Mechanisms of Reduction of Mitral Regurgitation by Cardiac Resynchronization Therapy: by Analysis of Left Ventricular Morphology

Abstract

Purpose: It's well known the mechanism of functional mitral regurgitation(MR) is geometric distortion of the mitral apparatus by left ventricular(LV) dilatation, which increases leaflet tethering and restricts closure. The purpose of this study is to assess the relationship between LV morphologic change and reduction of MR after cardiac resynchronization therapy(CRT). Methods: We studied 46 non-ischemic cardiomyopathy patients, and 29 normal controls. Echocardiography was used to assess the severity of MR, LV shape, mitral valve morphology, and displacement of papillary muscles(PM). Results: In patients, LV shape was more spherical (sphericity index: 1.55 ± 0.25 vs. 1.93 ± 0.25 p < 0.001), anterior PM shifted posteriorly (PM angle; the angle between anterior PM and posterior interventricular groove: 151.6 ± 19.4 vs. 176.7 ± 15.1° p < 0.001), and mitral leaflets were more tethered (tethering area: 1.66 ± 0.56 vs. 0.43 ± 0.06 cm2 p < 0.001) than that of normal controls. However at 6 months after CRT, sphericity index (1.51 ± 0.20 to 1.89 ± 0.40 p < 0.001) and PM angle (146.6 ± 16.5 to 167.7 ± 17.7° p < 0.001) increased significantly. Moreover tethering area (1.63 ± 0.72 to 1.03 ± 0.77 cm2 p < 0.001), and MR jet area (28.7 ± 16.1 to 16.1 ± 19.3% of LA area p < 0.01) were reduced in responder. Indeed, tethering area correlated with sphericity index (r=-0.39 p < 0.001), and PM angle (r=−0.29 p < 0.01). Conclusions: CRT reduced the subvalvar traction by changing the shape of LV and restored displaced anterior PM toward original position. These morphological change contributes to the reduction of functional MR in patients treated with CRT.