Radiofrequency Ablation Directionally Alters Geometry and Biomechanical Compliance of Mitral Valve Leaflets: Refinement of a Novel Percutaneous Treatment Strategy

Abstract

Myxomatous mitral valve disease is a form of mitral valve prolapse, which is characterized by a disorganized collagen matrix with excessive glycosaminoglycan content. Due to loss of mechanical competence and increased surface area of the mitral valve leaflets, this disease leads to regurgitation and cardiac dysfunction. There is a strong clinical need for percutaneous treatment of patients with myxomatous mitral valve disease and regurgitation as an alternative to open-chest surgery. We have previously examined the efficacy of radiofrequency ablation of the mitral valve leaflets as a strategy to reduce prolapse and regurgitation in a canine model. Prior to testing this strategy further in a large animal model, we sought to determine the ‘therapeutic window’ that should be targeted in vitro. Here, we quantified both the geometrical and biomechanical compliance changes of porcine mitral valve anterior leaflets before and after radiofrequency ablation at various powers (Watts) for 15 s. Following ablation, there was significant shortening in the circumferential direction after 15 and 25 W, which led to significant decreases in surface area at these powers. Under an equibiaxial membrane tension of 90 N/m, which approximates systolic loading of 120 mmHg, axial strain in the radial direction was predominantly affected following ablation with significant decreases following 10, 15, and 25 W. Circumferential strain was not different following any ablation power, except 25 W when it was significantly increased. Areal strain at 90 N/m was significantly decreased following 10 and 15 W ablations, but was increased following 25 W. These data indicate that radiofrequency ablation decreases mitral valve leaflet surface area and compliance, but only achieving both within a narrow therapeutic window. To maximize both of these effects, 15 W appears to be the target power. While 25 W leads to ~25% reduction in tissue area, it results in increased compliance. We speculate that at this power, collagen fibers may be failing due to rupture, either directly from ablation or once they are mechanically loaded.