Experimental and computational investigation of the impact of distorted stent expansion on the performance of transcatheter aortic valve replacements

Patients with calcific aortic valve stenosis present with calcium deposits on the aortic valve, which can result in non-circular and distorted expansion of self-expanding Transcatheter Aortic Valve Replacements. The effect of stent distortion on the fluid and shear environments downstream of the valve and the deformation of the leaflets of the prosthesis are not yet fully understood. Therefore the objectives of this thesis are to investigate the impact of non-circular stent deployment on: (1) the fluid mechanics and hemolytic potential of the device; (2) leaflet mechanics and deformation and (3) the development of a computational finite element framework of the deployment of a self-expanding Transcatheter Aortic Valve Replacement in a patient-specific aortic root anatomy. The results of this thesis demonstrate that: (1) eccentric stent distortion alters the fluid and shear environments downstream of the valve; (2) eccentric stent distortion causes deleterious bending of the leaflet causing an increase in peak strains in the vicinity of the leaflet commissures; (3) stent deployment asymmetry is dependent upon location and distribution of calcium deposits on the aortic valve leaflets and (4) preoperative planning of stent orientation within the aortic valve has the potential to minimise the impact of the distorted stent on the deformation of leaflets of the prosthesis. The results of this thesis elucidate the effect of non-circular stent deployment on the coupled fluid and leaflet mechanics of Transcatheter Aortic Valve Replacements deployed in calcified aortic valves in vivo and provide a novel understanding of the biomechanical tissue-stent interaction during self-expanding stent deployment in patient-specific anatomies.2016-07-0