1,720,974 research outputs found
T Wave Alternans and T Wave Variability: Noninvasive indices of Vulnerability to Ventricular Tachyarrhytmias
No full textBeat-to-Beat Repolarization Variability in Amplitude and Duration in LQTS Patients with the SCN5A Sodium Channel Gene Mutation
No full text(ABSTR
Optimizing ECG Signal Sampling Frequency for T-Wave Alternans Detection
No full textComputer detection of microvolt T-wave alternans (TWA) is an non-invasive method to identify patients at high risk for ventricular arrhythmias. Since TWA is a transient phenomenon, there is the need for continuous long-term TWA analysis in Holter ECG recordings. TWA detection, usually detected in ECGs sampled at 1000 samples per second (sps), in computationally demanding. We determined the ability of our correlation method (CM) to identify TWA in ECGs sampled at lower frequencies. TWA was identified in 39 long QT syndrome patients, whose ECGs were originally acquired at 1000 sps, and then resampled at 100, 250, 500, and 750 sps. Results obtained at different sampling conditions were compared. We found that TWA can be effectively detected with the CM using sampling frequencies as low as 250 sps. Such sampling frequency seems to be optimal since it provides high accuracy of TWA measurements and substantial saving of computational time
Beat-to-Beat Repolarization Variability in LQTS Patients with the SCN5A Sodium Channel Gene Mutation
No full textCurrent techniques evaluating beat-to-beat variability of repolarization rely on accurate determination of T wave endpoints. This study proposes a T wave endpoint-independent method to quantify repolarization variability in a standard 12-lead ECG using a wavelet transformation. Our method was used to identify repolarization variability in long QT syndrome patients (LQTS) with the SCN5A sodium channel gene mutation. Using wavelet transformations based on the second Gaussian derivative, we evaluated repolarization variability in 11 LOTS patients with the mutation, 13 noncarrier family members, and 28 unrelated healthy subjects. Time-domain repolarization variability parameters (SDRTo, SDRTm) and wavelet parameters describing temporal (beat-to-beat) variability of repolarization in time (TVT) and in amplitude (TVA) were analyzed. Reproducibility of wavelet parameters and relationship of wavelet-based variability with heart rate and preceding RR interval were investigated. The wavelet-based method quantified beat-to-beat variability of the entire repolarization segment (regardless of QT interval identification) providing insight into variability in repolarization morphology. Our method showed that SCN5A carriers have significantly increased repolarization variability in amplitude (23% +/- 24% vs 8 +/- 4%, P < 0.001) and in time (14 +/- 17 ms vs 3 +/- 2 ms, P < 0.004) compared to noncarriers. Variability of repolarization amplitude was found to be heart rate dependent with variability decreasing with increasing heart rate. Relative error describing reproducibility of TVA and TVT was less than or equal to 5% and less than or equal to 10%, respectively. Our method quantifies repolarization variability in amplitude and in time without the need to identify T or U wave endpoints, wavelet-detected repolarization variability contributes to phenotypic identification of SCN5A carriers, with more pronounced beat-to-beat variability in repolarization amplitude than in time
Wavelet Transformation Method to Quantify Repolarization Abnormalities in LQTS Patients with SCN5A Sodium Channel Mutation
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Computer Detection of Non-Stationary T Wave Alternans using a New Correlation Method
No full textDetection of microvolt T wave alternans (TWA) is a non-invasive method to identify patients at risk for sudden cardiac death. ECGs show that visible TWA is often nonstationary. Thus, we developed a new correlation method (CM) for TWA detection, and we tested CM's ability to detect non-stationary TWA in comparison with accepted spectral method (SM). In a simulation study CM and SM were used to evaluate stationary and non-stationary TWA of different amplitude. Other simulated conditions included: background noise, poor synchronization and windowing of the T waves; and amplitude respiration modulation of the T wave
Detection of T-wave Abnormalities in LQTS Patients with SCN5A Sodium Channel Mutation Using Wavelet Technique
No full text(ABSTR
Detection of Non-Stationary T-Wave Alternans: New Correlation Method Compared to Spectral Method
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Detection of Abnormal Time-Frequency Components of the QT interval using a Wavelet Transformation Technique
No full textECG Repolarization abnormalities are likely to be manifested by different time-frequency (TF) components but no specific technique to detect them has yet been proposed. This study aims to describe the usefulness of a time-scale technique for the analysis of the repolarization segment components. Affected patients with Long QT Syndrome (LQTS) were used as group of patients with abnormalities in repolarization. Time-scale (TS) analysis of the repolarization interval revealed modification of the TF components with different shapes according to the leads. Comparison of ROC curves for QTc measurements and wavelet parameters demonstrates that wavelets are able to quantify T wave prolongation without the need for T endpoint determination
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