bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interobserver Reproducibility of QT Interval Measurement and QT Dispersion in Patients After Acute Myocardial Infarction
Authors: Kautzner Josef , Gang Yi , Kishore Ravi , Copie Xavier , Janota Tomas , Nagayoshi Hirokazu , Camm A. John , Malik Marek 
Published: October 2006

Background: The study evaluated interobserver differences in the classification of the T‐U wave repolarization pattern, and their influence on the numerical values of manual measurements of QT interval duration and dispersion in standard predischarge 12‐lead ECGs recorded in survivors after acute myocardial infarction.Methods: Thirty ECGs recorded at 25 mm/s were measured by six independent observers. The observers used an adopted scheme to classify the repolarization pattern into 1 of 7 categories, based on the appearance of the T wave, and/or the presence of the U wave, and the various extent of fusion between these. In each lead with measurable QRST(U) pattern, the RR, QJ, QT‐end, QT‐nadir (i.e., interval between Q onset and the nadir or transition between T and U wave) and QU interval were measured, when applicable. Based on these measurements, the mean RR interval, the maximum, minimum, and mean QJ interval, QT‐end and/or QT‐nadir interval, and QU interval, the difference between the maximum and minimum QT interval (QT dispersion [QTD]), and the coefficient of variation of QT intervals was derived for each recording. The agreement of an individual observer with other observers in the selection of a given repolarization pattern were investigated by an agreement index, and the general reproducibility of repolarization pattern classification was evaluated by the reproducibility index. The interobserver agreement of numerical measurements was assessed by relative errors. To assess the general interobserver reproducibility of a given numerical measurement, the coefficient of variance of the values provided by all observers was computed for each ECG. Statistical comparison of these coefficients was performed using a standard sign test.Results: The results demonstrated the existence of remarkable differences in the selection of classification patterns of repolarization among the observers. More importantly, these differences were mainly related to the presence of more complex patterns of repolarization and contributed to poor interobserver reproducibility of QTD parameters in all 12 leads and in the precordial leads (relative error of 31%–35% and 34%–43%, respectively) as compared with the interobserver reproducibility of both QT and QU interval duration measurements (relative error of 3%–6%, P < 0.01). This observation was not explained by differences in the numerical order between QT interval duration and QTD, as the reproducibility of the QJ interval (i.e., interval of the same numerical order as QTD was significantly better (relative error of 7.5%–13%, P < 0.01) than that of QTD.Conclusions: Poor interobserver reproducibility of QT dispersion related to the presence of complex repolarization patterns may explain, to some extent, a spectrum of QT dispersion values reported in different clinical studies and may limit the clinical utility in this parameter.
Comparison of Computerized and Standard Visual Criteria of Exercise ECG for Diagnosis of Coronary Artery Disease
Authors: DelCampo Jaime , Do Dat , Umann Tianna , McGowan Vernell , Froning Jeffrey , Froelicher Victor 
Published: October 2006

Objective: To review past and current studies of computerized exercise ECG criteria in order to establish which, if any, are superior to standard visual analysis for the diagnosis of coronary artery disease (CAD).Methods: Prior studies that compared multiple computerized ECG criteria were reviewed. In addition, we investigated two sets of patients that had both exercise testing and coronary arteriography at two university‐affiliated Veteran's Affairs Medical Centers. Patients with previous myocardial infarction or coronary artery bypass surgery, valvular heart disease, left bundle branch block, or any diagnostic Q waves present on their resting ECGs were excluded from analysis. Sensitivity and specificity values were compiled for standard visual analysis and for the following computerized ECG criteria: ST0; ST60; ST slope; ST integral; ST index; R wave adjusted ST; ST/heart rate (HR) index; Hollenberg's Treadmill exercise score; and discriminant function analysis (DFA).Results: Despite the effects of limited challenge and work‐up bias, the compiled results indicate that ST measurements recorded during the time of recovery from exercise are substantially more diagnostic than those recorded at maximal exercise. ST integral, ST60, and R wave adjusted ST60 during recovery are especially discriminating of CAD, while Hollenberg's treadmill exercise score is not. There were inconclusive results for HR adjustments to ST depression and ST index. DFA including visual analysis of the ECG consistently exhibited the greatest discriminating power of all computerized results.Conclusion: Although DFA, ST integral during recovery, or ST60 during recovery exhibited improved predictive value, further research is necessary before we can clearly offer a superior alternative to standard visual analysis.
Vagal Influence on Deterministic Chaos of Heart Rate in Patients after Acute Myocardial Infarction
Authors: Hagerman Inger , Berglund Margareta , Ericson Mats , Sylvén Christer 
Published: October 2006

