A novel heart valve design reduces turbulence in aortic flow

Abstract Background/Introduction Antithrombotic therapy for mechanical heart valve (MHV) prostheses remains critical in balancing the risks of thrombosis or thromboembolism (TTE) events against bleeding complications. The PROACT trial 1 showed that patients with On-X valves (Artivion, Inc.) in the aortic position can be managed with a lower target international normalized ratio INR of 1.5 to 2.0 using warfarin, without increased risk of TTE. However, the bleeding risk persists and the recent PROACT Xa trial failed to show the noninferiority of apixaban to warfarin in patients with an On-X valve 2. Purpose The role of turbulence on thrombus production has been established by in-vitro, in-silico and in-vivo animal studies 3. The On-X valve is perhaps the only commercially available MHV designed with a focus on hydrodynamics 4, leading to measurable clinical benefits. In this study, we propose a novel design methodology driven by fluid mechanical principles aimed at further reducing the MHV-induced turbulence in aortic flow, ultimately lowering the TTE risk and providing more options for antithrombotic therapy strategies. Methods Based on the Richardson-Kolmogorov theory, turbulence can be reduced by breaking the coherence of flow structures. This principle was applied in the Chevron design of aircraft engines and inspired our introduction of fractal design features into a MHV (figure 1). These modifications do not require significant changes in the manufacturing process and have no impact on interventional procedures. To evaluate performance, we conducted quasi Direct Numerical Simulations by solving the Navier-Stokes equations directly on a grid with 30 million cells within a straight ascending aortic model, including the aortic sinus. Two MHV models were tested, the On-X valve and its modified version with our novel design features (FMV). The inlet boundary condition was prescribed with a physiologically realistic time-varying flow rate profile at 70 beats per minute with a peak flow rate of 20 L/min. Results The vortical structures distal to the FMV during systole were less coherent compared to the On-X valve, as demonstrated by the shorter and smaller vortex tubes in figure 2 (A, C). During diastole, significantly fewer vortices were present in the downstream flow of the FMV (figure 2 B, D), indicating a faster decay of turbulence. This was equivalent to a total of 23% reduction in turbulent kinetic energy, highlighting the effectiveness of our design methodology. Conclusion(s) Our proposed design features effectively mitigated excessive turbulence in a realistic aortic flow setting. By further optimizing the design parameters, this novel approach has the potential to significantly reduce TTE risk in patients with prosthetic heart valves. Additionally, this methodology can be readily applied to valves in the mitral position and bioprosthetic valves, extending its benefits to a broader patient population.