Hemocompatibility of styrenic block copolymers for use in prosthetic heart valves.

Certain styrenic thermoplastic block copolymer elastomers can be processed to exhibit anisotropic mechanical properties which may be desirable for imitating biological tissues. The ex-vivo hemocompatibility of four triblock (hard-soft-hard) copolymers with polystyrene hard blocks and polyethylene, polypropylene, polyisoprene, polybutadiene or polyisobutylene soft blocks are tested using the modified Chandler loop method using fresh human blood and direct contact cell proliferation of fibroblasts upon the materials. The hemocompatibility and durability performance of a heparin coating is also evaluated. Measures of platelet and coagulation cascade activation indicate that the test materials are superior to polyester but inferior to expanded polytetrafluoroethylene and bovine pericardium reference materials. Against inflammatory measures the test materials are superior to polyester and bovine pericardium. The addition of a heparin coating results in reduced protein adsorption and ex-vivo hemocompatibility performance superior to all reference materials, in all measures. The tested styrenic thermoplastic block copolymers demonstrate adequate performance for blood contacting applications.

A bio-inspired microstructure induced by slow injection moulding of cylindrical block copolymers.

It is well known that block copolymers with cylindrical morphology show alignment with shear, resulting in anisotropic mechanical properties. Here we show that well-ordered bi-directional orientation can be achieved in such materials by slow injection moulding. This results in a microstructure, and anisotropic mechanical properties, similar to many natural tissues, making this method attractive for engineering prosthetic fibrous tissues. An application of particular interest to us is prosthetic polymeric heart valve leaflets, mimicking the shape, microstructure and hence performance of the native valve. Anisotropic layers have been observed for cylinder-forming block copolymers centrally injected into thin circular discs. The skin layers exhibit orientation parallel to the flow direction, whilst the core layer shows perpendicularly oriented domains; the balance of skin to core layers can be controlled by processing parameters such as temperature and injection rate. Heart valve leaflets with a similar layered structure have been prepared by injection moulding. Numerical modelling demonstrates that such complex orientation can be explained and predicted by the balance of shear and extensional flow.

Community prevalence, mechanisms and outcome of mitral or tricuspid regurgitation.

OBJECTIVE: The study aims were (1) to identify the community prevalence of moderate or greater mitral or tricuspid regurgitation (MR/TR), (2) to compare subjects identified by population screening with those with known valvular heart disease (VHD), (3) to understand the mechanisms of MR/TR and (4) to assess the rate of valve intervention and long-term outcome. METHODS: Adults aged ≥65 years registered at seven family medicine practices in Oxfordshire, UK were screened for inclusion (n=9504). Subjects with known VHD were identified from hospital records and those without VHD invited to undergo transthoracic echocardiography (TTE) within the Oxford Valvular Heart Disease Population Study (OxVALVE). The study population ultimately comprised 4755 subjects. The severity and aetiology of MR and TR were assessed by integrated comprehensive TTE assessment. RESULTS: The prevalence of moderate or greater MR and TR was 3.5% (95% CI 3.1 to 3.8) and 2.6% (95% CI 2.3 to 2.9), respectively. Primary MR was the most common aetiology (124/203, 61.1%). Almost half of cases were newly diagnosed by screening: MR 98/203 (48.3%), TR 69/155 (44.5%). Subjects diagnosed by screening were less symptomatic, more likely to have primary MR and had a lower incidence of aortic valve disease. Surgical intervention was undertaken in six subjects (2.4%) over a median follow-up of 64 months. Five-year survival was 79.8% in subjects with isolated MR, 84.8% in those with isolated TR, and 59.4% in those with combined MR and TR (p=0.0005). CONCLUSIONS: Moderate or greater MR/TR is common, age-dependent and is underdiagnosed. Current rates of valve intervention are extremely low.

How to prevent infective endocarditis in 2020? Practical issues.

The incidence of infective endocarditis (IE) continues to rise in many populations and is typically accompanied by a shift to healthcare­associated staphylococcal species. Despite efforts with aggressive antibiotic therapy and increasing rates of surgical intervention, little progress has been made to reduce mortality. Disease prevention is therefore a crucial part of limiting its effects. Prevention should target each point in the pathogenic triad of IE: initiating bacteremia, adhesion to substrate, and proliferation of pathogenic species. Preventative strategies should focus on at­risk patients undergoing high­risk procedures, and these patients and procedures can now be identified by quantitative risk estimates. The attendant risk resulting from a procedure must then be placed in the perspective of the day­to­day risk, and the resulting balance can inform the benefit of prophylactic antibiotics. Implantable devices are a major risk factor for IE, and novel coatings and designs may be effective in risk reduction. Guidelines differ worldwide and a consensus has yet to be reached on who should receive pre­ and periprocedural antibiotics.

