Modes of Leaflet Fluttering: Quantitative Characterization of a Bovine Bioprosthetic Heart Valve

Oscillations of aortic bioprosthetic heart valve (BHV) leaflets during systole are known as leaflet fluttering (LF). LF may be relevant for assessing valvular function and could play a role in structural valve deterioration. However, a quantitative characterization of LF and its underlying physical processes is still missing. The objectives of this study are to systematically characterize LF for a BHV in vitro and to investigate the associated flow structures using a computational model. Leaflet motion of a bovine BHV was captured with high-speed cameras in an in vitro flow loop under varying experimental conditions (cardiac output (CO), inflow, and valve and aortic root orientation). A fluid-structure interaction (FSI) study was conducted for the same BHV for one condition to examine the blood flow patterns associated with LF. In vitro, LF presents in two different modes: either as high-frequency (150-380 Hz), low-amplitude (0.2-0.8 mm) vibrations of the leaflet tips (V-mode) or low frequency (30-90 Hz), high-amplitude (0.4-2.6 mm) waves travelling from leaflet base to tip (T-mode). We observed that LF depends on individual leaflet properties, is more likely to occur, and increases in amplitude and frequency with higher CO, and is also affected by the inflow. The FSI study confirms the presence of the same two modes. We identified large-scale vortex shedding related to the T-mode, superimposed with small-scale vortex shedding connected to vibrations of the leaflet tip (V-mode). Both identified LF modes are potential factors in BHV degeneration and should be considered in the BHV's design.