of the valve (a) from simulation [4] and (b) from experimental measurements [10]. The contour levels are identical. c Instantaneous vortical structures visualized by iso-surfaces of q-criteria. The dots on the inflow waveform shown at the bottom of each column indicate the time instant during the cycle for that column. Taken from [4]

Fig. 5

Comparison of the upper and lower leaflet kinematics during the opening (top) and closing (bottom) phases. In each figure the inset shows the asymmetric rebound of the leaflets. During the opening phase the calculations are carried out with SC-FSI while both LC and SC-FSI algorithms are stable during closing. Taken from [4]

Fig. 6

Simulations of a BMHV implanted in an anatomic aorta [3, 5]. Left instantaneous out-of-plane vorticity contours on the midplane of the valve. Right 3D instantaneous vortical structures visualized by iso-surfaces of q-criterion