Near-Optimal Signal Preprocessor for Positive Cardiac Arrhythmia Identification

Extremely high reliability of waveform detection is fundamental for computer-assisted identification of cardiac arrhythmias. The problem is formulated in terms of one of the basic aspects in digital signal processing, namely, detection of an unknown deterministic signal in noise. The signal is considered band limited and the noise as Gaussian with zero mean. The theory presented leads to an energy based detector. No a priori assumption is made about the morphology of the waveforms to be detected; only energy thresholding is necessary for event detection. The addition of a linear filter as a front end to the energy detector has resulted in an entire detection process described as suboptimal matched nonlinear filtering. The SNR gain at the input of the energy detector has given performances almost identical to the matched filter. The method has been implemented with an original fast algorithm to allow reasonable execution time for the processing of continuous long-duration signals (1 h). The design of such a fillter is described along with its application to the processing of two simultaneously recorded cardiac signals. The two signals are an auricular electrogram (OEG from an esophageal pill electrode) and an ECG (lead II or III). Systematic evaluation and detection performance results show that the proposed method could be seriously considered as a near-optimal approach to waveform detection, since it is based on proven signal processing theory and is far superior to heuristic methods.     

A finite element model for radiofrequency ablation of themyocardium

A finite element model was developed to simulate the temperature distributions produced by radiofrequency catheter ablation. This model incorporated blood, myocardium and torso tissues. The Laplace equation was solved to determine the steady-state electric field. The heat generation in the tissues was then computed from the power density distribution and the bioheat equation was solved to determine the time-varying temperature distribution, taking into account the convective energy exchange at the blood-myocardium and torso-air interfaces. This model was used to predict the lesion depth and to evaluate the effects of electrode location, changes of the electrical and thermal conductivities, and the electrode radius on the thermally induced damage to the myocardium. Temperature distributions induced by radiofrequency ablation were found to be: i) not very sensitive to the reference electrode location, ii) more sensitive to electrical conductivity changes than to thermal conductivity changes, and iii) larger electrodes allow a current distribution at higher level of power with reducing the chance of impedance rise     

Performance degradation of the coherent averaging technique by amolding effect

In coherent averaging, we show that when temporal alignment is performed by matched filtering, the SNR improvement may reach a stable limit after a certain number of averaged events. The source of this degradation lies in the noise that can be contained in the template of the matched filter. This effect depends on the SNR and the morphology of the signal and it can be reduced by a multipass averaging procedure or by a template updating technique.     

Refining Genotypes and Phenotypes in KCNA2-Related Neurological Disorders

Pathogenic variants in KCNA2, encoding for the voltage-gated potassium channel K_v1.2, have been identified as the cause for an evolving spectrum of neurological disorders. Affected individuals show early-onset developmental and epileptic encephalopathy, intellectual disability, and movement disorders resulting from cerebellar dysfunction. In addition, individuals with a milder course of epilepsy, complicated hereditary spastic paraplegia, and episodic ataxia have been reported. By analyzing phenotypic, functional, and genetic data from published reports and novel cases, we refine and further delineate phenotypic as well as functional subgroups of KCNA2-associated disorders. Carriers of variants, leading to complex and mixed channel dysfunction that are associated with a gain- and loss-of-potassium conductance, more often show early developmental abnormalities and an earlier onset of epilepsy compared to individuals with variants resulting in loss- or gain-of-function. We describe seven additional individuals harboring three known and the novel KCNA2 variants p.(Pro407Ala) and p.(Tyr417Cys). The location of variants reported here highlights the importance of the proline(405)–valine(406)–proline(407) (PVP) motif in transmembrane domain S6 as a mutational hotspot. A novel case of self-limited infantile seizures suggests a continuous clinical spectrum of KCNA2-related disorders. Our study provides further insights into the clinical spectrum, genotype–phenotype correlation, variability, and predicted functional impact of KCNA2 variants.     

Effects of Particle Size on the Fusion of Soda–Lime–Silicate Glass Containing NaCl

The coupled effects of particle size and 1 wt% NaCl additions on the sequence of melting reactions in a multicomponent system (sand–soda ash–calcite–dolomite–feldspar) were studied using data from DTA, DTGA, and XRD interactively. Glass batches varied in average particle size from 250 μm to finer than 45 μm. Milestone events in the fusion process of the coarse particle base glass were elucidated. The termination temperature of the last significant reaction associated with CO₂ release was 35°C lower in the fine particle size batch than with the coarsest batch. Liquid-phase formation at ∼523°C in the batch with 1 wt% NaCl occurred to an increasingly sizable extent with decreasing particle size. This contrasts with a similar effect at ∼630°C for a comparable batch without NaCl via eutectic melting between soda ash and dolomite. Sodium chloride additions significantly enhanced dissolution of CaO relic.     

