bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relation Between Autonomic Nerve Activity and QT Interval in Patients with Congenital Long QT Syndrome: Analysis Using 24‐Hour Holter ECG Monitoring
Authors: Shimono Mayumi , Fujiki Akira , Inoue Hiroshi 
Published: October 2006

BackgroundThe aim of this study was to determine the relation between the autonomic nerve activity and the QT interval in patients with the long QT syndrome (LQTS) using spectral analysis of the heart rate variability from 24‐hour Holter ECG recordings.MethodsSeven patients with LQTS (QTc interval > 0.46 s) who had had no recent episode of syncope and nine control subjects without QT prolongation were analyzed. Autoregressive spectral analysis was performed to determine spectral power of low (LF: 0.04–0.15 Hz) and high (HF: 0.15–0.40 Hz) frequency components. The QT interval and RR interval were measured from ECGs that were selected from 24‐hour Holter tape at 1‐hour intervals.ResultsIn patients with LQTS and control subjects, there was a positive correlation between the QT interval and RR interval (LQTS: r2= 0.76 ± 0.18, Control: r2= 0.90 ± 0.10, mean ± SD). The slope of the linear regression lines (QT/RR) did not differ between LQTS and control subjects (LQTS: 0.18 ± 0.05, Control: 0.18 ± 0.04), but the intercept of the regression lines in LQTS was significantly larger than in control (LQTS: 0.28 ± 0.05, Control: 0.21 ± 0.02). In LQTS, positive correlation between the QT interval and InHF (r2= 0.53 ± 0.09) and inverse correlation between the QT interval and In(L/H) were identified (r2= 0.50 ± 0.14) as in control subjects. There was no significant difference in the slopes of the regression lines of the QT interval with heart rate variability indices (InHF, In[L/H]) between LQTS and control subjects. The correlation coefficient of the QT interval with RR interval was higher than that with heart rate variability indices both in LQTS (P < 0.01) and control subjects (P < 0.05). In three patients with recent syncopal episodes, the prolongation of QT interval was exaggerated at short RR intervals, and the significant correlations of the QT interval with RR interval and heart rate variability indices observed from the recordings without episodes of syncope could not be identified. Both 24‐hour averaged value of InHF and L/H did not show any significant difference between LQTS and control.ConclusionsThese results indicate that in LQTS without having recent episodes of syncope, the QT interval was regulated mainly through the change in RR intervals as in control subjects. Exacerbation of QT prolongation during syncopal episodes may be due to different modulation of the QT interval by autonomic nerve system and heart rate.
Variability of the Interlead Synchronization of the T Wave: Beat‐to‐Beat ECG Analyses
Authors: Lund Birgit , Lund Kaspar , Christiansen Evald Høj , Pedersen Anders Kirstein 
Published: October 2006

BackgroundThe mean intraobserver (two measurements) and interobserver (two observers) errors of dispersion of QT‐end (QTe‐d), corrected for heart rate, are 12 ms and 15 ms, respectively. One possible contribution to the low reproducibility is beat‐to‐beat variations, so we developed a surrogate of these variations, called the variability of the interlead synchronization of T waves (VST).MethodsVST can be calculated for any pair of digitized leads, by cross‐correlation of the T wave and a substep alignment procedure that increases the precision from 0.5–0.2 ms. The precision of VST is relatively good (≠ 0.4 ms), because it bypasses the uncertain measurement of QT intervals.ConclusionThe method was applied to Frank orthogonal leads of a small population of subjects (n = 9) with no cardiac history. The mean magnitudes and standard deviations (SD) of the magnitude of VST were in the range (mean ± SD) of 0.37 ± 0.28 to 2.93 ± 2.11 ms. This confirms the existence of a subject‐specific lower physical limit for the precision of QTe‐d in normal subjects. The results indicate that QTe‐d should be measured as a mean value of several beats if measured on the raw signal. This should, however, be verified by measurement of VST on larger populations. The results also indicate that optimal alignment of T waves requires the waves to be aligned individually, lead by lead. Notice, however, that if the mean beat is used for measurement of QTe‐d, then the alignment must be the same for all leads in each beat.
Effects of Beta‐Blockers on the Relation Between QT Interval and Heart Rate in Survivors of Acute Myocardial Infarction
Authors: Hintze Ulrik , Wüpper Finn , Mickley Hans , Mφller Mogens 
Published: October 2006

