Potential mechanism of left ventricular spherical remodeling: association of mitral valve complex-myocardium longitudinal tissue remodeling mismatch.

Since mitral valve (MV) complex (MVC) longitudinally bridges left ventricular (LV) base end and its middle, insufficient MVC longitudinal tissue length (TL) elongation relative to whole LV myocardial longitudinal TL elongation could limit LV-base-longitudinal-TL elongation, leading to predominant LV-base-transverse-TL elongation, constituting LV spherical remodeling. In 30 patients with dilated cardiomyopathy (DCM), 30 with aortic regurgitation (AR), and 30 controls, LV sphericity, LV-apex- or base-transverse- and longitudinal-TL, MVC-longitudinal-TL, and whole-LV-longitudinal-TL were measured by three-dimensional (3D) echocardiography. Ratio of each measure versus mean normal value (i.e., LV-apex-transverse-TL ratio) was considered to express the directional and regional tissue elongation. [LV-base-longitudinal-TL ratio/global-LV-TL ratio] and [MVC-longitudinal-TL ratio/whole-LV-longitudinal-TL ratio] were obtained as the degree of LV-base-longitudinal-TL or MVC-longitudinal-TL elongation relative to the whole LV elongation. LV-apex-transverse-, LV-apex-longitudinal-, and LV-base-transverse-TL ratios were significantly increased (1.27 to 1.42, < 0.01) in both DCM and AR, while the LV-base-longitudinal-TL ratio was not increased in DCM [1.04 ± 0.19, not significant (ns)] and only modestly increased in AR (1.12 ± 0.21, < 0.01). Whole-LV-longitudinal-TL ratio was significantly increased in both DCM and AR (1.22 ± 0.18 and 1.20 ± 0.16, < 0.01), while MVC-longitudinal-TL ratio was not or only modestly increased in both groups (1.07 ± 0.15, ns, and 1.12 ± 0.17, = 0.02, respectively). Multivariable analysis revealed that LV sphericity was independently related to a reduced [LV-base-longitudinal-TL ratio/global-LV-TL ratio] (standard β = -0.42, < 0.01), which was further related to a reduced [MVC-longitudinal-TL ratio/whole-LV-longitudinal-TL ratio] (standard β = 0.72, < 0.01). These are consistent with the hypothesis that relatively less MVC-longitudinal-TL elongation in the process of primary LV myocardial tissue elongation may limit LV-base-longitudinal-TL elongation, contributing to LV spherical remodeling. Left ventricular (LV) spherical remodeling is associated with poor prognosis and less-effective cardiac performance, which commonly develops in dilated cardiomyopathy. However, its mechanism remains unclear. We hypothesized and subsequently clarified that less mitral valve complex (MVC) tissue longitudinal elongation relative to whole LV myocardial tissue longitudinal elongation is related to disproportionately less LV base longitudinal versus transverse myocardial tissue elongation, constituting spherical remodeling. This study suggests modification of MVC tissue elongation could be potential therapeutic targets.