Biomedical subjects

D Sadeh

Publications and source records attributed to D Sadeh.

At least 19 recordsLinked to original sources

PubMed1992

Real-time abdominal fetal ECG recording using a hardware correlator.

A real-time fetal ECG monitoring system using abdominal recording is presented. The system is based on an IBM AT compatible personal computer. The computer lacks the performance required for real-time analysis. Therefore, a new design of a fast hardware correlator board was developed to enhance the computer throughput. The technique is based on a cross-correlation procedure. An averaged maternal ECG waveform is derived using the cross-correlation function for the waveform's alignment. With this procedure a template signal corresponding to one complete maternal ECG is obtained. The averaged maternal ECG is then subtracted from the abdominal signals. Thus, it is possible to detect all the fetal ORS complexes in spite of their coincidence with the maternal ECG. An average fetal ECG is then extracted to improve the signal-to-noise ratio, making it possible to recognize fetal P and T waves.

Algorithms↗

PubMed1991

Simulation of high-resolution QRS complex using a ventricular model with a fractal conduction system. Effects of ischemia on high-frequency QRS potentials.

Recent studies have analyzed the high-fidelity surface electrocardiographic signal, and efforts have been made to increase the diagnostic sensitivity of the electrocardiogram by observing its high-frequency components. It was found that the high-frequency (150-250-Hz) electrocardiogram appears to detect evidence of transient ischemia with greater sensitivity than visual inspection of the surface electrocardiogram. A finite-element three-dimensional model of the ventricles with a self-similar (fractal) conduction system has been introduced as a bridge to the understanding of electrocardiographic phenomena related to high-frequency potentials. The model was activated, and the dipole potential generated by adjacent activated and resting cells was calculated to obtain a high-resolution QRS complex. Normal and ischemic activation processes was stimulated by regional reduction in conduction velocity. It was found that although the resulted low-frequency QRS complex was not significantly altered from normal conditions, the high-frequency components exhibited morphological changes similar to the ones observed during animal experiments and human studies. Based on the results obtained from the model, it can be concluded that these morphological changes can be attributed to a slowing of conduction velocity in the region of ischemia and that the model is adequate for meeting the challenges imposed by the requirements of high-frequency methods applied in clinical cardiology.

Computer Simulation↗

PubMed1990

Quantification of the fetal electrocardiogram using averaging technique.

A signal analysis procedure is described for obtaining time intervals parameters of the fetal electrocardiogram as recorded from the maternal abdomen. Applying averaging to the fetal electrocardiogram quantification of the PR interval, QRS duration and QT interval were measured. This technique which includes the subtraction of an averaged maternal ECG waveform using cross-correlation function and fast Fourier transform algorithm, enables the detection of all the fetal QRS complexes in spite of their coincidence with the maternal ECGs. Results that were obtained from 21 pregnant women at the gestational age of 32-41 weeks and an example of a recording with fetal premature ventricular contractions are presented. This method shows an important improvement with respect to detection of fetal heart rate and detection of arrhythmia disturbances in the fetal ECG. The averaging procedure can be used to evaluate long-lived alterations in the fetal ECG.

Algorithms↗

PubMed1990

Power spectrum analysis of fetal heart rate variability using the abdominal maternal electrocardiogram.

A signal analysis procedure is described for obtaining the power spectrum of the fetal and maternal heart rates as recorded from the abdomen. This technique, which includes the subtraction of an averaged maternal ECG waveform using a cross-correlation function and the fast Fourier transform algorithm, enables the detection of all the fetal QRS complexes in spite of their coincidence with the maternal ECGs. The power spectrum of the fetal heart rates (FHR) obtained from 15 women at 32-41 weeks gestation were studied and two indices were measured which are related to the long term and short term variabilities in the FHR signal. It was found that quantitative evaluation of the FHR variability can be obtained using power spectrum analysis.

Adult↗

PubMed1990

A spectral analysis of the high frequency QRS potentials observed during acute myocardial ischemia in dogs.