Backgroundβ‐blockade has been found to reduce the heart rate dependency of the QT interval in healthy individuals, but the effect of β‐blockade on the QT/RR relationship in patients suffering from myocardial infarction (Ml) is unknown.MethodsPatients with a first Ml were enrolled in a double‐blind, placebo‐controlled study. A 24‐hour ambulatory ECG was performed at discharge before study medication was initiated, and repeated after 4 weeks of therapy. QT and RR intervals were assessed beat to beat for all sinus beats by a computer program. For each patient, the mean QT interval duration for every RR value was determined on an hourly basis and the QT/RR relation was described as the best fit linear regression line.ResultsBefore randomization, no differences between the groups could be demonstrated. After 4 weeks of drug study (37 patients receiving metoprolol 100 mg per day and 34 patients receiving placebo), the day, night, and 24‐hour regression lines differed significantly between the groups. Metoprolol reduced the QT/RR slope, increased the intercept, and blunted the day‐night difference of the QT/RR slope.ConclusionLong‐term β‐blockade in Ml patients results in a reduction of the QT/RR slope with a prolongation of the QT interval at higher heart rates. These effects, which are similar to observations found in healthy individuals, may be related to the decreased susceptibility to life‐threatening arrhythmias in patients treated with beta‐blockers, possibly suggesting the QT/RR relationship as a marker of ventricular autonomic tone.
Dispersion of the QTend, QTpeak and Tpeak‐Tend Interval: Comparison of Reproducibility in Normal Subjects and Patients with Hypertrophic Cardiomyopathy
Authors: Savelieva Irina , Yi Gang , Malik Marek 
Published: October 2006

BackgroundProlonged QT interval and QT dispersion have been reported to be associated with arrhythmogenesis in patients with cardiac disorders. However, the use of QT dispersion for risk stratification is limited by its low reproducibility. Recently, measurement of the interval between the peak and the end of the T wave (Tp‐Te interval) has been suggested for detection of repolarization abnormalities, but its clinical utility has not been studied in a systematic fashion.MethodsThis study assessed the intrasubject reproducibility of automatic measurements of QTend, QTpeak, and Tp‐Te interval dispersion in 71 normal subjects and 37 patients with hypertrophic Cardiomyopathy (HC). A set of 20 ECGs (10 in supine and 10 in standing position) was evaluated in each subject. Measurements were performed automatically using an advanced commercial computer system.ResultsHC patients showed significantly higher values of QTtend, QTpeak, Tp‐Te intervals, and QTend, QTpeak dispersion compared to normal subjects (42 ± 20 vs 20 ± 12 ms and 45 ± 24 vs 33 ± 12 ms, respectively; P < 0.04), but no significant difference was observed in Tp‐Te dispersion between both groups (32 ± 16 vs 29 ± 8 ms; NS). The reproducibility of QTend, QTpeak, and Tp‐Te dispersion, expressed as coefficients of variation, was poor in both groups (14%‐28% in normal subjects and 18% to 37% in HC patients).ConclusionDespite higher values of QTend, QTpeakTp‐Te intervals and QTend, QTpeak dispersion in HC patients than in normal subjects, Tp‐Te dispersion was similar in both groups. The reproducibility of QTend, QTpeak, and Tp‐Te dispersion was low. Automatic measurement of Tp‐Tp dispersion failed to differentiate normal subjects and HC patients.
Reproducibility, Circadian Variability, and Limit Values of Ventricular Late Potentials in Healthy Men
Authors: Schmid Johann‐Jakob , Zuber Michel , Evéquoz Dominique , Erne Paul 
Published: October 2006

Objectives: The aim of the study was to examine the reproducibility of late potential parameters over time and to assess the influence of circadian rhythm, type of activity (rest, exercise) and autonomous state on these parameters in healthy subjects.Background: Late potentials are used as a marker for an elevated arrhythmic risk in patients after myocardial infarction. The method is increasingly used in cardiovascular hospital departments. However, the relatively high percentage of false‐positive results compared to the outcome of electrophysiological testing precludes its more general use.Methods: In a population of healthy volunteers, the normal values, the reproducibility, and the dependence from a circadian rhythm of ventricular late potentials were examined. The dependence of the late potentials from the type of activity was studied.Results: The limit values of the late potential parameters found in this study did not differ from the proposed standard limits in the Euro‐American guidelines. Circadian variability of heart rate and duration of QRS and QT‐interval were documented. No circadian variation was found in the late potential parameters in the subjects studied. The values for late potential parameters did not significantly differ in measurements repeated after 24 hours and 7 days, thus resulting in good reproducibility. The heart rate changes induced by ergometry and autonomous blockade had no influence on late potential parameters.Conclusions: Late potential parameters are reproducible and are not changed significantly by circadian rhythm, type of activity, or autonomous state in these healthy volunteers.
Standard 12‐Lead and 24‐Hour Ambulatory Electrocardiographic Abnormalities in Survivors of Tachyarrhythmic Cardiac Arrest
Authors: Perkiömäki Juha S. , Koistinen M. Juhani , Huikuri Heikki V. 
Published: October 2006

