An In Vitro Evaluation of the Impact of Eccentric Deployment on Transcatheter Aortic Valve Hemodynamics

Abstract

Patients with aortic stenosis present with calcium deposits on the native aortic valve, which can result in non-concentric expansion of Transcatheter Aortic Valve Replacement (TAVR) stents. The objective of this study is to evaluate whether eccentric deployment of TAVRs lead to turbulent blood flow and blood cell damage. Particle Image Velocimetry was used to quantitatively characterize fluid velocity fields, shear stress and turbulent kinetic energy downstream of TAVRs deployed in circular and eccentric orifices representative of deployed TAVRs in vivo. Effective orifice area (EOA) and mean transvalvular pressure gradient (TVG) values did not differ substantially in circular and eccentric deployed valves, with only a minor decrease in EOA observed in the eccentric valve (2.0 cm(2) for circular, 1.9 cm(2) for eccentric). Eccentric deployed TAVR lead to asymmetric systolic jet formation, with increased shear stresses (circular = 97 N/m(2) vs. eccentric = 119 N/m(2)) and regions of turbulence intensity (circular = 180 N/m(2) vs. eccentric = 230 N/m(2)) downstream that was not present in the circular deployed TAVR. The results of this study indicate that eccentric deployment of TAVRs can lead to altered flow characteristics and may potentially increase the hemolytic potential of the valve, which were not captured through hemodynamic evaluation alone.

Total ellipse of the heart valve: the impact of eccentric stent distortion on the regional dynamic deformation of pericardial tissue leaflets of a transcatheter aortic valve replacement

“…The optical transparency required in order to image the complex leaflet deformation of the prosthesis necessitated the use of a geometrically simplified and rigid material behaviour of the aortic root model. The rigid aortic root does not represent the compliant behaviour of the aortic root tissue or undergo the pulsatile changes in annulus shape that occur in vivo [12,34]. However, calcium deposits [35], age-related reduced arterial compliance [36] in patients requiring TAVRs, and the scaffolding provided by oversizing of the valve stent may reduce compliance and dimensional changes of the aortic root during TAVR of stenotic valves in vivo and as such a rigid model was deemed a reasonable assumption.…”

“…The TAVR used in this study is a supra-annular design, wherein the valvular portion is distal to the inflow segment of the valve. In such designs non-circular expansion at the inflow portion of the valve stent, owing to contact with the calcified aortic valve, is minimized at the valvular portion [12]. In intra-annular balloon-expandable (e.g.…”

“…Leaflets in distorted stents in both self-expanding and balloon expandable TAVRs have been observed to have increased tautness, reduced mobility and inadequate coaptation (due to buckling and coaptation mismatch) at valve closure [6,7,9,18]. While we have previously shown that stent distortion may increase the haemolytic response of the valve [12], the impact of this distorted stent geometry on the dynamic deformation of the leaflets compared to leaflets in an optimal circular expanded stent remains to be fully understood.…”

“…A 23 mm supra-annular TAVR representative of a commercial valve design was studied (n ¼ 3) [12], consisting of bovine pericardial leaflets (thickness ¼ 0.35 mm) sutured to a selfexpanding Nitinol valve stent with a dedicated commissure post assembly and inflow segment [12,26]. The TAVR used was representative of supra-annular valve designs whereby the valvular section of the device was located distally to the inflow section that is used to anchor the device in the calcified aortic annulus.…”

“…We have previously reported that eccentric distortion can alter the flow characteristics through a TAVR, causing an altered asymmetric systolic jet formation, increased shear stresses and turbulence in flow fields downstream of the valve [12]. It has also been proposed that stent distortion can have a negative impact on the pericardial tissue leaflets of a TAVR specifically that non-circular stent expansion might lead to leaflet distortion, strain concentrations at the commissures of the leaflet and incorrect valve closure [5,9], albeit these changes have yet to be quantified.…”