Creation of Nonischemic Functional Mitral Regurgitation by Annular Dilatation and Nonplanar Modification in a Chronic In Vivo Swine Model

Abstract

Background— Mechanisms and treatments of nonischemic functional mitral regurgitation (NIMR) are not fully established, in part, because of a lack of proper large animal models. We developed a novel technique of NIMR creation in a swine model by making multiple small incisions in the mitral annulus. Methods and Results— Ex vivo experiments using isolated swine hearts (n=10) showed a 15% increase in annular area (6.8–7.8 cm 2 ) after 16 incisions were made along the posterior mitral annulus of a pressurized left ventricle. In an in vivo swine model (n=7; 46.4±2.2 kg), NIMR was created by making fourteen to twenty-six 2-mm incisions in the atrial aspect of the mitral annulus using a cardioport video-assisted imaging system in the beating heart. Animals were euthanized at 4 weeks (n=4) and 6 weeks (n=3). Three-dimensional (3D) echocardiography was obtained before and immediately after NIMR creation and at euthanasia; vena contracta area, mitral annular dimension, left ventricular volume, and inter-papillary muscle distance were measured. The mitral annular incisions resulted in mild to moderate mitral regurgitation and an increased vena contracta area. NIMR creation altered mitral valve geometry by decreasing mitral annular nonplanarity and increasing annular area, primarily in the anteroposterior dimension. NIMR creation did not significantly change left ventricular volume or inter-papillary muscle distance. Longer follow-up period did not significantly affect these outcomes. Conclusions— NIMR can successfully be created in a beating heart swine model and results in dilatation and 3D changes in mitral annular geometry. This model can enhance the experimental validation of new valve repair devices and techniques.