Chima Ofoegbu1, Deon Bezuidenhout1,2 and Peter Zilla1,2 1. Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, South Africa; 2. Strait Access Technologies (SAT), Cape Town, South Africa
The challenge during the past decade, TAVI has revolutionised our approach to heart valve disease. Whilst calcific aortic valve disease remains the dominant underlying pathology for patients in need of a heart valve replacement in the first world, rheumatic heart disease (RHD) still accounts for the majority of patients in need of a heart valve intervention in developing countries and emerging economies.1 Tragically, the majority of these patients have limited or no access to cardiac surgery.2 Moreover, given the unique differences between calcific degenerative and rheumatic pathologies, positioning and placement of a TAVI device for RHD require several considerations, which include the absence of a fluoroscopic footprint for placement and the absence of calcium deposits for anchorage.
Taking this into consideration, we have developed a non-occlusive, self-homing TAVI system which can be inserted even in the absence of sophisticated imaging equipment. Its unique design features include self-locating retractable balloon trunks for easy positioning, a hollow balloon that obviates the need for rapid ventricular pacing – as cardiac output is maintained throughout deployment – and a temporary balloon valve that prevents backflow through the hollow balloon during inflation. This allows for a slow and controlled implantation of the TAVI.
A supra-annularly anchoring TAVI stent design secures the valve in noncalcified, compliant roots utilizing the entire native leaflet body. The issue of valve durability in these typically younger ‘rheumatic’ patients is addressed by the use of special heparinised polymer leaflets and alternatively by de-cellularised, triple crosslinked pericardium.
Following successful proof of concept studies in an acute large-animal model3, a preclinical chronic animal study has been commenced to evaluate valve performance and outcomes up to five-months following implantation. At this year’s EACTS Techno College we present a Live-in-a-Box implantation in a juvenile sheep model to demonstrate the ease of implantation of this novel non-occlusive, self-locating TAVI system.
The ex-vivo performance of the SAT polymer valve has been extremely promising, having already achieved more
than 600 million cycles in fatigue testing. This is further supported by eight-week sheep explants demonstrating pristine polyurethane leaflets, with further chronic animal implants ongoing. Previous attempts to use polyurethane for heart valves were unsuccessful due to material degradation. Our accelerated in-vivo degradation studies show impressive resistance of the polyurethane used in the SAT TAVI. Calcification studies comparing our leaflet materials with conventional glutaraldehyde fixed pericardium show 40x lower calcification in our pericardial and total abolition of calcium in our polyurethane leaflets.
Not only in the developing world, but also in emerging economies such as China and India, rheumatic heart disease still accounts for the major burden of disease in patients needing heart valve interventions. We have demonstrated that polymeric TAVIs are feasible as an appealing, cost-effective solution. Furthermore, we demonstrated that compliant or non-calcific aortic roots can be treated with TAVIs by using self-anchoring stent designs implanted with a non-occlusive self-locating delivery system. The timing of this award is particularly exciting for us. As we celebrate the 50th anniversary of the first heart transplant in Cape Town in a few weeks time – with the who’s who in cardiac surgery attending – it gives us a major boost to our spirits to see that 50 years on, the University of Cape Town is still part of the cutting-edge developments in our fast moving field.
1. Sliwa K, Zilla P. Rheumatic heart disease: the tip of the iceberg. Circulation. 2012;125(25):3060-2. 2. Pezzella AT. Global aspects of cardiothoracic surgery with focus on developing countries. Asian Cardiovasc Thorac Ann. 2010;18(3):299-310. 3. Scherman J, Bezuidenhout D, Ofoegbu C, Williams DF, Zilla P. TAVI for low to middle income countries. Eur Heart J. 2017; 38(16): 1182-1184.