S Tzamtzis

Manufacturing and hydrodynamic assessment of a novel aortic valve made of a new nanocomposite polymer.

Synthetic leaflet heart valves have been widely studied as possible alternatives to the current mechanical and bioprosthetic valves. Assessing the in vitro hydrodynamic function of these prostheses is of great importance to predict their hemodynamic behaviour prior to implantation. This study introduces an innovative concept of a low-profile semi-stented surgical aortic valve (SSAV) made of a novel nanocomposite polyurethane with a polycarbonate soft segment (PCU) and polyhedral oligomeric silsesquioxane (POSS) nanoparticles covalently bonded as a pendant cage to the hard segment. The POSS-PCU is already used in surgical implants, including lacrimal duct, bypass graft, and recently, a tracheal replacement. Nine valves of three leaflet thicknesses (100, 150 and 200 μm) and 21 mm internal diameter were prepared using an automated dip-coating procedure, and assessed in vitro for their hydrodynamic performance on a pulse duplicator system. A commercially available porcine bioprosthetic valve (Epic™, St. Jude Medical) of equivalent size was selected as a control model. Compared to the bioprosthetic valve, the SSAVs showed a considerably lower transvalvular pressure drop and larger effective orifice area (EOA). They were also characterised by a lower systolic energy loss, especially at high cardiac outputs. The leaflet thickness was found to significantly affect the hydrodynamics of these valves (P<0.01). The SSAVs with 100 μm leaflets demonstrated improved flow characteristics compared to the bioprosthetic valve. The enhanced hydrodynamic function of the SSAV suggests that the proposed design together with the advanced POSS-PCU material can represent a significant step towards the introduction of polyurethane valves into the clinical application.

Transcatheter aortic valves produce unphysiological flows which may contribute to thromboembolic events: An in-vitro study

Purpose Transcatheter aortic valve implantation (TAVI) has been associated with large incidence of ischemic events, whose sources are still unclear. In fact, sub-acute complications cannot be directly related to the severity of the calcification in the host tissues, nor with catheter manipulation during the implant. A potential cause could be local flow perturbations introduced by the implantation approach, resulting in thrombo-embolic consequences. In particular, contrary to the surgical approach, TAVI preserves the presence of the native leaflets, which are expanded in the paravalvular space inside the Valsalva sinuses. The purpose of this study is to verify if this configuration can determine hemodynamic variations which may promote blood cell aggregation and thrombus formation. Methods The study was performed in vitro, on idealized models of the patient anatomy before and after TAVI, reproducing a range of physiological operating conditions on a pulse duplicator. The fluid dynamics in the Valsalva sinuses was analyzed and characterized using phase resolved Particle Image Velocimetry. Results Comparison of the flow downstream the valve clearly indicated major alterations in the fluid mechanics after TAVI, characterized by unphysiological conditions associated with extended stagnation zones at the base of the sinuses. Conclusion The prolonged stasis observed in the Valsalva sinuses for the configuration modelling the presence of transcatheter aortic valves provides a fluid dynamic environment favourable for red blood cell aggregation and thrombus formation, which may justify some of the recently reported thromboembolic and ischemic events. This suggests the adoption of anticoagulation therapies following TAVI, and some caution in the patients׳ selection.

A NEW GENERATION OF AORTIC VALVE PROSTHESIS: DESIGN, MANUFACTURE AND HYDRODYNAMIC ASSESSMENT

Aortic valve replacement (AVR) is the second most common cardiac procedure after coronary artery bypass grafting, accounting for more than 200,000 transplantations annually worldwide [1]. Currently available mechanical and bioprosthetic heart valve replacements are not ideal as they are associated with relevant complications. The tri-leaflet polymeric heart valves (PHVs) have been widely investigated as possible alternative to these substitutes. However, the clinical application of PHVs has been limited by their suboptimal design and poor durability of available polymeric materials. This study presents a new concept of surgical aortic valve using a novel nanocomposite polymer.© 2012 ASME