BackgroundThe aim of the present work was to compare the accuracies of variables obtained from a standard 12‐lead ECG and a 24‐hour ambulatory ECG in discriminating between patients with and patients without tachyarrhythmic cardiac arrest after a previous myocardial infarction.MethodsQTc interval and QTc dispersion measured from a 12‐lead ECG and an analysis of ventricular premature depolarization, nonsustained ventricular tachycardia, and heart rate variability from a 24‐hour ECG were compared in survivors of tachyarrhythmic cardiac arrest (n = 57) and in postmyocardial infarction control patients without a history of arrhythmic events and an arrhythmic‐free survival in a 2‐year follow‐up (n = 57). The groups were matched for age, gender, left ventricular ejection fraction, and the usage of beta‐blocking medication.ResultsQTc dispersion (103 ± 44 vs 71 ± 32 ms, P < 0.001) and the QTc interval maximum, defined as the longest QTc interval in any of the 12 leads of ECG (508 ± 52 vs 459 ± 42 ms, P < 0.001), were longer in the cardiac arrest survivors than in the controls. The standard deviation of R‐R intervals, a measure of heart rate variability, was lower in the cardiac arrest survivors (86 ± 38 vs 108 ± 32 ms, P < 0.001), who had also experienced more commonly ≥; 10 ventricular premature depolarizations/hour (61% vs 35%, P < 0.01) on the 24‐hour ECG. In a stepwise multiple regression analysis, the QTc interval maximum and the standard deviation of R‐R intervals were the most significant independent variables that differed between the groups (P = 0.0002, P = 0.0023, respectively). Their combination yielded a high positive predictive accuracy (91%).ConclusionsSimple measurement of the maximum QTc interval from a standard 12‐lead ECG performs equally well or even better than the other more time‐consuming 12‐lead or 24‐hour ambulatory ECG variables in discriminating between patients with a history of tachyarrhythmic cardiac arrest and patients without a history of ventricular tachyarrhythmias after a remote myocardial infarction.
The Presence of a Q Wave in Lead V5 Excludes Manifest Preexcitation
Authors: Pavri Behzad B. , Coyne Robert F. , Kocovic Dusan Z. 
Published: October 2006

BackgroundThe degree of preexcitation in patients with the Wolff‐Parkinson‐White syndrome may vary depending on autonomic tone, heart rate, pathway location, and atrioventricular node conduction. When subtle, preexcitation may be difficult to detect with a 12‐lead electrocardiogram (ECG). Furthermore, the pattern of preexcitation may be mimicked in patients with QRS widening and rapid atrioventricular node conduction.MethodsWe studied 50 patients with manifest accessory pathways who underwent electrophys‐iological study and pathway ablation. Pre‐ and postablation ECGs for the presence or absence of a Q wave in leads V5 and V6 were studied. ECGs from an additional 19 patients were used to validate the observations.ResultsWe found that no patient with preexcitation had a Q wave in lead V5 and only 1 of 50 patients had a Q wave in V6. This was a reproducible finding in the 26 patients with multiple ECGs obtained on separate days. The results were validated in an additional 19 patients none of whom had a Q wave in V5, and 1 had a Q wave in V6.ConclusionsThe presence of a Q wave in lead V5 reliably excludes manifest preexcitation.
Silent Myocardial Ischemia and Late Ventricular Repolarization in the Genesis of Ventricular Fibrillation in Humans
Authors: Santinelli Vincenzo , Modano Pasqualina , Ferraiuolo Maria , De Santo Daniela , Oppo Igino , Fornaro Pasquale , Chiariello Massimo 
Published: October 2006