Electrocardiographic manifestations of transient myocardial ischemia were studied in 10 dogs undergoing occlusion of the left anterior descending coronary artery, using frequency domain analysis of the high frequency QRS potentials. Ischemia was induced via a balloon occluding cuff placed around the coronary artery. Electrocardiographic waveforms recorded before and during the ischemic state were averaged together and then filtered between 150 and 250 Hz to obtain the high frequency QRS complex. The spectral curve in the power spectrum of the high frequency QRS components was calculated using an algorithm for fast Fourier transformation. Balloon inflation was accompanied by morphological changes in the spectral curve in 7 of 10 experiments. Morphological changes, seen as zones of reduced amplitude in the time domain, appear as two separate peaks in the frequency domain. These changes were seen early in ischemia and were not accompanied by significant changes in the QRS complex or ST segment of the conventional surface electrocardiogram. The power spectrum of the high-frequency QRS potentials appears to detect evidence of transient ischemia and may provide useful information regarding the presence of myocardial ischemia.

Action Potentials↗

PubMed1989

Spectral analysis of the fetal electrocardiogram.

The spectral curves of the averaged fetal and maternal electrocardiograms as recorded from the abdomen were studied. The power spectrums were obtained using a technique which includes the subtraction of an averaged maternal ECG waveform using cross-correlation function and fast Fourier transform algorithm. The spectral curves of the averaged maternal and fetal ECG waveforms obtained from 21 pregnant women who had gestation periods of 32-41 weeks were studied. It was found that the poor signal to noise ratio, the high rate of coincidence between maternal and fetal ECGs and the similar frequency spectra of the signal and the noise components make an analysis of the abdominal ECG using conventional filtering technique rarely possible and an alternative method should be used.

Electrocardiography↗

PubMed1989

High frequency electrocardiography of three orthogonal leads in dogs during a coronary artery occlusion.

The ability to detect cardiac ischemia in dogs was studied using high frequency electrocardiography and signal averaging technique. Ischemia was induced via a balloon occluding cuff placed around the left anterior descending coronary artery. Three surface orthogonal bipolar leads (X, Y, and Z) were recorded prior to inflation of the occluding cuff. The cuff was then inflated, causing a complete occlusion of the coronary artery. The surface electrocardiogram was recorded before and during ligation and during reperfusion. The recorded waveforms were divided into sequential 10-15 second segments representing different stages of the ischemic state and were aligned using cross-correlation scheme, averaged and band pass filtered between 150-250 Hz. Analysis of the filtered high frequency QRS complexes revealed that coronary ligation was accompanied by changes in waveform morphology including the appearance of zones of reduced amplitude. In seven out of ten experiments reduced amplitude zones were absent before the ligation, present during the occlusion and absent following reperfusion. In two experiments, reduced amplitude zones that were present prior to ligation became wider during occlusion. In one experiment no reduced amplitude zone was present during any stage of the experiment. Such zones may represent slow conduction in regions of the heart rendered ischemia during coronary ligation. Therefore, the morphology of the high frequency QRS complex, as determined by analysis of the signal averaged electrocardiogram, may provide useful information regarding the presence of myocardial ischemia.

Animals↗

PubMed1987

Altered cardiac repolarization in some victims of sudden infant death syndrome.

Abnormal prolongation of cardiac repolarization, as reflected by a long QT interval with respect to the RR interval on the electrocardiogram, is known to be associated with ventricular tachyarrhythmias. To test the hypothesis that prolonged cardiac repolarization may characterize some babies who die of sudden infant death syndrome (SIDS), we studied the dependence of the QT interval on the preceding RR interval in 10 babies with SIDS and 29 healthy control babies. We analyzed approximately 5000 pairs of QT and RR intervals in each subject over a wide range of RR intervals. We found that the QT intervals demonstrated less dependence on the preceding RR intervals in 5 of 10 babies who subsequently died of SIDS than in normal controls. No ventricular arrhythmias were observed, however, during the six-hour recording period. Our data suggest that in some babies with SIDS the ability to shorten the QT interval as the heart rate increases is impaired. These observations are consistent with the hypothesis that relatively prolonged cardiac repolarization may predispose such babies to ventricular arrhythmias.

Electrocardiography↗

PubMed1987

Detection of transient myocardial ischemia by computer analysis of standard and signal-averaged high-frequency electrocardiograms in patients undergoing percutaneous transluminal coronary angioplasty.

