Mechanism of mitral valve tethering caused by apical sparing contractility pattern in transthyretin amyloid cardiomyopathy

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BACKGROUND: In transthyretin amyloid cardiomyopathy (ATTR-CM), pathological changes occur in the mitral valve, but the mechanism remains largely unknown. This study aimed to clarify the mechanism through quantitative analysis of the morphology and function of the mitral valve using three-dimensional (3D) echocardiography. METHODS: A total of 69 patients with ATTR-CM who underwent 3D transthoracic echocardiography from December 2015 to October 2022 were compared with 30 healthy controls. RESULTS: 3D echocardiographic analysis revealed increased mitral annular dilation and mitral valve tethering in patients with ATTR-CM. In the preserved left ventricular ejection fraction (ATTR-pEF) subgroup (n = 36), mitral valve tethering was more pronounced, despite normal mitral annular area. The rate of change in the distance between mitral annulus and papillary muscle was significantly higher in ATTR-CM patients and was an independent predictor of mitral valve tethering in the ATTR-pEF group. Among indices of left ventricular function, only the apical sparing ratio was correlated with this change ratio in the multivariate analysis. CONCLUSION: Mitral valve tethering is observed in ATTR-CM regardless of EF. Apical sparing at systole increases in the mitral annulus-papillary muscle distance, leading to mitral valve tethering.

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