ObjectivesTo test heart rate variability (HRV) in patients with acute myocardial infarction (AMI) for nonlinear deterministic complex behavior and for its dependence on autonomic tone.MethodsFifteen patients (mean age 55, 14 men) with AMI and 16 healthy individuals (mean age 41, 11 men) with ongoing beta‐adrenergic receptor blockade were investigated after intravenouse administration of atropine (0.03 mg/kg). Nonlinear indices for HRV were assessed by local sensitive dependence on initial conditions as quantitated by the Lyapunov exponent, fractal dimension (FD), and correlation dimension. Linear indices for HRV were assessed in the time domain by the standard deviation of the RR interval (SD‐RR), the coefficient of variation (CV%), and the mean successive difference (MSD). In the frequency domain, the following indices were used: very low frequency power (VLF), low frequency power (LF), high frequency power (HF), total power (TP), and the ratio between low and high frequency power (LF/HF).ResultsSurrogate data analysis revealed independent behavior of the Lyapunov exponent, the FD, and the correlation dimension, suggesting the presence of deterministic chaos in HRV. The Lyapunov exponent was positive in both groups at baseline but was significantly lower in the patient group. Following atropine, the value decreased while remaining positive, but no differences between the groups were found. The FD and the correlation dimension reacted similarly to the Lyapunov exponent. All time‐domain indices were significantly lower in the patients along with power in LF and HF bands. The differences were abolished by the administration of atropine.ConclusionsThe heart rate of patients with AMI exhibits characteristics of deterministic chaotic behavior with a positive Lyapunov exponent but with significantly less complex behavior than in healthy controls. The difference was eliminated by atropine, suggesting that vagal tone is a major cause. The nonlinear indices have a discriminating capacity for changes in HRV comparable to linear indices.
Effects of β‐Blocker Therapy on the Dynamic QT/RR Relation in Patients with Long QT Syndrome During 24‐Hour Holter ECG Monitoring
Authors: Emori Tetsuro , Ohe Tohru , Aihara Naohiko , Kurita Takashi , Shimizu Wataru , Kamakura Shiro , Shimomura Katsuro 
Published: October 2006

Objective:Patients with long QT syndrome (LQTS) have an abnormality in the dynamic relationship between the QT and RR intervals (QT/RR relation) assessed by 24‐hour Holter ECG monitoring. The clinical efficacy of β‐blocker therapy in LQTS patients has been established, but its antiarrhythmic mechanism has not been fully elucidated. In the present study, the influences of β‐blocker therapy on the QT/RR relation were investigated in LQTS patients with no arrhythmic event during β‐blocker therapy.Methods:Holter ECG recordings before and after the therapy were obtained from seven LQTS patients (all female, age range 10–45 years). The QT/RR relation was analyzed by our original computer algorithm with automatic measurement of the Q‐aT interval (time interval from the QRS onset to the T wave apex. The correlation coefficient (r), and the slope of the best fit linear regression line between the Q‐aT and RR intervals (Q‐aT/RR slope) after β‐blocker therapy were compared with those before the therapy. To determine whether the dose of β‐blockers was sufficient for suppression of the sympathetic nervous activity, a frequency‐domain analysis of the heart rate variability was performed (low frequency power [LF]: 0.04–0.15 Hz, high frequency power [HF]: 0.15–0.40 Hz).Results:The LF component of the heart rate variability decreased and the HF component increased during the daytime after β‐blocker therapy. However, the Q‐aT/RR relation after β‐blocker therapy was the same as that before the therapy (mean slope before = 0.20 ± 0.07, mean slope after = 0.19 ± 0.08; P = not significant; mean r before = 0.82 ± 0.17; mean r after = 0.76 ± 0.15; P = not significant).Conclusion:β‐Blocker therapy did not affect the unique Q‐aT/RR relation, which reflects an intrinsic abnormality of the ventricular repolarization in LQTS patients.
Risk Stratification of Patients After Myocardial Infarction Based on Wavelet Decomposition of the Signal‐Averaged Electrocardiogram
Authors: Sierra Gilberto , Reinhardt Lutz , Fetsch Thomas , Martínez‐Rubio Antoni , Mäkijärvi Markku , Yli‐Mäyry Sinikka , Montonen Juha , Katila Toivo , Borggrefe Martin , Breithardt Günter 
Published: October 2006

