Detection of reentry currents in atrial flutter bymagnetocardiography

We discuss the use of magnetocardiography to detect reentry currents in cardiac flutter and fibrillation. The magnetic field produced by induced atrial flutter was measured in isolated rabbit hearts. A moving dipole model is proposed to treat the experimental data and to locate the reentry path.     

A new method for detection of P waves in electrocardiograms

A new procedure for searching the P wave in the corrected orthogonal electrocardiogram (VCG) was developed on the basis of VCG representation in spherical coordinates. The time course of the angle azimuth shows a well defined configuration P_? which is suitable for searching the P wave. At least normal VCGs regularly show the P_? configuration even if P waves are not visible in any of the related amplitude curves.The validity of P_? for the P wave recognition is discussed by electrophysiological considerations, and it was tested by comparison of the time course of P_? with that of well visible P waves in the magnitude curve of the very same VCG. Superposition with disturbance vectors yielded that P_? is more stable against distortions than the P wave in the magnitude curve.A digital algorithm was examined by comparison with data obtained by visual evaluation and with the output data of a common computer program for the very same VCGs. Additionally, the P wave duration and the azimuth of the atrial repolarization vector were compared with related data taken from literature. The results show that P wave recognition by using the P_? configuration is a valid and reliable method.     

Spectral analysis of arterial blood pressure in the rat during atrial fibrillation

This paper describes the development of a systems identification protocol in the rat for use in studies of the dynamics of blood pressure control The method is based on Taylor's canine random heart model and employs electrically induced atrial fibrillation to generate random fluctuations in arterial blood pressure. In order to evaluate the utility of the protocol, recordings of pulsatile blood pressure were obtained from the femoral arteries of anesthetized rats during atrial fibrillation. The data were reduced to spectral density function estimates using standard techniques of discrete spectral analysis. The results indicate that during atrial fibrillation, the time course of arterial blood pressure constitutes a white noise source in the frequency band from 0.01 to 10 Hz, in sharp contrast to the concentration of energy from the normal cardiac cycle into narrow frequency bands within this range. Thus, the protocol should be useful in the analysis of the dynamics of most physiological processes which respond to changes in blood pressure.     

Propagation pattern analysis during atrial fibrillation based on sparse modeling

In this study, sparse modeling is introduced for the estimation of propagation patterns in intracardiac atrial fibrillation (AF) signals. The estimation is based on the partial directed coherence function, derived from fitting a multivariate autoregressive model to the observed signal using least-squares (LS) estimation. The propagation pattern analysis incorporates prior information on sparse coupling as well as the distance between the recording sites. Two optimization methods are employed for estimation of the model parameters, namely, the adaptive group least absolute selection and shrinkage operator (aLASSO), and a novel method named the distance-adaptive group LASSO (dLASSO). Using simulated data, both optimization methods were superior to LS estimation with respect to detection and estimation performance. The normalized error between the true and estimated model parameters dropped from 0.20 ± 0.04 for LS estimation to 0.03 ± 0.01 for both aLASSO and dLASSO when the number of available data samples exceeded the number of model parameters by a factor of 5. For shorter data segments, the error reduction was more pronounced and information on the distance gained in importance. Propagation pattern analysis was also studied on intracardiac AF data, the results showing that the identification of propagation patterns is substantially simplified by the sparsity assumption.     

A new method for analysis of atrial activation during chronicatrial fibrillation in man

To further clarify the mechanisms maintaining chronic atrial fibrillation (CAF), a method identifying preferable activation patterns of the atria during fibrillation, by time averaging of multiple discrete excitation vectors, was developed. Repeated recordings, each of 56 atrial bipolar electrograms simultaneously acquired during 8 s, were made at multiple sites in the right atrial free wall and the left atrial appendage in 16 patients with CAF using a 2.17×3.54 cm electrode array. The local activation times (LAT's) in each recording were estimated as the median activation time at the respective measurement point. By calculating the time difference between the LAT's at adjacent measurement points in two spatial dimensions, a direction vector was created for each activation wave passing each set of measurement points, a total of 42 sets. By time averaging of the individual direction vectors (typically n=55) at each set of measurement points, preferable activation patterns were determined. Three types of activation patterns were found: 1) inconsistent activation (n=5), 2) consistent activation with preferential propagation directions (n=7) and 3) consistent activation with impulses originating from a localizable site within the recording area (n=4). All activation patterns were reproducible and the two latter patterns were proven significant using statistical tests. It is concluded that this new method is useful in further clarification of the mechanisms involved in the maintenance of atrial fibrillation     

Noninvasive mapping of transmural potentials during activation in Swine hearts from body surface electrocardiograms

