Comparison of performance of self-expanding and balloon-expandable transcatheter aortic valves

Abstract

Objective: To evaluate the flow dynamics of self-expanding and balloon-expandable transcatheter aortic valves pertaining to turbulence and pressure recovery. Transcatheter aortic valves are characterized by different designs that have different valve performance and outcomes.

Methods: Assessment of transcatheter aortic valves was performed using self-expanding devices (26-mm Evolut [Medtronic], 23-mm Allegra [New Valve Technologies], and small Acurate neo [Boston Scientific]) and a balloon-expandable device (23-mm Sapien 3 [Edwards Lifesciences]). Particle image velocimetry assessed the flow downstream. A Millar catheter was used for pressure recovery calculation. Velocity, Reynolds shear stresses, viscous shear stress, and pressure gradients were calculated.

Results: The maximal velocity at peak systole obtained with the Evolut R, Sapien 3, Acurate neo, and Allegra was 2.12 ± 0.19 m/sec, 2.41 ± 0.06 m/sec, 2.99 ± 0.10 m/sec, and 2.45 ± 0.08 m/sec, respectively (P < .001). Leaflet oscillations with the flow were clear with the Evolut R and Acurate neo. The Allegra shows the minimal range of Reynolds shear stress magnitudes (up to 320 Pa), and Sapien 3 the maximal (up to 650 Pa). The Evolut had the smallest viscous shear stress magnitude range (up to 3.5 Pa), and the Sapien 3 the largest (up to 6.2 Pa). The largest pressure drop at the vena contracta occurred with the Acurate neo transcatheter aortic valve with a pressure gradient of 13.96 ± 1.35 mm Hg. In the recovery zone, the smallest pressure gradient was obtained with the Allegra (3.32 ± 0.94 mm Hg).

Conclusions: Flow dynamics downstream of different transcatheter aortic valves vary significantly depending on the valve type, despite not having a general trend depending on whether or not valves are self-expanding or balloon-expandable. Deployment design did not have an influence on flow dynamics.

Keywords: PDF, probability density function; PG, pressure gradient; RSS, Reynolds shear stress; TAV, transcatheter aortic valve; TAVR; VSS, viscous shear stress; blood damage; pressure recovery; turbulence.

Graphical abstract

Comparison of self- and balloon-expandable TAV performance.

Figure 1

Phase-averaged velocity vectors and vorticity contours at different phases in the cardiac cycle. The dark streaks of red and blue vorticity contours represent the shear layers corresponding to the jet boundaries and the distance between them represents the width of the jet. The resulting shear layers and jet stability are consequences of the interaction between flow and leaflets and thus, it gives important information on the visualization of the opening of the valves and the resulting flow. The maximal velocity at peak systole obtained with the Evolut R (Medtronic), Sapien 3 (Edwards Lifesciences), Acurate neo (Boston Scientific), and Allegra (New Valve Technologies) was found to be 2.12 ± 0.19 m/sec, 2.41 ± 0.06 m/sec, 2.99 ± 0.10 m/sec, and 2.45 ± 0.08 m/sec, respectively (P < .001).

Figure 2

Principal Reynolds shear stresses (RSS) at different phases in the cardiac cycle. The dark blue patches indicate an elevated RSS magnitude, and the more prevalent elevated RSS magnitudes are, the more turbulent the flow is considered to be. Evolut R (Medtronic), Sapien 3 (Edwards Lifesciences), Acurate neo (Boston Scientific), and Allegra (New Valve Technologies).

Figure 3

Probability density function (PDF) of the (A) Reynolds shear stress (RSS) distribution and the (B) viscous shear stress (VSS) distribution downstream of the Evolut R (Medtronic), Sapien 3 (Edwards Lifesciences), Acurate neo (Boston Scientific), and Allegra (New Valve Technologies) transcatheter aortic valves in semi-log scale. 0.1 KPa represents a potential blood damage threshold. The Acurate neo and the Evolut R present the largest distributions of RSS in all 3 phases (acceleration, peak systole, and deceleration). The Allegra shows the minimal range of RSS magnitudes (up to 320 Pa), followed by the Evolut R (up to 600 Pa) and then the Acurate neo and Sapien 3 (up to 650 Pa).