BackgroundWe report a well‐documented case of a patient, a 62‐year‐old man, with severe and asymptomatic left main coronary artery disease who had several episodes of silent myocardial ischemia and a syncopal attack during Holter recording.Methods and ResultsAmbulatory monitoring showed isolated giant U waves separated from the T wave 60 minutes before syncope that was due to reversible ventricular fibrillation lasting about 4 minutes and spontaneously reverting to asystole (7 seconds) and then to atrial fibrillationConclusionOur experience suggests that myocardial ischemia may differently affect the repolarization times within the myocardium leading to widely disparate repolarization gradients that may represent the arrhythmogenic substrate for the occurrence of life‐threatening ventricular tachyarrhythmias. A.N.E. 1999; 4(2):250–254
Accuracy of QTc and QTI for Detection of Autonomic Dysfunction
Authors: Whitsel Eric A. , Boyko Edward J. , Siscovick David S. 
Published: October 2006

Background:Correlates of QT interval duration have been described although their effects on its ability to identify autonomic neuropathy have not. Methods:We examined the ability of QTc and QTI to detect pharmacologically simulated autonomic dysfunction (PSAD) in persons without bundle branch block, U waves, or long QT syndrome by reviewing 249 articles published through 1996 describing the influence of adrenergic beta antagonists or atropine on QT duration. Six of the articles described effects of intravenous drug administration on the ECG among 94 individuals in sinus rhythm. Autonomic dysfunction was pharmacologically simulated in a subset of 30 men and women via coadministration of both drugs. We used logistic regression to estimate accuracy of QTc and QTI for PSAD, reported as area under summary receiver operating characteristic curves (AUC [95% Cl]) and sensitivity (95% Cl) of test thresholds with specificity of 0.80. Results:Sensitivity of QTC > 436 ms1/2 was 0.20 (0.09–0.38) and AUCQTC, 0.54 (0.41–0.66). A QTI < 95% was similarly insensitive, 0.30 (0.16–0.48), and AUCQTI equally low. However, stratum‐specific AUCQTI' was higher than overall AUCQTI, 0.69 (0.64–0.74) when age mean (37.7 years), 0.77 (0.73–0.81) in males, and 0.87 (0.77–0.97) in participants without history of arrhythmia. Sensitivity of QTI thresholds in these strata, range 0.41 to 0.62, was 2.2 to 7.8 times greater than sensitivity, range 0.08 to 0.19, of equally specific QTc thresholds. In a model combining age (y), gender, and arrhythmia, AUCQTI was 0.88 (0.86–0.90). Conclusions: In isolation, QTc and QTI inaccurately detect PSAD. When confounding is taken into consideration, low QTI identifies PSAD with greater sensitivity and accuracy than high QTc. A.N.E. 1999;4(3):257–266
Coronary Artery Disease May Alter the Spatial Dispersion of the QT Interval at Rest
Authors: Hailer Birgit , Van Leeuwen Peter , Lange Silke , Pilath Martin , Wehr Michael 
Published: October 2006

Background:Increases of QT dispersion (QTd) have been observed in patients with coronary artery‐disease (CAD) under stress. In contrast to ECG, multichannel magnetocardiography (MCG) allows the assessment of the spatial distribution of QTd, which may be altered earlier than standard QTd. The aim of this study was the investigation of repolarization patterns in patients with CAD at rest. Methods:12‐lead ECG and 36‐channel MCG were performed in 20 healthy subjects (N) (6 m; aged 54 ± 7) and 23 patients with CAD (14 m; aged 59 ± 9). QT intervals were determined for each ECG lead and MCG registration site. QTd was calculated as QTmax‐QTmin for both methods. In MCG, QTd was also examined spatially by calculating the difference between QTmin and QT at each registration site and plotting this value relative to its position. Spatial variability was quantified using two indexes: SI, which quantifies the mean dispersion at each registration site and Sin, which normalizes SI by taking the overall spatial dispersion pattern into account. Results:In contrast to ECG, the MCG QTd values were higher in patients with CAD (P < 0.05). These patients also displayed more QT variability between neighboring sites and an alteration in global pattern. Accordingly, the SI and Sin values differed most clearly between groups (P < 0.001). Conclusions:CAD may lead to increased heterogeneity of repolarization at rest. Spatial changes are better able to identify patients with CAD than standard QTd based on ECG. Their visualization and quantification is possible on the basis of multichannel magnetocardiography. A.N.E. 1999;4(3):267–273
Reproducibility of Minimum, Maximum and Median QT Intervals in the 12‐Lead Resting ECG
Authors: Lund Kaspar , Arildsen Hanne , Perkiömäki Juha S. , Huikuri Heikki V. , May Ole , Pedersen Anders Kirstein 
Published: October 2006

