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  • 1
    Electronic Resource
    Electronic Resource
    Seasonal Variability of QT Dispersion in Healthy Young Males (2003)
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    Annals of noninvasive electrocardiology 8 (2003), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: There are few data related to the seasonal influences on the QT dispersion. Methods: We analyzed the effects of seasons on QT dispersion in a large group of healthy young males. We studied the seasonal variability of QT dispersion in 523 healthy male subjects aged 22 ± 4 years (ranging from 20 to 26). Four seasonal 12-lead resting electrocardiograms (ECGs) recorded at double amplitude were performed at 25 mm/s at intervals of 3 months. Subsequent ECGs were recorded within 1 hour of the reference winter recording. QT dispersion was defined as the difference between the longest and the shortest mean QT intervals. Results: There was a significant seasonal variation in QT dispersion (P = 0.001), with the largest QT dispersion in winter (71 ± 18 ms) and the smallest one in spring (43 ± 19). Conclusion: There exists a significant seasonal variation in QT dispersion of healthy subjects and such variability should be taken into consideration in the evaluation process of QT dispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1542-474X.2003.08102.x
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  • 2
    Electronic Resource
    Electronic Resource
    Agreement Between Automatic and Manual Measurement of Atrial and Ventricular Signal-Averaged Electrocardiograms in Healthy Subjects (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
    Notes: Background: Although prolonged duration of the signal-averaged (SA) P wave has been proposed as a noninvasive marker of atrial arrhythmias, clinical value of atrial SAECG is limited, largely due to the difficulty with detection of the onset and offset of the high gain P wave. The aim of this study was to assess the reliability of automatic measurement of the atrial SAECG.Methods: Fifty-one healthy volunteers (30 men; 32 ± 8 years) underwent a session of 3 atrial and 3 ventricular SAECG recordings. Automatically detected onset and offset of SA QRS complex (QRStot) and SA P wave (Ptot) were subsequently-corrected by two independent observers. For ventricular SAECG, three conventional time-domain parameters were calculated. For atrial SAECG, the following five parameters were measured: Ptot, root mean square voltages of the entire Ptot (RMS-P) and of the terminal 40, 30, and 20 ms of Ptot. Relative errors of the different pairs of measurements were used to assess the interobserver and observer-computer variability. The Bland-Altman method was applied to express the agreement between measurements.Results: Although the mean interobserver relative errors were low for QRStot and Ptot (1.1% vs 1.5%), the observer-computer error was significantly higher for Ptot than for QRStot (1.7% vs 7.1%; P 〈 0.0001). For the voltage parameters, the lowest interobserver and observer-computer relative errors were found for RMS-P (6.6% vs 7.3%, P = ns). For RMS voltages of the terminal 40–20 ms of Ptot, relative errors exceeded 10%, but the interobserver error was significantly lower than the observer-computer error (P 〈 0.0001).Conclusion: Automatic detection of the SA P-wave onset and offset is unreliable and the atrial SAECG requires manual correction. Given a good interobserver agreement, such a correction is unlikely to introduce any significant observer-dependent bias. A.N.E. 2000; 5(2):133–138
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2000.tb00378.x
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  • 3
    Electronic Resource
    Electronic Resource
    Increased P Wave Dispersion and Maximum P Wave Duration after Hemodialysis (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: Atrial fibrillation is a frequent arrhythmia in patients undergoing hemodialysis. The consequences of hemodialysis on P wave durations and P wave dispersion have not been fully understood. The objective of this study was to study the effect of dialysis on P wave maximum (Pmax), P wave minimum (Pmin), and P wave dispersion (Pd). Methods: We studied Pmax, Pmin, and Pd in 32 patients (17 men and 15 women, mean age 54 ± 18 years) with chronic renal failure undergoing hemodialysis. The difference between maximum and minimum P wave duration was calculated and defined as P wave dispersion (Pd= Pmax− Pmin). Results: There was a significant increase in Pmax at the end of dialysis compared to the beginning (98 ± 13 ms vs. 125 ± 12 ms, P 〈 0.001). Pmin did not show any significant change (71 ± 11 ms vs. 73 ± 10 ms, P = 0.42). Pd was significantly increased at the end of dialysis (27 ± 9 ms vs. 52 ± 11 ms, P 〈 0.001). There was a negative correlation between serum potassium, magnesium, phosphate, blood urea nitrogen, and creatinin at the end of dialysis and Pmax and Pd, respectively (P 〈 0.05). A weak positive correlation was found between serum calcium, bicarbonate at the end of dialysis and Pmax and Pd (P 〈 0.05). Conclusion: Hemodialysis ends with significant increase in P wave maximum duration and P wave dispersion, which might be responsible for the increased occurrence of atrial fibrillation in these groups of patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2004.91529.x
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  • 4
    Electronic Resource
    Electronic Resource
    The Significance of P Wave Duration and P Wave Dispersion for Risk Assessment of Atrial Tachyarrhythmias in Patients with Corrected Tetralogy of Fallot (2004)
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2XG , UK . : Blackwell Publishing, Inc.
