Chordal force distribution determines systolic mitral leaflet configuration and severity of functional mitral regurgitation

OBJECTIVES The purpose of this study was to investigate the impact of the c hordae tendineae force distribution on systolic mitral leaflet geometry and mitral valve competence in vitro. BACKGROUND Functional mitral regurgitation is caused by changes in several elements of the valve apparatus. Interaction among these have to comply wit h the chordal force distribution defined by the chordal coapting forces (F- C) created by the transmitral pressure difference, which close the leaflets and the chordal tethering forces (F-T) pulling the leaflets apart. METHODS Porcine mitral valves (n = 5) were mounted in a left ventricular mo del where leading edge chordal forces measured by dedicated miniature force transducers were controlled by changing left ventricular pressure and papi llry muscle position. Chordae geometry and occlusional leaflet area (OLA) n eeded to cover the leaflet orifice for a given leaflet configuration were d etermined by two-dimensional echo and reconstructed three-dimensionally. Oc clusional leaflet area was used as expression for incomplete leaflet coapta tion. Regurgitant fraction (RF) was measured with an electromagnetic flowme ter. RESULTS Mixed procedure statistics revealed a linear correlation between th e sum of the chordal net forces, Sigma[F-C - F-T](s), and OLA with regressi on coefficient (minimum - maximum) beta = -115 to -65 [mm(2)/N]; p < 0.001 and RF (beta = -0.06 to -0.01 [%N]; p < 0.001). Increasing FT by papillary muscle malalignment restricted leaflet mobility, resulting in a tented leaf let configuration due to an apical and posterior shift of the coaptation li ne. Anterior leaflet coapting forces increased due to mitral leaflet remode ling, which generated a nonuniform regurgitant orifice area. CONCLUSIONS Altered chordal force distribution caused functional mitral reg urgitation based on tented leaflet configuration as observed clinically. (C ) 1999 by the American College of Cardiology.