1,720,965 research outputs found
Effects of clopidogrel on "aspirin specific" pathways of platelet inhibition
No full textThe most widely accepted methods of assessing response to clopidogrel involve isolated ADP-induced platelet aggregation. Whilst poor response determined by these assays correlates with adverse clinical events, the number of “poor responders” is far higher than the number of events attributed to treatment failure. Clopidogrel may have effects that cannot be assessed using isolated ADP-induced aggregation. We have investigated the effect of clopidogrel on Arachidonic Acid (AA) induced platelet activation-an “aspirin specific” pathway using a novel near patient assay. Thirty four volunteers on no medication and 36 patients, on maintenance therapy with aspirin 75 mg daily, were recruited. Blood tests for Thrombelastogram PlateletMapping were taken immediately prior to and 6 hours after administration of a 600 mg clopidogrel loading dose. Changes in the area under the response curve at 15 minutes (AUC15) with both ADP- and AA-stimulation were calculated as were the corresponding percentage platelet and percentage clotting inhibition (%PIn and %CIn). There were predictable and significant changes in the AUC15 of the ADP channel in response to clopidogrel and the corresponding %PIn and %CIn in both volunteers and patients. There were also significant reductions in the AUC15 of the AA channel (presented as Mean +/- 95%CI), by 27.2 +/- 11.8%, p = 0.005 in volunteers and 35.0 +/- 8.2%, p < 0.001 in patients) and increases in the %PIn and %CIn calculated using the AA channel in volunteers (by 20.0 +/- 11.4%, p + 0.02 and 32.3 +/- 12.8%, p < 0.001 respectively) and patients (by 24.2 +/- 8.6%, p < 0.001 and by 18.0 +/- 8.6, p < 0.001 respectively). Clopidogrel has both independent and aspirin-synergistic effects on AA-induced platelet activation suggesting potentiation of the antiplatelet activity of aspirin. This effect may be clinically important and is not detected by current “gold standard” methods of assessing response to clopidogrel
Leakage current from transvenous and subcutaneous implantable cardioverter defibrillators (ICDs): A risk to the rescuer?
No full textBackground Implantable cardioverter-defibrillators (ICDs) are a well-established therapy for patients at risk of life-threatening ventricular arrhythmias. With rising implant rates, the risk of a rescuer performing chest compressions during discharge is increasing, leading to concerns over rescuer safety from the resultant leakage current. More recently, subcutaneous ICDs (S-ICD) have been developed, which utilise a higher energy and more superficial electrodes compared with transvenous ICDs (T-ICD), raising safety concerns further. Objective We measured the current a rescuer would potentially receive from T-ICDs and S-ICDs if they were in contact with the patient at the time of ICD discharge to assess its magnitude in relation to international safety standards. Methods Surface voltages adjacent to ICD electrodes were measured on patients undergoing defibrillation threshold checks. Rescuer current was then calculated assuming a total rescuer circuit impedance of 1696 Ω. Results Twenty-five patients were recruited. Rescuer current from S-ICDs was significantly higher than those from T-ICDs (S-ICD: Median RMS 135 mA range 91 mA–164 mA, T-ICD: Median RMS 31 mA, range 9 mA–75 mA, P < 0.0001). Surface voltages (median RMS) to which the rescuer is likely to be exposed are higher when performing chest compressions from the patient's left side compared with the right (127 V vs 67 V respectively, 95% CI of difference −34 V to −67 V, P < 0.0001). Conclusions Rescuers performing chest compressions on ICD patients are at risk from leakage current, particularly from S-ICDs. Chest compressions should be performed from the opposite side to the ICD to reduce rescuer risk.</p
Radiofrequency ablation of the diseased human left ventricle
No full textBackground: predictors of effective ablation lesion delivery in the human left ventricle are not established, particularly in scar. Impedance drop and electrogram (EGM) attenuation are potential surrogates to assess this.Objectives: this study sought to establish the relationships between ablation index (AI) and force-time integral (FTI) with impedance drop and EGM attenuation in the human left ventricle.Methods: patients undergoing ventricular tachycardia ablation were recruited. EGMs were collected preablation and postablation, with impedance, AI, and FTI measured during. Based on preablation bipolar voltage, myocardium was adjudged a low-voltage myocardium (LVM) (1.50 mV). Relationships between these parameters were explored.Results: a total of 402 ablations were analyzed in 15 patients. The percent impedance drop correlated with AI and FTI (P < 0.0005; repeated-measures correlation coefficient: 0.54 and 0.44, respectively), a relationship that became weaker with increased myocardial fibrosis, (repeated-measures correlation coefficient for NVM, IVM, and