    Annals of noninvasive electrocardiology 9 (2004), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: The aim of the present study was to determine the potential role of P wave duration and P wave dispersion for risk assessment of atrial tachyarrhythmias in patients with corrected tetralogy of Fallot (ToF). Methods: The maximum P wave duration, minimum P wave duration, and the P wave dispersion from the 12-lead surface electrocardiogram of the patients and controls were measured. Electrophysiological study was performed only in the patient group. Results: The study group consisted of 25 patients with corrected ToF with a mean age of 16.4 ± 4.25 years and 25 age-matched healthy control subjects. Patients underwent repair at a mean age of 4.6 ± 3.41 years (range: 1–19), and the mean duration of follow-up of 11.8 ± 1.7 years (range: 9–15) after surgery. On electrophysiological study sinus node dysfunction was detected in 3 patients (12%), atrial tachyarrythmias—atrial flutter or fibrillation—in 5 patients (20%), both sinus node dysfunction and atrial flutter in 1 patient (4%), and AV conduction delay in 1 patient (4%). P wave dispersion is significantly higher in patients with atrial tachyarrhythmia inducible by electrophysiological study than in other patients (P 〈 0.05). A P wave dispersion value of 〉35 ms has a high predictive accuracy (sensitivity = 83% and specificity = 89%) for inducible atrial tachyarrhythmia in patients with corrected tetralogy of Fallot. Conclusion: P wave dispersion is an easily measured electrocardiographic marker with a good sensitivity and specificity for predicting atrial arrhythmias in patients after correction of ToF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2004.94569.x
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  • 5
    Electronic Resource
    Electronic Resource
    Assessment of Heart Rate Turbulence in the Acute Phase of Myocardial Infarction for Long-Term Prognosis (2003)
    350 Main Street , Malden , MA 02148-5018 , USA . : 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: SADE, E., et al.: Assessment of Heart Rate Turbulence in the Acute Phase of Myocardial Infarction for Long-Term Prognosis. This study is designed to assess the value of heart rate turbulence (HRT) in the acute phase of MI for prediction of long-term mortality risk. The study included 128 consecutive acute MI patients with 24-hour Holter recordings to evaluate HRT (turbulence onset and slope), SDNN, mean RR interval, and ventricular premature beat frequency. LVEF was evaluated by two-dimensional echocardiography. Data from 117 patients (mean age 58 ± 11 years) were available for further analysis. Twelve patients died during follow-up (mean 312 ± 78 days). Although SDNN 〈 70 ms was the most powerful predictor of mortality among all presumed risk factors (hazard ratio 20 [95% CI 2.6–158]; P = 0.004) in univariate Cox regression analysis, in multivariate analysis LVEF ≤ 0.40 and turbulence slope ≤2.5 ms/RR interval were the only independent predictors of mortality (hazard ratio 6.9 [95% CI 1.8–26]; P = 0.006, hazard ratio 7.3 [95% CI 1.4–37]; P = 0.016, respectively). Addition of HRT parameters for LVEF increased remarkably the positive predictive value (60%) without any decrease in the negative predictive value (92%). Blunted HRT reaction within the first 24 hours of acute MI is an independent predictor of long-term mortality. Furthermore, its predictive power is comparable and also additive to that of LVEF. (PACE 2003; 26[Pt. I]:544–550)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9592.2003.00092.x
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  • 6
    Electronic Resource
    Electronic Resource
