Understanding the Interaction Between Transcatheter Aortic Valve Prostheses and Supra-Annular Structures From Post-Implant Stent Geometry

Objectives: The authors sought to better understand the stent geometry of the Lotus valve after transcatheter aortic valve replacement (TAVR) and its potential implications for valve size selection.

Background: The authors hypothesized that the greatest interference between the frame and aortic valvar complex occurs across the aortic valve leaflets.

Methods: The authors retrospectively analyzed the multidetector computed tomography (MDCT) scans of 32 consecutive patients undergoing Lotus valve (Boston Scientific, Natick, Massachusetts) implantation. The prosthesis cross section was analyzed at 3-mm increments along its length. The plane where the frame had the smallest area was defined as the waist. The corresponding plane of the waist on pre-procedural MDCT was identified by surrounding structures such as calcium deposits, commissural fusion, and commissural gaps, and was referred to as the supra-annulus. The spline of the supra-annulus was circumscribed with reference to the post-implant stent geometry at the waist.

Results: The waist was 5.8 ± 1.7 mm higher than the native annulus on post-procedural MDCT. The waist had a nearly 2-fold larger compression rate than the stent at the native annulus level (36.3 ± 10.4% vs. 18.9 ± 9.6%; p < 0.01), irrespective of valve morphologies. The supra-annulus was 5.9 ± 1.6 mm higher than the annulus on pre-procedural MDCT. Patients had an approximately 17% decrease in area from the annulus to the supra-annulus (18.3 ± 4.4% for bicuspid morphology and 16.0 ± 3.5% for tricuspid morphology).

Conclusions: Major interference between the implanted prosthesis and anatomy occurred at a level above the annulus. The decrease in area from the annulus to supra-annulus may explain the feasibility of implanting a smaller valve than that suggested by traditional annular measurements.