1,721,046 research outputs found
Optimal Site for Proximal Optimization Technique in Complex Coronary Bifurcation Stenting: A Computational Fluid Dynamics Study
Full text linkBackground/purpose: The optimal position of the balloon distal radio-opaque marker during the post optimization technique (POT) remains debated. We analyzed three potential different balloon positions for the final POT in two different two-stenting techniques, to compare the hemodynamic effects in terms of wall shear stress (WSS) in patients with complex left main (LM) coronary bifurcation. Methods/materials: We reconstructed the patient-specific coronary bifurcation anatomy using the coronary computed tomography angiography (CCTA) data of 8 consecutive patients (6 males, mean age 68.2± 18.6 years) affected by complex LM bifurcation disease. Subsequently a virtual bench test was performed in each patient using two different double stenting techniques represented by the DK and Nano crush using the reconstruction of Orsiro stents (Biotronik IC, Bulack, Switzerland). Results: A significant reduction in the mean WSS values in all the lesion's sites was observed when the final POT was performed 1 mm distally the carina cut plane in both techniques. Moreover, a significant improvement in the mean WSS values of the entire SB (e.g. LCX) was obtained performing the POT 1 mm distally to the carina cut plane. The proximal POT resulted in larger area of lower WSS values at the carina using both the Nano crush and the DK crush techniques. Conclusions: In patients with complex LM bifurcation disease the use of a final POT performed 1 mm distally to the carina cut plane might results in more favorable WSS patterns (i.e. higher WSS values) along all stented segments and, especially, along the entire LCX lesions
Transcatheter Aortic Valve with Embolic Filter: Experiments and Simulations
No full textCerebrovascular events are one of the most critical complications following transcatheter aortic valve replacement. The majority of these events are associated to calcium debris generated by the stenotic valve manipulation. Embolic protection devices were accordingly designed to reduce the risk of these adverse events. Within this context, an innovative transcatheter aortic valve with embolic filter is proposed, which is temporarily released in the ascending aorta, and avoids severe regurgitation while treating the native valve before the replacement. Experimental tests and computational analyses were conducted on a prototype of the Nitinol frame of the device. The frame integrity throughout the clinical procedure was assessed, radial force curves were experimentally measured and used to calibrate a finite element model
Biomechanical Evaluation of Different Balloon Positions for Proximal Optimization Technique in Left Main Bifurcation Stenting
No full textBackground: Proximal optimization technique (POT) is a key step during left main (LM) bifurcation stenting. However, after crossover stenting, the ideal position of POT balloon is unclear. We sought to evaluate the biomechanical impact of different POT balloon positions during LM cross-over stenting procedure. Methods: We reconstructed the patient-specific LM bifurcation anatomy, using coronary computed tomography angiography data of 5 consecutive patients (3 males, mean age 66.3 ± 21.6 years) with complex LM bifurcation disease, defined as Medina 1,1,1, evaluated between 1st January 2018 to 1st June 2018 at our center. Finite element analyses were carried out to virtually perform the stenting procedure. POT was virtually performed in a mid (marker just at the carina cut plane), proximal (distal marker 1 mm before the carina) and distal (distal marker 1 mm after the carina) position in each investigated case. Final left circumflex obstruction (SBO%), strut malapposition, elliptical ratio and stent malapposition were evaluated. Results: The use of both proximal and distal POT resulted in a smaller LM diameter compared to the mid POT. SBO was significantly higher in both proximal and distal configurations compared to mid POT: 38.3 ± 5.1 and 29.3 ± 3.1 versus 18.3 ± 3.6%, respectively. Similarly stent malapposition was higher in both proximal and distal configurations compared to mid POT: 1.3 ± 0.4 and 0.82 ± 1.8 versus 0.78 ± 1.2, respectively. Conclusions: Mid POT offers the best results in terms of LCx opening maintaining slightly smaller but still acceptable LM and LAD diameters compared to alternative POT configuration
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Plaque heterogeneity influences in-stent restenosis following drug-eluting stent implantation: Insights from patient-specific multiscale modelling
Full text linkIn-stent restenosis represents a major cause of failure of percutaneous coronary intervention with drug-eluting stent implantation. Computational multiscale models have recently emerged as powerful tools for investigating the mechanobiological mechanisms underlying vascular adaptation processes during in-stent restenosis. However, to date, the interplay between intervention-induced inflammation, drug delivery and drug retention has been under-investigated. Here, an original patient-specific multiscale agent-based modelling framework was developed to investigate the interplay between drug release, plaque composition and intervention-induced inflammation on in-stent restenosis following drug-eluting stent implantation. The framework integrated a finite element simulation of stent expansion, with a drug transport simulation and an agent-based model of cellular dynamics. A patient-specific coronary cross-section with heterogeneous diseased tissue was considered and rigorously analyzed through a variety of scenarios, including different plaque compositions and different inflammatory responses. The analysis revealed three significant findings: (i) calcifications substantially impeded drug transport, resulting in drug-depleted regions and reduced stent efficacy; (ii) by impacting drug transport, variations in plaque composition influenced arterial wall response, with the fully-calcific scenario showing the greatest lumen area reduction; (iii) the impact of different drug receptor saturation conditions (obtained with different plaque compositions) was particularly evident under conditions of persistent inflammatory state. This study represents a significant advancement in multiscale modelling of in-stent restenosis following drug-eluting stent implantation. The results obtained provided deeper insights into the complex interactions among patient-specific plaque composition, inflammation and drug retention, suggesting a patient-specific management of the intervention, particularly in cases of complex disease
Location-specific comparison between a 3D in-stent restenosis model and micro-CT and histology data from porcine in vivo experiments
Full text linkBackground
Coronary artery restenosis is an important side effect of percutaneous coronary intervention. Computational models can be used to better understand this process. We report on an approach for validation of an in silico 3D model of in-stent restenosis in porcine coronary arteries and illustrate this approach by comparing the modelling results to in vivo data for 14 and 28 days post-stenting.
Methods
This multiscale model includes single-scale models for stent deployment, blood flow and tissue growth in the stented vessel, including smooth muscle cell (SMC) proliferation and extracellular matrix (ECM) production. The validation procedure uses data from porcine in vivo experiments, by simulating stent deployment using stent geometry obtained from micro computed tomography (micro-CT) of the stented vessel and directly comparing the simulation results of neointimal growth to histological sections taken at the same locations.
Results
Metrics for comparison are per-strut neointimal thickness and per-section neointimal area. The neointimal area predicted by the model demonstrates a good agreement with the detailed experimental data. For 14 days post-stenting the relative neointimal area, averaged over all vessel sections considered, was 20 ± 3% in vivo and 22 ± 4% in silico. For 28 days, the area was 42 ± 3% in vivo and 41 ± 3% in silico.
Conclusions
The approach presented here provides a very detailed, location-specific, validation methodology for in silico restenosis models. The model was able to closely match both histology datasets with a single set of parameters. Good agreement was obtained for both the overall amount of neointima produced and the local distribution. It should be noted that including vessel curvature and ECM production in the model was paramount to obtain a good agreement with the experimental data
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