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Gradients in myocardial blood flow, metabolism and mechanics across the ischemic left ventricular wall
Get PDFGoing Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Cardiac resynchronization therapy: refinements in patient selection and technology
No full textMore than twenty years of research has established the role of cardiac resynchronization therapy (CRT) in patients with medically refractory systolic heart failure with abnormal QRS complex morphology and duration. In this patient population, CRT bestows a mortality benefit, a reduction in heart failure hospitalizations and an improved functional status. The first CRT implantation took place back in March 1993 in the University Medical Center of Utrecht. Its introduction has been no less than revolutionary for patients with advanced heart failure whose only previous option was cardiac transplantation. Nowadays CRT is also a realistic and cost-effective treatment option for patients with mild heart failure. One could probably say that CRT has been one of the most exciting recent advancements in heart failure treatment. Despite that CRT has become one of the pillars of heart failure management, it continues to face a relatively high non-responder rate of 30-40%, depending on the definition for non-response used. Accordingly, there is still room for improvement of the therapy. The determination to increase CRT response rates is the inspiration of all the scientific research performed worldwide to improve the therapy. By taking advantage of some of the latest developments in device technology, cardiac imaging, and electrophysiology, this dissertation addresses several treatment-refinement strategies aimed to improve response to CRT. Roughly these can be divided into strategies to i) improve patient selection, ii) improve CRT delivery, and to iii) optimize CRT configurations. In the first part of this dissertation, the electromechanical substrate amendable by CRT is addressed. In doing so, several electrical (obtained with vectorcardiography) and mechanical (obtained with echocardiographic strain imaging) parameters are proposed which may be used for the improvement of patient selection in clinical practice. After selection of the right patient for CRT, a next key step for ensuring the best possible patient outcome is optimization of the CRT implantation procedure. Placing the left ventricular (LV) lead at an optimal position is one of the most challenging technical aspects of a CRT device implantation. Improving and facilitating CRT delivery, therefore, is the next strategy evaluated for the refinement of CRT in this dissertation. After LV lead placement, multiple device settings are programmable to increase the effect of CRT. The third and final part of this dissertation, therefore, examines optimization of device programming using pressure-volume loop analyses and evaluates the role of multipoint pacing over conventional biventricular pacing in patients with a strict left bundle branch block. By addressing these strategies, this thesis aims to provide more insight into the possibilities to better diagnose and treat patients with dyssynchronous heart failure
Patient-Tailored Cardiac Resynchronization Therapy: Imaging and Exercise Strategies
No full textBetter characterisation of the electromechanical substrate (part I) may promote more appropriate patient selection for cardiac resynchronization therapy (CRT) implantation. By developing an and-to-end automated and explainable deep learning-based approach, we were able to identify a patient cluster with the predicted combination of non-response and poor outcome after CRT (chapter 2). This approach allows for objective risk-stratification that outperforms contemporary electrocardiogram characteristics and QRSAREA, and thereby reliable excludes the presence of a CRT-amendable substrate. Chapter 3 illustrates how incorporating the mechanical substrate may extend the accuracy of such prediction models, which in turn is illustrated in the form of a combined assessment of the electrical substrate and mechanical dysfunction in chapter 4. Here, a simple four-variable model was shown to be associated with a sustained volumetric response, which indicates stable disease remission.
Optimizing left ventricular (LV) lead position (part II) may improve outcome after CRT, whereas poor placement may preclude response despite an underlying amendable substrate or favourable patient characteristics. Hence, chapter 5 discusses the importance of optimizing LV-lead placement. It is shown how the optimal pacing site is highly variable, patient-specific, difficult to predict during implantation, and especially critical in the presence of atypical LV activation or myocardial scar. In these patients, image-guidance, rather than electrical-guidance, is likely the most important approach for achieving the optimal transvenous lead position. Hence, chapter 6 demonstrates that real-time navigation of the LV-lead is feasible in a multicentre setting. Not only were leads adequately positioned in 76% of patients, echocardiographic response was achieved in 86% of patients. Chapter 7 then discusses the protocol of the multicentre randomised controlled ‘Advanced Image Supported Lead Placement in Cardiac Resynchronization Therapy’ (ADVISE) trial, which will further investigate the clinical efficacy of this approach.
Lastly, part III explores the potential diagnostic (chapter 8), prognostic (chapter 9), and therapeutic (chapter 10) implications of exercise in heart failure. In chapter 8, the feasibility of strain-based discoordination-imaging during stress echocardiography was demonstrated. Stress echocardiography could unmask dynamic changes in mechanical dyscoordination. Although feasible, many challenges remain to overcome. Chapter 9 demonstrates that submaximal oxygen uptake (VO2) kinetics are associated with volumetric response to CRT. While at least equally effective as measuring VO2 Peak, submaximal VO2 kinetics may provide a more relevant characterisation of exercise tolerance, which is also more reliable and patient-friendly. Finally, in chapter 10, we illustrate how differences in cardiac output and VO2 kinetics during submaximal exercise distinguish the severity of functional impairment in chronic heart failure, rather than differences in resting echocardiography. Moreover, we demonstrate that both high-intensity interval training and CRT improve submaximal exercise tolerance. By contrast, only CRT induces cardiac reverse remodelling, whereas only an exercise training program improved exercising haemodynamics. Hence, combining both therapies may further improve functional recovery through differential effects
Variations on the Author
Get PDF“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
Get PDFWe 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
Echo-Physiologic Aspects of Dyssynchrony and Resynchronization
No full textThe research described in the thesis explores the key mechanisms through which a dyssynchronous electrical activation of the heart leads to cardiac mechanical dysfunktion. It also explores the working mechanisms of a highly effective therapy in these patients, known as Cardiac Resynchronization Therapy (CRT). Hence, the physiology of cardiac dyssynchrony and resynchronization is explored. The technique used for this exploration is a new echocardiographic technique (speckle tracking deformation imaging), which examines th timing and amount of myocardial shortening (contraction) and stretching. Applying known physiologic aspects to improve our echocardiographic approach in the field of dyssynchrony and CRT, and inversely improving our physiologic knowledge from the results of the study, has led to the development of new indices of dyscoordination. Dyscoordination of the heart, and abnormal stretch in the septum following early shortening (septal rebound stretch), are found to have major impact on the functional consequences of cardiac dyssynchrony, but simultaneously represent the substrate to CRT. Comparing to classical dyssynchrony measures that measure only the difference in timing of motion or shortening, measuring stretch-based dyscoordination metrics as septal rebound stretch, improves our capacity to predict who exactly will respond to CRT, and who will not
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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