Objective: The objective of this study was to investigate the prognostic significance of the wavelet decomposition (WD), when applied to single leads of the signal‐averaged ECG (SAECG) of postinfarction patients, as well as to compare it with conventional time‐domain (TD) analysis in order to optimize the utility of high resolution ECG techniques in risk stratification. Comparisons with clinical variables were also performed.Methods: SAECGs of 769 patients were analyzed (mean age 53 ± 7 years). A total of 42 arrhythmic events occurred within 54 months. For numerical calculations of WD, relative energies of the QRS complex were obtained in seven frequency bands. Conventional parameters of late potential analysis in TD were calculated at 25 and 40 Hz high pass filter.Results: No significant correlation was found between parameters of both methods. Several parameters of the WD of single leads showed slightly higher sensitivity (e.g., 52% vs 36%) and positive predictive values (e.g., 13.3% vs 10.2%) compared with those obtained with the QRS duration of TD analysis. In multivariate analysis, combination of QRS duration with WD parameters (relative risk [rr] =4.55, P < 0.0001), followed by the WD of single leads (rr = 4.19, P < 0.0001), nonsustained ventricular tachycardia in the long‐term ECG (rr = 3.72, P = 0.0005) and the history of previous infarction (rr = 2.72, P = 0.0035) were the most significant predictors in risk stratification.Conclusion: Time domain and wavelet transform of SAECG resulted in an improvement in postinfarction risk stratification compared with the clinical variables included in this study. Wavelet parameters may not be vastly superior to QRS duration, but they are a new index measuring intra‐QRS phenomena.
Power Spectral Changes of Spontaneous Beat‐to‐Beat Variability of the RT Interval in Patients with Coronary Artery Disease
Authors: Müller Christian , Dambacher Martin , Spadacini Giammario , Roskamm Helmut , Frey Axel W. 
Published: October 2006

Objective:This study sought to evaluate the spontaneous beat‐to‐beat variability of the RT interval (RTV) as a marker of autonomic balance at the ventricle in patients with coronary artery disease (CAD), as heart rate variability (HRV) primarily reflects sympathovagal interactions at the sinus node.Methods:ECG and peripheral blood pressure signals were analyzed in supine and passive head‐up tilt in 19 patients with CAD. RT intervals were measured between the maximum of the QRS complex and the maximum of the T wave. Power spectral analysis of RR intervals, RT intervals, systolic and diastolic pressure were performed using discrete Fourier transformation. We calculated the area under the spectral density curve in the low (LF = 0.05–0.18 Hz) and high frequency range (HF = 0.18–0.50 Hz).Results:Tilting results in a decrease of HF in HRV to 45%± 10% (P < 0.05) and an increase of HF in RTV to 266%± 83% (P < 0.01). Total RTV was 2.4% of total HRV. In systolic blood pressure variability HF increased to 396%± 124% (P < 0.05), in diastolic blood pressure variability to 231%± 69% (P < 0.05).Conclusion:If the transfer‐function of sympathetic activity to the ventricle and to the sinus node are similar, the increase of HF in RTV cannot be explained by the increase in sympathetic activity induced by tilting. It is most likely a mechanical phenomenon induced by respiration synchronous changes of the position of the heart in the thorax and transferred variabilities of the central venous pressure that can also be identified in systolic and diastolic pressure variabilities.
Two‐Dimensional Vector Analysis of Beat‐to‐Beat Dynamics of Ventricular Repolarization
Authors: Huikuri Heikki V. , Airaksinen K.E. Juhani , Koistinen M. Juhani , Palmgren Jan‐Erik , Linnaluoto Markku K. , Tikkanen Pauli , Sellin Lawrence 
Published: October 2006

