Browsing by Author "Weich, Hellmuth Stephan von Heyderhoff"

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    Development of an improved approach to transcatheter heart valve heart valve replacement in younger patients
    (Stellenbosch : Stellenbosch University, 2024-03) Weich, Hellmuth Stephan von Heyderhoff; Doubell, Anton F.; Smit, Francis E.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine: Cardiology.
    ENGLISH ABSTRACT: Rheumatic heart disease [RHD] globally affects four times as many people as degenerative aortic valve stenosis, yet all the current transcatheter aortic valves are aimed at treating degenerative disease in mostly affluent societies. There is a lack of access to cardiac surgery in low- to middle income countries where RHD is prevalent and affects mostly younger patients. Less invasive transcatheter alternatives may improve this but current devices are not appropriate because they are not designed to anchor in less calcified anatomy and the bioprosthetic tissue used for their leaflets are not durable in younger patients. We aimed to address three challenges faced in the development of a TAVI valve suitable for use in younger patients, namely more accurate positioning of the device, better anchoring of the device and better durability. We postulated that a novel non-occlusive balloon [NOB] has the potential to deliver a balloon expandable transcatheter heart valve [THV] to the aortic position with greater accuracy and stability than current [occlusive] balloons. Such a balloon was tested in an acute sheep experiment. The balloon could be inflated in the aortic valve position without compromising the animals’ hemodynamics. The NOB holds promise for a deployment device for balloon expandable THVs in younger patients with less calcified aortic valves. We designed and 3D printed a novel anchor stent to improve anchorage in the aortic valve position. The aim of the stent was as a docking station for a THV, but the principle could potentially be applied to a THV itself. The stent anchored securely in an ex-vivo study but deployment in an ovine experiment was unpredictable. Our failure to anchor it however identified a number of areas for improvement allowing us to propose an alternate design to overcome these obstacles. Our team developed a THV and collaborated with the Frater Centre at the University of the Free State which has extensive experience with pericardial tissue processing. Our approach for improved durability of the bovine pericardial leaflet tissue in young people focused on reducing glutaraldehyde exposure and decellularization of the tissue. We manufactured 3 sets of THVs [one decellularized according to the Frater Center’s technique (DE), one decellularized in the same way but fixed with very low dose monomeric glutaraldehyde (DF) and one with an industry standard (Glycar ®) fixed with high dose glutaraldehyde]. These valves were implanted for 6 months in an ovine right ventricular outflow conduit. At explant, the DF and DE valves outperformed the Glycar ® valves in a number of areas: better hemodynamic performance and strength; no inflammatory response; no pannus formation in DE and limited on DF tissue; no calcification of either DE or DF. The most notable finding was that the DE tissue had no cellular ingrowth [essentially inert] but despite this, was not mechanically inferior to the two glutaraldehyde fixed tissues and comparable to the same tissue prior to implant. This finding is unique and warrants validation in longer term implants and higher pressure environments. Based on our results, these two novel tissues has the potential to perform better in younger patients. This work brings us three steps closer to finding a THV that can be accurately delivered, implanted in a stable position and prove to be durable in younger patients.