1,720,975 research outputs found
Preliminary findings on left atrial appendage occlusion simulations applying different endocardial devices
Full text linkAtrial fibrillation (AF) is one of the most investigated arrhythmias since it is
associated with a five-fold increase in the risk of strokes. Left atrium dilation
and unbalanced and irregular contraction caused by AF favour blood stasis
and, consequently, stroke risk. The left atrial appendage (LAA) is the site of the
highest clots formation, increasing the incidence of stroke in AF population. For
many years oral anticoagulation therapy has been the most used AF treatment
option available to decrease stroke risk. Unfortunately, several contraindications
including bleeding risk increase, interference with other drugs and with multiorgan
functioning, might outweigh its remarkable benefits on thromboembolic events.
For these reasons, in recent years, other approaches have been designed, including
LAA percutaneous closure. Unfortunately, nowadays, LAA occlusion (LAAO) is
restricted to small subgroups of patients and require a certain level of expertise
and training to successfully complete the procedure without complications. The
most critical clinical problems associated with LAAO are represented by peridevice
leaks and device related thrombus (DRT). The anatomical variability of the
LAA plays a key role in the choice of the correct LAA occlusion device and in its
correct positioning with respect to the LAA ostium during the implant. In this
scenario, computational fluid dynamics (CFD) simulations could have a crucial
role in improving LAAO intervention. The aim of this study was to simulate the fluid
dynamics effects of LAAO in AF patients to predict hemodynamic changes due
to the occlusion. LAAO was simulated by applying two different types of closure
devices based on the plug and the pacifier principles on 3D LA anatomical models
derived from real clinical data in five AF patients. CFD simulations were performed
on the left atrium model before and after the LAAO intervention with each device.
Blood velocity, particle washout and endothelial damage were computed to
quantify flow pattern changes after the occlusion in relation to the thrombogenic
risk. Our preliminary results confirmed an improved blood washout after the
simulated implants and the capability of foreseeing thrombogenic risk based on
endothelial damage and maximum blood velocities in different scenarios. This
tool may help to identify effective device configurations in limiting stroke risk for
patient-specific LA morphologies
Towards a repository of synthetic electrograms for atrial activation detection in atrial fibrillation
No full textBackground: Recently, the analysis of the spatio-temporal behavior of atrial fibrillation activation patterns has been widely investigated with the aim to better understand the arrhythmia implications on the heart electrical activity. Most of the proposed techniques are based on atrial activation timing detections. Unfortunately atrial activation timings are not easily recognizable on the electrograms (EGMs) and an approach to support the validation of such techniques is highly desirable. The aim of this study is to provide an effective workflow for the generation of synthetic unipolar atrial electrograms (SEGMs) in atrial fibrillation (AF) condition and with different levels of noise. Method: Real EGMs signals were obtained from a dataset of 6 subjects that underwent ablation. Each SEGM was obtained by modeling the three principal components of an EGM starting from real signals: atrial far-field (Afar), atrial near-field (Anear) and the ventricular far-field (Vfar). Afar was generated using an autoregressive model applied on segments from real EGMs not characterized by ventricular or atrial activations; Anear and Vfar were extracted directly from the real signals. A Gamma distribution and an atrio-ventricular node model were used to locate both Anear and Vfar on Afar, respectively. Three electrophysiologists with different levels of expertise evaluated the realism of the SEGMs on a set of 100 randomly selected signals including 50 EGMs and 50 SEGMs. Analysis was repeated by the three experts on a subset of 21 signals. Results: The time required to generate the synthetic EGMs was less than 1 min once annotated EGMs are available. The cardiologists succeeded in distinguishing real from synthetic EGMs in 45%, 43% and 35% of the signals, respectively. By repeating the evaluation, 28%, 0% and 48% of signals were classified differently, including 67%, 52% and 36% of correct classifications. Conclusion: The proposed approach proved to be effective in producing SEGMs which are difficult to distinguish from real EGMs. This study provides a tool for realistic SEGM generation from real EGMs in AF condition with different levels of noise and at different AF rates. The tool may be easily adopted to obtain SEGMs in different arrhythmic conditions. SEGMs generated in this study are shared with the scientific community as a first step towards a repository of synthetic and real atrial signals supporting the benchmarking of new approaches to investigate AF
Optimizing Model Pruning in Decentralized Learning Networks with DFL-Trim
No full textIn recent decades, applications in environmental sustainability, education, and housekeeping have become increasingly distributed and sophisticated, leveraging a wide range of devices to perform complex tasks. While a large number of agents can reduce computation time, managing these distributed systems presents significant challenges due to resource constraints such as power consumption and storage. To address this, the literature has explored various model compression techniques, such as pruning, to optimize performance in distributed environments. In this paper, we propose DFL-Trim, a solution for trimming models in Decentralized Federated Learning (FL) that meets network constraints while maintaining satisfactory performance. We demonstrate how pruning can be implemented in decentralized settings, analyze its effect on bandwidth usage, and discuss the trade-offs between compression and model accuracy
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
Quantification of Left Atrium Fibrosis From Late Gadolinium Enhanced MRI in Atrial Fibrillation
No full textLate gadolinium enhanced magnetic resonance
imaging (LGE-MRI) is a recent technique used for
fibrosis distribution assessment in the left atrium (LA)
wall. Unfortunately, LGE-MRI analysis does not rely on
a standardized image processing protocol. The aim of the
study was to compare different methods to quantify
fibrosis in the LA in the 3D domain. LGE-MRI from 60
AF patients were analyzed applying five different
approaches for fibrosis segmentation: an histogrambased (H-6SD), the image intensity ratio (IIR), the blood
pool normalization (BP), the Chan-Vese (CV) and the
graph-cut (GC) method. For each method we quantified
the percentage of fibrosis with respect to the entire LA
wall mass. Results showed these five approaches can be
divided in two groups; the group composed by the H6SD, CV and GC is characterized similar results (mean
coefficient of variation=0.3), while the results obtained
applying BP and IIR strongly depend on the quality of the
acquisition (mean coefficient of variation=0. 62). Utah
stage classification resulted in a wide disagreement
(22/60 patients, 37%) among BP and IIR. The two
approaches which best matched the Utah classification
were the CV and GC (49/60 patients, 82%). This study
confirmed the evaluation of the quantification method
appears critical and further research is needed to define
a satisfactory standard for atrial fibrosis segmentation
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
Development of New Left Atrial Anatomical Models for the Study of the Left Atrial Appendage Implications in Atrial Fibrillation
No full textAtrial fibrillation is associated with a five-fold increase
of the stroke risk. Left atrial appendage (LAA) is the atrial
site with the highest blood stasis risk, increasing thrombus formation and stroke. Recent studies have been focused on the association between the left atrial appendage
anatomical features and the stroke risk. However, conflicting results have been published. In this context, clinical
studies suggested the stroke risk stratification could be improved by using haemodynamics information on the left
atrium and mainly on the left atrial appendage. Therefore,
the aim of this study was the design and development of a
method which enabled to reconstruct and generate several
LA anatomical models, where each one was characterized
by a different LAA morphology. These anatomical models
represent the computational domain for the computational
fluid dynamics simulations of the haemodynamics within
the left atrium and LAA
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
- …
