Gradient and pressure recovery of a self-expandable transcatheter aortic valve depends on ascending aorta size: In vitro study

Abstract

Objective: In this study we aimed to understand the role of interaction of the Medtronic Evolut R transcatheter aortic valve with the ascending aorta (AA) by evaluating the performance of the valve and the pressure recovery in different AA diameters with the same aortic annulus size.

Methods: A 26-mm Medtronic Evolut R valve was tested using a left heart simulator in aortic root models of different AA diameter (D): small (D = 23 mm), medium (D = 28 mm), and large (D = 34 mm) under physiological conditions. Measurements of pressure from upstream to downstream of the valve were performed using a catheter at small intervals to comprehensively assess pressure gradient and pressure recovery.

Results: In the small AA, the measured peak and mean pressure gradient at vena contracta were 11.5 ± 0.5 mm Hg and 7.8 ± 0.4 mm Hg, respectively, which was higher (P < .01) compared with the medium (8.1 ± 0.4 mm Hg and 5.2 ± 0.4 mm Hg) and large AAs (7.4 ± 1.0 mm Hg and 5.4 ± 0.6 mm Hg). The net pressure gradient was lower for the case with the medium AA (4.1 ± 1.2 mm Hg) compared with the small AA (4.7 ± 0.8 mm Hg) and large AA (6.1 ± 1.4 mm Hg; P < .01).

Conclusions: We have shown that small and large AAs can increase net pressure gradient, because of the direct interaction of the Medtronic Evolut R stent with the AA (in small AA) and introducing higher level of turbulence (in large AA). AA size might need to be considered in the selection of an appropriate device for transcatheter aortic valve replacement.

Keywords: AA, ascending aorta; AS, aortic stenosis; BE, balloon-expandable; Echo, Doppler echocardiography; LV, left ventricle; LVOT, left ventricular outflow tract; PG, pressure gradient; PI, pinwheeling index; PR, pressure recovery; SE, self-expandable; T, instantaneous time during cardiac cycle; TAVR, transcatheter aortic valve replacement; THV, transcatheter heart valve; VC, vena contracta; ascending aorta; left heart simulator; pressure gradient; pressure recovery; transcatheter aortic valve.

Graphical abstract

For the same Evolut R (Medtronic) and annulus size, gradients strongly depend on the ascending aorta size.

Figure 1

The experimental setup of a deployed Evolut R (Medtronic) transcatheter aortic valve in aortic root chambers of the left heart simulator. X = 0 denotes the annulus. The Evolut R valve is deployed in chambers with different ascending aorta (AA) size: (A) small AA (D₁ = 23 mm), (B) medium AA (D₂ = 28 mm), and (C) large AA (D₃ = 34 mm). The diameter of the aortic annulus is D₀ = 22 mm in (A), (B), and (C). D₀, aortic annulus size; D₁, small AA size; D₂, medium AA size; D₃, large AA size.

Figure 2

Peak and net gradients. Upstream and downstream of the valve represent left ventricular outflow tract (LVOT) and the recovery zone, respectively. By crossing blood flow through the aortic valve, pressure does not recover to the LVOT pressure values, because of energy losses. The amount of pressure recovered at the recovery zone (difference between peak pressure and net pressure) is called pressure recovery (PR). The typical pullback range is 5 to 8 cm from the annulus. D_o, aortic annulus size; D, diameter; PG_max, PG at VC; PG_net, PG at recovery zone; VC, vena contracta.

Figure 3

Averaged and standard deviation of the measured pressures as a function of axial length. Each curve is an average of 200 consecutive cardiac cycles. Averaged pressures at 8 different time points during systole from aortic flow acceleration to deceleration are plotted at (A) small ascending aorta (AA), (B) medium AA, and (C) large AA. The horizontal axis represents the longitudinal direction along the aortic chamber center line. Pressure standard deviation at 8 different time points during systole from aortic flow acceleration to deceleration are plotted at (D) small AA, (E) medium AA, and (F) large AA. The maximum flow rate occurs at T = 0.26 seconds (magenta line). The green shaded area represents the region of the valve from the inflow entrance to the edge of the fully-opened leaflet (dashed line).

Figure 4

Measured aortic flow rates and calculated pressure gradients (PG) and corresponding standard deviations (SD) at different ascending aorta (AA) sizes. A, Averaged 200 consecutive cardiac cycles of aortic flow rate in different sizes of AA. Error bars represent standard deviations. Pressure gradient contours at continuous time points (T) from the start of systole (T = 0 seconds) to approximately the end of systole (T = 0.36 seconds) at different AA sizes: (B) small AA, (C) medium AA, and (D) large AA. The horizontal axis in (B-G) represents the longitudinal direction along the aortic chamber center line. Pressure gradient standard deviation contours at continuous time points from the start of systole (T = 0 seconds) to the end of systole (T = 0.36 seconds) at different AA sizes: (E) small AA, (F) medium AA, and (G) large AA. The vertical dashed line in (A) and also the horizontal line in (B-G) shows the peak flow rate (T = 0.26 seconds). The vertical dashed lines in (B-G) represent the region of the valve from the inflow entrance to the edge of the fully-opened leaflet and the rightmost one shows the end of the stent frame.

Figure 5

Pressure gradient (PG) curves as a function of axial distance at different ascending aorta (AA) size. A, Peak PG and (B) Mean PG. Shaded curves indicate standard deviations. The horizontal axis represents the longitudinal direction along the aortic chamber center line. The green shaded area represents the region of the valve from the inflow entrance to the edge of the fully-opened leaflet (dashed line). The orange shaded region shows the typical pullback traces of the pressure catheter perform by surgeons. The vertical dashed black line shows X = 7 cm, where we calculated PG at recovery zone (PG_net).

Figure 6

Pressure gradient (PG) and pressure recovery at 3 different ascending aorta (AA) sizes. Each data point is an average of 200 consecutive cardiac cycles. Pressure gradient at peak flow and mean pressure gradient are summarized as a function of the diameter of AA to the diameter of the annulus ratio at (A) vena contracta and (B) recovery zone. C, Pressure recovery percentage, which is defined as the difference between peak gradient and net gradient divided by peak gradient. Error bars denote standard deviations. PG_max, PG at VC; D_AA, AA diameter; D_Annulus, aortic annulus diameter; PG_net, PG at recovery zone.

Figure 7

Pressure recovery comparison between small and large geometries. Pressure recovery plotted as the echocardiography pressure gradient subtracted by the catheter pressure gradient on the y-axis versus small and large geometries on the x-axis defined by the ratio of the ascending aorta (AA) diameter to the CoreValve (Medtronic) size with small being below the average and large being above the average. The upper and lower borders of the box represent the upper and lower quartiles. The middle horizontal line represents the median. The upper and lower whiskers represent the maximum and minimum values of nonoutliers. Extra dots outside the whiskers represent outliers. PG_Doppler, echocardiography pressure gradient; PG_Catheter, catheter pressure gradient.

Figure 8

For the first time, the influence of the varying ascending aorta (AA) diameters within an acceptable range on an self-expandable transcatheter aortic valve (TAV) device's performance and pressure recovery have been examined. We studied gradients of the Evolut R (Medtronic) transcatheter aortic valve replacement (TAVR) device at 3 different AA sizes. We showed that for the same Evolut R and annulus size, peak and mean gradients strongly depend on the AA size. As a result, the size of AA might be an important parameter for the self-expandable transcatheter heart valve sizing and valve choice. D₁, small AA size; D₂, medium AA size; D₃, large AA size; PG, pressure gradient; VC, vena contracta.