Interpapillary muscle distance independently affects severity of functional mitral regurgitation in patients with systolic left ventricular dysfunction

Abstract

Surgical papillary muscle (PM) imbrication has been reported to be effective to relieve leaflet tethering in patients with functional mitral regurgitation (FMR). However, the mechanism that contributes to improvement of FMR by shortening the interpapillary muscle distance (IPMD) has not been well investigated. The purpose of the present study was to investigate whether IPMD can affect MR severity independently ofPMtethering distance in patients with left ventricular dysfunction (LVD) using multislice computed tomography. We analyzed volumetric multislice computed tomography images of mitral apparatus in 83 patients with LVD (ejection fraction <50%): 37 patients with FMR and 46 patients without FMR. By using the original software, we assessed the 3-dimensional geometry of mitral apparatus including IPMD, tethering distances, andmitral tenting volume at end-systole. The severity of FMR was assessed using vena contracta (VC) width by 2-dimensional echocardiography. Posterior and anterior tethering distance and IPMD were increased significantly in patients with FMR than in those without FMR. Patients with IPMD in the highest tertile had a significantly higher degrees of MR (mean ± standard error VC width, 4.5 ± 0.3 mm) compared with patients in the lowest and the middle tertiles, adjusting for PM tethering distance (mean ± standard error VC width, 3.0 ± 0.4 and 2.9 ± 0.3 mm; P<.001, respectively). Multivariate analysis showed that anteroposterior annular diameter and IPMD were the strongest determinants of FMR severity and mitral tenting volume. IPMD, which affects leaflet tethering independently of PM tethering distance, was the major determinant of mitral tenting volume and FMR severity in patients with LVD.