Electrocardiology of atrial fibrillation

This article provides an overview and discussion of different available electrocardiographic approaches that my prove useful in the clinical management of patients with atrial fibrillation (AF). At the atrial level, characterization of fibrillation waves during AF using spectral analysis techniques or using P-wave signal averaging during (restored) sinus rhythm has been successfully applied in order to monitor and predict outcome of antiarrhythmic drug therapy and cardioversion. At the ventricular level, heart rate variability (HRV) analysis, RR interval histogram, and Poincare plot analysis have been applied to predict AF onset and recurrence. As with the P-SAECG, the majority of recordings were made, however, during sinus rhythm in paroxysmal or after cardioversion in persistent AF. Developments of new and easy-to-use algorithms for fibrillatory wave classification and ventricular response pattern are examples of possible collaboration between clinicians and bioengineers. Hopefully, in the near future, examination of any AF patient will include direct information on individual electrophysiological, structural, and autonomic characteristics that, at the moment, can only be obtained in a limited number of patients     

A multimodal imaging approach to the evaluation of post-traumatic epilepsy

Object

Electroencephalography-functional magnetic resonance imaging (EEG-fMRI) coregistration and high-density EEG (hdEEG) can be combined to map noninvasively abnormal brain activation elicited by epileptic processes. By combining noninvasive imaging techniques in a multimodal approach, we sought to investigate pathophysiological mechanisms underlying epileptic activity in seven patients with severe traumatic brain injury.

Materials and methods

Standard EEG and fMRI data were acquired during a single scanning session. The EEG-fMRI data were analyzed using the general linear model and independent component analysis. Source localization of interictal epileptiform discharges (IEDs) was performed using 256-channel hdEEG. Blood oxygenation level dependent (BOLD) localizations were then compared to EEG source reconstruction.

Results

On hdEEG, focal source localization was detected in all seven patients; in six out of seven it was concordant with the expected epileptic activity as defined by EEG data and clinical evaluation; and in four out of seven in whom IEDs were recorded, BOLD signal changes were observed. These activities were partially concordant with the source localization.

Conclusion

Multimodal integration of EEG-fMRI and hdEEG combining two different methods to localize the same epileptic foci appears to be a promising tool to noninvasively map abnormal brain activation in patients with post-traumatic brain injury.     

Analysis of electrocardiograms during atrial fibrillation

The research discussed in this article is motivated by the search for an optimal classification of the different types of atrial fibrillation (AF) on the basis of recorded atrial signals. This would facilitate the selection of an optimal therapy. This article focuses on the biophysical models of the genesis of ECG waveforms during AF. The model of the electric activity of the atria was found to have sufficient realism to be used to describe the electric sources during AF. The inclusion of the volume conduction model resulted in electrocardiographic signals that are in all aspects similar to those observed clinically. The model is currently applied to solve various problems related to optimal signal preprocessing and extraction of features in AF signals for the classification of AF abnormalities. The biophysical model of the atrial activity is an essential element in this research, since it is capable of describing the electric source specifications derived from different hypotheses relating to the etiology of AF     

Processing of intracardiac electrograms in atrial fibrillation

This paper presents a method for the automated processing of atrial fibrillation (AF) electrograms for the diagnosis of the electropathological substrate of AF and to monitor the effects of ablation procedures and anti-arrhythmic drug treatment on the characteristics of AF. Template matching is a well-known signal processing technique that has been proven useful in various other applications like processing of medical images and fingerprint verification. One of the advantages of this technique is that, because the involved calculations are not very complex, it can easily be applied in real time by using digital hardware. All it requires is the acquisition of fibrillation electrograms, analog-to-digital conversion, and a template matching algorithm downloaded in state-of-the-art digital signal processors. This will provide an objective characterization of fibrillation electrograms that in case of recording of multiple electrograms will produce real-time movies of the propagation of fibrillation waves through the atria. This will allow real-time identification of areas with preferential intra-atrial conduction block, rotor activity, or a focal spread of activation. The further development of algorithms for automatic analysis of fibrillation electrograms, therefore, is not only of scientific interest but may also allow individual evaluation of the atrial substrate, thus providing a basis for selecting the most appropriate treatment of AF     

A wavelet approach to detecting electrocautery noise in the ECG.

A software approach has been developed for detecting electrocautery noise in the electrocardiogram (ECG) using a wavelet decomposition of the signal. With this approach, a clinical monitoring expert system can be forewarned of potential artifacts in trend values derived from the ECG, allowing it to proceed with caution when making decisions based on these trends. In 15 operations spanning 38.5 h of ECG data, we achieved a false positive rate of 0.71% and a false negative rate of 0.33%. While existing hardware approaches detect the source of the noise without any ability to assess its impact on the measured ECG, our software approach detects the presence of noise in the signal itself. Furthermore, the software approach is cheaper and easier to implement in a clinical environment than existing hardware approaches.     

An approach to the evaluation of electromechanical transient processes in power systems

The paper presents an approach to the evaluation of electromechanical transient processes in power systems. On the basis of identification of the physical properties of the system considered, for an adequately chosen time interval, quasilinearization and decomposition of the original system of nonlinear differential equations into subsystems is performed. A linear transformation is introduced which transforms the state matrix of the sub-systems into diagonal form. These simplifications enable the use of numerical integration schemes based on difference state equations, which have an elementary form. As a result, a model is formed which is very suitable for numerical treatment. The integration is performed without numerical instability, quickly and effectively, with the desired simulation accuracy, and with low memory requirements.     

