Flow in Prosthetic Heart Valves: State-of-the-Art and Future Directions

Abstract

Since the first successful implantation of a prosthetic heart valve four decades ago, over 50 different designs have been developed including both mechanical and bioprosthetic valves. Today, the most widely implanted design is the mechanical bileaflet, with over 170,000 implants worldwide each year. Several different mechanical valves are currently available and many of them have good bulk forward flow hemodynamics, with lower transvalvular pressure drops, larger effective orifice areas, and fewer regions of forward flow stasis than their earlier-generation counterparts such as the ball-and-cage and tilting-disc valves. However, mechanical valve implants suffer from complications resulting from thrombus deposition and patients implanted with these valves need to be under long-term anti-coagulant therapy. In general, blood thinners are not needed with bioprosthetic implants, but tissue valves suffer from structural failure with, an average life-time of 10-12 years, before replacement is needed. Flow-induced stresses on the formed elements in blood have been implicated in thrombus initiation within the mechanical valve prostheses. Regions of stress concentration on the leaflets during the complex motion of the leaflets have been implicated with structural failure of the leaflets with bioprosthetic valves. In vivo and in vitro experimental studies have yielded valuable information on the relationship between hemodynamic stresses and the problems associated with the implants. More recently, Computational Fluid Dynamics (CFD) has emerged as a promising tool, which, alongside experimentation, can yield insights of unprecedented detail into the hemodynamics of prosthetic heart valves. For CFD to realize its full potential, however, it must rely on numerical techniques that can handle the enormous geometrical complexities of prosthetic devices with spatial and temporal resolution sufficiently high to accurately capture all hemodynamically relevant scales of motion. Such algorithms do not exist today and their development should be a major research priority. For CFD to further gain the confidence of valve designers and medical practitioners it must also undergo comprehensive validation with experimental data. Such validation requires the use of high-resolution flow measuring tools and techniques and the integration of experimental studies with CFD modeling.

Near Valve Flows and Potential Blood Damage During Closure of a Bileaflet Mechanical Heart Valve

“…The flow structures and mitral heart valve closing dynamics investigated here were used to validate computational models such as that by Govindarajan et al [37]. While the valve tip appears to be a major site for blood damage, other locations such as the hinge region are also expected to contribute to hemolysis [3]. When designing bileaflet valves, manufacturers should also carefully consider how the following features will affect fluid stresses: impact location between the leaflet and housing, gap between the housing and the valve in its closed position, the shape/curvature of the leaflet, effective orifice area, and the design of the leaflet tip [38].…”

“…Furthermore, valve design can greatly impact the likelihood or extent of blood damage [2]. In recent years, there has been a shift in focus of both in vitro experimentation and computation towards interpreting the local flow dynamics near the valve housing of tilting disk and bileaflet valves and around the hinges of bileaflet valves, since hemolysis or platelet activation are more likely to occur in these regions [3].…”

A New Method for Assessing Haemolysis in a Rotary Blood Pump Using Large Eddy Simulations (LES)

“…Tavoularis et al (2003) and Yoganathan et al (2005) recognized LES as a very promising tool in modeling phenomena inside the artificial heart.…”

Erratum to: Quantitative Assessment of Turbulence and Flow Eccentricity in an Aortic Coarctation: Impact of Virtual Interventions

“…6 The overall poor performance of Reynolds Average Navier-Stokes (RANS) based models and the inapplicability of using Direct Numerical Simulation (DNS) schemes for realistic high Reynolds number vascular flows are well accepted. 32,39,48,49,59 In between DNS and RANS modeling, Large Eddy Simulation (LES) on the other hand only resolves the largest energycontaining scales whereas the remaining unresolved part of the flow is handled by a subgrid-scale (SGS) model. LES have been performed in a number of idealized stenotic flow studies, 19,39,45 showing excellent agreement with experimental data.…”