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Biomedical subjects

P Rubel

Publications and source records attributed to P Rubel.

At least 19 recordsLinked to original sources
PubMed1995

Wavelet analysis of high-resolution ECGs in post-infarction patients: role of the basic wavelet and of the analyzed lead.

Wavelet analysis provides a fruitful alternative to standard techniques for the detection of fractionated potentials in signal averaged high-resolution (SA-HR) ECGs. In this study, an attempt is made to optimize the discrimination of post infarction patients prone to ventricular tachycardia (VT), using wavelet analysis. Optimization is based on the choice of the ECG leads or lead combinations to be analyzed, and on the analyzing wavelet to be computed. A set of 40 post-infarction patients (20 patients with VT and 20 patients without any arrhythmia) is analyzed. Individual leads and lead combinations of the SA-HR ECGs are processed using a multiparametric algorithm, based on coherent detection of aligned local maxima of the wavelet transform. Seven basic wavelets are tested: the Morlet's wavelet, and the six first derivatives of a Gaussian function. The first derivative of a Gaussian function provides poor results, and is discarded. All other wavelets prove to perform equivalent classification. A vector magnitude computed from the wavelet transforms of the three SA-HR ECGs achieves better results than individual leads. An optimized risk stratification algorithm leads to 90% sensitivity and 100% specificity in the 40 patients learning set.

Adult↗
PubMed1994

Clinical relevance of assessing QT dynamicity in Holter recordings.

Ventricular repolarization (VR) duration is an electrophysiologic parameter that is poorly explored in the conventional electrocardiogram. The heart rate (HR) and the autonomic nervous system (ANS) condition its variations. The static QT measurement in the surface electrocardiogram and its correction using the Bazett formula constitute inadequate tools. The three-dimensional Holter recordings and their computerized analysis are better adapted to assess the dynamicity of VR, a relevant image of the myocardial state. QT and RR values are linearly correlated over 24 hours, but this does not allow one to study specifically the respective roles of HR and ANS on repolarization changes. To do so, it is necessary to select appropriately the QRST complexes according to their environment: not only the last RR cycle but the mean HR over the preceding minutes, and the circadian influences must be controlled to differentiate the role of the short- and long-term influences. Combining the ATREC and the CAVIAR softwares now permits control of both time and space dimensions and to measurement of the QT variations with a precision of the order of 1 ms, a performance necessary to assess tiny but meaningful changes. The QT interval is shorter, and the slope of the QT/RR regression line is steeper at daytime compared with night, and many situations modify this normal behavior. Aging lengthens the QT interval and reduces the day-to-night differences of QT duration and dynamicity. In contrast with duration, dynamicity does not depend on gender. Any heart disease, left ventricular hypertrophy, or heart failure alter QT dynamicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Management of serial ECGs and control strategies for the comparison process.

Serial ECG management and control of the comparison process should be dynamically driven by patient data. The functional architecture requirements are specified for a computerized ECG processing system integrating serial analysis. The concepts of reference investigations and temporal events are first explained. A conceptual reference model is proposed which stratifies the serial analysis process into a few generic strategies which will be instantiated into several types of serial comparison processing tasks as a function of the clinical evolution of the patient. This model is an extension of the OEDIPE core data model developed and implemented during the AIM #2026 project.

Cardiac Surgical Procedures↗
PubMed1993

Wavelet analysis of high-resolution signal-averaged ECGs in postinfarction patients.

The authors present an original method for the discrimination of patients prone to ventricular tachycardia. The wavelet transform, which is a new time-scale technique suitable for transient signal detection, was applied to bipolar unfiltered X, Y, Z signal-averaged electrocardiograms in 20 postinfarction patients with sustained ventricular tachycardia, in 20 myocardial infarction patients without ventricular tachycardia, and in 10 healthy subjects. An improved automated algorithm for the detection and localization of sharp variations of the signal, based on coherent detection of the local maxima of the wavelet transform, was developed. A risk stratification method, based on the detection of at least one singularity at or after a point defined with reference to the QRS onset, was assessed. The optimum cutoff point, found 98 ms after the onset of QRS, provides a specificity of 90% and a sensitivity of 85%. The authors conclude that wavelet analysis makes it possible, in this group of patients, to discriminate those with ventricular tachycardia. It yields better results than those obtained from the conventional time-domain approach.

Algorithms↗
PubMed1993

Electrophysiologic effects of a potassium channel activator (pinacidil) on repolarization parameters in healthy volunteers: a surface ECG study.

