Abstract

Despite the marked improvement in prosthetic heart valve design and functionality, thromboembolism, structural failure, endocarditis and hemolysis are still possible complications. In such cases, native heart valve disease is replaced with “prosthetic heart valve disease”. Bileaflet Mechanical Heart Valve (BMHV) dysfunction can cause serious and potentially fatal complications.
In vivo, in vitro, and Computational Fluid Dynamics (CFD) studies were conducted on dysfunctional BMHVs in order to: (1) investigate the relationship between blood flow patterns downstream of the dysfunctional BMHV and the levels of hemolysis and/or thrombus formation; (2) to evaluate the limitations of the hemodynamic parameters and cutoff values suggested by the American Society of Echocardiography (ASE) guidelines; and (3) to improve the accuracy of the current diagnosis methods using the same clinical modalities and settings.
Pulsatile two-dimensional and two phase flow numerical simulations revealed that the flow upstream and downstream of a dysfunctional mechanical heart valve was highly influenced by dysfunction severity and this resulted in discrepancies between Doppler echocardiography and numerically derived transvalvular pressure gradients. Moreover, the flow downstream of the dysfunctional valve was characterized by abnormally elevated shear stress and large-scale vortices. These flow characteristics can predispose to blood components damage.
Three-dimensional Fluid-Structure Interaction (FSI) numerical modeling showed that the flow nature is three-dimensional and time dependent, especially with the existence of valve dysfunction. A pulsatile 3-D FSI numerical model should be used when the evolution of the vortical structure downstream of the BMHV is the objective of the study. Only flow characteristics through the central orifice are measured by the current diagnosis methods. Therefore, revisiting the assumptions and the theory behind the current clinical method is critical in order to include the flow through the two lateral orifices.
A practical mathematical model was proposed for predicting the normal reference values of Doppler-derived parameters for BMHVs. The new theoretical model overcomes the shortcomings of the parameters suggested by the ASE guidelines by taking into account flow conditions (Left Ventricle Outflow Tract (LVOT) measurements), valve size and valve type. The accuracy of diagnosis significantly improved using the new theoretical parameters compared to those suggested by the ASE. Finally, the new method improved the way to evaluate of the performance of BMHVs, not only after implantation, but also early during the stage of design and manufacturing.