Does transcatheter aortic valve alignment matter?

Abstract

Objective: This study investigates the effect of transcatheter aortic valve (TAV) angular alignment on the postprocedure haemodynamics. TAV implantation has emerged as an effective alternative to surgery when treating valve dysfunction. However, the benefit of avoiding surgery is paid back by the inability to remove the native diseased leaflets and accurately position the device in relation to the aortic root, and the literature has shown the root anatomy and substitute position can play an essential role on valve function.

Methods: A commercial TAV was placed in a silicone mock aortic root in vitro, including mock native leaflets, and either aligned commissure-to-commissure or in maximum misalignment. Haemodynamic performance data at various stroke volumes were measured, and Particle Image Velocimetry analysis was performed at a typical stroke volume for rest conditions. The two configurations were also studied without mock native leaflets, for comparison with previous in vitro studies.

Results: Haemodynamic performance data were similar for all configurations. However, imaging analysis indicated that valve misalignment resulted in the central jet flow not extending to the root wall in the native commissures' vicinity, replaced by a low shear flow, and a reduction of upper sinus flow of 40%, increasing flow stagnation in the sinus.

Conclusions: TAV misalignment did not result in a significant change in valve hydrodynamic performance, but determined some change in the fluid flow patterns, which may promote pathological scenarios, such as increased thrombogenicity of blood flow within the sinuses of Valsalva, and plaque formation around the lumen of the sinotubular junction.

Keywords: transcatheter aortic valve; valsalva sinuses; valve alignment.

Figure 1

Valve-root configurations considered in study. (A) Configuration C1—commissures of TAV and aortic root model aligned, TAV placed within a cylinder to simulate native leaflets. (B) Configuration C2—TAV 60° out of phase with ideal alignment, native leaflets model again incorporated. (C) Configuration C3—the same valve-root alignment at C1, no native leaflets modelled. (D) The same valve-root alignment at C2, no native leaflets modelled.

Figure 2

Particle image velocimetry measurement details. (A) Top view of the system setup. (B) Typical diagram of the flowrate versus time during systolic phase, with the instants analysed labelled A–E. (C) Diagram of the sinus area within cross-section image, with the upper half of the sinus indicated by red shading and the lower half by orange shading. (D) Example of fast flow width measurement.

Figure 3

Valve performance during forward flow for each configuration at each stroke volume. (A) Effective orifice area. (B) Transaortic pressure drop. (C) Transaortic energy losses.

Figure 4

Native leaflet velocity contour maps and streamlines. (A) Configuration C1, aligned valve within native leaflets). (B) Configuration C2, misaligned valve within native leaflets.

Figure 5

Non-native leaflet velocity contour maps and streamlines. (A) Configuration C3, aligned valve with no native leaflets. (B) Configuration C4, misaligned valve with no native leaflets.

Figure 6

PIV derived data. (A) Downstream velocity across sinotubular junction for the five instants analysed via particle image velocimetry for each configuration. (B) Fast flow width at instants A–E of each configuration. (C) Average velocity within the (i) whole-sinus, (ii) upper-sinus and (iii) lower- sinus for each instant of each configuration.

Figure 7

Vortical behaviour changes due to valve alignment. (A) Commissure to commissure alignment results in centre of moving leaflet and maximum sinus bulge being aligned, resulting in a single, larger vortex next to the sinus. (B) Non-alignment of the commissures means the two factors are not aligned, resulting in two weaker vortices forming, one next to the bioprosthetic commissure and one next to the sinus.