The structure of collisionless shock waves is often modified by the presence of energetic particles that are not equilibrated with the thermal plasma (such as pickup ions PUIs and solar energetic ...particles SEPs). This is relevant to the inner and outer heliosphere and the Very Local Interstellar Medium (VLISM), where observations of shock waves (e.g., in the inner heliosphere) show that both the magnetic field and thermal gas pressure are less than the energetic particle component pressures. Voyager 2 observations revealed that the heliospheric termination shock (HTS) is very broad and mediated by energetic particles. PUIs and SEPs contribute both a collisionless heat flux and a higher-order viscosity. We show that the incorporation of both effects can completely determine the structure of collisionless shocks mediated by energetic ions. Since the reduced form of the PUI-mediated plasma model is structurally identical to the classical cosmic ray two-fluid model, we note that the presence of viscosity, at least formally, eliminates the need for a gas sub-shock in the classical two-fluid model, including in that regime where three are possible. By considering parameters upstream of the HTS, we show that the thermal gas remains relatively cold and the shock is mediated by PUIs. We determine the structure of the weak interstellar shock observed by Voyager 1. We consider the inclusion of the thermal heat flux and viscosity to address the most general form of an energetic particle-thermal plasma two-fluid model.
It is unknown whether transcatheter valves will have similar durability as surgical bioprosthetic valves. Definitions of structural valve deterioration (SVD), based on valve related reintervention or ...death, underestimate the incidence of SVD.
This study sought to determine and compare the 5-year incidence of SVD, using new standardized definitions based on echocardiographic follow-up of valve function, in intermediate-risk patients with severe aortic stenosis given transcatheter aortic valve replacement (TAVR) or surgical aortic valve replacement (SAVR) in the PARTNER (Placement of Aortic Transcatheter Valves) 2A trial and registry.
In the PARTNER 2A trial, patients were randomly assigned to receive either TAVR with the SAPIEN XT or SAVR, whereas in the SAPIEN 3 registry, patients were assigned to TAVR with the SAPIEN 3. The primary endpoint was the incidence of SVD, that is, the composite of SVD-related hemodynamic valve deterioration during echocardiographic follow-up and/or SVD-related bioprosthetic valve failure (BVF) at 5 years.
Compared with SAVR, the SAPIEN-XT TAVR cohort had a significantly higher 5-year exposure adjusted incidence rates (per 100 patient-years) of SVD (1.61 ± 0.24% vs. 0.63 ± 0.16%), SVD-related BVF (0.58 ± 0.14% vs. 0.12 ± 0.07%), and all-cause (structural or nonstructural) BVF (0.81 ± 0.16% vs. 0.27 ± 0.10%) (p ≤ 0.01 for all). The 5-year rates of SVD (0.68 ± 0.18% vs. 0.60 ± 0.17%; p = 0.71), SVD-related BVF (0.29 ± 0.12% vs. 0.14 ± 0.08%; p = 0.25), and all-cause BVF (0.60 ± 0.15% vs. 0.32 ± 0.11%; p = 0.32) in SAPIEN 3 TAVR were not significantly different to a propensity score matched SAVR cohort. The 5-year rates of SVD and SVD-related BVF were significantly lower in SAPIEN 3 versus SAPIEN XT TAVR matched cohorts.
Compared with SAVR, the second-generation SAPIEN XT balloon-expandable valve has a higher 5-year rate of SVD, whereas the third-generation SAPIEN 3 has a rate of SVD that was not different from SAVR. (The PARTNER II Trial: Placement of AoRTic TraNscathetER Valves - PII A PARTNERII A; NCT01314313; The PARTNER II Trial: Placement of AoRTic TraNscathetER Valves II - PARTNER II - PARTNERII - S3 Intermediate PARTNERII S3i; NCT03222128)
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Percutaneous aortic valve implantation by an antegrade transvenous approach has been described but is problematic. Retrograde prosthetic aortic valve implantation via the femoral artery has potential ...advantages. Percutaneous prosthetic aortic valve implantation via the femoral arterial approach is described and the initial experience reported.
The valve prosthesis is constructed from a stainless steel stent with an attached trileaflet equine pericardial valve and a fabric cuff. After routine aortic balloon valvuloplasty, a 22F or 24F sheath is advanced from the femoral artery to the aorta. A steerable, deflectable catheter facilitates manipulation of the prosthesis around the aortic arch and through the stenotic valve. Rapid ventricular pacing is used to reduce cardiac output while the delivery balloon is inflated to deploy the prosthesis within the annulus. Percutaneous aortic prosthetic valve implantation was attempted in 18 patients (aged 81+/-6 years) in whom surgical risk was deemed excessive because of comorbidities. Iliac arterial injury, seen in the first 2 patients, did not recur after improvement in screening and access site management. Implantation was successful in 14 patients. After successful implantation, the aortic valve area increased from 0.6+/-0.2 to 1.6+/-0.4 cm2. There were no intraprocedural deaths. At follow-up of 75+/-55 days, 16 patients (89%) remained alive.
