To our knowledge, the present study is the first to use ECG-gated cardiac CT to assess the geometric differences within the mitral valve complex between improved and persistent secondary mitral regurgitation after TAVR in patients with aortic regurgitation, and to identify risk factors for persistent mitral regurgitation. In this single-center retrospective study, the proportion of improved secondary mitral regurgitation occurring at 1 month after TAVR was 65.3%, with 34.7% of patients remaining unchanged. Mitral annular area (OR, 1.41; 95%CI: 1.05, 1.90; p = 0.02) and MVTA (OR, 7.24; 95%CI: 1.72, 30.44; p = 0.007) were independent predictors of less mitral regurgitation improvement after TAVR.
Secondary mitral regurgitation is characterized by the preservation of normal structure. However, correct work of the mitral valve depends on the coordinated and synchronized work of its anatomic components, which in turn are tightly reliant on the function of the LV and LA[11]. Secondary mitral regurgitation in patients with aortic regurgitation arises as a result of adverse LV remodeling stemming from significantly increased volume and pressure load, characterized by papillary muscle displacement, leaflet tethering, annular dilatation, reduced valvular closing forces, and inadequate leaflet coaptation[14, 15]. In addition to LV remodeling, enlarged LA contributes to a proportion of secondary mitral regurgitation, resulting in further annular dilatation, particularly in patients with atrial fibrillation[16, 17]. CT allows a comprehensive assessment of the mitral valve through precise measurement of annulus size and detailed evaluation of the subvalvular apparatus geometry[18, 19]. In addition to trigone-to-trigone distance, larger D-shaped mitral annulus measurements, including area, perimeter, anteroposterior and intercommissural distance, were associated with less mitral regurgitation improvement after TAVR in the present study. In multivariable analysis, the mitral annular area was confirmed as an independent predictors of less mitral regurgitation improvement after TAVR. Thus, a larger annulus is susceptible to sustained mitral regurgitation after TAVR. This finding is consistent with previous studies in patients with aortic stenosis[20]. The triangle-to-triangle distance denotes the distance between two triangular fibrous structures located at both ends of the base of the anterior leaflet and is relatively resistant to deformation and change[21]. Therefore, the triangle-to-triangle distance may remain unchanged or increase slightly in patients with a significantly enlarged mitral annulus, making it a poor indicator of mitral regurgitation evolution after TAVR.
In the current study, MVTA was identified as an independent risk factor for less mitral regurgitation improvement after TAVR. The extent of mitral valve tenting is indicative of the severity of secondary mitral regurgitation and has a strong correlation with the prognosis[22]. Systolic tenting was initially thought to be the consequence of LV remodeling, by displacing the papillary muscle away from the mitral annular plane, thus causing leaflet tension and tethering[23]. Advances in three-dimensional echocardiography have led to a better understanding of the complex mechanisms of secondary mitral regurgitation, and the concept of ‘atriogenic’ leaflet tethering caused by the enlarged LA has been proposed to further explain the generation of secondary mitral regurgitation[24, 25]. Although both papillary muscle displacement and mitral valve tenting are primary markers of subvalvular remodeling in mitral regurgitation, the former is solely influenced by LV remodeling, whereas the latter is influenced by both LV and LA remodeling. This may partially explain why the degree of mitral valve tenting was associated with mitral regurgitation improvement after TAVR in this study, while the relationship of papillary muscle displacement to mitral regurgitation was not identified.
Limitations
Limitations exist in the present study. The retrospective nature and the small sample size are major limitations. Therefore, the conclusions drawn are not sufficiently robust and need to be further verified by future prospective large sample size studies. In addition, it is possible that the mitral valve parameters derived from CT at end-systole are over- or underestimated. As the images are reconstructed within 10% intervals of the cardiac cycle, end-systole may not be captured optimally. Furthermore, conventional 2-dimensional echocardiography to assess the severity of secondary mitral regurgitation is challenging, particularly in the presence of eccentric regurgitant jets or multiple regurgitant jets, resulting in an underestimation of the degree of regurgitation.