Electrocardiographic manifestations of transient myocardial ischemia were studied, in 11 patients undergoing angioplasty (PTCA) of a left anterior descending coronary artery stenosis, by the visual inspection of the standard surface electrocardiogram (S-ECG) and the intracoronary ECG (IC-ECG) as well as computer-assisted analysis of the S-ECG. Cross-correlation analysis (CCA) performed by computer was used to compare beat-to-beat variability in ST-T morphology of the S-ECG during different stages of PTCA. CCA was also applied to the signal-averaged high-frequency QRS (SA-HFQ). All patients developed angina during balloon inflation, accompanied by transient marked ST-T changes in IC-ECG in 10 of 11 patients (90%). Visual inspection of S-ECG revealed transient ST-T changes in only 6 of 11 (54%). In contrast, CCA of the S-ECG revealed transient ST-T changes in 9 of 11 (82%). Analysis of SA-HFQ revealed that balloon inflation was associated with a marked reduction in the calculated root-mean-square (RMS) voltage for such signals (2.31 +/- 1.04 microV) as compared with RMS values before (3.27 +/- 1.12 microV, p less than .05) PTCA or after conclusion of PTCA (3.79 +/- 1.39 microV, p less than .01). Balloon inflation was also accompanied by changes in waveform morphology of the SA-HFQ, including the development of new or more prominent time zones of reduced amplitude in 10 of 11 individuals (90%). Such zones may represent slow conduction in regions of the heart rendered ischemic during PTCA. CCA of the S-ECG and of SA-HFQ appears to detect evidence of transient ischemia with greater sensitivity than simple visual inspection of S-ECG, and may therefore prove to be of use in the evaluation of patients with chest pain of uncertain origin.

Adult↗

PubMed1987

A new technique to determine the correlation between the QT interval and heart-rate for control and SIDS babies.

The ability of the autonomic nervous system to alter the QT interval in response to heart rate changes is essential to cardiovascular control. An accurate way to determine the relation between QT intervals and their corresponding RR intervals is described. A computer algorithm measures the RR intervals using digital filtering and cross-correlating the QRS sections of consecutive waveforms. The QT intervals is calculated by choosing a section of, the ECG that includes the T wave and cross-correlating it with all the consecutive T waves. At least 4000 pairs of QT-RR intervals are computed for each subject and a best fit correlation function determines the relations between the QT and RR intervals. This technique enables to establish a precise correlation between RR and QT in order to distinguish between control and SIDS babies.

Algorithms↗

PubMed1987

Signal averaging technique for noninvasive recording of late potentials in patients with coronary artery disease.

An advanced non invasive signal averaging technique was used to detect late potentials in two groups of patients: Group A (24 patients) with coronary artery disease (CAD) and without sustained ventricular tachycardia (VT) and Group B (8 patients) with CAD and sustained VT. Recorded analog data were digitized and aligned using a cross correlation function with fast Fourier transform schema, averaged and band pass filtered between 60 and 200 Hz with a non-recursive digital filter. Averaged filtered waveforms were analyzed by computer program for 3 parameters: (1) filtered QRS (fQRS) duration (2) interval between the peak of the R wave peak and the end of fQRS (R-LP) (3) RMS value of last 40 msec of fQRS (RMS). Significant change was found between Groups A and B in fQRS (101 -/+ 13 msec vs 123 -/+ 15 msec; p < .0005) and in R-LP vs 52 -/+ 11 msec vs 71-/+18 msec, p <.002). We conclude that (1) the use of a cross correlation triggering method and non-recursive digital filter enables a reliable recording of late potentials from the body surface; (2) fQRS and R-LP durations are sensitive indicators of CAD patients susceptible to VT.

Algorithms↗

PubMed1986

An improved method for on-line averaging and detecting of ECG waveforms.