About a quarter to a third of patients receiving pinacidil, a new cyanoguanidine vasodilator, show ECG changes, in particular T-wave modifications that sometimes mimic myocardial ischemia. To investigate these changes, we performed a randomized placebo-controlled trial in 10 carefully selected, healthy subjects who received single oral doses of either pinacidil (25 mg), quinidine (330 mg), and placebo. Quinidine, which induces specific modifications to the surface ECG signal, was used as an internal control. The complete experimental design involved five consecutive administrations of the drugs in random order: pinacidil (twice), quinidine (twice), and placebo (once), separated by a week-long washout period. Electrophysiologic data acquisition and signal analysis were performed with the Lyon vectocardiographic processing system. Pinacidil decreased T-wave amplitude (-0.26 +/- 0.1 mV) significantly as compared with placebo (-0.14 +/- 0.06 mV), but did not change the duration of the T-wave. Although the cardiac rate increased with pinacidil, the QTc interval remained constant. Conversely, quinidine did not modify the RR interval but significantly increased duration of the T-wave (+67 +/- 20 ms) and QTc interval (+53 +/- 13 ms) as compared with placebo (+17 +/- 13 and +18 +/- 11 ms). In addition, no specific ischemic changes to the T-loop were observed with pinacidil. The modifications to the surface ECG signal caused by pinacidil appear to be drug-specific and related to its electrophysiologic properties rather than involving any ischemic mechanism. Such an approach may be useful for describing morphologic ECG changes caused by new drugs and identifying possible underlying electrophysiologic mechanism(s), which should then be confirmed in further studies.

Administration, Oral↗
PubMed1993

New trends in serial ECG analysis.

The prerequisite for future development and assessment of serial electrocardiographic analysis programs is the availability of easy to use database management systems for storage and retrieval of electrocardiographic data and results and efficient means for electronic interchange of digital electrocardiographic data. The basic aim of project 2026 of the European program for advanced informatics in medicine is to encourage "open European data interchange and processing for electrocardiography" (OEDIPE) and to provide objective decision support techniques in the field of quantitative electrocardiology. The final objective is to develop demonstration systems for the follow-up evaluation of (1) selected populations with heart disease, (2) integrating serial analysis, (3) decision support, (4) open databases, and (5) communication protocols, which will foreshadow large-scale monitoring of ambulatory or critically ill patients at home, during their transportation in an emergency vehicle, or during their stay in a hospital. The first-year objectives and achievements of the OEDIPE project are briefly described. Emphasis is put on the management of serial electrocardiographic records and data and on the control strategies for the management of the serial analysis process.

Aged↗
PubMed1992

Quantitative assessment of 12-lead ECG synthesis using CAVIAR.

The objective of this study is to assess the performance of patient-specific segment-specific (PSSS) synthesis in QRST complexes using CAVIAR, a new method of the serial comparison for electrocardiograms and vectorcardiograms. A collection of 250 multi-lead recordings from the Common Standards for Quantitative Electrocardiography (CSE) diagnostic pilot study is employed. QRS and ST-T segments are independently synthesized using the PSSS algorithm so that the mean-squared error between the original and estimated waveforms is minimized. CAVIAR compares the recorded and synthesized QRS and ST-T segments and calculates the mean-quadratic deviation as a measure of error. The results of this study indicate that estimated QRS complexes are good representatives of their recorded counterparts, and the integrity of the spatial information is maintained by the PSSS synthesis process. Analysis of the ST-T segments suggests that the deviations between recorded and synthesized waveforms are considerably greater than those associated with the QRS complexes. The poorer performance of the ST-T segments is attributed to magnitude normalization of the spatial loops, low-voltage passages, and noise interference. Using the mean-quadratic deviation and CAVIAR as methods of performance assessment, this study indicates that the PSSS-synthesis algorithm accurately maintains the signal information within the 12-lead electrocardiogram.

Electrocardiography↗
PubMed1992

A standard communications protocol for computerized electrocardiography.

In an international collaborative project aimed at producing common standards for quantitative electrocardiography, a standard communications protocol (SCP-ECG) was developed for computerized electrocardiography. The protocol consisted of standards for the interchange, encoding, and storage of digital ECG data. The work was performed in three distinct, but closely related, work-packages and in close collaboration with representatives from 13 manufacturers of computerized electrocardiographs from all over the world. The objectives and results of SCP-ECG are briefly described in this paper.

Computer Communication Networks↗
PubMed1990

Methodology of ECG interpretation in the Lyon program.

To provide an in-depth interpretation of the spatial QRS-T contour, we established a set of vectorcardiographic parameters computed octant by octant. For each statement the criteria constitute a model which is closely related to pathophysiological patterns. The diagnostic strategy is of the heuristic type. For each diagnosis a table lists several criteria providing both specific and differential diagnostic information. Inter-table competition is handled by specific logic. The program classifies diagnoses according to the number of non-satisfied criteria. Three versions are available including 124, 51 and 7 diagnoses, respectively. The first, intended for interpretation of complex situations, has given satisfactory results in such situations. Rhythm analysis is performed from 8-second recordings. All functions--acquisition, quality control, choice of a dominant complex, wave recognition, parameter extraction, interpretation, editing, storage--are integrated into a mobile cart. A complementary program performs serial analysis of successive tracings. It highlights with great precision morphological changes in the spatial loops and interval variations.

