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Contemporary metallic drug-eluting stents are associated with very good 1-year outcomes but an ongoing risk of stent-related adverse events (thrombosis, myocardial infarction, restenosis) after 1 year. The pathogenesis of these very late events is likely related to the permanent presence of the metal stent frame or polymer. Bioresorbable scaffolds have been developed to provide drug delivery and mechanical support functions similar to metallic drug-eluting stents, followed by complete resorption with recovery of more normal vascular structure and function, potentially improving very late clinical outcomes. A first-generation bioresorbable scaffold has been demonstrated to be noninferior to a contemporary metallic drug-eluting stents for overall 1-year patient-oriented and device-oriented outcomes. Increased rates of scaffold thrombosis and target vessel-related myocardial infarction were noted that may be mitigated by improved patient and lesion selection, procedural technique, and device iteration. Large-scale, randomized, clinical trials are ongoing to determine the long-term relative efficacy and safety of bioresorbable scaffolds compared with current metallic drug-eluting stents.
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Stiffness reduction provides a practical means for the instability assessment of structural steel members. In this paper, a stiffness reduction approach for the design of web-tapered steel members fabricated through the welding of individual plates is presented. Stiffness reduction functions for welded members, which fully take into account the adverse influence of plasticity and imperfections on the strength and stability, are described. The proposed approach is implemented by (i) dividing the tapered member into prismatic segments along its length, (ii) reducing the flexural stiffness of each segment through the developed stiffness reduction functions considering the withstood forces and the cross-section properties of each segment, (iii) performing Geometrically Nonlinear Analysis using beam elements and (iv) making cross-section strength checks. The accuracy of the proposed approach is assessed against the results of nonlinear shell finite element modelling for a large number of tapered members, with various slenderness values, tapering ratios (i.e. the ratios between the cross-section depths of deep and shallow ends) and loading conditions. It is observed that the proposed stiffness reduction method provides a very accurate and efficient way to design web-tapered steel members.
Sixty-eight patients (58 men, 10 women, mean age 56.3 years, range 31 to 72) with unstable angina pectoris, either initially stabilized with or refractory to optimal pharmacologic treatment, were studied to determine whether regional dysfunction due to stunning of the myocardium caused by attacks of chest pain at rest could be improved with percutaneous transluminal coronary angioplasty (PTCA). Patients were included in the study if they had successful 1-vessel PTCA, no angiographic restenosis, no reocclusion or late myocardial infarction and 2 serial left ventriculograms of sufficient quality to allow automated contour analysis before and after PTCA. Global ejection fraction increased significantly (from 56% to 60%, p < 0.05) only after successful dilatation of a stenosis of the left anterior descending coronary artery. Analysis of regional wall displacement showed significant improvement of regional wall motion in the areas supplied by the dilated vessel of either the left anterior descending, the left circumflex or the right coronary artery. Thus, regional myocardial dysfunction due to stunning of the myocardium in patients with unstable angina improves after successful PTCA.
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