1,721,056 research outputs found
Three-Dimensional Principal Strain Analysis for Characterizing Subclinical Changes in Left Ventricular Function
No full textBackground: Subendocardial strain analysis is currently feasible in two-dimensional and three-dimensional (3D) echocardiography; however, there is a lack of clarity regarding the most useful strain component for subclinical disease detection. The aim of this study was to test the hypothesis that strain analysis along the direction of strongest and weakest systolic compression (referred to as principal and secondary strain, respectively) circumvents the need for multidirectional strains and provides a more simplified assessment of left ventricular subendocardial function.
Methods: Strain analyses were performed by using two-dimensional and 3D echocardiography in 41 consecutive subjects with normal results on electron-beam computed tomography, including 15 controls and 26 patients with systemic hypertension. The direction of principal strain referenced the myofiber geometry obtained from diffusion tensor magnetic resonance imaging of a normal autopsied human heart. The incremental value of principal strain over multidirectional two-dimensional and 3D strain was analyzed.
Results: In healthy subjects, 50 6 3% of the subendocardial shortening occurred in the cross-fiber direction (left-handed helical); this balance was significantly altered in patients with hypertension (P = .01). The magnitude of longitudinal and circumferential strain was similar in patients with hypertension and controls. However, the alteration of the directional contraction pattern resulted in reduced secondary strain magnitude in patients with hypertension (P = .01), and the differences were further exaggerated when the secondary strain was normalized by the principal strain magnitude (P = .004).
Conclusions: Two-component principal and secondary strain analysis can be related to left ventricular myo-fiber geometry and may simplify the assessment of 3D left ventricular deformation by circumventing the need to assess multiple shortening and shear strain components
CRT Improves LV Filling Dynamics
No full textEchocardiographic particle imaging velocimetry allows blood flow visualization and characterization of diastolic vortex formation that may play a key role in filling efficiency. We hypothesized that abrupt withdrawal of cardiac resynchronization therapy (CRT) would alter the timing of left ventricular diastolic vortex formation and modify cardiac time intervals. In patients with heart failure (HF) who had chronically implanted CRT devices, the timing of the onset of the diastolic vortex (TDV) from mitral valve opening, transmitral flow, and cardiac time intervals was measured at baseline and after deactivation and reactivation of CRT. Compared with control patients with cardiovascular risk factors but structurally normal hearts, TDV was significantly delayed in patients with HF. Deactivation of CRT resulted in striking delay in TDV due to disorganized flow and reduced flow acceleration, and reactivation reversed these characteristics instantly. In addition, CRT deactivation also prolonged the isovolumic contraction interval, which closely correlated with the changes in the TDV. These data suggest that CRT plays an important role in optimization of left ventricular diastolic filling
Myocardial Stretch in Early Systole is a Key Determinant of the Synchrony of Left Ventricular Mechanical Activity in vivo
No full textBackground: Recent in-vitro observations suggest that left ventricular (LV) contraction is powered by ‘stretch
activation’, an intrinsic mechanism by which the stretching of an activated cardiomyocyte causes delayed force redevelopment.
We hypothesized that mechanical dyssynchrony is related to prolonged early systolic stretch that
delays the timing of peak segmental shortening.
Methods and Results: The time intervals from R wave to segmental longitudinal stretch in early systole (Tstretch)
and peak shortening (Tpeak) and the respective standard deviations (σTstretch and σTpeak) were measured by speckletracking
echocardiography in 57 patients undergoing cardiac resynchronization therapy (CRT). The percentage of
time spent in shortening, normalized to Tpeak duration [corrected ΔT=(Tpeak – Tstretch)/Tpeak] correlated with LV reverse
remodeling (reduction in end-systolic volume ≥15%). Of the 57 patients, 40 (70.2%) demonstrated LV reverse remodeling
at an average follow-up of 263±125 days after CRT. At baseline, Tstretch and σTstretch correlated with Tpeak
and σTpeak, respectively. Though there was no difference in Tstretch, Tpeak, σTstretch and σTpeak between responders and
non-responders, corrected ΔT in the mid-lateral and mid-septal segments was shorter in the responders (P<0.05 for
both) and the average of the 2 independently predicted LV reverse remodeling (area under the curve: 0.77, P=0.001).
Conclusions: Mapping LV segmental shortening in relation to early systolic stretch may aid dyssynchrony assessment
in patients undergoing CRT
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
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