LVM, AI: 0.67, 0.60, and 0.52, respectively; FTI: 0.59, 0.51, and 0.42, respectively). The curve between AI/FTI and impedance drop plateaued at 763 AI and 713 gram-seconds, an impedance drop of 7.5%. Shallower curves occurred progressively from NVM to LVM (P < 0.0005). Mixed models demonstrated that AI and FTI had a greater effect on impedance drop than myocardial fibrosis, drift, or orientation, (standardized β: 0.54 and 0.48, respectively). EGMs were attenuated with ablation (29.3%; IQR: 4.4%-53.3%; P < 0.0005), but attenuation did not correlate with AI or FTI.Conclusions: on biophysical analysis, ablation beyond an AI of 763 and FTI of 713 gs offers minimal additional efficacy on average. Fibrosis blunts ablation efficacy. AI is a stronger correlate with impedance drop than FTI. EGM attenuation does not correlate with ablation parameters. (Late Potentials and Ablation Index in Ventricular Tachycardia Ablation; NCT03437408
Comparison of voltages between atria: differences in sinus rhythm and atrial fibrillation
No full textBackground: ultra high-density mapping systems allow for comparison of atrial electroanatomical maps in unprecedented detail. Atrial scar determined by voltages and surface area between atria, rhythm and atrial fibrillation (AF) types was assessed.Methods: left (LA) and right atrial (RA) maps were created using Rhythmia HDx in patients listed for ablation for paroxysmal (PAF, sinus rhythm (SR) maps only) or persistent AF (PeAF, AF and SR maps). Electrograms on corresponding SR/AF maps were paired for direct comparison. Percentage surface area of scar was assigned low- (LVM, ≤ 0.05 mV), intermediate- (IVM, 0.05–0.5 mV) or normal voltage myocardium, (NVM, > 0.5 mV).Results: thirty-eight patients were recruited generating 96 maps using 913,480 electrograms. Paired SR-AF bipolar electrograms showed fair correlation in LA (Spearman’s ρ = 0.32) and weak correlation in RA (ρ = 0.19) and were significantly higher in SR in both (LA: 0.61 mV (0.20–1.67) vs 0.31 mV (0.10–0.74), RA: 0.68 mV (0.19–1.88) vs 0.47 mV (0.14–1.07), p Significantly more IVM/LVM surface areas were seen in AF over SR (LA only, p Conclusions: ultra high-density mapping shows paired electrograms correlate poorly between SR and AF. SR electrograms are typically (but not always) larger than those in AF. Patients with PeAF have a lower global electrogram voltage than those with PAF. Electrogram voltages are similar between atria within individual patients
Establishing safe, effective ablation in the diseased human ventricle: an analysis of generator impedance and electrogram attenuation
No full textFunding acknowledgements: type of funding sources: Private company. Main funding source(s): Biosense Webster IncBackground: predictors of effective and safe lesion delivery in the human left ventricle have not been established. Generator impedance (GI) drop and electrogram (EGM) attenuation are indices which can be used as surrogates for ablation lesion parameters. Tissue pops are a complication of myocardial overheating preceded by a rise in GI and can have adverse consequences.Purpose: to establish the relationships between Ablation Index (AI), Force Time Integral (FTI) and contact force with GI and EGM attenuation. To establish factors early in ablation that are predictive of a GI rise.Methods: patients undergoing ventricular tachycardia ablation were recruited. All ablations were performed with contact force sensing surround flow catheters. Electrograms were collected pre and post ablation, with GI, AI, FTI measured during. Ablations were divided into low (LVM, < 0.50mV), intermediate (IVM, 0.51 – 1.50mV) and normal voltage (NVM, > 1.50mV) based upon pre-ablation bipolar EGM amplitude. Ablations with a 5% rise in GI from maximal drop were noted and predictors of this explored.Results: in 15 patients, 402 ablations were analysed. Filtered percentage GI drop correlated with AI and FTI, (p < 0.0005, Spearman’s ρ = 0.522 and 0.524) and reached a plateau at 763AI and 713gs, a filtered GI drop of 7.5% (Figure 1). Shallower curves occurred progressively from NVM to IVM to LVM, (p < 0.0005), (Figure 2)The bipolar EGM significantly attenuated with ablation, (median attenuation 0.14mV, [29.3%], p Parameters associated with a GI rise during ablation were greater mean CF to maximum GI drop, (p = 0.002), greater initial percentage GI drop at 5 seconds, (p < 0.0005), power of 50W (p = 0.005), and perpendicular orientation, (p = 0.006). Percentage GI drop at 5 seconds was the best predictor of ablations with a GI rise, (AUCROC 0.773; 95% CI 0.708 – 0.838; optimal cut-off 2.44%). Mean contact force to maximum GI drop was a poor predictor of a GI rise (AUCROC 0.647; 95% CI 0.577 – 0.718, optimal cut-off 14.7g).Conclusion: during left ventricular ablation, AI of 763 and FTI of 713gs should be targeted, with a lower impedance drop observed for more scarred myocardium. A GI drop of <br/
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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