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Many Transcatheter Aortic Valve Implant (TAVI) devices currently on the market offer little control over the rotational alignment of the bioprosthesis with the aortic root they are being inserted into, and the resultant flow dynamics are not fully understood. This study aims to identify how the valve orientation affects haemodynamics, both neglecting and including the presence of the native leaflets.Using an in vitro approach, commercially available TAVI devices were implanted into a mock silicone aortic root in four configurations encompassing the variations of aligned/non-aligned and without/with native leaflets present (Figure 1). Global flow information was obtained using pressure and flow transducers, and 2D Particle Image Velocimetry (PIV) was used to provide local and instantaneous flow data across the various configurations.Analysis of the PIV images shows that a vortex is generated above each opening leaflet of the TAVI device, and another above or within the sinus of the root. If the commissures of the root and prosthetic valve are aligned, this results in these vortices merging to form only one major vortex. On the contrary, if the valve and root are misaligned, the two vortices remain separate, each impinging the central jet of fluid flow (Figure 2). This raises pressure losses, decreasing valve performance, and increasing turbulence and Reynolds shear stresses. This effect occurs both with and without the native leaflets, whose presence results in a significant reduction in the flow velocity observed in the sinuses.These results show that misalignment of a TAVI device with its destination root can lead to an alteration in vortical behaviour, leading to diminished valve performance. There is also increased occurrence of conditions which are conducive to the generation of thrombosis. The presence of native leaflets does not mitigate this vortical behaviour, and also reduces the systolic flow in the sinuses, possibly leading to increased stagnation. This fluid behaviour should be taken into account when considering design and insertion of TAVI devices.