Objective
Valve in valve (ViV) procedures using transcatheter aortic valves
(TAV) are increasingly performed to treat degenerated bioprosthetic surgical
aortic valves (SAV) due to being less invasive than redo aortic valve
replacement. The objective of this study is to quantify the changes in
aortic sinus blood flow dynamics before and after ViV to gain insight into
mechanisms for clinical and sub-clinical thrombosis of leaflets.
Methods
A detailed description of the sinus hemodynamics for ViV implantation
was performed in-vitro. A Medtronic Hancock II porcine bioprosthesis was
modeled as SAV and a Medtronic CoreValve and Edwards Sapien were used as the
TAVs. High-resolution particle image velocimetry (PIV) was employed to
compare the flow patterns from these two valves within both the left
coronary and non-coronary sinuses in vitro.
Results
Velocity and vorticity within the surgical valve sinuses reached peak
values of 0.7 m/s and 1000 s−1, with a 70%
decrease in peak fluid shear stress near the aortic side of the leaflet in
the non-coronary sinus. With the introduction of TAV, peak velocity and
vorticity were reduced to around 0.4 m/s and 550 s−1 and
0.58 m/s and 653 s−1 without coronary flow and 0.60 m/s
and 631 s−1 and 0.81 m/s and 669 s−1
with coronary flow for CoreValve and Sapien ViV respectively. Also, peak
shear stress was around 38% higher along the aortic side of the
coronary vs non-coronary TAV leaflet.
Conclusions
Decreased flow and shear stress in ViV indicates higher risk of
leaflet thrombosis secondary to flow stasis in the non-coronary sinus.