A Tabu search algorithm for the network pricing problem

In this paper, we propose an efficient Tabu Search procedure for solving the NP-hard network pricing problem. By exploiting the problem's features, the algorithm allows the near-optimal solution of problem instances that are out of reach of exact combinatorial methods.     

Variation in Cyanogenic Glycosides Across Populations of Wild Lima Beans (Phaseolus lunatus) Has No Apparent Effect on Bruchid Beetle Performance

Cyanogenic glycosides (CNGs) act as feeding or oviposition deterrents and are toxic after enzymatic hydrolysis, thus negatively affecting herbivore performance. While most studies on CNGs focus on leaf herbivores, here we examined seeds from natural populations of Phaseolus lunatus in Mexico. The predominant CNGs, linamarin and lotaustralin, were quantified for each population by using ultra-high pressure liquid chromatography-mass spectrometry. We also examined whether there was a correlation between the concentration of CNGs and the performance of the Mexican bean beetle, Zabrotes subfasciatus, on seeds from each population^. The concentrations of CNGs in the seeds were relatively high compared to the leaves and were significantly variable among populations. Surprisingly, this had little effect on the performance of the bruchid beetles. Zabrotes subfasciatus can tolerate high concentrations of CNGs, most likely because of the limited β-glucosidase activity in the seeds. Seed herbivory does not appear to liberate hydrogen cyanide due to the low water content in the seed. This study illustrates the importance of quantifying the natural variation and activity of toxic compounds in order to make relevant biological inferences about their role in defense against herbivores.     

Pre-harvest accumulation of deoxynivalenol in sweet corn ears inoculated with Fusarium graminearum

Three types of commercial sweet corn hybrids [sugary (su1), shrunken or 'supersweet' (sh2) and sugary enhancer (se1)] were silk channel inoculated in 1996 and 1997 with a macroconidial suspension of Fusarium graminearum to determine how early the mycotoxin deoxynivalenol accumulates in kernels. Disease symptoms rapidly developed on all hybrids and were apparent 4 days after inoculation. Symptoms stabilized by 28 days after inoculation. Toxin levels were greater than 1 μg/g in kernels as early as 2 weeks after silk emergence and rapidly increased to extremely high levels. Susceptibility in all hybrids decreased as the silk dried out. Deoxynivalenol concentrations were correlated to disease severity. There was some indication that the sh2 genotype was more susceptible than the su1 or se1 genotypes. These results suggest that improvement needs to be made in sweet corn with respect to resistance to gibberella ear rot.     

Spectral analysis of electrograms during ventricular tachycardia in a canine model: relation with epicardial isochronal maps

The purpose of this study was to assess the capability of magnitude-squared coherence and bicoherence to differentiate monomorphic ventricular tachycardia (MVT) and polymorphic ventricular tachycardia (PVT) in a canine model and to relate these results to the epicardial isochronal maps on a beat-to-beat basis. Unipolar electrograms were simultaneously recorded from the surface of both ventricles with a 127-lead sock electrode array in 12 open-chest anesthetized dogs. The sampling frequency was 500 Hz. Atrioventricular block was induced by formaldehyde injection into the atrioventricular node. The left anterior descending coronary artery was occluded for 60 minutes under ventricular pacing (140 beats/min). During reperfusion, 12 MVT episodes lasting more than 42 seconds were recorded. Left stellate ganglion stimulation induced five PVT episodes lasting more than 42 seconds. Each of these recordings was divided into seven segments of 3,072 points (6.144 seconds). After visual selection, 104 segments were extracted and classified as 73 MVT and 31 PVT segments. Magnitude-squared coherence was estimated as the cross-spectrum from two epicardial signals (on the right and left ventricles, respectively), normalized with the respective autopower spectrum. Bicoherence was estimated as the bispectrum normalized with the autopower spectrum. Magnitude-squared coherence correctly identified 96% of MVT and 81% of PVT segments for a total accuracy of 91%. Bicoherence estimated with the left ventricular lead correctly identified 100% of MVT and 77% of PVT segments with an accuracy of 93%. Beat-to-beat epicardial maps of MVT displayed a cluster of sites of origin close to the reperfusion area, while the sites of origin from beats during PVT were much more dispersed over both ventricles. A strong and significant correlation was found between the number of electrodes with the earliest epicardial activation and coherence (r = .76, P < .0001) and bicoherence (r = .68, P < .0001), respectively. A high and significant correlation was also found between both spectral estimators (r = .74, P < .0001). Coherence and bicoherence discriminated accurately between MVT and PVT. Coherence achieved better results compared with bicoherence. Coherence and bicoherence measurements showed a quantitative relation with the spatial dispersion of the sites of origin. Both spectral techniques seemed powerful enough to be used in the development of implantable devices.