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

AbstractOBJECTIVESThe purpose of this study was to investigate the impact of the chordae tendineae force distribution on systolic mitral leaflet geometry and mitral valve competence invitro.BACKGROUNDFunctional mitral regurgitation is caused by changes in several elements of the valve apparatus. Interaction among these have to comply with the chordal forcedistribution defined by the chordal coapting forces (FC) created by the transmitral pressure difference, which close the leaflets and the chordal tethering forces(FT) pulling the leaflets apart.METHODSPorcine mitral valves (n = 5) were mounted in a left ventricular model where leading edge chordal forces measured by dedicated miniature force transducers werecontrolled by changing left ventricular pressure and papillary muscle position. Chordae geometry and occlusional leaflet area (OLA) needed to cover the leaflet orifice for a givenleaflet configuration were determined by two-dimensional echo and reconstructed three-dimensionally. Occlusional leaflet area was used as expression for incomplete leafletcoaptation. Regurgitant fraction (RF) was measured with an electromagnetic flowmeter.RESULTSMixed procedure statistics revealed a linear correlation between the sum of the chordal net forces, ∑[FC−FT]s, and OLA with regression coefficient (minimum − maximum) beta = −115 to −65 [mm2/N]; p< 0.001 and RF (beta = −0.06 to −0.01 [%/N]; p < 0.001). Increasing FTby papillary muscle malalignment restrictedleaflet mobility, resulting in a tented leaflet configuration due to an apical and posterior shift of the coaptation line. Anterior leaflet coapting forces increased due to mitralleaflet remodeling, which generated a nonuniform regurgitant orifice area.CONCLUSIONSAltered chordal force distribution caused functional mitral regurgitation based on tented leaflet configuration as observed clinically