Biomedical subjects

S Abboud

Publications and source records attributed to S Abboud.

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

Fourier transform versus bidirectional digital filters for late potentials recording in the electrocardiogram.

Late potentials occur after the QRS complex and can be detected by using signal averaging and filtering techniques. In this study the filtered averaged electrocardiograms (ECGs) obtained using two types of filters were compared: the bidirectional digital recursive filter with a 40 Hz high-pass cut-off frequency, and the Fourier transform non-recursive digital filter with a 60 Hz high-pass cut-off. Strong correlation was found between the numerical values obtained when using these two filtering procedures. In addition, close diagnostic concordance was found between the late potential parameters in patients with normal and abnormal signal averaged ECGs. Visual comparison between the bidirectional and the Fourier plots revealed a close morphological similarity between the vector magnitudes. There was no significant difference in the mean root mean square voltage of the terminal 40 ms and the late potential duration, less than 40 mV, between the bidirectional and the Fourier filters in patients with a normal or an abnormal signal averaged ECG. The QRS duration was found to be significantly longer using Fourier filtering. This can be explained by the contributions of two factors: using the bidirectional procedure with a phase delay from each end of the data window, a shortening of the filtered QRS duration may occur and, alternatively, when using the Fourier filter, minimal stretching of the QRS complex may occur.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Late potentials recording with a precordial signal-averaged electrocardiogram in 53 consecutive patients with a first acute myocardial infarction: incidence and early natural history.

Signal-averaged electrocardiograms were obtained in 53 consecutive patients with a first acute myocardial infarction (AMI) who survived the first 10 days of hospitalization. The recording was performed twice, at Day 1 and at Day 10 of hospitalization, in patients without bundle-branch block and who did not receive antiarrhythmic therapy. Signal-averaged ECGs were obtained with an instrument which analyzes the presence of late potentials (LP) in each individual precordial lead. There were 41 men and 12 women, mean age of 67 years. On Day 1, three patients had LP (5.6%). On Day 10, LP was recorded in 11 patients (21%). In only one patient was LP transient. Patients who developed LP by Day 10 (absent in Day 1) had statistically significant lower root mean square (rms) voltage and higher QRS duration than patients who did not develop LP on Day 10. In conclusion, in patients with a first AMI who survive the initial hospitalization period and are not in need of antiarrhythmic therapy have an incidence of LP of 21%. A predischarge recording is preferable since this will maximize the chances of detecting LP.

Aged↗

PubMed1990

Effects of thrombolysis on the 12-lead signal-averaged ECG in the early postinfarction period.

Signal-averaged ECG has been used to identify patients at risk for ventricular tachycardia and sudden death after myocardial infarction. The goals of this prospective study were to examine the effects of reperfusion achieved with thrombolytic therapy on the 12-lead signal-averaged ECG and on ventricular arrhythmias in the early period after acute myocardial infarction (AMI). A total of 190 consecutive patients with AMI who fulfilled the inclusion criteria were enrolled. Thrombolysis was attempted in 80 patients and was considered successful in 57 (group I) and unsuccessful in 23 (group II); 110 patients were not treated with thrombolytic agents (group III). Signal averaging of 12 ECG leads was performed within 2 days in all patients and between 7 and 10 days after admission in 163 patients. The filtered QRS complex duration (QRSD) was significantly shorter in group I compared to group III in 7 of 12 ECG leads at 2 days and in 10 of 12 leads at 7 to 10 days. The root mean square voltage of the terminal 40 msec of the QRS complex (RMS40) did not change between the two signal-averaged ECG recordings in group I, whereas it became lower in three ECG leads in group II and in seven ECG leads in group III. There was no correlation between infarct site and significant changes in infarct-related signal-averaged ECG leads. The occurrence of complex ventricular arrhythmias was not significantly different among the three groups. We conclude that successful reperfusion, compared with failed and nonattempted reperfusion, is associated with fewer abnormalities in the 12-lead signal-averaged ECG in the early period after AMI.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

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↗

PubMed1990

Effect of thrombolysis on the evolution of late potentials within 10 days of infarction.

Patients with late potentials in the signal averaged electrocardiogram are more at risk of lethal arrhythmias in the period after acute myocardial infarction. To test the effects of thrombolysis on the incidence and evolution of late potentials, 158 consecutive patients were prospectively studied during the first 10 days after acute myocardial infarction. The study population consisted of two groups: 93 control patients treated conservatively and 65 patients treated with intravenous thrombolysis. Recordings of signal averaged electrocardiogram were obtained within two days and 7-10 days after infarction. The incidence of late potentials in the first two days after infarction was not significantly different in the thrombolytic and control groups (14% v 11.8%). By 7-10 days the incidence of late potentials among patients who underwent thrombolysis remained unchanged (14%); however, it increased significantly in the control group (11.8% to 22.5%). Thus thrombolysis seems to reduce the evolution of late potentials within 10 days of infarction. Because the risk of fatal arrhythmias is higher in patients with late potentials this study may partly explain the reduced mortality after thrombolysis.

