Effects of Transcatheter Heart Valve Oversizing Left Ventricular Outflow on Valve Leaflet Bending Stress Following Transcatheter Aortic Valve Implantation With The Corevalve: An In-vitro Study
The objective of this in-vitro study was to evaluate on a pulse duplicator, leaflet bending stress in the CoreValve for different sizes of silicon native valve model, stroke volumes and degrees of valve oversizing.
Background and objectives
Transcatheter heart valve (THV) replacement has become a viable alternative with promising results for high and intermediate risk patients with severe aortic stenosis. However, the durability of THV remains currently largely unknown and remains to be investigated. In order to prevent paravalvular regurgitation and valve embolization, moderate valve oversizing (5-20% in area) is recommended. The effect of such oversizing on valve durability is still unknown. This in vitro study aims at evaluating, on a pulse duplicator, leaflet bending stress (LBS) in the CoreValve (CV) for different valve sizes, stroke volumes (SV) and degrees of valve oversizing (OS).
Three different sizes of CoreValve were tested on a pulse duplicator under the following configurations: 1) CV23 mm implanted in aortic annuli (AA) ranging from 17 to 20 mm (%OS of 15%-35%); 2) CV26 mm implanted in AA ranging from 20 to 23 mm (%OS of 13%-30%); 3) CV29 mm implanted in AA ranging from 23 to 26 mm (%OS of 11.5%-26%). Geometric orifice area (GOA) and LBS were measured using high-speed camera imaging (1000 img/sec) during both systole and diastole. For each configuration tested, the heart rate was set to 70 bpm, mean aortic pressure to 100 mmHg and stroke volume to 30,50,70,90 ml.
For each given CV and annulus size, the GOA increased significantly with OS (1.25±0.14 to 2.56±0.08 cm2, p<0.001) and SV (range: 1.17 to 2.72 cm2, p=0.001). LBS decreased with OS, increasing prosthesis size and AA size while increasing with SV (p<0.03). The smallest value of peak LBS (0.99 MPa) was obtained with the CV29 mm in AA of 26 mm (%OS=11.5%), SV 30 ml and the largest value (3.79 MPa) for the CV23 mm in AA of 17 mm (%OS=35%), SV 90 ml. Interestingly, for each configuration, the peak of LBS was not obtained when the valve was fully open but during valve opening or closing. Higher peak LBS was associated with larger %OS (r=0.52, p<0.001) and higher SV (r=0.31, p=0.03).
Effects of SV on higher LBS are more significant in small CV and annuli size. Moderate valve OS, such as generally used for transcatherter aortic valve implantation, is associated with increased LBS during valve opening and closing. This might negatively impact long-term durability of the valve.