scholarly journals Maximizing the Capture of the Excitable Gap During Ventricular Arrhythmias for Low-energy Defibrillation

2020 ◽  
Author(s):  
Angel Moreno ◽  
Richard Walton ◽  
Olivier Bernus ◽  
Edward Vigmond ◽  
Jason Bayer
Keyword(s):  
Ventricular Arrhythmias ◽  
Low Energy ◽  
Excitable Gap

P6555A self-adaptive approach to antitachycardia pacing - a head to head comparison using advanced computational modeling

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
D Swenson ◽  
J Blauer ◽  
R Taepke ◽  
E Kwan ◽  
E Ghafoori ◽  
...  
Keyword(s):  
Ventricular Arrhythmias ◽  
Border Zone ◽  
Patient Specific ◽  
Programmed Electrical Stimulation ◽  
Antitachycardia Pacing ◽  
Cardiac Arrythmias ◽  
Modeling Software ◽  
Excitable Gap ◽  
Infarct Border Zone ◽  
Infarct Border

Abstract Background Antitachycardia pacing (ATP) for monomorphic VT (MVT) reduces painful defibrillation shocks. Most ICD-treated ventricular arrhythmias are MVT, suggesting an opportunity for improved ATP to decrease shocks. We report on a new algorithm (Yee, Circ AE 2017) that uses electrophysiologic (EP) first-principles to design ATP sequences in real-time. Heart-rate history is used to design the first ATP sequence, and failed ATP post-pacing interval is used to design later sequences. Purpose The purpose of this modeling study was to understand how this new ATP algorithm would perform in a head-to-head comparison with traditional burst ATP. Modeling allows direct comparison of the two algorithms in identical, realistic, patient-derived cardiac arrythmias. Methods Patient-specific late gadolinium enhanced MRI and EP data were used to build an adjudicated cohort of realistic numerical heart models with varied EP, infarct, border zone. Publicly available EP modeling software CARPentry was used to calculate sustained reentrant VT initiated with the programmed electrical stimulation used to induce VT clinically. The VTs were physician-adjudicated to validate models. Burst ATP was 3 sequences of 8 pulses at 88% of VT cycle length, each decremented by 10ms. The new ATP was limited to 3 automatically designed sequences. Results Three hundred unique VT scenarios were generated from 6 human hearts with multiple VT circuits, 5 electrophysiologic states, and 10 pacing locations. Burst ATP terminated 168/300 VTs (56%) and accelerated 2.7%. The new ATP terminated 234/300 VTs (78%) with the same acceleration. The two dominant ATP failure mechanisms were identified as 1) insufficient prematurity to close the excitable gap, and 2) failure to reach the critical isthmus of the VT circuit. For these mechanisms, the new ATP algorithm reduce failures from 64 to 28 (44% reduction) without increasing acceleration. Conclusion The new automated ATP algorithm successfully adapted ATP sequences for VT episodes that burst ATP failed to terminate. The new ATP was successful even with complex scar geometries and electrophysiology heterogeneity as seen in the real world.

Dissociated Σ=27 boundaries in silicon

1988 ◽  
Vol 46 ◽  
pp. 624-625
Author(s):  
A. Garg ◽  
W.A.T. Clark ◽  
J.P. Hirth
Keyword(s):  
Electron Diffraction ◽  
Local Minimum ◽  
Boundary Energy ◽  
Coincidence Site Lattice ◽  
Boundary Plane ◽  
Low Energy ◽  
Theoretical Understanding ◽  
Site Lattice ◽  
Kikuchi Pattern ◽  
Analysis Techniques

In the last twenty years, a significant amount of work has been done in the theoretical understanding of grain boundaries. The various proposed grain boundary models suggest the existence of coincidence site lattice (CSL) boundaries at specific misorientations where a periodic structure representing a local minimum of energy exists between the two crystals. In general, the boundary energy depends not only upon the density of CSL sites but also upon the boundary plane, so that different facets of the same boundary have different energy. Here we describe TEM observations of the dissociation of a Σ=27 boundary in silicon in order to reduce its surface energy and attain a low energy configuration.The boundary was identified as near CSL Σ=27 {255} having a misorientation of (38.7±0.2)°/[011] by standard Kikuchi pattern, electron diffraction and trace analysis techniques. Although the boundary appeared planar, in the TEM it was found to be dissociated in some regions into a Σ=3 {111} and a Σ=9 {122} boundary, as shown in Fig. 1.

