Modelling and application of mitral valve dynamics for reproducing the flow in the left ventricle of the human heart

The fluid dynamics in the left ventricle of the human heart is considered an important player for the prediction of long term cardiovascular outcome. To this end, numerical simulations represent an important tool for integrating the existing medical imaging technology and uncover physical flow phenomena. This study presents a computational method for the fluid dynamics inside the left ventricle designed to be efficiently integrated in clinical scenarios. It includes an original model of the mitral valve dynamics, which describes an asymptotic behavior for tissues with no elastic stiffness other than the constrain of the geometry obtained from medical imaging; in particular, the model provides an asymptotic description without requiring details of tissue properties that may not be measurable in vivo. The advantages of this model with respect to a valveless orifice and its limitations with respect to a complete tissue modeling are verified. Its performances are then analyzed in details to ensure a correct interpretation of results. It represents a potential option when information about tissue mechanical properties is insufficient for the implementations of a full fluid-structure interaction approach. Geometries of left ventricle (LV) and mitral valve (MV) are extracted from 4D-transesophageal echocardiography. MV geometries are extracted in open and closed configurations and the intraventricular fluid dynamics is reproduced by a dedicated approach to direct numerical simulation (DNS) that includes flow-tissue interaction for the MV leaflet (Collia et al. 2019). This approach is applied to normal and pathological ventricles to investigate the dynamics of the MV during the cardiac cycle: how it interacts with the ventricular flow and how it affects clinical measurements. The dynamics of mitral opening at the onset of diastole, as well as the closure at the transition between diastole and systole, is governed by the high pressure gradients associated with the bulk cardiac flow. On the opposite, during the flow diastasis in the middle of the diastolic filling, valvular motion is primarily influenced by the intraventricular circulation that gives an increased tendency to close in enlarged ventricles. This observation provides a physical interpretation to echocardiographic measurements commonly employed in the clinical diagnostic process. Results demonstrated the properties of false regurgitation, blood that did not cross the open MV orifice and returns into the atrium during the backward motion of the MV leaflets, whose entity should be accounted when evaluating small regurgitation (Collia et al. 2019). The regurgitating volume is found to be proportional to the effective orifice area, with the limited dependence of the LV geometry and type of prolapse. These affect the percentage of old blood returning to the atrium which may be associated with thrombogenic risk. This non-invasive method is useful for the assessment of blood flow, to improve early detection of cardiac dysfunctions and for provide a concrete helpful in clinical routines.