This initial experience suggests that percutaneous transarterial aortic valve implantation is feasible in selected high-risk patients with satisfactory short-term outcomes.
The impact of aortic valve replacement (AVR) on progression/regression of extravalvular cardiac damage and its association with subsequent prognosis is unknown.
The purpose of this study was to ...describe the evolution of cardiac damage post-AVR and its association with outcomes.
Patients undergoing transcatheter or surgical AVR from the PARTNER (Placement of Aortic Transcatheter Valves) 2 and 3 trials were pooled and classified by cardiac damage stage at baseline and 1 year (stage 0, no damage; stage 1, left ventricular damage; stage 2, left atrial or mitral valve damage; stage 3, pulmonary vasculature or tricuspid valve damage; and stage 4, right ventricular damage). Proportional hazards models determined association between change in cardiac damage post-AVR and 2-year outcomes.
Among 1,974 patients, 121 (6.1%) were stage 0, 287 (14.5%) stage 1, 1,014 (51.4%) stage 2, 412 (20.9%) stage 3, and 140 (7.1%) stage 4 pre-AVR. Two-year mortality was associated with extent of cardiac damage at baseline and 1 year. Compared with baseline, cardiac damage improved in ∼15%, remained unchanged in ∼60%, and worsened in ∼25% of patients at 1 year. The 1-year change in cardiac damage stage was independently associated with mortality (adjusted HR for improvement: 0.49; no change: 1.00; worsening: 1.95; P = 0.023) and composite of death or heart failure hospitalization (adjusted HR for improvement: 0.60; no change: 1.00; worsening: 2.25; P < 0.001) at 2 years.
In patients undergoing AVR, extent of extravalvular cardiac damage at baseline and its change at 1 year have important prognostic implications. These findings suggest that earlier detection of aortic stenosis and intervention before development of irreversible cardiac damage may improve global cardiac function and prognosis. (PARTNER II Trial: Placement of AoRTic TraNscathetER Valves II - XT Intermediate and High Risk PII A, NCT01314313; The PARTNER II Trial: Placement of AoRTic TraNscathetER Valves - PII B PARTNERII B, NCT02184442; and PARTNER 3 Trial: Safety and Effectiveness of the SAPIEN 3 Transcatheter Heart Valve in Low Risk Patients With Aortic Stenosis P3, NCT02675114)
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ABSTRACT Computational and observational evidence is accruing that heliospheric shocks, as emitters of vorticity, can produce downstream magnetic flux ropes and filaments. This led Zank et al. to ...investigate a new paradigm whereby energetic particle acceleration near shocks is a combination of diffusive shock acceleration (DSA) with downstream acceleration by many small-scale contracting and reconnecting (merging) flux ropes. Using a model where flux-rope acceleration involves a first-order Fermi mechanism due to the mean compression of numerous contracting flux ropes, Zank et al. provide theoretical support for observations that power-law spectra of energetic particles downstream of heliospheric shocks can be harder than predicted by DSA theory and that energetic particle intensities should peak behind shocks instead of at shocks as predicted by DSA theory. In this paper, a more extended formalism of kinetic transport theory developed by le Roux et al. is used to further explore this paradigm. We describe how second-order Fermi acceleration, related to the variance in the electromagnetic fields produced by downstream small-scale flux-rope dynamics, modifies the standard DSA model. The results show that (i) this approach can qualitatively reproduce observations of particle intensities peaking behind the shock, thus providing further support for the new paradigm, and (ii) stochastic acceleration by compressible flux ropes tends to be more efficient than incompressible flux ropes behind shocks in modifying the DSA spectrum of energetic particles.
A deterministic model is developed for the spatial spread of an epidemic disease in a geographical setting. The disease is borne by vectors to susceptible hosts through criss-cross dynamics. The ...model is focused on an outbreak that arises from a small number of infected hosts imported into a subregion of the geographical setting. The goal is to understand how spatial heterogeneity of the vector and host populations influences the dynamics of the outbreak, in both the geographical spread and the final size of the epidemic.
Partial differential equations are formulated to describe the spatial interaction of the hosts and vectors. The partial differential equations have reaction-diffusion terms to describe the criss-cross interactions of hosts and vectors. The partial differential equations of the model are analyzed and proven to be well-posed. A local basic reproduction number for the epidemic is analyzed.
