By Mohamed Abdel-Wahab
Transcatheter aortic valve implantation (TAVI) is a new technique with the potential for transforming the treatment of high-risk patients with aortic stenosis. Expansion and refinement of transcatheter approaches for aortic valve implantation is an area of active research and development. While a variety of transcatheter valves are currently in the pipeline, the Edwards Sapien and Medtronic CoreValve represent the two currently established devices in Europe, and both have been reported to have excellent flow characteristics.
Accumulating data have reported promising results concerning procedural success, quality of life improvement, and short-, mid- and more recently long-term outcomes. Nevertheless, among the clinically relevant complications following TAVI is the development of aortic regurgitation following valve implantation, which is mainly of paravalvular origin. Mild aortic regurgitation has been reported to occur in 50% of patients. Higher degrees of regurgitation, though less frequent, are clinically significant and have been reported in frequencies between 7% and 20%, and a paucity of data has accounted for the negative influence of post-procedural aortic regurgitation on clinical outcome.
The development of aortic regurgitation following TAVI is multifactorial and depends on several factors related to the aortic root anatomy and its relation to the implanted prosthesis including the shape and size of the aortic annulus, degree of annular and leaflet calcifications, left-ventricular outflow tract (LVOT) anatomy, and the prosthesis/annulus discongruence. Proper device positioning is also an important factor related to the occurrence of aortic regurgitation, and deep implantation would result in severe aortic regurgitation, since the covered skirt of the prosthesis would be situated below the native annulus, allowing blood to regurgitate through the holes of the uncovered portion of the stent frame. The CoreValve prosthesis is a long device and allows for a wide range of implant depths. Moreover, the haemodynamic performance of the prosthesis within the aortic annulus may depend on a number of factors including the ascending aorta and the LVOT, which may affect the ability of the nitinol-stent to provide adequate radial force. Significant paravalvular regurgitation due to malposition of the valve is probably more evident with CoreValve as the valve will function normally without embolising under less precise deployment. Therefore, our group has looked at anatomical and procedural variables strongly linked to the occurrence of paravalvular aortic regurgitation after implantation of the CoreValve prosthesis, and analysed the incidence of paravalvular aortic regurgitation when a concept integrating these variables is applied for TAVI.
A total of 150 consecutive patients treated with the CoreValve prosthesis transfemorally for severe native aortic valve stenosis (mean age 79.5±7.3 years, 43% men, mean logistic EuroScore 24.2±14.9) were included in this study. Analysis of the first 50 patients (cohort A) revealed that the LVOT-to-ascending aorta angle and device depth in relation to the non-coronary cusp (NCC) were the strongest independent predictors for the occurrence of significant (≥2/4) paravalvular regurgitation identified on post-procedural aortic root angiography. A concept considering both factors during patient selection and device implantation was applied in all subsequent patients (n=100; cohort B). Consequently, cohort B patients had significantly smaller angles compared to cohort A (12.5±4.9 vs. 19.7±7.9, p<0.001), and the percentage of patients with large angles (≥25) decreased from 22% to 4% (p=0.001), reflecting a change in patient selection for the CoreValve prosthesis. Similarly, depth of valve implantation was significantly lower in cohort B compared to cohort A (6.9±3.2mm vs. 10.4±3.7mm for the NCC, p<0.001, and 7.8±3.6mm vs. 11.3±3.7mm for the left coronary cusp, p<0.001), indicating significantly higher device implantation. In addition, post-dilatation of the implanted valve in an attempt to reduce the degree of paravalvular regurgitation was performed in only four patients (8%) of cohort A and 33 patients (33%) of cohort B (p=0.001), indicating an increased operator awareness of the negative impact of residual aortic regurgitation on outcome. The cover index reflecting the congruence between annular size and selected device size did not differ between both groups. Consequently, the incidence of significant paravalvular regurgitation after CoreValve implantation decreased from 40% in our initial experience to 16% thereafter (p=0.001), resulting in a significantly higher device success rate as defined by the valve academic research consortium (60 % vs. 84%, respectively, p=0.001).
We therefore believe that a strategy incorporating measurable anatomical and procedural variables together with post-implantation corrective measures can reduce the incidence of paravalvular aortic regurgitation after transfemoral TAVI with the Medtronic CoreValve prosthesis.
Mohamed Abdel-Wahab is a consultant cardiologist, Heart Center, Segeberger Kliniken, Bad Segeberg, Germany. Abdel-Wahab reports receiving a research grant from Medtronic.