Defining the left ventricular base in mitral valve prolapse: impact on systolic function and regurgitation

In bileaflet mitral valve prolapse (BMVP) systolic leaflet displacement creates a pocket of blood on the left ventricular (LV) side of the leaflets, but on the atrial side of the annulus. This blood is excluded from the LV end-systolic volume if the mitral valve annulus is used to determine the most basal extent of the LV. The purpose of this study is to describe the quantitative implications of defining the LV base on mitral regurgitant severity and LV systolic function in BMVP. In 30 consecutive patients (53% male, 58 ± 14 years) with BMVP, LV endocardial and epicardial borders were determined from SSFP images. The LV base at end-systole was defined by the "Functional" method (at the mitral valve annulus) or the "Anatomic" method (at the mitral valve leaflets). Regurgitant volume was the difference between the LV stroke volume and mean forward flow. LV myocardial strain measurements were determined from the short axis endocardial and epicardial borders. The "Functional" method resulted in higher regurgitant volumes (mean difference: 22 ml, range 0-40 ml) and higher ejection fractions (mean difference: 9%, range 0-21%). The correlation between LV end-diastolic volume and regurgitant volume was better with the "Functional" method (r = 0.79, p < 0.0001) than the "Anatomic" method (r = 0.67, p < 0.0001). The correlation between global myocardial radial strain and LV EF was better with the "Functional" method (r = 0.86, p < 0.0001) than the "Anatomic" method (r = 0.68, p < 0.0001). In BMVP, the base of the LV should be defined at the level of the mitral valve annulus so that regurgitant volume most accurately reflects the functional significance of the mitral valve disease and LVEF most accurately reflects global systolic LV function. Defining the basal extent of the LV at the mitral valve leaflets leads to substantially lower regurgitant volumes and lower ejection fractions that could have important clinical consequences.