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EXPERIMENTAL STUDIES

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

Sten Lyager Nielsen, MD^* , Hans Nygaard, DMSc^* , Arnold A. Fontaine, PhD, J. Michael Hasenkam, MD, DMSc^* , Shengqui He, MD, Niels T. Andersen, PhD and Ajit P. Yoganathan, PhD

^* Department of Cardiothoracic and Vascular Surgery, Skejby Sygehus, Aarhus University Hospital, Aarhus, Denmark
Institute of Experimental Clinical Research, Skejby Sygehus, Aarhus University Hospital, Aarhus, Denmark
Institute for Bioengineering Bioscience and School of Chemical Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
Institute of Biostatistics, Aarhus University, Aarhus, Denmark

Manuscript received July 27, 1998; revised manuscript received September 18, 1998, accepted November 18, 1998.

Reprint requests and correspondence: Sten Lyager Nielsen, MD, Department of Cardiothoracic and Vascular Surgery, Skejby Sygehus, Aarhus University Hospital, 8200 Aarhus N, Denmark

OBJECTIVES

The purpose of this study was to investigate the impact of the chordae 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 with 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 model where leading edge chordal forces measured by dedicated miniature force transducers were controlled by changing left ventricular pressure and papillary muscle position. Chordae geometry and occlusional leaflet area (OLA) needed to cover the leaflet orifice for a given leaflet configuration were determined by two-dimensional echo and reconstructed three-dimensionally. Occlusional leaflet area was used as expression for incomplete leaflet coaptation. Regurgitant fraction (RF) was measured with an electromagnetic flowmeter.

RESULTS

Mixed procedure statistics revealed a linear correlation between the sum of the chordal net forces, [F_C – F_T]_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 F_T by papillary muscle malalignment restricted leaflet 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 mitral leaflet remodeling, which generated a nonuniform regurgitant orifice area.

CONCLUSIONS

Altered chordal force distribution caused functional mitral regurgitation based on tented leaflet configuration as observed clinically.

Abbreviations and Acronyms   APL = apical posterolateral   APM = anterolateral papillary muscle   DAL, DPL = distance from the anterior/posterior leaflet tip to the annular plane   FC, FT = chordal coapting and tethering force component. Subscripts AA, AP, PA, PP refer to chordae location (chordae from APM to the anterior leaflet, from APM to the posterior leaflet, from PPM to the anterior leaflet and from PPM to the posterior leaflet). Subscripts APM and PPM refer to the chordal forces emanating from APM and PPM. Subscripts AL and PL refer to the chordal forces supplying the anterior and posterior leaflet. Subscript S refers to the sum of the chordal force components   LAL, LPL = horizontally projected anterior and posterior leaflet length   LAPM, LPPM, LPM = papillary muscle lengths (distance from APM/PPM tip to the annular plane through the midpoint of the corresponding half mitral systolic coaptation point). LPM is the mean of LAPM and LPPM   LVP – LAP = transmitral pressure difference   MR = mitral valve regurgitation   OLA = occlusional leaflet area of the mitral valve. Subscript ACOM/PCOM refers to the anterolateral/posteromedial commissural half portion   PPM = posteromedial papillary muscle   RF = mitral regurgitant fraction   2D = two-dimensional   AL, PL = coaptation angle of the anterior/posterior leaflet   AL, PL = anterior/posterior leaflet excursion angle

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