Objective: Duration of ventricular repolarization is a result of complex interaction between autonomic modulation and heart rate (HR).Methods: To study the dynamics of ventricular repolarization of the human right ventricle, beat‐to‐beat variability of ventricular repolarization was measured by plotting the duration of each monophasic action potential at the 90% phase of repolarization (APD90) as a function of the previous APD90 both in sinus rhythm and during steady‐state atrial pacing (cycle length of 600 rns) in 12 subjects without structural heart disease.Results: Quantitative analyses of APD90 and RR interval variability in sinus rhythm showed that the total standard deviation (SD) of APD90 was only 8% of the SD of all RR intervals. Both longterm, continuous variability (SD2) of APD90 (3.9 ± 1.5 ms) and instantaneous beat‐to‐beat variability (SD1) of APD90 (1.2 ± 0.3 ms) were smaller than the SD2 and SD1 of RR intervals (46 ± 17 ms and 15 ± 9 ms, respectively) (P < 0.001 for both), but the shapes of the APD90 and RR interval plots and the SD1/SD2 ratio did not differ. SD1 of APD90 correlated well with the SD1 of RR intervals (r = 0.64, P < 0.05) but no significant correlation was observed between the SD2 of APD90 and SD2 of RR intervals (r = 0.32, NS). During steady‐state atrial pacing, only minimal instantaneous beat‐to‐beat variability in APD90 (0.9 ± 0.3 rns) was observed but the SD2 was larger than the SD2 of RR intervals (2.3 ± 1.0 ms vs. 1.6 ± 0.8 ms, P < 0.001).Conclusion: The results suggest that instantaneous beat‐to‐beat variability of ventricular repolarization is mainly due to beat‐to‐beat fluctuation of HR, but the long‐term dynamics of repolarization are partly influenced by other factors than the HR variability.
Quantitative Aspects of Ventricular Repolarization
Authors: Badilini Fabio , Fayn Jocelyne , Maison‐Blanche Pierre , Leenhardt Antoine , Forlini Marie Claire , Denjoy Isabelle , Coumel Philippe , Rubel Paul 
Published: October 2006

Introduction:QT dispersion assesses repolarization inhomogeneity on 12‐lead standard ECG. However, the implications of the electrical cardiac vector during the repolarization phase (the T wave loop) with the genesis of this phenomenon are unknown.Methods and Results:The aim of this study was to explore conventional 12‐lead resting ECG QT dispersion and the corresponding morphology of the spatial three‐dimensional (3‐D) T wave loop in 25 normals subjects, 30 postmyocardial infarction (Ml) patients, and in 17 individuals with congenital long QT syndrome (LQTS). Standard and XYZ ECG leads were simultaneously digitized (250 Hz) and automatically analyzed. Ventricular repolarization dispersion was estimated by the range (RAN12o) and standard deviation (SD12o) of the 12 rate corrected QTo intervals (between the Q wave onset and the T wave offset). Spatial T wave loops were extracted from XYZ data and analyzed with a 3‐D algorithm which provides quantitative parameters related to the loop morphology. All scalar measurements of dispersion were significantly larger in the two pathological populations; however none of them could discriminate post‐MI from LQTS groups (RAN12o = 33.3, 61.4, and 62.7 ms respectively, for the three populations). Conversely, a loss of planarity and an increased roundness of the T wave loop were observed in the two pathological groups, with the former effect more pronounced in the LQTS (P = 0.04 compared to post‐MI) and the latter in the post‐MI group (P = 0.02 compared to LQTS). Furthermore, multiple regression and principal component analyses showed that planarity and roundness are independently involved with QT dispersion.Conclusion:Changes in the morphology of the spatial T wave loop associated with QT dispersion were identified. These changes discriminate different substrates of repolarization inhomogeneity. The use of a 3‐D technique to assess repolarization inhomogeneity may bring additional information on the intrinsic nature of this disorder.
The Initial Electrocardiographic Pattern in Acute Myocardial Infarction
Authors: Birnbaum Yochai , Sclarovsky Samuel 
Published: October 2006

Background: The ECG is the most widely used accessory for early diagnosis and risk stratification of patients with acute myocardial infarction (AMI). Previous studies have concentrated on the association between either the number of leads with ST segment deviation (elevation and depression) or the total amount of ST segment elevation and/or depression and prognosis. However, the results are conflicting.Methods: A different method is to use the grades of ischemia as an estimate of infarct or size and prognosis. Grade I ischemia is defined as tall peak T waves with < 0.1 mV ST segment elevation; grade II as ST segment elevation with positive T waves, without distortion of the terminal portion of the QRS; and grade III as ST segment elevation, positive T waves, and distortion of the terminal portion of the QRS. Grade III ischemia on the admission ECG is associated with larger final infarct size and increased mortality.Results: In patients with inferior wall AMI, especially those with prior infarction, the pattern of precordial ST segment depression is even more important and maximal ST depression in V4‐V6 is associated with high mortality. Moreover, meticulous interpretation of the initial ECG pattern provides information about the probable site of the culprit obstructive coronary lesion.Conclusion: Thus, the admission ECG of AMI can assist not only in diagnosis, but also in estimation of infarct size, correlation with the underlying coronary anatomy and risk stratification.
Vector Quantization of T Wave Abnormalities Associated with a Predisposition to Ventricular Arrhythmias and Sudden Death
Authors: Riccio Mark L. , Moïse N. Sydney , Otani Niels F. , Belina John C. , Gelzer Anna R. M. , Gilmour Robert F. 
Published: October 2006

