Novel In Vitro Test Systems and Insights for Transcatheter Mitral Valve Design, Part II: Radial Expansion Forces

Abstract

Transcatheter mitral valve (TMV) replacement technology has great clinical potential for surgically inoperable patients suffering from mitral regurgitation. An important goal for robust TMV design is maximizing the likelihood of achieving a geometry post-implant that facilitates optimal performance. To support this goal, improved understanding of the annular forces that oppose TMV radial expansion is necessary. In Part II of this study, novel circular and D-shaped Radial Expansion Force Transducers (C-REFT and D-REFT) were developed and employed in porcine hearts (N=12), to detect the forces required to radially expand the mitral annulus to discrete oversizing levels. Forces on both the septal-lateral and inter-commissural axes (F SL and F IC ) scaled with device size. The D-REFT experienced lower F SL than the C-REFT (19.8±7.4 vs. 17.4±10.8N, p=0.002) and greater F IC (31.5±14.0 vs. 36.9±16.2N; p=0.002), and was more sensitive to degree of oversizing. Across all tests, F IC /F SL was 2.21±1.33, likely reflecting low resistance to radial expansion at the aorto-mitral curtain. In conclusion, the annular forces opposing TMV radial expansion are non-uniform, and depend on final TMV shape and size. Based on this two-part study, we propose that radial force applied at the commissural aspect of the annulus has the most potent effect on paravalvular sealing.

Novel In Vitro Test Systems and Insights for Transcatheter Mitral Valve Design, Part I: Paravalvular Leakage

“…This notion is further discussed in Part II. 27 The following limitations to this study are noteworthy. First, water was used as the working medium.…”

“…Part II of this study, which directly quantified the radial expansion forces associated with these circular and D-shaped stent profiles, offered further insights into this question. 27 TMV designers must make decisions about both outer profile shape and intended approach to sizing. A circular stent is likely simplest to develop, and is insensitive to rotational orientation during implantation.…”

“…Note, no differences were detected between the pre-procedural dimensions of these hearts and those tested in Part II. 27 The PVL experimental protocol caused the MV annulus to stretch plastically. On average, the PVL protocol caused 20.9% increase in valve perimeter, 58.6% increase in valve area, 32.7% increase in D SL , and 18.0% increase in D IC .…”

“…In Part I, presented herein, paravalvular leakage rates were studied in explanted porcine hearts, using mock TMV models manufactured across discrete shape-size combinations. In Part II, 27 the radial forces necessary for a TMV to expand the porcine MV annulus to the same shapes and sizes was quantified via a novel force transducer system.…”