Design and evaluation of QRS and noise detectors for ambulatory e.c.g. monitors

In ambulatory e.c.g. monitoring, a high level of noise results in false QRS detection. We present a compact low-powered QRS detector design. We present a noise detector circuit that identifies most false QRS detections so that it can disable alarms. We present a standardised exercise protocol for testing the QRS detector. Data collected from subjects bending forward (for baseline drift), lifting a weight (for e.m.g.), and jogging (for motion artefact) present a realistic test set for an ambulatory QRS detector. We observe error rates of the order of 1%, the noise detector identifies more than half of these. These techniques should reduce false alarms in arrhythmia monitoring systems.     

基于心电图QRS波群的心肌缺血时域分析

目的 ST-T段变化是心电图检测心肌缺血主要的临床表现,代表了心室复极的电位变化;但其特征点定位存在很大的不准确性,为了克服这一难点,本研究从心电图QRS波群出发进行心肌缺血分析.方法 从心电图QRS波群(代表了心室的除极过程)出发,综合提取QRS波群的各个时域参数,然后进行心肌缺血与非心肌缺血条件下的统计检验.结果 ...     

一种新的基于三次样条插值技术的心电图基线漂移消除方法

现有的基于三次样条插值技术的基线消除方法都是从PR段上提取“基准点”，这种提取“基准点”方法如果应用于PR段不平直或噪声较大的信号时，其准确性要下降。本文利用QRS波段的高频特性，先用一个FIR基线滤波器对ECG信号进行粗略滤波，求出R波波峰的位置和其幅度在滤波前后的变化值，经过实验论证，所求得的位置和变化值可分别被看作是一个“基准点”的位置和幅度。然后，对在周期上找到的所有的“基准点”进行三次样条插值计算，得到的拟合曲线就是基线。文章把该方法和文献^[3]所述方法进行了比较，结果表明该方法具有更好的性能。     

基于小波变换的小鼠QRS复合波检测

采用二进小波变换与斜率和幅度相结合的方法，对小鼠QRS复合波进行检测。根据小鼠QRS复合波的特点，采用Daubechics小波为母函烽，按照ECG的频谱特点选用尺度因子，对有噪声污染和形态变异的QRS复合波进行了检测。结果表明：小波变换对小鼠QRS复合波的检测是一种有效的方法。     

Modeling of the heart's ventricular conduction system using fractal geometry: Spectral analysis of the QRS complex

Many biological systems having one or more characteristics that remain constant over a wide range of scales may be considered self-similar or fractal. Geometrical and functional overview of the ventricular conduction system of the heart reveals that it shares structures common to a tree with repeatedly bifurcating “branches,” decreasing in length with each generation. This system may further simplify by assuming that the bifurcating and decreasing process is the same at any generation, that is, the shortening factor and the angle of bifurcation are the same for each generation. Under these assumptions, the conduction system can be described as a fractal tree. A model of the heart's ventricles which consists of muscle cells and a fractal conduction system is described. The model is activated and the dipole potential generated by adjacent activated and resting cells is calculated to obtain a QRS complex. Analysis of the frequency spectrum of the QRS complex reveals that the simulated waveforms show an enhancement in the high frequency components as generations are added to the conduction system. It was also found that the QRS complex shows a form of an inverse power law, which was predicted by the fractal depolarization hypothesis, with a highly correlated straight line for a log-power versus log frequency plot with a slope of approximately −4. Similar results were obtained using real QRS data from healthy subjects.     

Detection of QRS complexes in electrocardiogram using support vector machine

This paper presents the application of a support vector machine (SVM) for the detection of QRS complexes in the electrocardiogram (ECG). The ECG signal is filtered using digital filtering techniques to remove noise and baseline wander. The support vector machine is used as a classifier to delineate QRS and non-QRS regions. Two different algorithms are presented for the detection of QRS complexes. The first uses a single-lead ECG at a time for the detection of QRS complexes, while the second uses 12-lead simultaneously recorded ECG. Both algorithms have been tested on the standard CSE ECG database. A detection rate of 99.3% is achieved when tested using a single-lead ECG. This improves to 99.75% for the simultaneously recorded 12-lead ECG signal. The percentage of false negative detection is 0.7% and the percentage of false positive detection is 12.4% in the single-lead QRS detection and it reduces to 0.26% and 1.61% respectively for QRS detection in simultaneously recorded 12-lead ECG signals. The performance of the algorithms depends strongly on the selection and the variety of the ECGs included in the training set, data representation and the mathematical basis of the classifier.     

Fast Walsh transform data-compression algorithm: E.c.g. applications

The feasibility of using a fast Walsh transform algorithm to implement a real-time microprocessor-based e.c.g. data-compression system was studied. Using the mean square error between the original and reconstructed e.c.g. signals as a measure of the utility of the reconstructed signals, the limit to which an e.c.g. signal could be compressed and still yield an acceptable reconstruction was determined. The possibility of enhancing the quality of the reconstructed signals using linear filtering techniques was also investigated.     