Quantifying the Shift Toward Transcatheter Aortic Valve Replacement in Low-Risk Patients: A Meta-Analysis.

BACKGROUND: In recent years, use of transcatheter aortic valve replacement has expanded to include patients at intermediate- and low-risk cohorts. We sought to determine disease prevalence and treatment distribution including transcatheter aortic valve replacement eligibility in low-risk patients across 37 advanced economies. METHODS AND RESULTS: Four systematic searches were conducted across MEDLINE, EMBASE, and the Cochrane database for studies evaluating disease prevalence, severity, decision making, and survival in patients with aortic stenosis. Estimates of disease prevalence and treatment eligibility were calculated using stochastic simulation and population data for the 37 countries comprising the International Monetary Fund's advanced economies index. Fifty-six studies comprising 42 965 patients were included across 5 domains: prevalence, severity, symptom status, treatment modality, and outcome. The pooled prevalence in the general population aged 60 to 74 years and >75 years was 2.8% (95% confidence interval [CI], 1.4%-4.1%) and 13.1% (95% CI, 8.2%-17.9%), respectively-corresponding to an estimated 16.1 million (95% CI, 12.2-20.3) people in 37 advanced economies. Of these, an estimated 3.2 million (95% CI, 2.2-4.4) patients have severe aortic stenosis with 1.9 million (95% CI, 1.3-2.6) eligible for surgical aortic valve replacement. There are ≈485 230 (95% CI, 284 550-66 7350) high-risk/inoperable patients, 152 690 (95% CI, 73 410-263 000) intermediate-risk patients, and 378 890 (95% CI, 205 130-610 210) low-risk patients eligible for transcatheter aortic valve replacement. CONCLUSIONS: With a prevalence of 4.5%, an estimated 16.1 million people aged ≥60 years across 37 advanced economies have aortic stenosis. Of these, there are ≈1.9 million patients eligible for surgical aortic valve replacement and 1.0 million patients eligible for transcatheter aortic valve replacement.

A Newly Developed Tri-Leaflet Polymeric Heart Valve Prosthesis.

The potential of polymeric heart valves (PHV) prostheses is to combine the hemodynamic performances of biological valves with the durability of mechanical valves. The aim of this work is to design and develop a new tri-leaflet prosthetic heart valve (HV) made from styrenic block copolymers. A computational finite element model was implemented to optimize the thickness of the leaflets, to improve PHV mechanical and hydrodynamic performances. Based on the model outcomes, 8 prototypes of the designed valve were produced and tested in vitro under continuous and pulsatile flow conditions, as prescribed by ISO 5840 Standard. A specially designed pulse duplicator allowed testing the PHVs at different flow rates and frequency conditions. All the PHVs met the requirements specified in ISO 5840 Standard in terms of both regurgitation and effective orifice area (EOA), demonstrating their potential as HV prostheses.

Fluid dynamic characterization of a polymeric heart valve prototype (Poli-Valve) tested under continuous and pulsatile flow conditions.

PURPOSE: Only mechanical and biological heart valve prostheses are currently commercially available. The former show longer durability but require anticoagulant therapy; the latter display better fluid dynamic behavior but do not have adequate durability. New Polymeric Heart Valves (PHVs) could potentially combine the hemodynamic properties of biological valves with the durability of mechanical valves. This work presents a hydrodynamic evaluation of 2 groups of newly developed supra-annular, trileaflet prosthetic heart valves made from styrenic block copolymers (SBC): Poli-Valves. METHODS: 2 types of Poli-Valves made of SBC and differing in polystyrene fraction content were tested under continuous and pulsatile flow conditions as prescribed by ISO 5840 Standard. A pulse duplicator designed ad hoc allowed the valve prototypes to be tested at different flow rates and frequencies. Pressure and flow were recorded; pressure drops, effective orifice area (EOA), and regurgitant volume were computed to assess the behavior of the valve. RESULTS: Both types of Poli-Valves met the minimum requirements in terms of regurgitation and EOA as specified by the ISO 5840 Standard. Results were compared with 5 mechanical heart valves (MHVs) and 5 tissue heart valves (THVs), currently available on the market. CONCLUSIONS: Based on these results, PHVs based on styrenic block copolymers, as are Poli-Valves, can be considered a promising alternative for heart valve replacement in the near future.