Salmonsmith, Jacob Andrew; (2019) Haemodynamic alterations after percutaneous valve implantation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Many patients who suffer from aortic valve dysfunction are too weak to be eligible for valve replacement via surgery, due to co-morbidities and old age. Transcatheter aortic valve (TAV) implantation has been developed as an alternative to surgery, enabling replacement of the dysfunctional valve percutaneously. However, the inability to remove the native leaflets leads to the bioprosthetic being held in place inside a pseudo-cylindrical structure. The passive nature of heart valves means the surrounding fluid environment’s dynamics are critical in producing optimum performance, and would ideally be returned to the healthy, physiological state. The association of TAVs with thrombotic events, such as strokes, has not yet been fully explained. A pulse duplicator and particle image velocimetry were used to model and characterise the flow fields of a healthy, physiological aortic root and valve, which was then compared to those resulting from a number of typical post- surgical outcomes, identifying the fluid mechanisms promoted by the root geometry to optimise the ejection and closing phases of the cardiac cycle, and revealing the importance of an optimal integration of valve and root architecture, and characterising common post-surgical environments. The same techniques were then used to examine the flow dynamics of the region following TAV implantation, revealing the effect of TAV alignment with its hosts’ commissures, and how the presence of native leaflets, commonly omitted from in vitro TAV testing, affect the valve performance. Slow and stagnant flow was observed within the sinuses due to the native leaflets, whilst global valve performance was broadly unaffected, and omission of the native leaflets resulted in improved haemodynamic performance. A model of coronary arteries was incorporated into the benchtop simulation, revealing increase of flow in the upper coronary sinuses, but flow at the base of all sinuses remained very slow following TAV implantation. The elucidation of this stagnation, associated with thrombotic events, provides an explanation for the increased levels of thrombotic-associated pathologies following TAV implantation.

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