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  • 1
    Electronic Resource
    Electronic Resource
    Heart Rate Variability in Patients with Congenital Long QT Syndrome (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of noninvasive electrocardiology 6 (2001), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: The congenital long QT syndrome (LQTS) affecting myocardial repolarization is caused by mutations in different cardiac potassium or sodium channel genes. Adrenergic triggers are known to initiate life-threatening torsade de pointes ventricular tachycardias in LQTS patients, and anti-adrenergic therapy has been shown to be effective in many cases. Despite this well-documented adrenergic component, the data about autonomic modulation of the heart rate in LQTS, as described by heart rate variability (HRV) analysis, are very limited.Methods: Conventional time- and frequency-domain and newer nonlinear measures of HRV were compared in resting conditions among 27 LQTS patients with gene mutations at the LQT1 (n = 8), LQT2 (n = 10) or LQT3 (n = 9) loci and 34 LQTS noncarrier family members.Results: None of the conventional time- or frequency-domain or newer nonlinear measures of HRV differed significantly between the LQTS carriers and LQTS noncarriers or between the LQT1, LQT2, and LQT3 carriers.Conclusions: These findings suggest that baseline cardiac autonomic modulation of the heart rate measured in resting conditions by traditional or newer nonlinear measures of HRV is not altered in LQTS patients. Furthermore, no differences are observed in HRV parameters between LQTS patients with potassium (KvLQT1, HERG), and sodium (SCN5A) ion channel gene mutations. HRV analysis in resting conditions does not improve phenotypic characterization of LQTS patients. A.N.E. 2001;6(4):298–304
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2001.tb00122.x
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  • 2
    Electronic Resource
    Electronic Resource
    What to Expect from Electrocardiology at the Beginning of 2000? (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of noninvasive electrocardiology 5 (2000), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2000.tb00240.x
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  • 3
    Electronic Resource
    Electronic Resource
    Contribution of the Wavelet Analysis to the Noninvasive Electrocardiology (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of noninvasive electrocardiology 3 (1998), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.1998.tb00030.x
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  • 4
    Electronic Resource
    Electronic Resource
    Assessment of the Stability of the Individual-Based Correction of QT Interval for Heart Rate (2005)
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2XG , UK . : Blackwell Publishing, Inc.
    Annals of noninvasive electrocardiology 10 (2005), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Modeling the relationship between QT intervals and previous R-R values remains a challenge of modern quantitative electrocardiography. The technique based on an individual regression model computed from a set of QT–R-R measurements is presented as a promising alternative. However, a large set of QT–R-R measurements is not always available in clinical trials and there is no study that has investigated the minimum number of QT–R-R measurements needed to obtain a reliable individual QT–R-R model. In this study, we propose guidelines to ensure appropriate use of the regression technique for heart rate correction of QT intervals. Method: Holter recordings from 205 healthy subjects were included in the study. QT–R-R relationships were modeled using both linear and parabolic regression techniques. Using a bootstrapping technique, we computed the stability of the individual correction models as a function of the number of measurements, the range of heart rate, and the variance of R-R values. Results: The results show that the stability of QT–R-R individual models was dependent on three factors: the number of measurements included in its design, the heart-rate range used to design the model, and the T-wave amplitude. Practically our results showed that a set of 400 QT–R-R measurements with R-R values ranging from 600 to 1000 ms ensure a stable and reliable individual correction model if the amplitude of the T wave is at least 0.3 mV. Reducing the range of heart rate or the number of measurements may significantly impact the correction model. Conclusion: We demonstrated that a large number of QT–R-R measurements (∼400) is required to ensure reliable individual correction of QT intervals for heart rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2005.00593.x
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  • 5
    Electronic Resource
    Electronic Resource
    Electrocardiographic Identification of Drug-Induced QT Prolongation: Assessment by Different Recording and Measurement Methods (2004)
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    Annals of noninvasive electrocardiology 9 (2004), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Careful assessment of QT interval prolongation is required before novel drugs are approved by regulatory authorities. The choice of the most appropriate method of electrocardiogram (ECG) acquisition and QT/RR interval measurement in clinical trials requires better understanding of the differences among currently available approaches. This study compared standard and Holter-derived 12-lead ECGs for utility in detecting sotalol-induced QT/QTc and RR changes. Manual methods (digitizing pad and digital on-screen calipers) were compared for precision of QT and RR interval measurement. Methods and Results: Sixteen hundred pairs of serial 12-lead digital ECGs were recorded simultaneously by standard resting ECG device and by continuous 12-lead digital Holter over 3 days in 39 healthy male and female volunteers. No therapy was given on the 1st day followed by 160 mg and 320 mg of sotalol on the 2nd and 3rd day, respectively. Holter-derived and standard ECGs produced nearly identical sotalol-induced QT/QTc and RR changes from baseline, as did the manual digipad and on-screen caliper measurements. The variability of on-screen QT measurement in this study was greater than that of digipad. Conclusions: Digital 12-lead Holter and standard 12-lead ECG recorders, as well as the manual digitizing pad and digital on-screen calipers, are of equal utility for the assessment of drug-induced change from baseline in QT and RR interval, although the variability of the on-screen method in this study was greater than of the digipad.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2004.91546.x
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  • 6
    Electronic Resource
    Electronic Resource
    ISHNE Guidelines for Electrocardiographic Evaluation of Drug-related QT Prolongation and Other Alterations in Ventricular Repolarization: Task Force Summary (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of noninvasive electrocardiology 6 (2001), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2001.tb00127.x
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  • 7
    Electronic Resource
    Electronic Resource
    Temporal Complexity of Repolarization and Mortality in Patients with Implantable Cardioverter Defibrillators (2003)
    350 Main Street , Malden , MA 02148-5018 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Futura Publishing, Inc.
    Pacing and clinical electrophysiology 26 (2003), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Increased repolarization variability has been observed in various cardiac conditions. However, data on its relation to heart rate variability and on its value in predicting adverse outcomes in high risk patients are limited. Forty-seven patients with decreased left ventricular function and ICDs had high resolution 10-minute ECG recordings and were followed for 781 ± 258 days (mean ± SD) on average. The interval from the R peak to the T wave peak with maximum amplitude (RTmax) and from the R peak to the T wave offset (RToff) were determined automatically on a beat-to-beat basis. Temporal beat-to-beat RTmax and RToff variability were analyzed using traditional summary statistics, a complexity measure (approximate entropy [ApEn]), and the short-term scaling exponent (α1). Eight (17%) patients died and 16 (34%) patients experienced death/appropriate ICD shock during follow-up. RTmax-ApEn was significantly higher in patients who died compared with patients who survived (1.24 ± 0.13vs1.01 ± 0.21, respectively, P = 0.008). When RTmax-ApEn was tested together with the α1 of the RR intervals, occurrence of ventricular arrhythmias before ICD implantation, and β-blockers usage in the Cox regression analysis, it still independently predicted mortality; hazard ratio = 3.36 (1.28–8.83, 95% CI, P = 0.014) for every 0.10-increase in RTmax-ApEn. None of the repolarization variability parameters independently predicted death/appropriate ICD shocks. Increased temporal complexity of repolarization (RTmax-ApEn) independently predicts mortality in ICD patients. (PACE 2003; 26:1931–1936)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9592.2003.00298.x
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  • 8
    Electronic Resource
    Electronic Resource
    Beat-to-Beat Repolarization Variability in LQTS Patients with the SCN5A Sodium Channel Gene Mutation (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 22 (1999), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Current 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 LQTS 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%± 14% 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 ± 5% and ± 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.1999.tb00376.x
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