房颤智能检测中的心电特征选择和机器学习

房颤是最常见的心律失常疾病,因其临床诊断率低而促进了实时自动检测算法的发展.但大多算法缺乏模型或数据库间的对比,难以评判模型的优劣.为此考虑选择3种机器学习算法(支持向量机、随机森林、逻辑回归)构建3个独立的房颤检测模型.3种模型分别在MIT-BIH房颤数据库上训练,并在3个独立数据库上进行测试和对比,同时进一步分析特...     

A new approach for evaluation of the bus admittance matrix from synchrophasors: (A statistical Ybus estimation approach)

In this research, a new parameter estimation technique for determining the bus admittance matrix (Ybus) is proposed to further calibrate power system models. Ybus estimation is done using recorded PMU synchrophasor measurements. The approach proposed in this research is based on recognizing that bus injection currents Ibus can be viewed as signals produced by a random process. In this manner, the corresponding bus voltages Vbus are also stochastic signals that are related through a cross-covariance matrix to the vector Ibus. Using estimation techniques developed for statistical signal processing, the cross-covariance matrix is shown to be Zbus. Research done previously in this area requires the prior knowledge of the electrical interconnection as well as full availability of PMU measurements. This method does not depend on prior knowledge of the electrical interconnection between the buses. It extracts the electrical interconnection and the parameters of the network model in the form of Ybus. It also does not require full availability of PMU measurements at each bus in the system. It estimates the partial Ybus based on the available PMUs.     

A fundamental approach to transformer thermal modeling. II. Fieldverification

For pt.I see ibid., vol.16, no.2, p.171-5 (2001). This paper has two main objectives. One is to show that the top oil rise thermal model proposed in part I is valid, for a large power transformer in service. The second is to show that there is a convenient way of estimating the parameters without removing the transformer from service. A Manitoba Hydro 250 MVA OFAF transformer was chosen and instrumented with data-gathering equipment. Two twenty-four hour test runs were performed, one in February of 1999 and the other in July of 1999. The most basic parameter to be determined was the rated top oil rise but also found were the top oil line constant and the nonlinearity exponent, commonly given the symbol n. The results are very positive     

配电系统元件故障率的估算方法研究

配电系统元件故障率的分析与确定是系统可靠性评估的基础。针对配电系统元件不同故障原因共存和故障统计时段较短、故障统计数据不完整的现状,提出了配电系统元件故障率估算的一种新方法。首先在分析元件故障原因的基础上,建立了元件偶然故障和老化失效的混合分布模型;然后针对收集到的元件故障统计数据,在故障统计时段较长的情况下,直接采用极大似然(MLE)方法对混合分布模型中的未知参数进行估计,在故障统计时段较短、截尾现象较严重的情况下,针对这些双边定时截尾故障数据,采用EM算法进行参数估计,从而得出元件的混合故障率函数;最后对某地区配电系统10 kV架空线的故障率进行了相关计算。通过对不同统计时段以及不同方法得出的结果进行对比,验证了该方法的有效性和实用性。     

A digital approach to the cardiac cycle

The timing diagram model could provide the cardiologist with the ways and means of quantifying interval/segment patterns. This analysis would be more exact than present use of electrocardiograms, which relies on subjective analyses of pathological events and the graph patterns they present. Improving the predictability of pathological events by filtering out overriding ventricular depolarization could identify sequential patterns of the atrial repolarization interval/segment. A healthy heart could provide a standard against which specific syndromes might be compared and contrasted for diagnostic purposes. The clinician would have yet another diagnostic tool which could identify patterns requiring aggressive preventive therapy much earlier in the clinical cycle of the patient with a family history of cardiovascular disease. Results of various treatments prescribed for the broad spectrum of cardiological pathologies could also be evaluated in relation to the manner in which these treatments bring the cardiac cycle into synchrony with normal patterns. This comparison would be accomplished by comparing the sequencing and length of time for specific interval/segment patterns demonstrated before, during, and after the treatment occurs. If successful, the proposed analysis of the ECG would ultimately contribute to more positive outcomes for patients who presently may have a poor prognosis     

大型发电系统健康性评估方法研究

系统处于健康、亚健康、风险状态的概率统称为健康性指标,健康性指标比传统的失负荷概率指标包含更多的确定性信息,因此它能更好地指导系统运行。传统计算健康性指标的方法为状态枚举法．当系统规模变大或系统负荷曲线不规则时用枚举法计算健康性指标极为费时费力。根据条件概率的思想,提出了一种计算系统健康性指标的新方法,该方法不仅能快速计算出恒定负荷时系统的健康性指标,而且能快速处理负荷曲线不规则的系统。     

A scientific approach to math

The authors demonstrate how computers can be used for mathematical discovery; they have provided two experiments as examples. The first experiment deals with the behavior of consecutive sums of integers. The second experiment allows one to generalize a property of the eigenvalues of square matrices to matrices of arbitrary dimensions. They close by explaining how to set up an experiment designed to discover something new     

A fundamental approach to transformer thermal modeling. I. Theoryand equivalent circuit

A simple equivalent circuit to represent the thermal heat flow equations for power transformers is presented. Key features are the use of a current source analogy to represent heat input due to losses, and a nonlinear resistor analogy to represent the effect of air or oil cooling convection currents. The effect was first quantified in 1817. It is shown that the idea of “exponential response” is not the best way to think of the dynamics of the situation. It is also shown that one can consider ambient temperature to be a variable input to the system, and that it is properly represented as an ideal voltage source