A multidimensional dynamic quantification tool for the mitral valve

The mitral valve (MV) is a complex three-dimensional (3D) intracardiac structure. 3D transthoracic and transoesophageal echocardiography are used to evaluate and describe the changes in the mitral valve apparatus due to degenerative or functional mitral regurgitation. These techniques are, however, not accurate enough to capture the dynamic changes during the cardiac cycle. We describe a novel multistage modelling (MSM) technique, using three-dimensional transoesophageal echocardiography (3D TOE), to visualize and quantify the MV during all the phases of the cardiac cycle.

Using 3D TOE, sets of images were obtained from 32 individuals who were undergoing surgery for other reasons and who did not have MV disease. These images were divided into six steps whereby every step represented one cardiac cycle. The image sets were then cropped and sliced at the level of MV, then imported and segmented by the open source software (3D Slicer) to create 3D mathematical models. The models were synchronized with patient's ECGs and then reunited and exported as multiphase dynamic models. The models were analysed in two steps: (i) direct step-by-step visual inspections of the MV from various angles and (ii) direct measurements of anteroposterior, intercommissural, anterolateral-posteromedial diameters, anterolateral angles and anteroposterior angles in systole and diastole at different levels.

The segmentation results in 32 × 6 high-quality cropped MV. The division of models into six steps allows quantification and tracking of MV movement. Reunion of the models leads to creation of a full real-time simulation of the MV during the cardiac cycle. Synchronization of the models with ECG enables accurate simulation. Measurements of the diameters showed: median intercommissural diameters were increased with 10% from mid-systole to mid-diastole [31.9 mm (28.9-34.9), 34.8 mm (31.2-38.2), respectively, P-value <0.001]. This was also observed for anteroposterior diameters [33.8 mm (29.8-35.2), 37.1 mm (31.8-38.5), respectively, P-value <0.001]. Anterolateral-posteromedial diameter did not change significantly in both phases [43.7 mm (36.3-48.9), 43.5 mm (35.5-47.5), respectively]. Intercommissural and anteroposterior diameters were approximately the same in systole [31.9 mm (28.9-34.9) and 32.5 mm (29.8-35.2)] and diastole [34.8 mm (31.2-38.2) and 35.2 mm (31.8-38.5)]. Measurements of anteroposterior angle at the anterolateral junction showed that this angle was accentuated acutely in diastole rather in systole [115° (104-129), 126° (113-137), respectively, P-value <0.001]. It was the same when measuring the anterolateral angle [105° (97-113), 119° (106-130), respectively, P-value <0.001].

The novel MSM technique allows precise quantification of shape changes in MV, which may help in better understanding the normal MV physiology, facilitate the diagnosis of MV pathologies and lead to numerical simulation of MV flow and displacement. It can also help cardiac surgeons and cardiologists gain a better understanding of the MV and assist them in obtaining a reliable orientation in order to choose optimal treatment strategies and plan surgical interventions. The measurement of the new anterolateral angle allowed better quantification of mitral annulus angulation and could be considered as new parameter that may help in future development of a new generation of mitral rings.