    P Wave Dispersion on 12-Lead Electrocardiography in Patients with Paroxysmal Atrial Fibrillation (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 23 (2000), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The prolongation of intraatrial and interatrial conduction time and the inhomogeneous propagation of sinus impulses have been shown in patients with atrial fibrillation. Recently P wave dispersion (PWD), which is believed to reflect inhomogeneous atrial conduction, has been proposed as being useful for the prediction of paroxysmal atrial fibrillation (PAF). Ninety consecutive patients (46 men, 44 women; aged 55 ± 13 years) with a history of idiopathic PAF and 70 healthy subjects (42 men, 28 women; mean age, 53 ± 14 years) were studied. The P wave duration was calculated in all 12 leads of the surface ECC. The difference between the maximum and minimum P wave duration was calculated and this difference was defined as P wave dispersion (PWD = Pmax - Pmin). All patients and controls were also evaluated by echocardiography to measure the left atrial diameter and left ventricular ejection fraction (LVEF). There was no difference between patients and controls in gender (P = 0.26), age (P = 0.12), LVEF (66 ± 4% vs 67 ± 5%, P = 0.8) and left atrial diameter (36 ± 4 mm vs 34 ± 6 mm, P = 0.13). P maximum duration was found to be significantly higher in patients with a history of PAF (116 ± 17 ms) than controls (101 ±11 ms. P 〈 0.001). P wave dispersion was also significantly higher in patients than in controls (44 ± 15 ms vs 27 ± 10 ms, P 〈 0.001). There was a weak correlation between age and P wave dispersion (r = 0.27, P 〈 0.001). A P maximum value of 106 ms separated patients with PAF from control subjects with a sensitivity of 83%, a specificity of 72%, and a positive predictive accuracy of 79%. A P wave dispersion value of 36 ms separated patients from control subjects with a sensitivity of 77%, a specificity of 82%, and a positive predictive accuracy of 85%. In conclusion, P maximum duration and P wave dispersion calculated on a standard surface ECG are simple ECG markers that could be used to identify the patients with idiopathic paroxysmal atrial fibrillation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.2000.tb00910.x
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison of Formulae for Heart Rate Correction of QT Interval in Exercise Electrocardiograms (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: The study investigated the differences in five different formulae for heart rate correction of the QT interval in serial electrocardiograms recorded in healthy subjects subjected to graded exercise. Twenty-one healthy subjects (aged 37 ± 10 years, 15 male) were subjected to graded physical exercise on a braked bicycle ergometer until the heart rate reached 120 beats/min. Digital electrocardiograms (ECG) were recorded on baseline and every 30 seconds during the exercise. In each ECG, heart rate and QT interval were measured automatically (QT Guard package, Marquette Medical Systems, Milwaukee, WI, USA). Bazett, Fridericia, Hodges, Framingham, and nomogram formulae were used to obtain QTc interval values for each ECG. For each formula, the slope of the regression line between RR and QTc values was obtained in each subject. The mean values of the slopes were tested by a one-sample t-test and the comparison of the baseline and peak exercise QTc values was performed using paired t-test. Bazett, Hodges, and nomogram formulae led to significant prolongation of QTc intervals with exercise, while the Framingham formula led to significant shortening of QTc intervals with exercise. The differences obtained with the Fridericia formula were not statistically significant. The study shows that the practical meaning of QTc interval measurements depends on the correction formula used. In studies investigating repolarization changes (e.g., due to a new drug), the use of an ad-hoc selected heart rate correction formula is highly inappropriate because it may bias the results in either direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.1999.tb00635.x
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  • 8
    Electronic Resource
    Electronic Resource