Background: Heterogeneity in the recovery of ventricular refractory periods is an important factor in the development of ventricular arrhythmia. The QT dispersion (QTD) is increasingly used to measure this heterogeneity but its clinical value is limited due to methodological problems. QTD is defined as the maximum minus the minimum QT intervals that are suspected to be the least reproducible of the QT measurements.Objective: To analyze the reproducibility of the minimum, maximum and median QT intervals.Material: One database consisted of 356 subjects: 169 with diabetes and 187 nondiabetic control persons. The other database consisted of 110 subjects with remote myocardial infarction: 55 with no history of arrhythmia, and 55 with a recent history of ventricular tachycardia or fibrillation.Methods: 12‐lead surface ECGs were recorded with an amplification of 10 millimeters per millivolt at a paper speed of 50 mm/s. QT was measured manually by the tangent‐method. The reproducibility was calculated from measurements of QT in successive beats.Results: The standard deviation (SD) of QTs reproducibility was 9 ms for the arrhythmia data and 8 ms for the diabetes data. The reproducibility of QTmax and QTmin were on average 30% and 15% worse than for QTmedian. The SD of QTmax was significantly higher than for QTmedian in both database (P < 0.001), whereas SD of QTmin was only significantly higher than for QTmedian for the diabetes data (P < 0.001).Conclusions: The reproducibility of QTmin and in particular QTmax was significantly lower than for QTmedian. This indicates that the QT dispersion is based on the least reproducible of the QT measurements. A.N.E. 2000;5(4):354–357
Computer Detection of Atrial Flutter
Authors: Morrison Steven , Macfarlane Peter W. 
Published: October 2006

Background: As part of ongoing research into methods for rhythm analysis in the Glasgow Program, a new algorithm has been developed for the detection of atrial flutter.Methods: The new algorithm uses two approaches to detect atrial waves. The first approach uses existing methods for “P” wave detection, searching various leads for patterns of positive and negative gradients satisfying amplitude and duration criteria. A threshold crossing technique is applied to the first difference of leads II and VI. Atrial regularity is measured using a scoring method that takes account of undetected waves. This measure of regularity is used, along with the estimated atrial rate, as criteria for atrial flutter. To develop the algorithm, 422 ECGs, including 49 cases of atrial flutter, were used as a training set. Optimization was achieved using a trial and error approach. A further 462 ECGs, including 75 atrial flutters, were used as a test set.Results: Using the new algorithm, a sensitivity of 72.0% was achieved, with a specificity of 98.4%. This compares favorably to existing flutter detection logic in the Glasgow Program, which had a sensitivity of 26.7% and specificity of 99.7% on the same difficult test set. The combination of the old and the new algorithms gave a sensitivity of 78.7% with a specificity of 98.1%.Conclusions: The new algorithm is successful in detecting a wide variety of cases of atrial flutter. However, further refinement is required to deal with certain types of atrial flutter, particularly at high ventricular rates. A.N.E. 2000;5(4):358–364
Dispersion of Repolarization: Time to Move Beyond QT Dispersion
Authors: Zareba Wojciech 
Published: October 2006

Background: Over the last few years, the concept of dispersion of repolarization, evaluated as interlead variability of QT interval duration in surface ECG, emerged as a possible tool to identify patients at high‐risk for cardiac arrhythmias. Despite substantial progress in understanding of the electrophysiological basis for dispersion of repolarization, the question remains whether interlead differences in ECG‐ recorded T‐wave duration and morphology (QT dispersion) indicate heterogeneity in ventricular recovery time and pattern.Methods and Results: Several studies investigated the prognostic significance of QT dispersion for predicting all‐cause mortality, sudden cardiac, and arrhythmic deaths. Some of those studies indicated significant and independent predictive value of QT dispersion whereas others negated such an association. Despite these controversial results, there is concern that substantial overlap in QT dispersion values between patients with and without cardiac events limits or even precludes clinical usefulness of QT dispersion for predicting future cardiac events. The methodological and conceptual limitations of QT dispersion measurements further discourage the bedside use of this noninvasive ECG parameter. Ionic channel phenomena determine the voltage and time components of the T‐wave, the T‐loop, and the QT interval duration. Since the ST‐T area is more representative of recovery times than QT interval duration, future efforts should be focused on developing and testing new automatically quantified parameters describing abnormalities of the T‐wave configuration and/or T‐loop morphology. Electrophysiologic meaning and prognostic significance of these ECG parameters remain to be studied.Conclusion: In light of conceptual and methodological limitations of QT dispersion analysis, bedside use of this method should be discouraged and the time has come to move beyond QT dispersion and focus on evaluating clinical usefulness of repolarization morphology in risk‐stratification. studies. A.N.E. 2000;5(4):373‐381