Arrhythmias, Cardiac↗

PubMed1989

Frequency content of the QRS notching in high-fidelity canine ECG.

High-fidelity ECGs, defined as ECG signals including high-frequency components, have been studied and variations in the incidence of fine notches and slurs on the QRS complex were reported in different myocardial pathologies. These observations might be of clinical importance since they suggested a noninvasive marker for cardiac dysfunctions. We studied high-fidelity ECG waveforms displaying pronounced notches and slurs. Signals were obtained from 12 anesthetized dogs. Computer analysis included digital averaging, followed by digital filtering in different frequency bands in order to determine the frequency range corresponding to notches and slurs. Low-pass filtering of the low-noise average waveforms was performed while gradually lowering the upper frequency limit, until the fine notch (or slur) could no longer be visually detected, thus determining the lower limit of its frequency content. A band cutoff filter was then applied to the original average waveform. The lower limit of the band cutoff filter was set at the frequency previously determined as the lower limit of the notch (or slur), and its upper limit was determined by gradual raising until the notch (or slur) was visually indistinct. Following this approach, the notches were found to contribute to a frequency range of 40-185 Hz, whereas the slurs contributed only to the lower subrange of this frequency band below 100 Hz.

Animals↗

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

An improved detection algorithm in fetal electrocardiography.

Fetal electrocardiogram signals from abdominal recordings were digitized and processed by a personal computer. An averaged maternal signal was derived from the cross-correlation function and nonrecursive digital filtering. The cross-correlation function was calculated from 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 found by (1) searching for the similarity between the waveforms (for elimination of artifacts) and (2) measuring the relative time delay (for the waveform's alignment in the averaging process) between the ECG waveforms. Prior to this procedure each of the ECG waveforms was filtered through a nonrecursive digital high-pass filter. With this procedure a template signal corresponding to one complete maternal ECG signal is obtained. The fetal ECG and the electromyogram (EMG) are suppressed in the maternal template waveform, since they are not correlated with the maternal ECG. The averaged maternal ECG was then subtracted from the abdominal signals. The subtraction results in complete elimination of the maternal signal, thus it is possible to detect all of the fetal QRS complexes in spite of their coincidence with the maternal ECG. An averaged fetal ECG is then extracted using the same averaging process to improve the signal-to-noise ratio, making it possible to recognize fetal P and T waves. The performance of this method was assessed using simulated and recorded (real) abdominal ECG signals. This method shows a significant improvement with respect to detection of fetal heart rate, evaluation of short-term variation in the heart rate, and detection of arrhthymia disturbances in the fetal ECG.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

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

Subtle alterations in the high-frequency QRS potentials during myocardial ischemia in dogs.

The high-frequency components in the QRS complex were examined before and during the occlusion of the left anterior descending coronary artery. ECG waveforms from different stages of the ischemia state were averaged using cross-correlation technique and fast Fourier transform algorithm. The average waveforms were the filtered with nonrecursive digital filters (150-250 Hz) to obtain the high-frequency QRS complex. We tested our nonrecursive digital filter for ringing and the trigger jitter during the averaging process. We demonstrated that the high-frequency signal left after filtering is the result of a subtle low-amplitude constituent of the QRS complex and that the morphological change during ischemia (as zone of reduced amplitude) is a result of changes in these components of the original ECG signal.

Algorithms↗

PubMed1987

Effects of coronary occlusion on high-frequency content of the epicardial electrogram and body surface electrocardiogram.

The very high-frequency content (150 to 250 Hz) of epicardial electrogram waveforms was studied in 19 anesthetized dogs subjected to occlusion of left anterior descending coronary artery. Computer techniques of digital averaging and digital band-pass filtering were applied. Signals were obtained from epicardial electrodes placed in the ischemic left ventricular region and on the noninjured right ventricular surface, and from the body surface electrocardiogram. All recordings were made simultaneously before, during, and after coronary occlusion and subjected to the same analysis. The waveforms obtained from the ischemic left ventricular region showed a considerable decrease in high-frequency content, while those obtained from the noninjured right ventricular surface remained unchanged. The results correlated with the appearance of a zone of reduced amplitude in the body surface high-frequency QRS complex. Therefore, this macroscopic phenomenon measured noninvasively from the body surface is explained by local reduction of high-frequency activity in the ischemic region of the myocardium.

Animals↗

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↗

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↗