The most widely used methods for accurate signal averaging were studied and compared in order to gain a better understanding of the qualities and performances of each method. The level-triggering, contour-limiting, and correlation methods were simulated and compared. A new correlation method which is a weighted correlation of differences proved to be most suitable for real-time signal averaging, and detection of waveforms' variations. Simulated ECG waveforms and real ECG recordings were analyzed in this study. Twenty-eight ECG recordings of unipolar leads for noninvasive detection of the His-Purkinje activity were averaged separately by each method. The success in detection and the signal to noise ratio of the detected His activity obtained by each method was compared. Simulated ECG waveforms with random noise added were analyzed by four methods and the correct alignment as a function of the noise level was measured. The performance of our method in rejection of noisy waveforms and in detection of small variations in the waveforms is demonstrated.

Electrocardiography↗

PubMed1986

Frequency and time domain analysis of airflow breath patterns in patients with chronic obstructive airway disease.

Airflow patterns from patients with chronic obstructive airway diseases (COAD) and normal subjects were analyzed using time and frequency domain analysis. Data were recorded during tidal breathing with a pause between the breaths, digitized at 320 samples per second (10-bit resolution), and processed with a CDC 6600 computer. The appearance of high-frequency components (10-20 Hz) in the time domain waveform and the spectral curve in the power spectrum were studied. One complete waveform was taken as a reference signal and all subsequent waves were analyzed using the cross-correlation function which was employed via the cross spectrum and the fast Fourier transform algorithm. The energy content from the averaged spectrum and the root mean square (RMS) value from the filtered waveforms were calculated. Our study indicated that the RMS and the power content estimated from a part of the filtered wave (10-20 Hz) which included the time interval from the peak of the expiratory flow (tE) to the end of the flow curve (tN) were significantly greater in normal subjects (n = 13; 0.86 +/- 0.30 X 10(-2) I/s; P less than 0.00005 for RMS value, and 0.76 +/- 0.32 I/s; P less than 0.00005 for the power content) than in patients with chronic airways obstruction (n = 19; 0.40 +/- 0.13 X 10(-2) I/s; for RMS value and 0.35 +/- 0.16 I/s; for the power content). It is concluded that the RMS and the power values of the filtered flow curve during tidal breathing over the time interval tE-tN can detect chronic airway obstruction.

Electronic Data Processing↗

PubMed1986

High frequency electrocardiography using an advanced method of signal averaging for non-invasive detection of coronary artery disease in patients with normal conventional electrocardiogram.

The ability to detect coronary artery disease (CAD) in patients with normal, conventional electrocardiograms (ECG) was studied using high frequency electrocardiography and an advanced method of signal averaging in three groups of subjects. Group A consisted of ten healthy subjects under the age of 30; Group B of 15 patients with chest pains and normal coronary arteries; and Group C of 20 patients with chest pains and CAD. Four hundred ECG waveforms from leads V3, V4 and V5 were recorded, and the recorded analog data were digitized. The digitized waveforms were averaged using a cross-correlation function which operates in the frequency domain (fast-Fourier transform algorithm). The signals were filtered with a digital band pass filter with 150 and 250 Hz low and high cut-off frequencies, respectively. Zones of reduced amplitude in the envelope of the filtered QRS complex of at least two precordial leads were found more significantly in patients with CAD (75%) than in patients without CAD (12% for Groups A and B, p less than 0.00003). However, no significant difference was found between the voltage over the high frequency QRS complex and that of its envelope between the three groups. It is concluded that the morphology of the high frequency QRS complex as determined by this advanced method of analysis of the signal averaged ECG may be a useful indicator for the presence of CAD in patients with normal conventional ECG's.

Adult↗

PubMed1985

Cross-correlation technique for arrhythmia detection using PR and PP intervals.

A combined, cross-correlation procedure for computerized arrhythmia detection is presented. It enables the classification of a wide range of arrhythmia and is based upon the determination of both P and QRS waves. The electrocardiogram (ECG) signal is recorded from external leads, digitized (10 bits of resolution) at 1.28 kHz and processed with a CDC 6600 computer. A normal beat is stored as a reference signal and the onsets of the P wave and the QRS complex are measured for determining the PR, PP, and RR intervals. The combined cross-correlation procedure is carried out between the template and each successive ECG waveform over two time intervals, the first of which includes the P wave and the second, the QRS complex. Prior to this correlation procedure each of the ECG waveforms is filtered through a nonrecursive digital bandpass filter (10 and 100 Hz for low and high cutoff frequencies, respectively). The cross-correlation functions are then calculated by means of a cross spectrum and Fast Fourier Transform algorithm. The maximum value of the normalized cross-correlation function and the time shift providing that value are searched for, allowing (1) determination of the similarity between the present beat and the normal reference beat, allowing for the discrimination of abnormal P and QRS shapes; (2) accurate measurement of the RR, PP, and PR intervals of this subsequent waveform. Applying this method enables a reliable detection of a wide variety of arrhythmia.

