• echocardiography
• mitral regurgitation
• mitral insufficiency
• mitral valve replacement
• vector flow mapping
• energy loss
• mitral valve repair

Background. Heart valve diseases and, in particular, mitral regurgitation are a group of pathologies that in the last two decades have undergone profound changes in terms of epidemiology, diagnosis, prognosis, and therapy. Echocardiography has progressively gained importance, enabling to obtain an early recognition of these pathologies, to provide a more accurate selection of patients, and to identify the optimal treatment timing. In this subset, researchers focused on the study and characterization of parameters that could provide information on the severity of mitral insufficiency and left ventricle function. In the first group of parameters, we include: 1) qualitative parameters, as valve morphology, regurgitation jet color Doppler signal, and regurgitation jet continuous wave (CW) doppler signal; 2) semi-quantitative parameters, as vena contracta and inflow and upstream venous flow; 3) quantitative parameters, as EROA, RVol, and heart chambers dilatation. The second group includes the left ventricle ejection fraction (LVEF) and the left ventricle stroke volume (SV). Although these parameters are widely used, new ones emerged in recent years, to achieve a comprehensive understanding of the pathology and its possible therapeutic implications. Among these, speckle-tracking echocardiography with Strain and Strain rate calculation gained particular importance. Another important derived parameter is the coupling that describes the relationship between cardiac function and the arterial system, expressing ventricular performance. Finally, vector flow mapping (VFM) has been also used to assess the left ventricle.

Purpose of study. Analyze and describe the key role of the mitral valve on the generation of physiologic flow dynamics in control patients and basics aspects of vortex behavior in the left ventricle. Examine 1) how mitral regurgitation determines inefficient non-physiological flow within the left ventricle, resulting in abnormal vortex formation and energy loss (EL), 2) how its treatment can influence the distribution of flow inside the left ventricle, 3) how this could have a potential clinical impact.

Materials and methods. From the Cardio-Thoracic Department of Pisa, two populations of patients, one represented by patients with mitral regurgitation (n:30) and one control (n:20), were recruited. They were evaluated, using Vector Flow mapping, in terms of 1) vortices patterns in early diastole, late diastole, and systole, 2) number of vortices in early diastole, mid diastole, and late diastole, 3) energy loss, calculated in a complete cycle, in isolated systole, in isolated diastole, and as a percentage ratio between diastolic data and the total. To visualize the interventricular flow were used vectors and flow streamlines. From the MR population, 18 patients undergoing the main treatment options (repair and replacement) were selected, and their flow dynamics were analyzed, and energy loss was calculated.

Results. In the formation of the LV vortex, a primary role is played by the physiological eccentric position of the valve and by the difference between the anterior longer leaflet and the posterior shorter leaflet of the mitral valve, which leads to a pair of counter-rotating vortices. Normally, the anterior vortex rotates clockwise, and the posterior vortex rotates counterclockwise. In patients with Mitral Regurgitation, different patterns of interventricular flow were visualized. Those patterns are associated with an increase of EL, from 112 (91-158) J/(m3 ∙ s), in control patients, to 230 (165-299) J/(m3 ∙ s) in patients with mitral regurgitation (p-value <0.0001). Especially, Diastolic EL (p-value <0.0001) and Diastolic/total % (p-value = 0.007), presented a statistically significant increase in MR population. There is also a substantial difference, in terms of interventricular flows, between mitral valve repair and replacement: Mitral Valve repair tends not to alter the direction of the vortex and does not increase EL, in contrast, Mitral Valve replacement alters the direction of the intraventricular vortex and increases EL. In addition, there are important differences between the two types of treatment: the use of tri-leaflets bioprosthetic valves seem to cause multiple separated vortexes in the LV chamber, while the mechanical valve replacement (in anatomical position) would lead to a single large vortex. In contrast to these, Tendyne replacement appears to have the potential to generate physiological vortex patterns. These results were also confirmed by EL calculations, which show that flows other than physiological flows lead to increased energy expenditure. This is a preliminary study realized on a small population. Therefore, larger cohorts will be needed in the future to verify changes in EL and vortices and analyze differences in different treatment options.

Conclusions. VFM is an important tool for studying the dynamics of interventricular flows and related parameters (EL, vortex, WSS), under physiological, pathological, and therapeutic conditions.