The epidemic outcomes of the model are correlated to the spatially dependent parameters and initial conditions of the model. The partial differential equations of the model are adapted to seasonality of the vector population, and applied to the 2015-2016 Zika seasonal outbreak in Rio de Janeiro Municipality in Brazil.
The results for the model simulations of the 2015-2016 Zika seasonal outbreak in Rio de Janeiro Municipality indicate that the spatial distribution and final size of the epidemic at the end of the season are strongly dependent on the location and magnitude of local outbreaks at the beginning of the season. The application of the model to the Rio de Janeiro Municipality Zika 2015-2016 outbreak is limited by incompleteness of the epidemic data and by uncertainties in the parametric assumptions of the model.
Objectives This study sought to identify incidence, predictors, and impact of vascular complications (VC) after transfemoral (TF) transcatheter aortic valve replacement (TAVR). Background VC after ...TF-TAVR are frequent and may be associated with unfavorable prognosis. Methods From the randomized controlled PARTNER (Placement of AoRTic TraNscathetER Valve) trial, a total of 419 patients (177 from cohort B inoperable and 242 from cohort A operable high-risk) were randomly assigned to TF-TAVR and actually received the designated treatment. First-generation Edwards-Sapien valves and delivery systems were used, via a 22- or 24-F sheath. The 30-day rates of major and minor VC (modified Valve Academic Research Consortium definitions), predictors, and effect on 1-year mortality were assessed. Results Sixty-four patients (15.3%) had major VC and 50 patients (11.9%) had minor VC within 30 days of the procedure. Among patients with major VC, vascular dissection (62.8%), perforation (31.3%), and access-site hematoma (22.9%) were the most frequent modes of presentation. Major VC, but not minor VC, were associated with significantly higher 30-day rates of major bleeding, transfusions, and renal failure requiring dialysis, and with a significantly higher rate of 30-day and 1-year mortality. The only identifiable independent predictor of major VC was female gender (hazard ratio HR: 2.31 95% confidence interval (CI): 1.08 to 4.98, p = 0.03). Major VC (HR: 2.31 95% CI: 1.20 to 4.43, p = 0.012), and renal disease at baseline (HR: 2.26 95% CI: 1.34 to 3.81, p = 0.002) were identified as independent predictors of 1-year mortality. Conclusions Major VC were frequent after TF-TAVR in the PARTNER trial using first-generation devices and were associated with high mortality. However, the incidence and impact of major VC on 1-year mortality decreased with lower-risk populations.
ABSTRACT Shock waves, as shown by simulations and observations, can generate high levels of downstream vortical turbulence, including magnetic islands. We consider a combination of diffusive shock ...acceleration (DSA) and downstream magnetic-island-reconnection-related processes as an energization mechanism for charged particles. Observations of electron and ion distributions downstream of interplanetary shocks and the heliospheric termination shock (HTS) are frequently inconsistent with the predictions of classical DSA. We utilize a recently developed transport theory for charged particles propagating diffusively in a turbulent region filled with contracting and reconnecting plasmoids and small-scale current sheets. Particle energization associated with the anti-reconnection electric field, a consequence of magnetic island merging, and magnetic island contraction, are considered. For the former only, we find that (i) the spectrum is a hard power law in particle speed, and (ii) the downstream solution is constant. For downstream plasmoid contraction only, (i) the accelerated spectrum is a hard power law in particle speed; (ii) the particle intensity for a given energy peaks downstream of the shock, and the distance to the peak location increases with increasing particle energy, and (iii) the particle intensity amplification for a particular particle energy, is not 1, as predicted by DSA, but increases with increasing particle energy. The general solution combines both the reconnection-induced electric field and plasmoid contraction. The observed energetic particle intensity profile observed by Voyager 2 downstream of the HTS appears to support a particle acceleration mechanism that combines both DSA and magnetic-island-reconnection-related processes.
Low-field MRI scanners are significantly less expensive than their high-field counterparts, which gives them the potential to make MRI technology more accessible all around the world. In general, ...images acquired using low-field MRI scanners tend to be of a relatively low resolution, as signal-to-noise ratios are lower. The aim of this work is to improve the resolution of these images. To this end, we present a deep learning-based approach to transform low-resolution low-field MR images into high-resolution ones. A convolutional neural network was trained to carry out single image super-resolution reconstruction using pairs of noisy low-resolution images and their noise-free high-resolution counterparts, which were obtained from the publicly available NYU fastMRI database. This network was subsequently applied to noisy images acquired using a low-field MRI scanner. The trained convolutional network yielded sharp super-resolution images in which most of the high-frequency components were recovered. In conclusion, we showed that a deep learning-based approach has great potential when it comes to increasing the resolution of low-field MR images.
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