Changes of the e.e.g. during a c.n.v. paradigm

An experimental set-up and a method of analysis are described which permit the performance of e.e.g. analysis under contingent negative variation (c.n.v.) conditions with repeated stimulation. Investigations of six subjects showed a significant reduction in the average power in the alpha band immediately after the imperative stimulus, which lasted only about 1 second. In the interstimulus interval during the c.n.v. a less marked power reduction could be observed. Since the reduction of the average power in the alpha band was approximately the same for both hemispheres and since it was also dependent on the modality of the stimulus, an interrelation-ship is assumed between the directed attention and the reduction observed. This appears to allow the possibility of objectively analysing cortical functions by means of an analysis of scalp recordings under c.n.v. conditions.     

Model of the heart and its applications to the e.c.g.

The human body with the heart as an active electrical source has been modelled by three sets of harmonic polyphase generator voltages or spinning vectors; each set being confined to one of the three standard planes, i.e. the frontal plane, the horizontal plane and the sagittal plane. The equivalent circuit for one of the standard planes, the frontal plane, has been developed and analysed. The identical method of approach for the analysis of e.c.g. voltages in the two other planes has been pointed out and a typical multidimensional case analysis of this model is given. This model has been shown to satisfy a general version of the Burger law and also a general version of the Goldberger augmented lead voltages. The modified Wilson central terminal (w.c.t.) has also been found not to be at the electrical zero of the system. it has further been observed, and confirmed by experiment, that the vector sum of harmonic currents towards the modified w.c.t. is zero, irrespective of the different values of externally connected resistors and without assuming the modified w.c.t. at the electrical zero of the system, i.e. Kirchhoff’s harmonic-current law is satisfied at the modified w.c.t. For equal values of external resistors, the vector sum of the phase voltages and augmented lead voltages also become zero. The model has further been used to study the effect of a number of standard leads placed in the frontal plane while recording the e.c.g., on the maximisation of: (a) the e.c.g. voltages between the standard leads placed over the human body; (b) the e.g.c. voltage between the modified w.c.t. and a reference point on the body; (c) the ratio of the e.c.g. Goldberger voltage to the corresponding phase voltage; and (d) the values of the e.c.g. phase voltages. The effects of the number of electrodes placed in the horizontal and sagittal planes on the respective groups of e.c.g. voltages are discussed. By controlling the number of electrodes in any one of the three standard planes, when the e.c.g. voltages are maximised, it has been shown that the signal-to-noise ratio for those e.c.g. voltages will be increased.     

A real time QRS detection using delay-coordinate mapping for the microcontroller implementation

In this article, we propose a new algorithm using the characteristics of reconstructed phase portraits by delay-coordinate mapping utilizing lag rotundity for a real-time detection of QRS complexes in ECG signals. In reconstructing phase portrait the mapping parameters, time delay, and mapping dimension play important roles in shaping of portraits drawn in a new dimensional space. Experimentally, the optimal mapping time delay for detection of QRS complexes turned out to be 20 ms. To explore the meaning of this time delay and the proper mapping dimension, we applied a fill factor, mutual information, and autocorrelation function algorithm that were generally used to analyze the chaotic characteristics of sampled signals. From these results, we could find the fact that the performance of our proposed algorithms relied mainly on the geometrical property such as an area of the reconstructed phase portrait. For the real application, we applied our algorithm for designing a small cardiac event recorder. This system was to record patients ECG and R–R intervals for 1 h to investigate HRV characteristics of the patients who had vasovagal syncope symptom and for the evaluation, we implemented our algorithm in C language and applied to MIT/BIH arrhythmia database of 48 subjects. Our proposed algorithm achieved a 99.58% detection rate of QRS complexes. © 2002 Biomedical Engineering Society. PAC2002: 8719Nn, 8719Hh, 8780-y     

Online analysis of e.c.g. arrhythmias with a digital computer

Our online program was developed to identify premature atrial and ventricular contractions and missed beats. Special care is taken with the recognition of artefacts. 14 patients with a high rate of arrhythmias were studied and 108 000 beats analysed independently by cardiologists and correlated with the computer analysis. Of a total of 7458 premature ventricular contractions, 411 events were detected false positives or negatives. This is an error of 5%. Out of the 826 premature atrial contractions 140 mistakes were found (17%). In a group 1772 missed beats (av-block etc.) 159 were improperly identified (9%). Of 1410 ventricular ectopics without prematurity there were 164 incorrect results (12%). The vast majority of muscle potentials and artefacts was properly classified and detected (error 11–15%). The main reason for the errors is the bad signal-to-noise ratio experienced from time to time. With the help of a digital computer a reliable analysis of the most important arrhythmias in intensive care patients has been achieved. A main part of the program should be concerned with artefact detection.     

Progressive loss in circulating volume during haemodialysis can be monitored by time voltage integral area of QRS complex: pilot study

Introduction

Time voltage area of QRS is a parameter that showed a close association with modifications in endoventricular volume. The aim of the study was to investigate the efficacy of this parameter in identifying progressive reduction in circulating blood volume (BV) during haemodialytic treatment (HT).

Material and methods

Thirteen uraemic patients were studied. XYX like leads were monitored before, during and after HT. Summation of areas of each QRS complex was named QRS total area (TA).

Results

Increase in QRS TA and decrease in BV were found after vs. before HT. Progressive increase in QRS TA is strongly linked to a progressive reduction of BV during HT.

Conclusions

These findings encourage use of ECG monitoring during HT with a dual purpose: rhythm and haemodynamic control. In fact, excessive or insufficient subtractions of water, with consequent hypotensive or cardiorespiratory crisis, are the most frequent complications in these patients.