    Assessment of Autonomic Nervous System Functions in Patients with Vitamin B12 Deficiency by Power Spectral Analysis of Heart Rate Variability (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 23 (2000), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The purpose of this study was to test the autonomic nervous system function of patients with vitamin B12 deficiency (megaloblastic anemia) by measuring heart rate variability (HRV). The study population consisted of 17 vitamin B12 deficient patients and 15 age- and sex-matched normal volunteers. HRV was measured by power spectral analysis from which power of the low frequency (LF) peak (0.04–0.15 Hz), normalized units of the LF peak (LFNU), power of the high frequency (HF) peak (0.15–0.4 Hz), normalized units of the HF (HFNU), and ratio of power of LF to power of HF (LF:HF) were calculated. Vitamin B12 deficient patients had lower LF, LFNU, HF, HFNU, and LF:HF ratio than normal volunteers (P 〈 0.05). Decreases in sympathetic indices (LF and LFNU) were greater than those measured in parasympathetic indices (HF and HFNU). All HRV parameters correlated positively with the level of vitamin B12 (P 〈 0.001) and negatively with the duration of disease (P 〈 0.001). After vitamin B12 replacement the HEV parameters of patients and controls became comparable (P 〉 0.05). Our data suggest that autonomic sympathetic and parasympathetic nervous activities are decreased in patients with vitamin B12 deficiency, an abnormality that can be corrected by vitamin B12 replacement therapy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.2000.tb00883.x
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  • 9
    Electronic Resource
    Electronic Resource
    Short-, Mid-, and Long-Term Reproducibility of the Atrial Signal-Averaged Electrocardiogram in Healthy Subjects: Comparison with the Conventional Ventricular Signal-Averaged Electrocardiogram (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 23 (2000), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Although atrial signal-averaged electrocardiogram (SAECG) has been proposed for noninvasive identification of patients with atrial tachyarrhythmias, the substantial variability of the measurement limits the clinical value. The aim of the study was to assess the short- to long-term reproducibility of atrial SAECG and to compare it to that of the conventional ventricular SAECG in 51 healthy volunteers (30 men; age 32 ± 8 years). In each subject, SAECG recordings were obtained using MAC-VU electrocardiograph and HiRES and PHiRES software (Marquette Medical Systems) and repeated after 5 minutes, 1 day, 1 week, and 1 month. Automatically detected onset and offset of the filtered QRS complex and P wave were subsequently corrected by two independent observers, and the averaged values were used for the analysis. Conventional ventricular SAECG parameters: filtered QRS duration (QRStot), low amplitude signal duration, and root mean square voltage (RMS) of the terminal 40 ms of QRS; and 5 atrial parameters: filtered P wave duration (Ptot), RMS of the terminal 40, 30, 20 ms, and of the entire P wave were obtained. Relative errors of different pairs of measures were used to assess the intrasubject reproducibil-ity. QRStot and Ptot were the most reproducible parameters. The relative errors after 5 minutes, 1 day, 1 week, and 1 month were 0.8% to 2.4% for QRStot, and 1.3% to 4.2% for Ptot. For RMS voltages, the relative errors exceeded 15% in short-term and 20% in long-term recordings. Although Ptot was statistically less reproducible than QRStot, the reproducibility of the former was good and comparable to that of the QRStot. The reproducibility of the voltage parameters was significantly poorer than that of the duration parameters. The study showed a satisfactory short- and long-term reproducibility of Ptot in the atrial SAECG in healthy subjects. However, low reproducibility of the voltage parameters should be considered in clinical applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.2000.tb00657.x
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