Differences in Pressure Recovery Between Balloon Expandable and Self-expandable Transcatheter Aortic Valves

Abstract

Pressure recovery downstream of the aortic valve constitutes an important factor affecting the calculation of pressure gradient (PG) across the valve and therefore the accuracy of the calculated aortic valve area. Some clinical studies hypothesized that stent and valve cusps design contribute to flow acceleration and Doppler-measured valve gradients across the balloon-expandable transcatheter aortic valve. This study aims at elucidating the physical mechanisms behind pressure recovery variations between Edwards SAPIEN 3 and Medtronic Evolut TAVs through the measurements of sensitive and precise axial pressure profiles. A 23 mm Edwards SAPIEN3 and a 26 mm Medtronic Evolut were deployed in a pulse duplicator. A Millar catheter was used to record 50 cycles of pressure data along the centerline of the valve chamber upstream and downstream of the valve. The peak PG obtained with SAPIEN at vena contracta (VC) is 18.83 ± 0.75 mmHg and after recovery, 9.56 ± 0.78 mmHg. For Evolut at VC, peak PG is 18.25 ± 0.63 mmHg and after recovery, 10.3 ± 0.57 mmHg. The differences in peak PG at VC and at the recovery were statistically significant (p < 0.001). With SAPIEN 3 at VC, the mean PG obtained is 10.11 ± 0.63 mmHg and after recovery 7.06 ± 0.46 mmHg. For Evolut, mean PG at VC is 10.45 ± 0.67 mmHg and after recovery 7.99 ± 0.61 mmHg. The differences between the mean PG between the two valves was not statistically significant at VC (p = 0.71) but significant post-recovery (p < 0.00001). While gradients at the VC are higher with the SAPIEN 3, the net gradient after pressure recovery is significantly lower compared to Evolut TAV. Efficiency of pressure recovery significantly depends on valve type due to stent interference with the recovering blood flow.

Keywords: Catheterization; Doppler; Pressure gradient; Pressure recovery; Transcatheter aortic valve; Turbulence.

FIGURE 1.

Figure of the (a) SAPIEN 3 and (b) Evolut TAVs placed in the aortic root chambers of the experimental setup for hemodynamic assessment. Annotation 1 denotes the sinotubular junction limit at 4 cm and 2 the limit of Evolut stent at 6.5 cm.

FIGURE 2.

Variations of pressure as a function of axial distance at selected time points during systole with (a) SAPIEN 3 and (b) Evolut TAVs. The edge of the fully open leaflet is at (a) around 3.5 cm with SAPIEN and (b) around 4.2 cm with Evolut as highlighted with the dotted line. The shaded red area represent the location of the valve with respect to the measurement region.

FIGURE 3.

Variations of pressure gradient (obtained from subtracting the initial upstream pressure measurement from the other measurements) with (a) SAPIEN 3 and (b) Evolut at different locations in the aortic valve chamber at different time points during systole. The edge of the fully open leaflet is at (a) 3.5 cm with SAPIEN and (b) 4.2 cm with Evolut as highlighted with the dotted line. The shaded red area represent the location of the valve with respect to the measurement region.

FIGURE 4.

Variations of pressure standard deviations as a function of axial distance at selected time points during systole with (a) SAPIEN 3 and (b) Evolut TAVs. The edge of the fully open leaflet is at (a) 3.5 cm with SAPIEN and (b) 4.2 cm with Evolut as highlighted with the dotted line. The shaded red area represent the location of the valve with respect to the measurement region.

FIGURE 5.

Peak PG, PG at peak flow and mean pressure gradient variations as a function of axial distance with SAPIEN 3 and Evolut. Error bars represent standard deviations.

FIGURE 6.

Bar chart summarizing the mean pressure gradient, pressure gradient at peak flow and peak pressure gradient with SAPIEN 3 and Evolut at (a) the vena contracta (VC) and (b) in the recovery zone. Error bars represent standard deviations.

FIGURE 7.

Variations of the derivative of pressure gradient at peak flow as a function of axial distance with SAPIEN 3 and Evolut downstream of SAPIEN 3 vena contracta. Error bars represent standard deviations.