Hemodynamics of the Boston Scientific Lotus™ Valve: An In Vitro Study

Abstract

Transcatheter Aortic Valve Replacement (TAVR) is currently used for patients with aortic valve disease at high risk for surgical intervention. The Lotus™ Valve system (Boston Scientific) is a novel repositionable TAVR with bovine pericardial leaflets and a Nitinol® frame, including miniature buckles for repositioning. A detailed characterization of the fluid flow environment in the vicinity of the buckles and the sinus regions will help identify regions of potential flow stagnation and thrombosis. A Lotus Valve was deployed in an in vitro left heart simulator, and the fluid flow through the valve was quantitatively characterized using particle image velocimetry. Three planes of high spatial resolution velocity data were obtained across the valve through the entire cardiac cycle at three stroke volumes (SV). The resulting velocity fields were processed to obtain Reynolds shear stresses (RSS), viscous shear stresses (VSS) and turbulent kinetic energy (TKE) fields. The Lotus Valve showed a central systolic jet at all three SV in the central plane. This jet caused a strong sinus vortex, which persisted through entire systole for all three SV. The location of the vortex was dependent on the SV through the valve. High VSS, RSS and TKE regions were observed at the edge of the systolic jet distal to the valve, however high velocities in these regions caused washout of fluid, which may prevent thrombus formation. The buckle region did not appear to significantly increase the potential for hemolysis of this valve. The Lotus Valve showed very good hemodynamic performance and no regions of stagnation were observed in the vicinity of the valve. These results compare favorably with flow characteristics through bioprosthetic aortic valve replacements, and suggest good clinical performance with this valve system.