| 1. |
- Andlauer, Robin, et al.
(författare)
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Influence of left atrial size on P-wave morphology : differential effects of dilation and hypertrophy
- 2018
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Ingår i: Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology. - : Oxford University Press (OUP). - 1532-2092. ; 20:3, s. 36-44
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Chronic left atrial enlargement (LAE) increases the risk of atrial fibrillation. Electrocardiogram (ECG) criteria might provide a means to diagnose LAE and identify patients at risk; however, current criteria perform poorly. We seek to characterize the potentially differential effects of atrial dilation vs. hypertrophy on the ECG P-wave. Methods and results: We predict effects on the P-wave of (i) left atrial dilation (LAD), i.e. an increase of LA cavity volume without an increase in myocardial volume, (ii) left atrial concentric hypertrophy (LACH), i.e. a thickened myocardial wall, and (iii) a combination of the two. We performed a computational study in a cohort of 72 anatomical variants, derived from four human atrial anatomies. To model LAD, pressure was applied to the LA endocardium increasing cavity volume by up to 100%. For LACH, the LA wall was thickened by up to 3.3 mm. P-waves were derived by simulating atrial excitation propagation and computing the body surface ECG. The sensitivity regarding changes beyond purely anatomical effects was analysed by altering conduction velocity by 25% in 96 additional model variants. Left atrial dilation prolonged P-wave duration (PWd) in two of four subjects; in one subject a shortening, and in the other a variable change were seen. Left atrial concentric hypertrophy, in contrast, consistently increased P-wave terminal force in lead V1 (PTF-V1) in all subjects through an enlarged amplitude while PWd was unaffected. Combined hypertrophy and dilation generally enhanced the effect of hypertrophy on PTF-V1. Conclusion: Isolated LAD has moderate effects on the currently used P-wave criteria, explaining the limited utility of PWd and PTF-V1 in detecting LAE in clinical practice. In contrast, PTF-V1 may be a more sensitive indicator of LA myocardial hypertrophy.
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| 2. |
- Anzt, Hartwig, et al.
(författare)
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An environment for sustainable research software in Germany and beyond: current state, open challenges, and call for action
- 2020
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Ingår i: F1000 Research. - : F1000 Research Ltd. - 2046-1402. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Research software has become a central asset in academic research. It optimizes existing and enables new research methods, implements and embeds research knowledge, and constitutes an essential research product in itself. Research software must be sustainable in order to understand, replicate, reproduce, and build upon existing research or conduct new research effectively. In other words, software must be available, discoverable, usable, and adaptable to new needs, both now and in the future. Research software therefore requires an environment that supports sustainability. Hence, a change is needed in the way research software development and maintenance are currently motivated, incentivized, funded, structurally and infrastructurally supported, and legally treated. Failing to do so will threaten the quality and validity of research. In this paper, we identify challenges for research software sustainability in Germany and beyond, in terms of motivation, selection, research software engineering personnel, funding, infrastructure, and legal aspects. Besides researchers, we specifically address political and academic decision-makers to increase awareness of the importance and needs of sustainable research software practices. In particular, we recommend strategies and measures to create an environment for sustainable research software, with the ultimate goal to ensure that software-driven research is valid, reproducible and sustainable, and that software is recognized as a first class citizen in research. This paper is the outcome of two workshops run in Germany in 2019, at deRSE19 - the first International Conference of Research Software Engineers in Germany - and a dedicated DFG-supported follow-up workshop in Berlin.
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| 3. |
- Hoseini Hooshyar, Hamed, 1986, et al.
(författare)
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Initial corrosion attack of 304L and T22 in 2 MW biomass gasifier: a microstructural investigation
- 2015
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Ingår i: Materials at High Temperatures. - 0960-3409. ; 32:1-2, s. 197-204
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Tidskriftsartikel (refereegranskat)abstract
- The work investigates the initial corrosion attack on a low alloyed steel and a stainless steel in a 2 MW test gasifier. The gasifier environment generates homogenous deposits that consist mainly of carbon containing species, potassium sulphate, potassium chloride and zinc sulphide. The stainless steel exhibits better corrosion resistance compared to the low alloyed steel and the analysis indicates a protective thin scale covering parts of the surface after 4 h exposure. However, in some areas the oxide scale has lost its protective properties and thicker oxide scales are seen. The thick oxide islands consist of an inward growing Fe,Cr,Ni oxide and an outward growing iron oxide. The low alloyed steel shows a more homogenous and faster initial corrosion attack. The thick scales exhibit a sharp straight line in the middle of the scale that separates the bottom spinel oxide from the outer iron rich parts of the scale. It is considered that this flat interface corresponds to the original sample surface
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| 4. |
- Krueger, Martin W., et al.
