1,721,154 research outputs found
Time-Domain Analysis of Beat-to-Beat Variability of Repolarization Morphology in Patients with Ischemic Cardiomyopathy
No full textThere is growing evidence that beat-to-beat changes in ventricular repolarization contribute to increased vulnerability to ventricular arrhythmias. Beat-to-beat repolarization variability is usually measured in the electrocardiogram (ECG) by tracking consecutive QT or RT intervals. However, these measurements strongly depend on the accurate identification of T-wave endpoints, and they do not reflect changes in repolarization morphology. In this article, we propose a new computerized time-domain method to measure beat-to-beat variability of repolarization morphology without the need to identify T-wave endpoints. The repolarization correlation index (RCI) is computed for each beat to determine the difference between the morphology of repolarization within a heart-rate dependent repolarization window compared to a template (median) repolarization morphology. The repolarization variability index (RVI) describes the mean value of repolarization correlation in a studied ECG recording. To validate our method, we analyzed repolarization variability in 128-beat segments from Holter ECG recordings of 42 ischemic cardiomyopathy (ICM) patients compared to 36 healthy subjects. The ICM patients had significantly higher values of RVI than healthy subjects (in lead X: 0.045 ± 0.035 vs. 0.024 ± 0.010, respectively; P 0.044). No significant correlation was found between the RVI values and the magnitude of heart rate, heart rate variability, QTc interval duration, or ejection fraction in studied ICM patients. In conclusion, our time-domain method, based on computation of repolarization correlation indices for consecutive beats, provides a new approach to quantify beat-to- beat variability of repolarization morphology without the need to identify T- wave endpoints
Correlation Method for Detection of Transient T-Wave Alternans in Digital ECG Recordings
No full textBackground: Spectral and complex demodulation methods for detection of microvolt T-wave alternans (TWA) have limited ability to identify transient (nonstationary) TWA episodes. We aimed to develop and test new time-domain technique allowing TWA detection and quantification in as few as 7 consecutive beats from sinus rhythm ECGs. Methods and Results: Quantification of TWA during sinus rhythm required preprocessing consisting of: low-pass filtering, RR stability testing, baseline and respiratory modulation removal, and T-wave windowing and synchronization. Our time-domain correlation method (CM) detects TWA by computing, for each consecutive T wave, an alternans correlation index based on a cross-correlation technique. CM allows quantitative analysis of the amplitude, duration, and overall magnitude of the TWA episode. The technical performance of CM was confirmed in testing with simulated TWA of varying amplitude, duration, and noisy conditions. The clinical performance of CM was demonstrated by analyzing digital Holter recordings of 39 long QT syndrome patients compared to 36 healthy subjects. CM identified TWA in 17 (44%) patients with nonstationary TWA detected in 8. Conclusion: Our computer algorithms consisting of ECG preprocessing and TWA quantification by the correlation method provides the opportunity to detect nonstationary and stationary TWA in sinus rhythm of digital Holter ECG recordings
Comparison of adaptive match filter vs. correlation method to detect and characterize ECG T-wave alternans in clinics
No full textProceeding of the 5th Conference of European Study Group on Cardiovascular Oscillatio
Assessment of physiological amplitude, duration and magnitude of ECG T-wave alternans
No full textBackground: An association between T-wave alternans (TWA) and malignant ventricular arrhythmias is generally recognized. Because relatively low levels of TWA have also been observed in healthy (H) subjects, the question arises as to whether these are ascribable to noise and artifacts, or can be given the relevance of a physiological phenomenon characterizing a preclinical condition. Methods: To answer this question, in the present study 20-minute not noisy, sinus ECG recordings, from 138 H-subjects and 148 coronary artery diseased (CAD) patients, were submitted to our adaptive match filter (AMF) procedure to identify and parameterize TWA in terms of duration (TWAD), amplitude (TWAA), and