Left Ventricular Thinning and Distension in Pig Hearts as a ReproducibleEx VivoModel of Functional Mitral Regurgitation

Functional mitral regurgitation in the setting of an enlarged heart is challenging to repair surgically with an annular approach, and the need to develop subannular and ventricular approaches is recognized yet unrealized because of the lack of models for investigations. In this study, we report a novel model of functional mitral regurgitation induced by left ventricular thinning and distension in pig hearts. Seven pig hearts were explanted at a local slaughterhouse, and left ventricular distension induced by thinning the ventricular myocardium by 60-65% of its original thickness. Distension of the thinned hearts with a 120 mmHg column confirmed significant left ventricular dilatation and mitral valve tethering. These hearts were then mounted into a pulsatile flow model and animated at 120 mmHg left ventricular pressure, 5 L/min cardiac output at 70 beats/min. Echocardiography was used to assess valvular kinematics and hemodynamics. Left ventricular wall thickness reduced by 60.5% +/- 10.1% at the basal plane, 64.8% +/- 11.3% at the equatorial plane, and 64.0% +/- 11.4% at the apical plane after thinning. Upon distension, ventricular volumes increased by 852.4% +/- 639.8% after left ventricular thinning, with an 89.5% +/- 33.9% increase in sphericity index. Mitral valve systolic tenting height increased from 7.92 +/- 2.06 to 15.02 +/- 3.89 mm, systolic tethering area increased from 130.7 +/- 38.2 to 409.9 +/- 124.6 mm(2)and an average mitral regurgitation fraction of 24.4% +/- 16.6% was measured. In a case study, use of multimodality imaging to test the efficacy of transcatheter mitral devices was confirmed. Ventricular wall thinning leading to passive left ventricular distension and dilatation is a reproducibleex vivomodel of mitral valve tethering and functional mitral regurgitation, which in combination with multimodality imaging provides a good simulation model.