(författare)
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In-silico modeling of atrial repolarization in normal and atrial fibrillation remodeled state
- 2013
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Ingår i: Medical & Biological Engineering & Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 51:10, s. 1105-1119
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Tidskriftsartikel (refereegranskat)abstract
- Atrial fibrillation (AF) is the most common cardiac arrhythmia, and the total number of AF patients is constantly increasing. The mechanisms leading to and sustaining AF are not completely understood yet. Heterogeneities in atrial electrophysiology seem to play an important role in this context. Although some heterogeneities have been used in in-silico human atrial modeling studies, they have not been thoroughly investigated. In this study, the original electrophysiological (EP) models of Courtemanche et al., Nygren et al. and Maleckar et al. were adjusted to reproduce action potentials in 13 atrial regions. The parameter sets were validated against experimental action potential duration data and ECG data from patients with AV block. The use of the heterogeneous EP model led to a more synchronized repolarization sequence in a variety of 3D atrial anatomical models. Combination of the heterogeneous EP model with a model of persistent AF-remodeled electrophysiology led to a drastic change in cell electrophysiology. Simulated Ta-waves were significantly shorter under the remodeling. The heterogeneities in cell electrophysiology explain the previously observed Ta-wave effects. The results mark an important step toward the reliable simulation of the atrial repolarization sequence, give a deeper understanding of the mechanism of atrial repolarization and enable further clinical investigations.
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| 5. |
- Loewe, Axel, et al.
(författare)
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Left and Right Atrial Contribution to the P-wave in Realistic Computational Models
- 2015
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Ingår i: Lecture Notes in Computer Science. - Cham : Springer International Publishing. - 0302-9743 .- 1611-3349. ; 9126, s. 439-447
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Konferensbidrag (refereegranskat)abstract
- ECG markers derived from the P-wave are used frequently to assess atrial function and anatomy, e.g. left atrial enlargement. While having the advantage of being routinely acquired, the processes underlying the genesis of the P-wave are not understood in their entirety. Particularly the distinct contributions of the two atria have not been analyzed mechanistically. We used an in silico approach to simulate P-waves originating from the left atrium (LA) and the right atrium (RA) separately in two realistic models. LA contribution to the P-wave integral was limited to 30% or less. Around 20% could be attributed to the first third of the P-wave which reflected almost only RA depolarization. Both atria contributed to the second and last third with RA contribution being about twice as large as LA contribution. Our results foster the comprehension of the difficulties related to ECG-based LA assessment.
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| 6. |
- Loewe, Axel, et al.
(författare)
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Left atrial hypertrophy increases P-wave terminal force through amplitude but not duration
- 2017
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Ingår i: Computing in Cardiology Conference, CinC 2016. - 9781509008964 ; 43, s. 1-4
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Konferensbidrag (refereegranskat)abstract
- P-wave morphology correlates with the risk for a trial fibrillation (AF). Left atrial (LA) enlargement could explain both the higher risk for AF and higher P-wave terminal force (PTF) in ECG lead V1. However, PTF-V1 has been shown to correlate poorly with LA size. We hypothesize that LA hypertrophy, i.e. a thickening of the myocardial wall, also contributes to increased PTF-V1 and is part of the reason for the rather low specificity of increased PTF-V1 regarding LA enlargement. To show this, a trial excitation propagation was simulated in a cohort of four anatomically individualized models including rule-based myocyte orientation and spatial electrophysiological heterogeneity using the mono domain approach. The LA wall was thickened symmetrically in steps of 0.66mm by up to 3.96mm. Interatrial conduction was possible via discrete connections at the coronary sinus, Bachmann's bundle and posteriorly. Body surface ECGs were computed using realistic, heterogeneous torso models. During the early P-wave stemming from sources in the RA, no changes were observed. Once the LA got activated, the voltage in Vi tended to lower values for higher degrees of hypertrophy. Thus, the amplitude of the late positive P-wave decreased while the amplitude of the subsequent negative terminal phase increased. PTF-V1 and LA wall thickening showed a correlation of 0.95. The P-wave duration was almost unaffected by LA wall thickening (Δ <2 ms). Our results show that PTF-V1 is a sensitive marker for LA wall thickening and elucidate why it is superior to P-wave area. The interplay of LA hypertrophy and dilation might cause the poor empirical correlation of LA size and PTF-V1.
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