Reproducibility of Computerized Measurements of QT Interval from Multiple Leads at Rest and During Exercise (original) (raw)
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Circulation, 1992
Background. The interval from the R wave to the maximum amplitude of the T wave (RTm) contains the heart rate dependency of ventricular repolarization. Methods and Results. A computer algorithm was developed to quantify the RTm and preceding RR intervals for each of more than 50,000 beats on 24-hour ambulatory electrocardiographic (Holter) recordings to evaluate the dynamic relation between repolarization duration and cycle length. The relation of RTm to the preceding RR interval (RTm/RR slope) was determined by the best-fit linear regression equation between these two parameters. Eleven normal subjects and 16 patients with long QT syndrome (LQTS) were investigated. Six of the normal subjects had Holter recordings obtained before and after (-blocker therapy. (-Blockers were associated with a significant (p=0.005) reduction in the RTm/RR slope from 0.13±0.02 to 0.10±0.02. The mean value of the RTmIRR slope was significantly (p=0.003) larger in the LQTS patients (0.21±0.08) than in normal subjects (0.14+0.03). Conclusions. These findings indicate that 1) quantification of the dynamic relation between ventricular repolarization and RR cycle length can be obtained on a large number of Holter-recorded heart beats; 2) f-blockers reduce the RTm/RR slope in normal patients; and 3) LQTS patients have an exaggerated delay in repolarization at long RR cycle lengths. (Circulation 1992;85:1816-1821) KEY WoRDs * delayed repolarization * arrhythmias * sudden cardiac death From the Department of Electrical Engineering (M.M., M.A., F.B.), University of Rochester, Rochester, N.Y.; the Heart Research Follow-up Program (A.J.M.
Electrocardiographic quantitation of ventricular repolarization
Circulation, 1989
Quantification of the electrocardiographic ventricular repolarization involving the T-U wave complex is usually performed with reference to the axis of the T wave and the QT interval duration. A novel quantitative approach to improve the description of ventricular repolarization was applied to the digitized electrocardiograms of 423 normal subjects. Six electrocardiographic repolarization characteristics were identified: duration, rate, area, symmetry, late phenomena, and interlead heterogeneity. A computer algorithm was designed to automatically interpret the electrocardiographic repolarization segment and measure 11 variables that quantified these repolarization characteristics. The application of redundancy-reduction techniques selected a final set of seven variables that were used in the statistical analysis. The QT interval, which was included in the initial group of variables, was replaced by the time interval between S wave offset and T wave maximum. All selected electrocardi...
Effect of premature ventricular beats on manual and automatic repolarization measurements
Journal of Electrocardiology, 2004
Objective: To compare QT interval and QT dispersion in ventricular ectopic beats with measurements from the preceding and the immediately following sinus beats, and investigate differences between manual and automatic measurements. Patients: Eleven chronic uremic patients. Main outcome measures: ECGs were recorded during hemodialysis treatment and 12-lead sections containing five consecutive beats were extracted, each containing four sinus beats and one centrally-positioned premature ventricular beat. QT measurements were performed both manually and with a computer-automated technique. Results: T wave amplitude was greater in the ectopic beats compared to the sinus beats (0.61 Ϯ 0.18 vs. 0.23 Ϯ 0.06 mV, P Ͻ.001). The ectopic beats had a greater QT than the sinus beats when measured manually (415 Ϯ 35 ms vs. 386 Ϯ 28 ms, P Ͻ.001), or automatically (375 Ϯ 30 vs. 366 Ϯ 27 ms, PϽ.01). The sinus beats following the ectopics had a greater QT than the preceding sinus beats (400 Ϯ 27 vs. 386 Ϯ 28 ms, PϽ.001, manual; 382 Ϯ 24 vs. 366 Ϯ 27 ms, PϽ.001, automatic). Differences in QT dispersion were seen only between the ectopic and sinus beats (91 Ϯ 31 vs. 58 Ϯ 27 ms, P Ͻ.001, manual; 68 Ϯ 33 vs. 49 Ϯ 35 ms, P Ͻ.001, automatic). Conclusions: Manual measurement resulted in greater QT values than automatic measurement. Both techniques identified differences between sinus and ectopic beats. The ventricular ectopic beats resulted in an increase in the QT of the immediately following sinus beats. These results confirm the need to interpret QT measurements with care in the presence of ectopic beats.