The three-dimensional cardiac electrical imaging (3DCEI) technique was previously developed to estimate the initiation site(s) of cardiac activation and activation sequence from the noninvasively measured body surface potential maps (BSPMs). The aim of this study was to develop and evaluate the capability of 3DCEI in mapping the transmural distribution of extracellular potentials and localizing initiation sites of ventricular activation in an in vivo animal model. A control swine model (n = 10) was employed in this study. The heart-torso volume conductor model and the excitable heart model were constructed based on each animal's preoperative MR images and a priori known physiological knowledge. Body surface potential mapping and intracavitary noncontact mapping (NCM) were simultaneously conducted during acute ventricular pacing. The 3DCEI analysis was then applied on the recorded BSPMs. The estimated initiation sites were compared to the precise pacing sites; as a subset of the mapped transmural potentials by 3DCEI, the electrograms on the left ventricular endocardium were compared to the corresponding output of the NCM system. Over the 16 LV and 48 RV pacing studies, the averaged localization error was 6.1±2.3 mm, and the averaged correlation coefficient between the estimated endocardial electrograms by 3DCEI and from the NCM system was 0.62±0.09. The results demonstrate that the 3DCEI approach can well localize the sites of initiation of ectopic beats and can obtain physiologically reasonable transmural potentials in an in vivo setting during focal ectopic beats. This study suggests the feasibility of tomographic mapping of 3D ventricular electrograms from the body surface recordings.     

Telemetry of human electrocardiograms in aerial and aquaticenvironments

A technique for human electroencephalogram (ECG) telemetry that is equally useful on land and in water (i.e. amphibious ECG telemetry) with a single transmitter was developed. For the ECG on land, an electromagnetic wave of 79 MHz FM VHF was used, while for the ECG under water, a 77-kHz FM current was used. The VHF was received by an aerial of an FM radio and the current by two underwater antennas along course-marker ropes. When a subject jumped from a diving platform into the water, continuous recording of ECG signals was possible with only a short time disturbance of the signals due to change in posture of the subject before jumping. This indicates rapid switching from electromagnetic to conductive transmission. The ECGs on land and during surface or underwater swimming showed a clear difference in the QRS complex and T wave     

An atrioventricular node model for analysis of the ventricular response during atrial fibrillation

This paper introduces a model of the atrioventricular node function during atrial fibrillation (AF), and describes the related ECG-based estimation method. The proposed model is defined by parameters that characterize the arrival rate of atrial impulses, the probability of an impulse choosing either one of the two atrioventricular nodal pathways, the refractory periods of these pathways, and the prolongation of the refractory periods. These parameters are estimated from the RR intervals using maximum likelihood estimation, except for the shorter refractory period which is estimated from the RR interval Poincaré plot, and the mean arrival rate of atrial impulses by the AF frequency. Simulations indicated that 200-300 RR intervals are generally needed for the estimates to be accurate. The model was evaluated on 30-min ECG segments from 36 AF patients. The results showed that 88% of the segments can be accurately modeled when the estimated probability density function (PDF) and an empirical PDF were at least 80% in agreement. The model parameters were estimated during head-up tilt test to assess differences caused by sympathetic stimulation. Both refractory periods decreased as a result of stimulation, and the likelihood of an impulse choosing the pathway with the shorter refractory period increased.     

High-resolution analysis of ambulatory electrocardiograms to detect possible mechanisms of premature ventricular beats

For generations of electrocardiogram (ECG) analysis, the presence of premature ventricular beats (PVBs) has been characterized as a common event in the ECG without regard to the mechanism which has caused the PVB in the first place. At best, the coupling interval with the preceding sinus beat may be noted. This viewpoint persisted throughout the era of automated ECG analysis, as well as influencing the treatment of more life threatening events by PVB suppression strategies alone. This study proposed three hypotheses which would link the PVB to a specific mechanism or milieu. Each of these hypotheses requires significant signal processing of the continuously recorded high resolution ECG. Data are presented which demonstrate that abnormal intra-QRS potentials may be linked to a reentrant mechanism for the PVBs and that many patients have significant changes in these potentials in the sinus beats preceding the PVB. Changes in the characteristics of the repolarization as measured in the T/U wave period were also observed and could be linked to triggered activity mechanism for some PVBs. Finally, the role of subclinical ST segment changes also indicates that low grade ischemia may play a role in modulating either PVB mechanism. The data generated by this study suggest that a new view toward PVB mechanism as measured by ECG characteristics may warrant a more rational approach to renewed interest identifying the malignant PVBs and their eventual clinical management.     