BackgroundPrevious studies have suggested that irregular T wave morphologies are associated with an increased risk of sudden death. However, automated characterization of T wave abnormalities has been hampered by the lack of suitable analysis techniques. In this study, we tested a new method of T wave analysis in German shepherd dogs with inherited ventricular arrhythmias and sudden death.MethodsSets of 24‐hour ambulatory ECG recordings obtained from unaffected (n = 6) and affected (n = 5) dogs were digitized, automatically annotated to label each R wave, and placed into a matrix with the R waves aligned. A vector quantization algorithm separated the QRS‐T complexes into classes according to T wave morphology. The existence of notched T waves was determined by assessing the number of zero crossings of the first derivative during the T wave.ResultsThe duration of the QT interval was similar in affected and unaffected dogs (182 ± 14 ms vs 176 ± 16 ms, respectively). However, T wave morphology differed between the two groups. Specifically, affected dogs had a higher percentage of notched T waves than unaffected dogs (41.6%± 10.8% vs 5.0%± 1.2%, respectively). Notched T waves did not appear at all times of day, nor were they present in all leads.ConclusionVector quantization and first derivative analyses were feasible and effective methods for detecting T wave abnormalities associated with the development of ventricular arrhythmias These methods ultimately may be useful for risk stratification of patients susceptible to ventricular arrhythmias and sudden death.
High Resolution Electrocardiography—Its Application for the Measurement of the QT Interval in the Presence of Low Amplitude T Waves
Authors: Sosnowski Maciej , Zbigniew Czyz M.D.  , Ĺski Jacek , Petelenz Tadeusz , Tendera Michal 
Published: October 2006

ObjectiveWe describe a computer‐interactive method for determination of QT duration in the presence of unfavorably shaped T waves. We assumed that such a method should allow to determine QT duration with the same error irrespective of the T wave amplitude.MethodsThe study group comprised 20 patients following myocardial infarction and the control group, 10 healthy volunteers. ECGs were recorded from XYZ leads using a computer‐assisted low noise amplifier. After A/D conversion (16 bit, 2 kHz) fiducial points of R and T waves were determined and then the signal was aligned and averaged. A segment of 106.5‐ms duration was chosen that included either the initial portion of QRS complex or the terminal part of the T wave. This segment was scanned with a 32‐ms window every 0.5 ms. Spectrotemporal analysis was performed by use of the fast Fourier transform. The QRS onset and T wave offset were defined as points at which the percentage ratio of power in frequency range 62.7–121.6/0–121.6 Hz reached minimum. Signal‐averaged ECGs were printed out (120 mm/s, 2.1 mm/mV) for manual measurement of QT duration and T wave amplitude. Low amplitude T wave was defined as lower than 0.2 mV, otherwise normal amplitude T waves were recognized. Measurements were repeated separately by two observers for each lead.ResultsLow T waves were observed in 11 (37%) leads from controls and in 25 (42%) from post‐Ml patients. Manual measurements were possible in 82 leads (all normal and 28 low T waves), while the high resolution method allowed us to determine the QT duration in all leads. In the Ml group, the results of independent QT measurements by means of high resolution were: 412.0 ± 29.8 ms versus 411.5 ± 29.3 ms for flat, and 410.7 ± 30.4 versus 409.8 ± 30.0 ms for normal T waves. In controls, corresponding values were: 388.5 ± 32.0 versus 386.3 ± 23.8 ms and 392.9 ± 32.8 versus 392.2 ± 31.7 ms. The mean absolute error of two independent measurements was greater with use of the manual method, and reached 6.9 ms (median 5.5 ms) in normal and 12.9 ms (median 8.5 ms) in low T waves. With use of the new method, the errors were lower: 3.48 ms (median 0 ms) and 2.29 ms (median 0 ms), respectively. There was a close correlation between repeat measurements in normal T waves with both methods (r = 0.956 and r = 0.961; both P < 0.001). In low T waves the correlation was significantly lower (P < 0.05) with the manual (r = 0.879; P < 0.001), as compared with the high resolution method (r = 0.973; P < 0.001).ConclusionThe signal‐averaged, high resolution ECG analysis allows for the determination of QT duration in the presence of a flat T wave. The described method may provide the opportunity to measure QT duration in all leads and, therefore, to calculate spatial QT dispersion in the majority of post‐Ml patients.