Transfer optics for high spatial resolution electron spectroscopy

1988 ◽  
Vol 46 ◽  
pp. 666-667
Author(s):  
G. G. Hembree ◽  
Luo Chuan Hong ◽  
P.A. Bennett ◽  
J.A. Venables
Keyword(s):  
Magnetic Field ◽  
Scanning Transmission Electron Microscope ◽  
Low Energy ◽  
Objective Lens ◽  
State University ◽  
Arizona State University ◽  
Initial Field ◽  
Resolution Electron ◽  
Scanning Transmission ◽  
Low Energy Electrons

A new field emission scanning transmission electron microscope has been constructed for the NSF HREM facility at Arizona State University. The microscope is to be used for studies of surfaces, and incorporates several surface-related features, including provision for analysis of secondary and Auger electrons; these electrons are collected through the objective lens from either side of the sample, using the parallelizing action of the magnetic field. This collimates all the low energy electrons, which spiral in the high magnetic field. Given an initial field Bi∼1T, and a final (parallelizing) field Bf∼0.01T, all electrons emerge into a cone of semi-angle θf≤6°. The main practical problem in the way of using this well collimated beam of low energy (0-2keV) electrons is that it is travelling along the path of the (100keV) probing electron beam. To collect and analyze them, they must be deflected off the beam path with minimal effect on the probe position.

Performance Evaluation of a Novel Type of Low-Energy Electron Microscope

1990 ◽  
Vol 48 (1) ◽  
pp. 354-355
Author(s):  
Bertholdand Senftinger ◽  
Helmut Liebl
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Field Strength ◽  
Numerical Aperture ◽  
Low Energy ◽  
Energy Electron ◽  
High Resolution Imaging ◽  
Lens System ◽  
Resolution Imaging ◽  
Low Energy Electron

During the last few years the investigation of clean and adsorbate-covered solid surfaces as well as thin-film growth and molecular dynamics have given rise to a constant demand for high-resolution imaging microscopy with reflected and diffracted low energy electrons as well as photo-electrons. A recent successful implementation of a UHV low-energy electron microscope by Bauer and Telieps encouraged us to construct such a low energy electron microscope (LEEM) for high-resolution imaging incorporating several novel design features, which is described more detailed elsewhere.The constraint of high field strength at the surface required to keep the aberrations caused by the accelerating field small and high UV photon intensity to get an improved signal-to-noise ratio for photoemission led to the design of a tetrode emission lens system capable of also focusing the UV light at the surface through an integrated Schwarzschild-type objective. Fig. 1 shows an axial section of the emission lens in the LEEM with sample (28) and part of the sample holder (29). The integrated mirror objective (50a, 50b) is used for visual in situ microscopic observation of the sample as well as for UV illumination. The electron optical components and the sample with accelerating field followed by an einzel lens form a tetrode system. In order to keep the field strength high, the sample is separated from the first element of the einzel lens by only 1.6 mm. With a numerical aperture of 0.5 for the Schwarzschild objective the orifice in the first element of the einzel lens has to be about 3.0 mm in diameter. Considering the much smaller distance to the sample one can expect intense distortions of the accelerating field in front of the sample. Because the achievable lateral resolution depends mainly on the quality of the first imaging step, careful investigation of the aberrations caused by the emission lens system had to be done in order to avoid sacrificing high lateral resolution for larger numerical aperture.

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