Diagnosis, Computer-Assisted↗
PubMed1990

Value of scatter-graphs for the assessment of ECG computer measurement results.

A new method is presented, different from usual methods, for the discussion of the results of computer ECG measurement programs, based on a new graphical evaluation method. The proposed "scatter-graphs" both highlight the main program results and facilitate the comparison between various wave-recognition algorithms. They allow the distinction between the reliability of an algorithm, which is its capacity to provide a maximum of measurements with a minimum amount of errors, and its precision, i.e., the standard deviation of the differences between its point estimates and the reference. The method proves to be a powerful tool for the discussion of individual, as well as the median program results in CSE Measurement Study. It allows to highlight limitations induced in performance assessment by the variability of the reference itself, and to state that the median program is at least as close to the "Gold Standard" as the median of the referees.

Algorithms↗
PubMed1989

Planarity of the spatial QRS loop. Comparative analysis in normals, infarcts, ventricular hypertrophies, and intraventricular conduction defects.

An almost perfect planarity of the spatial QRS loop is known as a characteristic of normal hearts. The Lyon VCG program routinely computes an original planarity index based on the relative magnitude of a so-called geometrical area vector (GAV%). It provides an indirect assessment of any kind of loop distortion (distorted segments lying outside the preferential plane, concavities, figures of eight, narrow configuration). Mean intraindividual variations of GAV%, studied in three different conditions, showed its relatively good stability. Eleven groups totaling 1,435 subjects were investigated. The highest GAV% values (mean, 88%) and the smallest scatter (sigma = 7) were found in normal tracings. GAV% was lower in right (mean, 82%) and left (76-82%) ventricular hypertrophies, in inferior (82%) and anterior (61%) myocardial infarctions, and in right (55%) and left (49%) bundle branch blocks. The diagnostic value of this index was tested for the normal-abnormal discrimination. Using a threshold of 80%, specificity was 89.6%, sensitivity was 78.6% for anterior myocardial infarction, right BBB was 86.6%, left BBB was 91.0% and other groups had unsatisfactory sensitivity. Poor correlations were observed with six other structural parameters, demonstrating that GAV% is relatively independent and may provide new diagnostic information.

Adolescent↗
PubMed1988

CAVIAR: a serial ECG processing system for the comparative analysis of VCGs and their interpretation with auto-reference to the patient.

The authors present a new computer program for serial ECG analysis that allows a direct comparison of any couple of three-dimensional ECGs and quantitatively assesses the degree of evolution of the spatial loops as well as of their initial, central, or terminal sectors. Loops and sectors are superposed as best as possible, with the aim of overcoming tracing variability of nonpathological origin. As a result, optimal measures of evolution are computed and a tabular summary of measurements is dynamically configured with respect to the patient's history and is then printed. A multivariate classifier assigns each couple of tracings to one of four classes of evolution. Color graphic displays corresponding to several modes of representation may also be plotted.

Data Display↗
PubMed1988

New methods of quantitative assessment of the extent and significance of serial ECG changes of the repolarization phase.

The authors present a method for optimally measuring variations in T wave shape and time intervals for the quantitative assessment of the significance of serial changes of the repolarization phase. The results, established on a healthy population, show the inadequacy of Bazett's formula, the constancy of maximum of T to the end of the T time interval, and good stability of the spatial T loops' morphotype. Residual intrasubject variability of corrected QT interval is mainly ascribable to physiologic, heart rate-independent changes in true onset of Q to a maximum of T time interval. The optimized mean quadratic deviation between two serial T loops is well correlated with changes in drug concentration.

Adult↗
PubMed1982

[Discriminant analysis of graphic elements of the EEG. Application to the detection of episodes of diffuse spike-waves].

A database of EEG information was collected from EEG recordings performed in epileptic patients with diffuse spike-wave complex discharges. Normal activity, spike-waves, slow waves and artefacts were mixed up in these recordings. The analysis of EEGs stored in the database was performed, channel by channel, through a 2.56 s moving window. For each so defined EEG sequence, a set of 22 variables chosen for their discriminatory power was computed. A subset of 8 highly discriminating variables was selected by the means of a stepwise discriminant analysis. Each class of the learning set contained 40 up to 100 EEG sequences. A classifying algorithm that takes into account zones of uncertainty is proposed. It has been evaluated on a test set which was composed of 1981 EEG sequences issued from 15 different patients. The results have been checked by two neurologists. The agreement rate between each of them and the proposed algorithm was more than 92%; this result is comparable to the agreement rate between the two neurologists (94%). A contextual analysis algorithm, using bi-dimensional smoothing techniques, allowed to improve the agreement rates which exceeded 94%.

Computers↗