magnitude (TWAM, defined as the product of TWAD times TWAA). The 99.5th percentiles of mean values of TWAA, TWAD, and TWAM over 20-minute ECGs were used to define three threshold levels (THRD, THRA, and THRM), which allow discrimination of abnormal TWA levels. Results: Nonstationary TWA was found in all our H-subjects and CAD-patients. TWAD, TWAA, and TWAM levels were classified as being physiological in 99% of H-subjects and 87% of CAD-patients. A linear correlation (r = -0.52, P < 0.001) was found between TWAA and RR interval in the H-population. Conclusions: Our results support the hypothesis of the existence of physiological TWA levels, which are to be considered in the effort to improve reliability of nonphysiological TWA levels discrimination
Adaptive match filter based method to discriminate risky from noise-ascribable T-Wave alternans
No full textAutomatic detection of microvolt T-wave alternans in Holter recordings: Effect of baseline wandering
No full textECG deviations from the isoelectric line (baseline wandering) may affect a reliable detection of T-wave alternans (TWA), a phenomenon associated with increased risk of death. The present study was designed to demonstrate, making use of simulated ECG time series, that baseline wandering might cause erroneous TWA detection from TWA-free ECG tracings, or prevent correct TWA detection whenever TWA was present. Our simulated time series were obtained from a real ECG complex (0.75 s recording, sampled at 200 Hz) repeated 170 times. TWA was simulated by varying T-wave amplitude (10, 50, 100 and 500 μV) in a time window of 160 ms centered around the T-wave apex. TWA fundamental frequency was 0.67 Hz. Baseline fluctuations were simulated by sinusoidal waves of 0.1 mV amplitude and frequency of 0.30, 0.67 and 1.50 Hz, respectively. The presence of baseline oscillations at lower (0.30 Hz) and higher (1.50 Hz) frequency than TWA own frequency prevented TWA detection when TWA amplitude was lower or equal to that of baseline oscillations. TWA detection improved after removal of baseline oscillations by application of a third-order spline interpolation, only for frequencies lower than TWA frequency. For baseline oscillations at greater frequency than heart rate, however, spline interpolation became harmful. An improvement over the spline interpolation was obtained by a new heart-rate adapting match filter with a narrow bandwidth around TWA frequency, which allowed detection of TWA almost independently of baseline frequency components when these were different from TWA own frequency
Heart-rate adapting match filter detection of T-wave alternans in experimental Holter ecg recordings
No full textT-wave alternans (TWA) is an electrophysiological phenomenon associated with cardiac electrical instability. Recently we proposed a new heart-rate adapting match filter (AMF) to detect TWA in ECG tracings affected by baseline wanders. AMF performance was tested against the third-order spline (TOS) interpolation baselineremoval technique, the only other baseline-removal method proposed in literature for TWA-detection purposes. Using simulated data, we proved that our AMFmethod increased correct TWA identification by significantly reducing the number of TWA false-negative detections. The aim of the present study was to test AMF performance in Holter ECG recordings from 15 patients with acute myocardial infarction (AMI) and 15 healthy (H) subjects. Comparison with TOS was also made. Four AMI patients and two H subjects were identified as TWA-positive after application of AMF. By contrast, eight AMI patients (p<0.05) and nine H subjects (p<0.05) were identified as TWA-positive after application of TOS-method. According to clinical observations TWA is infrequent, especially in H-subjects. Thus, our results suggest that TOS-based technique may introduce falsepositive TWA detections. In conclusion, compared to TOS-method, our AMF-based method reduces both falsepositive (experimental study) and false-negative (simulation study) TWA detections, thus yielding an improvement over the TOS in the effectiveness of automatic TWA detection
Identification of T-Wave Alternans: Review of Methods and Clinical Perspectives
No full textProceeding of the VI Southern Symposium on Cardiac Pacin
Automatic detection of T-wave alternans in myocardial infarcted patients: role of magnitude threshold and ECG length
No full textABST
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