Electrocardiographic Quantitation of Heterogeneity of Ventricular Repolarization
Annals of Noninvasive Electrocardiology, 2000
Background: QT interval dispersion (QTd) measured from the surface ECG has emerged as the most common noninvasive method for assessing heterogeneity of ventricular repolarization. Although QTd correlates with dispersion of monophasic action potential duration at 90% repolarization and with dispersion of recovery time recorded from the epicardium, total T-wave area, representing a summation of vectors during this time interval, has been shown to have the highest correlation with these invasive measures of dispersion of repolarization. However, recent clinical studies suggest that the ratio of the second to first eigenvalues of the spatial T-wave vector using principal component analysis (PCA ratio) may more accurately reflect heterogeneity of ventricular repolarization. Methods: To better characterize the ECG correlates of surface ECG measures of heterogeneity of ventricular repolarization and to establish normal values of these criteria using an automated measurement method, the relations of QRS onset to T-wave offset (QT,d) and to T-wave peak (QT,d) dispersion and the PCA ratio to T-wave area and amplitude, heart rate, QRS axis and duration, and the QT, interval were examined in 163 asymptomatic subjects with normal resting ECGs and normal left ventricular mass and function. QT, d and QT, d were measured by computer from digitized ECGs as the difference between the maximum and minimum QT, and QT, intervals, respectively. Results: In univariate analyses, a significant correlation was found between the sum of the T-wave area and the PCA ratio (R =-0.46, P < O.OOl), but there was no significant correlation of the sum of T-wave area with QT, d (R = 0.1 1, P = NS) or QT, d (R=0.09, P = NS). There were only modest correlations between QT, d and QT, d (R = 0.45) and between the PCA ratio and QT, d (R = 0.29) and QT, d (R = 0.49) (each P < 0.001). In stepwise multivariate linear regression analyses, the PCA ratio was significantly related to the sum of T-wave area, T-wave amplitude in aVL, and to female gender (overall R = 0.54, P < 0.001 1, QT, d correlated only with the maximum QT, interval (R = 0.39, P < 0.001), and QT, d was related to heart rate and QRS axis (overall R = 0.36, P < 0.001). In addition, the normal interlead dispersion of repolarization as measured by QT, d was significantly greater than dispersion measured by QT, d (23.5 ? 11.5 ms vs 18.3 2 11.2 ms, P < 0.001). Conclusions: These findings provide new information on ECG measures of heterogeneity of repolarization in normal subjects, with a significantly higher intrinsic variability of Q to T-peak than Q to T-offset dispersion and only modest correlation between these two measures. The independent relation of the PCA ratio to the sum of T-wave area suggests that the PCA ratio may be a more accurate surface ECG computers; electrocardiography; electrophysiology; intervals; QT dispersion reflection of the heterogeneity of ventricular repolarization.
Normal Ventricular Repolarization and QT Interval
Cardiac Electrophysiology Clinics, 2017
Ventricular repolarization is a cellular electrophysiological process expressed in the electrocardiogram as the QT interval. Intramural differences in the ventricular repolarization are at the base of ST and T waves in the electrocardiogram. The QT interval is variable, and many factors affect its duration: heart rate, autonomic nervous activity, age, and gender are the main determinants. Many criteria correct the duration of QT interval for heart rate. Conditions provoking repolarization abnormalities (QT prolongation) are ionic changes, drugs, cardiac/noncardiac diseases, and genetic background (long QT syndromes).
Europace, 2011
The presence of early repolarization (ER) in inferior or inferolateral leads has been associated with malignant arrhythmias and increased mortality. Transmural dispersion of repolarization (TDR) has been proposed to underlie arrhythmogenesis in J-wave syndromes. The present study investigated specific electrocardiographic (ECG) markers including Tpeak-Tend interval and (Tpeak-Tend)/QT ratio that reflect TDR in subjects with ER. Methods and results The ECGs of 47 healthy individuals (43 males, mean age: 45.7 + 13.1 years) with an ER pattern in lateral (n ¼ 15) or infero-lateral leads (n ¼ 32) who successfully completed an exercise stress test were analysed at rest, peak workload, and recovery. The ER pattern was defined as slurring or notching of the terminal part of the QRS complex (J-point) ≥1 mm, in at least two contiguous leads. Thirty-five age-and sex-matched healthy subjects without ER (28 males, mean age: 48.6 + 10.2 years) served as comparative controls. Subjects with ER displayed increased Tpeak-Tend interval in lead V 2 , Tpeak-Tend dispersion of the precordial leads, and (Tpeak-Tend)/QT ratio in lead V 2 compared with those without ER in all three phases of the exercise test (P , 0.05). In addition, Tpeak-Tend dispersion and the (Tpeak-Tend)/QT ratio in lead V 2 were significantly increased at recovery phase compared with peak exercise only in subjects with ER (P , 0.05). There were no significant differences among the studied ECG parameters regarding the ER location (lateral vs. infero-lateral), the ER type (slurring or notching), or the maximum J-point amplitude (≥ 1.5 vs. ,1.5 mm) at baseline ECGs. Conclusions Individuals with ER display an increased TDR that may be related to an increased arrhythmic risk.
Frontiers in Physiology
Introduction: Cardiac repolarization abnormalities are among the major causes of ventricular arrhythmias and sudden cardiac death. In humans, cardiac repolarization duration has a 24-h rhythm. Animal studies show that this rhythm is regulated by 24-h rhythms in ion channel function and that disruption of this rhythm leads to ventricular arrhythmias. We hypothesized that 24-h rhythms in QT duration can be used as a predictor for sudden cardiac death and are associated with ventricular arrhythmias. Secondly, we assessed a possible mechanistic explanation by studying the putative role of hERG channel dysfunction. Materials and Methods: In 2 retrospective studies, measures of the 24-h variation in the QT and QTc intervals (QT and QTc diurnality, QTd and QTcd, respectively) have been derived from Holter analyses and compared between groups: 1) 39 post-infarct patients with systolic heart failure (CHF: EF < 35%), of which 14 with, and 25 without a history of ventricular arrhythmias and 2) five patients with proven (LQTS2) and 16 with potential (Sotalol-induced) hERG channel dysfunction vs. 22 controls. Results: QTd was twofold higher in CHF patients with a history of ventricular arrhythmias (38 ± 15 ms) compared to CHF patients without VT (16 ± 9 ms, p = 0.001). QTd was significantly increased in LQT2 patients (43 ± 24 ms) or those treated with Sotalol (30 ± 10 ms) compared to controls (21 ± 8 ms, p < 0.05 for both). Discussion: QT diurnality presents a novel clinical parameter of repolarization that can be derived from Holter registrations and may be useful for identification of patients at risk for ventricular arrhythmias.