A Study to Obtain Imaging Data in 40 Patients Having Transcatheter Aortic Valve Implantation (TAVI)

Inclusion Criteria: * ≥ 18 years of age * Symptomatic, degenerative, tricuspid, severe aortic stenosis * TTE derived aortic valve area (AVA) of ≤ 1.0 cm2 (or indexed effective orifice area (EOAi) ≤ 0.6 cm2 /m2) * TTE derived AV mean gradient ≥ 40 mmHg or peak jet velocity ≥ 4.0 m/s or Doppler Velocity Index (DVI) ≤ 0.25 * CT TAVI deemed of good quality (as per standard operating procedure) within past 6 months * TTE of good quality within past 6 months as defined by: * Doppler signal across the aortic valve and LVOT is a clear and artifact-free waveform * Correct alignment to the blood flow direction to ensure accurate velocity measurements * Following measurements available * Continuous-wave Doppler (CW) across the aortic valve * AV Vmax, AV Vmean, AV peak gradient (MaxPG), AV mean gradient (meanPG), AV Velocity-Time integral (VTI), heart rate (HR); * Pulse-wave Doppler (PW) across the LVOT * LVOT Vmax, LVOT Vmean, LVOT MaxPG, LVOT meanPG, LVOT VTI; * 2D LVOT diameter in plax view. * In sinus rhythm at time of any TTE or CT scans * Undergone a technically successful elective TAVI as defined by the operator using a Edwards Sapien 3 Ultra (20, 23, 26 or 29 mm): * Position and height as planned * Trivial aortic regurgitation * No vascular or other complications prolonging discharge Exclusion Criteria: * Life expectancy \<6 months * Rockwood frailty score \>6 * Mixed aortic valve disease with predominant aortic regurgitation that is at least moderate. * Moderate-severe mitral regurgitation and/or mitral stenosis. * Congenital unicuspid or congenital bicuspid aortic valve as verified by echocardiography or CT * Previous TAVI or Aortic Valve Replacement (AVR) * Left Ventricular Ejection Fraction (LVEF) \< 50% * On or planned oral anticoagulation * Chronic severe renal failure (estimated glomerule filtration rate (eGFR)) less than 30 mL/min/1.73m2 by the MDRD equation or requiring dialysis) * Evidence of an acute myocardial infarction within 30 days prior to index procedure * Untreated clinically significant coronary artery disease requiring revascularization * Blood dyscrasias as defined: leukopenia (WBC \< 3000mm3), acute anaemia (Hb \< 9g/dL), thrombocytopenia (platelet count \< 50,000 cells/mm3); history of bleeding diathesis or coagulopathy * Active peptic ulcer or upper GI bleeding within 3 months prior to index procedure that would preclude anticoagulation * Those lacking capacity to consent or are deemed vulnerable adults * Requires permanent pacemaker * Pregnancy or the possibility of pregnancy as reported by the participant.