487 research outputs found
Beat-to-beat variability of aortic pulse wave velocity:Implications for aortic stiffness measurements
Full text linkObjectives: Aortic pulse wave velocity (aPWV) predicts cardiovascular risk. Being the reference method for aortic stiffness evaluation, invasive aPWV is also recommended for validation of noninvasive devices. Because of intrinsic haemodynamic variability and processing issues, aPWV shows beat-to-beat variability. We aimed to quantify this variability and evaluate its implications for the reliability and use of aPWV as reference in validation and clinical application studies. Methods: The study included n = 84 patients, in whom two datasets of invasive data were recorded: 1) simultaneous ascending aorta and iliac pressure acquisitions using a dual-tip intra-aortic catheter, and 2) an additional ascending aorta pressure acquisition. By combining the iliac and ascending aorta pressure recordings from the first and second acquisitions, respectively, we evaluated how a sequential acquisition protocol affects variability. We compared three pressure waveform foot identification methods to investigate the effect of data processing on variability. Furthermore, we estimated how averaging over n beats consecutive heartbeats affects the standard deviation (SD) of such n beats-averaged estimate of aPWV. Results: The simultaneously acquired invasive aPWV showed a 5% beat-to-beat SD (variability), with small but significant differences between foot identification methods. The sequential acquisition protocol doubled aPWV variability compared to simultaneous acquisition. However, because averaging had a much stronger effect on sequentially measured aPWV, the two acquisition protocols yielded comparable variabilities at n beats = 10 (2% vs. 3%). Conclusions: Our study suggests that, independently from the acquisition protocol and data processing, the intrinsic beat-to-beat variability of aPWV becomes manageable when aPWV values of at least ten heartbeats are averaged
Is individualized corrected QT interval a silver bullet for the diagnosis of long QT syndrome?
No full textThe mechanistic interaction between mechanical dyssynchrony and filling pressure in cardiac resynchronization therapy candidates
No full textAims: Both left ventricular (LV) mechanical dyssynchrony and filling pressure have been shown to be associated with outcome in heart failure patient treated with cardiac resynchronisation therapy (CRT). To investigate the mechanistic link between mechanical dyssynchrony and filling pressure and to assess their combined prognostic value in CRT candidates. Methods and results: Left atrial pressure (LAP) estimation and quantification of mechanical dyssynchrony were retrospectively performed in 219 CRT patients using echocardiography. LAP was elevated (eLAP) in 49% of the population, normal (nLAP) in 40%, and indeterminate in 11%. CRT response was defined as per cent-decrease in LV end-systolic volume after 12 ± 6 months CRT. Clinical endpoint was all-cause mortality during 4.8 years (interquartile range: 2.7-6.0 years). To investigate the mechanistic link between mechanical dyssynchrony and filling pressure, the CircAdapt computer model was used to simulate cardiac mechanics and haemodynamics in virtual hearts with left bundle branch block (LBBB) and various causes of increased filling pressure. Patients with nLAP had more significant mechanical dyssynchrony than those with eLAP. The combined assessment of both parameters before CRT was significantly associated with reverse LV remodelling and post-CRT survival. Simulations revealed that mechanical dyssynchrony is attenuated by increased LV operational chamber stiffness, regardless of whether it is caused by passive or active factors, explaining the link between mechanical dyssynchrony and filling pressure. Conclusion: Our combined clinical-computational data demonstrate that in patients with LBBB, the presence of mechanical dyssynchrony indicates relatively normal LV compliance and low filling pressure, which may explain their strong association with positive outcomes after CRT.</p
Impact of myocardial phenotype on optimal atrioventricular delay settings during biventricular and left bundle-branch pacing at rest and during exercise:insights from a virtual patient study