Arrhythmias, Cardiac↗

PubMed1984

The use of cross-correlation function for the alignment of ECG waveforms and rejection of extrasystoles.

The cross-correlation function for alignment of ECG waveforms and rejection of artifacts was studied. ECG waveforms were recorded and digitized (10-bit resolution) at 1.28 KHz and were processed with a CDC 6600 computer. The cross-correlation function was calculated using the cross spectrum and the fast Fourier transform algorithm. The maximum value of the cross-correlation function and the time location of that value were searched for (a) the similarity between the waveforms (for elimination of extrasystoles), and (b) measuring the relative time delay (for the waveform's alignment in the averaging process) between the ECG waveforms. Prior to the correlation procedure each of the ECG waveforms was filtered through a nonrecursive digital bandpass filter. Experiments with various filters indicated that when low-frequency cutoff at 30 Hz and high-frequency cutoff at 250 Hz were used the maximum value of the cross-correlation function was higher than 0.9 for most of our recorded waveforms and more accurate results were obtained.

Arrhythmias, Cardiac↗

PubMed1984

Non-invasive recording of His bundle activity in patients with Wolff-Parkinson-White syndrome.

Ten patients with Wolff-Parkinson-White syndrome underwent external His bundle recording using an advanced signal-averaging technique. Surface ECG waveforms were recorded and digitized at 1.28 kHz (10 bit resolution) and then averaged with a CDC-6600 computer. A cross-correlation function, operating in the frequency domain (using the Fast Fourier Transform algorithm) was employed to extract fiducial synchronizing marks for the waveform alignment. Using this technique, reliable His bundle activity could be recorded in nine of ten patients. There was a good correlation between the HQ and HV intervals obtained during external and internal His bundle recordings, respectively, in seven patients who underwent both recordings. Administration of ajmaline enabled to obtain the His bundle activity using a digital filter with low frequency cut-off of 30 Hz as compared to the cut-off of 150 Hz which was necessary during control to reduce the electrical activity of the delta wave. We conclude that using a computerized cross-correlation signal-averaging technique enables the external His bundle recording in patients with WPW syndrome.

Adolescent↗

PubMed1983

Non-invasive recording of late ventricular activity using an advanced method in patients with a damaged mass of ventricular tissue.

Late potentials occurring after the QRS complex were detected on the body surface using an advanced signal averaging technique. ECG waveforms were recorded from patients with and without recurrent ventricular tachycardia who had a damaged mass of ventricular tissue (left ventricular aneurysm or right ventricular dysplasia). The recorded analog data were digitized by a 10 bit A/D converter with a sampling rate of 1280 Hz onto digital magnetic tape. The digitized waveforms were averaged with a CDC-6600 computer using an advanced algorithm which employs a cross correlation function to extract fiducial synchronizing marks for the signal averaging. Waveforms were filtered with a digital bandpass filter with 30 Hz and 250 Hz low and high cut-off frequencies, respectively. Late potentials were detected in seven out of ten patients with left ventricular aneurysm (or right ventricular dysplasia) and recurrent ventricular tachycardia and in four out of five patients with left ventricular aneurysm (or right ventricular dysplasia) but without recurrent ventricular tachycardia. The delayed depolarizations, which were recorded, had an amplitude of 3.0-27.0 microV and extended a mean of 90 msec beyond the termination of the QRS complex. In three patients with left ventricular aneurysm the delayed waveforms were abolished by aneurysmectomy. In nine control subjects no late potentials were detected. We conclude that late potentials which represent late depolarization of a damaged mass of ventricular tissue can be detected in patients with and without recurrent ventricular tachycardia.

Adolescent↗