Wavelet and wavelet packet compression of electrocardiograms

Wavelets and wavelet packets have recently emerged as powerful tools for signal compression. Wavelet and wavelet packet-based compression algorithms based on embedded zerotree wavelet (EZW) coding are developed for electrocardiogram (ECG) signals, and eight different wavelets are evaluated for their ability to compress Holter ECG data. Pilot data from a blind evaluation of compressed ECG's by cardiologists suggest that the clinically useful information present in original ECG signals is preserved by 8:1 compression, and in most cases 16:1 compressed ECG's are clinically useful     

Prediction of paroxysmal atrial fibrillation by analysis of atrial premature complexes

Currently, no reliable method exists to predict the onset of paroxysmal atrial fibrillation (PAF). We propose a predictor that includes an analysis of the R-R time series. The predictor uses three criteria: the number of premature atrial complexes (PAC) not followed by a regular R-R interval, runs of atrial bigeminy and trigeminy, and the length of any short run of paroxysmal atrial tachycardia. An increase in activity detected by any of these three criteria is an indication of an imminent episode of PAF. Using the Physionet database of the Computers in Cardiology 2001 Challenge, the predictor achieved a sensitivity of 89% and a specificity of 91%.     

Exact circuit analysis of spherical waves

A circuit representation for the impedance of spherical waves radiating from a spherical boundary was derived using a partial fraction expansion by Chu in order to establish gain bandwidth limitations for antennas. These circuits are derived directly from the recurrence relations for spherical Bessel functions. They provide an exact analog of the field solution both inside and outside of a spherical surface for any values of permittivity (epsilon) and permeability (mu). Since the circuits have the form of high-pass filters, they provide significant physical insight into scattering and radiation problems, suggest suitable asymptotic or approximate forms and allow circuit concepts and theorems to be brought to bear in order to solve specific configurations or to set general performance bounds. As an example of their application, compact computer programs for the radar cross section of conducting and dielectric spheres, the minimumQ's for antennas, theQ's and resonant frequencies of dielectric spheres and the induced current at the specular and shadow points of a conducting sphere are given. Other illustrative results are the short pulse responses of a solid dielectric and a dielectric-coated sphere computed using the circuit surge impedance and multiple reflection terms; and the response of a hypothetical scatterer in which the TE and TM modes are coupled.     

Variability of the QRS signal in high-resolution electrocardiograms and magnetocardiograms

The variability of electric and magnetic signals from the heart during the depolarization phase is investigated. A signal processing method is developed, which provides estimates for the beat-to-beat variability of the QRS-complex. The method is based on the decomposition of the depolarization signal into bandpass signals by means of the Morlet wavelet transform. The beat variability of the depolarization signal is estimated by normalized variances of the envelope and instantaneous frequency of bandpass signals. Time intervals of the bandpass filtered depolarization signals having a high signal-to-noise ratio are selected applying an analysis based on phase statistics. The method was tested by computer simulation and experimental data taken from electrocardiographic and magnetocardiographic measurements of healthy persons and patients prone to malignant ventricular tachycardia (VT) or ventricular fibrillation (VF). Results suggest that the calculated variance parameters permit the characterization of beat variable depolarization signals and distinguish VT/VF patients from healthy persons.     

Windows系统中特殊文件的提取与分析

在Windows系统中存在着一些隐藏的特殊系统文件,这些文件中实际上记录了大量的有取证价值的信息。通过运用一些取证分析工具来查看这些文件内容,并对其结构进行分析。     

Monitoring of electrocardiograms in bed without utilizing bodysurface electrodes

A system by which an electrocardiogram can be obtained without the individual's awareness was investigation. It involves placing the electrodes in a bed set composed of electrically conductive textiles. Electrocardiograms were successfully obtained during sleep. However, during the periods of the subject's movement in bed, the waveform became unrecognizable     

Geometric analysis of partially polarized electromagnetic waves

Some invariant properties of partially polarized electromagnetic waves are studied geometrically. Transformations of the complex degree of correlation and the degree of polarization are studied in the Poincaré and Cayley-Klein models of three-dimensional non-Euclidean hyperbolic space by means of simple geometric constructions which lucidly show the relationships between these quantities.     

Energy-dependent mobility in the small-signal analysis of waves in semiconductors

It is shown that the effect of energy-dependent mobility can be included in the small-signal analysis of semiconductot samples by an appropriate change in the square of the plasma frequency of the carriers.     

Application of adaptive signal processing for determining thelimits of P and T waves in an ECG

A new algorithm for the determination of the limits of P and T waves is proposed, and its foundations are mathematically analyzed. The algorithm performs an adaptive filtering so that the searched point corresponds to a minimum. Crucial properties of its performance are discussed, i.e., immunity to base line drifts and full adaptation to any cardiological criteria. A series of tests are made involving real registers with different morphologies for P and T-waves     

Evaluation and measurement of airplane flutter interference

Airplane flutter interference is picture disturbance in television reception caused by signals reflected off passing airplanes. Through indoor testing, the relationship between physical factors affecting airplane flutter and its subjective evaluation was analyzed. The factors necessary for flutter measurement as well as its range of influence are discussed. A method that was developed for measuring the physical amount of flutter is described. The method was confirmed through tests made near an airport using prototype test equipment discussed