No full textAims Previous studies have not examined the role of non-electrical myocardial disease substrates in determining the optimal atrio-ventricular delay (AVD) settings. We conducted virtual patient simulations to evaluate whether myocardial disease substrates influence the acute response to AVD optimization at rest and during exercise. Methods and results The CircAdapt cardiovascular model was used to simulate various left ventricular (LV) remodelling found in cardiac resynchronization therapy candidates. We simulated electrical dyssynchrony, LV dilatation with preserved and reduced contractility, and increased LV passive stiffness. We simulated cardiac resynchronization following biventricular (BiVP) and non-selective LBB pacing (nsLBBP). The paced-AVD ranged from 220 to 40 ms. Cardiac output and heart rate were increased to simulate different levels of exercise. The optimal AVD was the one leading to the highest stroke volume (SV) and the lowest mean left atrial pressure (mLAP). At rest, in simulations with healthy myocardium the gain in SV by AVD optimization was larger compared to those with reduced contractility and stiff myocardium. However, mLAP was comparably decreased by AVD optimization in both healthy and diseased myocardium. During exercise, the optimal AVD shifted to shorter values, and mLAP was more sensitive to AVD, particularly in the presence of hypo-contractile and stiff myocardium. Conclusion Simulations show that hypocontractility and stiffness reduce the effect of AVD optimization on SV but enhance its benefit in lowering mLAP. Notably, virtual patients with stiff ventricles experience greater benefits from AVD optimization during exercise compared to resting conditions. Furthermore, nsLBBP provides more favourable improvements in mLAP than BiVP.</p
Left ventricular underfilling and not septal bulging dominates abnormal left ventricular filling hemodynamics in chronic thromboembolic pulmonary hypertension
No full textLumens J, Blanchard DG, Arts T, Mahmud E, Delhaas T. Left ventricular underfilling and not septal bulging dominates abnormal left ventricular filling hemodynamics in chronic thromboembolic pulmonary hypertension. Am J Physiol Heart Circ Physiol 299: H1083-H1091, 2010. First published July 30, 2010; doi:10.1152/ajpheart.00607.2010.-Chronic thromboembolic pulmonary hypertension (CTEPH) is associated with abnormal left ventricular (LV) filling hemodynamics [mitral early passive filling wave velocity/late active filling wave velocity (E/A) <1]. Pulmonary endarterectomy (PEA) acutely reduces pulmonary vascular resistance, resulting in an increase of mitral E/A. The abolishment of leftward septal bulging and an increase in right ventricular (RV) output are thought to be responsible for the increase of mitral E/A. In this study, we quantified the separate effects of leftward septal bulging and RV output on LV hemodynamics. In 39 CTEPH patients who underwent PEA, transmitral flow velocities and RV hemodynamic data were obtained pre- and postoperatively. A mathematical model describing the mechanics of ventricular interaction was fitted to the preoperative average values of cardiac output (CO; 4.4 l/min), mean pulmonary artery pressure (mPAP; 50 mmHg), mitral E/A (0.74), and mean left atrial pressure (mLAP; 9.8 mmHg). Starting from this preoperative reference state with leftward septal bulging, PEA was simulated by changing mPAP and CO to average postoperative values (28 mmHg and 5.7 l/min, respectively). Simulated and postoperatively measured data on E/A (1.27 vs. 1.48), mLAP (12.6 vs. 11.5 mmHg), and septal curvature (both rightward) were consistent. When an exclusive decrease of mPAP was simulated, mitral E/A increased 26%, mLAP decreased 16%, and septal curvature became rightward. When an exclusive increase of CO was simulated, mitral E/A increased 53% and mLAP increased 62%, whereas leftward septal bulging persisted. Thus, our simulations suggest that the increase of mitral E/A with PEA is caused two-thirds by an increase of RV output and one-third by the abolishment of leftward septal bulging
Image-derived human left ventricular modelling with fluid-structure interaction
No full textIn this study, we have developed a human left ventricular model using a hybrid immersed boundary- finite element description. The left ventricle model is built based on clinical cardiac magnetic resonance images, and completed with the inflow (left atrium) and outflow (aorta) tracts. The model is used to simulate the left ventricular dynamics with fully-coupled fluid structure interaction, with parameters optimised, and the results are in reasonably good agreement with the in vivo measurements
The Quest for Citations: Drivers of Article Impact
Full text linkWhy do some articles become building blocks for future scholars, while many others remain unnoticed? We aim to answer this question by contrasting, synthesizing and simultaneously testing three scientometric perspectives – universalism, social constructivism and presentation – on the influence of article and author characteristics on article citations. To do so, we study all articles published in a sample of five major journals in marketing from 1990 to 2002 that are central to the discipline. We count the number of citations each of these articles has received and regress this count on an extensive set of characteristics of the article (i.e. article quality, article domain, title length, the use of attention grabbers and expositional clarity), and the author (i.e. author visibility and author personal promotion). We find that the number of citations