Normal Ventricular Repolarization and QT Interval (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.
Quantitative Aspects of Ventricular Repolarization
Annals of Noninvasive Electrocardiology, 1997
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.
QT interval dispersion: dispersion of ventricular repolarization or dispersion of QT interval?
Journal of electrocardiology, 1998
The QT interval (QTI) has long been useful as a clinical index of the duration of ventricular repolarization, particularly as a marker of prolonged repolarization and its well-established association with arrhythmogenic cardiac states. Likewise, inhomogeneity (dispersion) of repolarization has been linked definitively to increased susceptibility to reentrant arrhythmias. Recent studies have reported the use of QTI dispersion as a meaningful clinical index to identify patients at risk, but the interpretation of the measurement has been controversial. A Langendorff-perfused, isolated canine heart suspended in a torso-shaped, electrolytic tank filled with NaCl-sucrose solution was used to investigate the relationship between body surface QTIs and ventricular repolarization measured directly from the cardiac surface by using activation-recovery intervals, which have been documented to reflect the duration of local action potentials as well as local refractory periods. The data showed po...
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.
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...
Journal of Cardiovascular Electrophysiology, 2000
QT dispersion (QTd, range of QT intervals in 12 KCG leads) is thought to reflect spatial heterogeneity of ventricular refractoriness. However, QTd may be largely due to projections of the repolarization dipole rather than "nondipolar" signals. Methods and Results: Seventy-eight normal snhjects (47 ± 16 years, 23 women), 68 hypertrophie cardiomyopathy patients (HCM; 38 ± 15 years. 21 women), 72 dilated cardiomyopathy patients (DCM; 48 ± 15 years, 29 women), and 81 survivors of acute myocardial infarction (AMI; 63 ± 12 years, 20 women) had digital 12-lead resting supine ECGs recorded (10 FXGs recorded in each suhject and results averaged). In each ECG lead, QT interval was measured under operator review by QT Guard (GE Marquette) to ohtain QTd. QTd was expressed as the range, standard deviation, and highest-to-lowest quartile difference of QT interval in all nieasurahle leads. Singular value decompositicm transferred ECGs into a minimum dimensional time orthogonal space. The first three components represented the ECG dipole; other components represented nondipolar signals. The power of the T wave nondipolar within the total components was computed to measure spatial repolarization heterogeneity (relative T wave residuum, TWR). QTd was 33.6 ± 18.
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.