Mechanisms of changes in functional mitral regurgitation by preload alterations

Background: This study aimed to investigate the mechanisms of acute changes in functional mitral regurgitation (FMR) by preload alterations. Methods: Twenty-two consecutive patients with left ventricular ejection fraction <40% and at least mild FMR underwent transthoracic echocardiography. Passive leg lifting and sublingual administration of nitroglycerin were performed to alter preload. Mitral regurgitant volume (MRV) was assessed using the Doppler method. Results: MRV changed in parallel with preload alterations. MRV correlated better with tenting height (TH) than with mitral annular area (MAA) at baseline, whereas the difference in the correlate coefficients was not statistically significant (R = 0.69 and R = 0.40, respectively; p = 0.19). On the other hand, changes in MRV between each sequential stage correlated better with those in MAA than with those in TH (R = 0.68 and R = 0.44, respectively; p = 0.043). Multiple regression analysis revealed that baseline TH was the independent determinant of baseline MRV (R = 0.69, p = 0.0004), whereas changes in MAA with preload alteration were the independent determinant of the changes in MRV (R = 0.68, p <. 0.0001). Changes in left atrial (LA) volume were the independent determinant of the changes in MAA (R = 0.30, p = 0.0063). Conclusions: Acute changes in FMR with preload alterations resulted from the transverse changes in MAA rather than the longitudinal changes in tethering-tenting of mitral geometry, and mitral annular deformation was determined by changes in LA volume. Preload reduction might help heart failure treatment through the reduction in FMR resulting from the decrease in LA and mitral annular size.