Figure 4

A, Variations of pressure gradients as a function of axial distance at selected location points during peak systole with the 23-mm Sapien 3 (Edwards Lifesciences), 26-mm Evolut R (Medtronic), S Acurate neo (Boston Scientific), and 23-mm Allegra (New Valve Technologies) transcatheter aortic valves. The results are plotted from the ventricular side upstream of each valve to the downstream side up until the end of the aortic testing chamber (at 120 mm). As the flow crosses the valve, the pressure gradient decreases from the ventricular side to the aortic one until it reaches a minimum at the vena contracta (VC) (where the jet is the narrowest and where maximum jet velocity occurs). After that, the recovery process starts through a gradual increase in pressure gradient along the various points. B, Bar plot showing the pressure gradients at the VC and the recovery zone at x = 120 mm. The dark lines on the bar plots indicate the SDs. The largest pressure drop at the VC occurs with the Acurate neo transcatheter aortic valve where the minimal pressure reaches 13.96 ± 1.35 mm Hg. The pressure gradient with the Sapien 3, Evolut, and Allegra reach 10.54 ± 0.51 mm Hg, 10.64 ± 0.38 mm Hg, and 11.89 ± 0.61 mm Hg, respectively. The 23-mm Sapien 3 showed the smallest pressure gradient at the VC. The location of the VC varied with each valve. The VC of the Acurate neo was the closest to the valve entrance, and that of the Allegra was the furthest from the valve entrance. At 12 mm, in the recovery zone, the smallest pressure gradient was obtained with the Allegra (3.32 ± 0.94 mm Hg), followed by Sapien 3 (3.68 ± 0.76 mm Hg), then the Evolut R (4.77 ± 0.87 mm Hg) and the largest pressure gradient was obtained with the Acurate neo (5 ± 1.21 mm Hg). All differences in pressure gradients were statistically significant (P < .001) except for the Allegra and Sapien 3 at the VC (P = .1399) and the Acurate neo and Sapien 3 in the recovery zone (P = .2105).

Figure 5

Variations of pressure gradient standard deviations as a function of axial distance at selected location points during peak systole with the 23-mm Sapien 3 (Edwards Lifesciences), 26-mm Evolut R (Medtronic), S Acurate neo (Boston Scientific), and 23-mm Allegra (New Valve Technologies) transcatheter aortic valves. The fluctuations in the standard deviations are higher with the self-expanding valves compared with the Sapien 3. This complements the elevated turbulent stresses obtained in this study.

Figure 6

Flow dynamics downstream of self-expanding and balloon expandable transcatheter aortic valves (TAVs) relating to turbulence and pressure recovery. Evolut R (Medtronic), Sapien 3 (Edwards Lifesciences), Acurate neo (Boston Scientific), and Allegra (New Valve Technologies). PDF, Probability density function; RSS, Reynolds shear stress; VSS, viscous shear stress.

Figure E1

Box-and-whisker plot showing the pressure gradient distribution for each valve case. The lower and upper borders of the box (Q₁ and Q₃) represent the lower and upper quartiles (25th percentile and 75th percentile). The middle horizontal line (Q₂) represents the middle value in the data set (50th percentile). The lower and upper lines (Q₀ and Q₄, which are known as whiskers) represent variability outside the upper and lower quartiles (0th percentile and 100th percentile, respectively) and show the minimum and maximum values of nonoutliers. Extra dots represent outliers, which differ significantly from the rest of the dataset. Evolut R (Medtronic), Sapien 3 (Edwards Lifesciences), Acurate neo (Boston Scientific), and Allegra (New Valve Technologies). VC, Vena contracta.