an article in the marketing discipline receives, depends upon “what one says†(quality and domain), on “who says it†(author visibility and personal promotion) and not so much on “how one says it†(title length, the use of attention grabbers, and expositional clarity). Our insights contribute to the marketing literature and are relevant to scientific stakeholders, such as the management of scientific journals and individual academic scholars, as they strive to maximize citations. They are also relevant to marketing practitioners. They inform practitioners on characteristics of the academic journals in marketing and their relevance to decisions they face. On the other hand, they also raise challenges towards making our journals accessible and relevant to marketing practitioners: (1) authors visible to academics are not necessarily visible to practitioners; (2) the readability of an article may hurt academic credibility and impact, while it may be instrumental in influencing practitioners; (3) it remains questionable whether articles that academics assess to be of high quality are also managerially relevant.Impact;Citation Analysis;Referencing;Scientometrics;Cite
Atrial septostomy benefits severe pulmonary hypertension patients by increase of left ventricular preload reserve
No full textKoeken Y, Kuijpers NH, Lumens J, Arts T, Delhaas T. Atrial septostomy benefits severe pulmonary hypertension patients by increase of left ventricular preload reserve. Am J Physiol Heart Circ Physiol 302: H2654-H2662, 2012. First published April 27, 2012; doi:10.1152/ajpheart.00072.2012.-At present, it is unknown why patients suffering from severe pulmonary hypertension (PH) benefit from atrial septostomy (AS). Suggested mechanisms include enhanced filling of the left ventricle, reduction of right ventricular preload, increased oxygen availability in the peripheral tissue, or a combination. A multiscale computational model of the cardiovascular system was used to assess the effects of AS in PH. Our model simulates beat-to-beat dynamics of the four cardiac chambers with valves and the systemic and pulmonary circulations, including an atrial septal defect (ASD). Oxygen saturation was computed for each model compartment. The acute effect of AS on systemic flow and oxygen delivery in PH was assessed by a series of simulations with combinations of different ASD diameters, pulmonary flows, and degrees of PH. In addition, blood pressures at rest and during exercise were compared between circulations with PH before and after AS. If PH did not result in a right atrial pressure exceeding the left one, AS caused a left-to-right shunt flow that resulted in decreased oxygenation and a further increase of right ventricular pump load. Only in the case of severe PH a right-to-left shunt flow occurred during exercise, which improved left ventricular preload reserve and maintained blood pressure but did not improve oxygenation. AS only improves symptoms of right heart failure in patients with severe PH if net right-to-left shunt flow occurs during exercise. This flow enhances left ventricular filling, allows blood pressure maintenance, but does not increase oxygen availability in the peripheral tissue
Improving ventricular pacing in adults and children : to treat or to avoid dyssynchrony-induced cardiac failure
Full text linkThis research shows that even patients with mild cardiac failure induced by dyssynchrony (a badly coordinated contraction of the heart) can benefit from ‘resynchronizing’ both heart chambers by artificial stimulation of both heart chambers. In children and young adults for whom artificial stimulation of the heart chamber is necessary it is important to make sure that this artificial stimulation does not cause a deterioration of the heart function. The described studies show that the place where the heart is stimulated has an important influence on the heart function. The best heart function was witnessed in stimulation of the chamber that pumps the blood into the body. This research contributes to the improvement of pacemaker therapy in adults and children for the treatment or prevention of heart failure induced by dyssynchrony. This research was partly subsidized by the Nederlandse Hartstichting (Dr. E. Dekker grant for children’s cardiology research
Efficient Numerical Schemes for Computing Cardiac Electrical Activation over Realistic Purkinje Networks: Method and Verification
Full text linkWe present a numerical solver for the fast conduction system in the heart using both a CPU and a hybrid CPU/GPU implementation. To verify both implementations, we construct analytical solutions and show that the L2-error is similar in both implementations and decreases linearly with the spatial step size. Finally, we test the performance of the implementations with networks of varying complexity, where the hybrid implementation is, on average, 5.8 times faster
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