In this study the investigators will assess a variety of novel markers of heart strength (contractility) and assess whether they can give a clearer indication of how well patients with weak hearts respond to the TAVI procedure.~The investigators will perform a stress echocardiogram prior to each TAVI procedure and measure the global longitudinal strain (GLS) in the left ventricle (LV) heart muscle, a detailed marker of muscle strength.~The investigators will then proceed to the TAVI procedure and measure the contractility of the main pumping chamber in the heart before and after giving a very low dose of an adrenaline -like drug (dobutamine). The patient will already have received this short acting drug (at the same and higher doses) during their routine care planning stress echocardiogram.~The investigators will also measure the pressure across the aortic valve, known as the trans-aortic gradient, using the pressure wire (PW) and a standard (multipurpose) heart catheter. The investigators will repeat the resting measures (i.e. without pacing or dobutamine) at the end of the procedure to measure the early change in left ventricular contractility and then repeat the echocardiogram immediately and after 3 months to assess the outcome of the TAVI procedure in terms of left ventricular function volume and function
In this study the investigators will assess a variety of novel markers of heart strength (contractility) and assess whether they can give a clearer indication of how well patients with weak hearts respond to the TAVI procedure.~The investigators will perform a stress echocardiogram prior to each TAVI procedure and measure the global longitudinal strain (GLS) in the left ventricle (LV) heart muscle, a detailed marker of muscle strength.~The investigators will then proceed to the TAVI procedure and measure the contractility of the main pumping chamber in the heart before and after giving a very low dose of an adrenaline -like drug (dobutamine). The patient will already have received this short acting drug (at the same and higher doses) during their routine care planning stress echocardiogram.