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Mean QT (mean + qt)

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Medical Sciences	100%

Selected Abstracts

Heart rate and QT variability in children with anxiety disorders: A preliminary report

DEPRESSION AND ANXIETY, Issue 2 2001
Vikram K. Yeragani M.B.B.S.
Abstract This study compared beat-to-beat heart rate and QT variability in children with anxiety disorders (n=7) and normal controls (n=15) by using an automated algorithm to compute QT intervals. An increase in QT variability appears to be associated with a higher risk for sudden cardiac death. A decrease in heart rate variability is also linked to significant cardiovascular events. Supine detrended QT variability, QT variability corrected for mean QT interval, and QTvi (a log ratio of QT variance normalized for mean QT over heart rate variability normalized for mean heart rate) were significantly higher in children with anxiety compared to controls (P<0.05). The largest Lyapunov Exponent (LLE) of heart rate time series was significantly lower (P<0.05) in children with anxiety compared to controls. These findings suggest a relative increase in sympathetic activity and a relative decrease in cardiac vagal activity in children with anxiety disorders, and are discussed in the context of the effects of tricyclics on cardiac autonomic function in children, and the rare occurrence of sudden death during tricyclic antidepressant treatment. Depression and Anxiety 13:72,77, 2001. © 2001 Wiley-Liss, Inc. [source]

Increased QT variability in young asymptomatic patients with ,-thalassemia major

EUROPEAN JOURNAL OF HAEMATOLOGY, Issue 4 2007
Damiano Magrì
Abstract Background:, Despite recent progress in iron chelation therapy, sudden cardiac death due to malignant ventricular arrhythmias remains a vexing, clinical problem in patients with ,-thalassemia major (TM). In this study we assessed whether the major indices of QT variability, emerging tools for risk stratification of sudden cardiac death, differ in young asymptomatic patients with TM and healthy persons. Methods: Thirty patients with TM and 30 healthy control subjects underwent a 5-min electrocardiography recording to calculate the following variables: QT variance (QTv), QTv normalized for mean QT (QTVN) and QT variability index (QTVI). All subjects also underwent a two-dimensional and Doppler echocardiography study and magnetic resonance imaging (MRI) to determine cardiac and hepatic T2* values. Results: No differences were observed in clinical and conventional echo-Doppler findings in healthy control subjects and patients with TM whereas QTv, QTVN and QTVI values were significantly higher in patients than those in controls (QTv, P < 0.001; QTVN, P < 0.05 and QTVI, P < 0.001) and cardiac T2* and hepatic MRI T2* values were significantly lower in patients with TM (P < 0.001). The indices of temporal QT variability correlated significantly with MRI data. Conclusions: Young asymptomatic patients with TM have increased cardiac repolarization variability as assessed by QT variability indices, probably due to cardiac iron deposition. These easily assessed, non-invasive markers could be used to identify increased myocardial repolarization lability early in asymptomatic patients with TM. [source]

Dynamics of Ventricular Repolarization in Patients with Dilated Cardiomyopathy Versus Healthy Subjects

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2005
Jose Luis Alonso M.D.
Background: Patients with impaired left ventricular function have a high risk of developing ventricular arrhythmias and sudden death. Among different markers of risk, the prolongation and regional heterogeneity of repolarization are of increasing interest. However, there are limited data regarding feasibility of analyzing repolarization parameters and their dynamics in 24-hour Holter ECG recordings. Methods: Dynamic behavior of repolarization parameters was studied with a new automatic algorithm in digital 24-hour Holter recordings of 60 healthy subjects and 55 patients with idiopathic dilated cardiomyopathy (IDC). Repolarization parameters included the mean value of QT and QTc durations, QT dispersion, and peaks of QT duration and QT dispersion above prespecified thresholds. Results: In comparison to healthy subjects, patients with IDC had lower heart rate variability, longer mean QT and QTc durations, higher content of QTc peaks >500 ms, longer QT dispersion and its standard deviation, and a higher content of peaks >100 ms of QT dispersion (P < 0.01 for all comparisons). These repolarization parameters were significantly higher in IDC patients after adjustment for age, sex, and heart rate variability. The parameters of repolarization dynamics correlated with SDNN in healthy subjects but not in dilated cardiomyopathy patients. Conclusions: The automatic assessment of repolarization parameters in 24-hour digital ECG recordings is feasible and differentiates dilated cardiomyopathy patients from healthy subjects. Patients with dilated cardiomyopathy have increased QT duration, QT dispersion, and increased variability of QT dispersion reflecting variations in T-wave morphology, the factors which might predispose them to the development of arrhythmic events. [source]

Spatial Properties of QT and the T-Wave Morphology

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2000
Kaspar Lund M.S.S.E.
Objective: To describe the relation between the QT interval and the T-wave morphology. Material and methods: Frank orthogonal leads X, Y, Z of one subject and resting 12-lead ECG of 40 subjects. QT was measured by the tangent method. The QT values are organized according to the anatomic orientation of the leads: I, -aVR, II, aVF, III, -aVL, -I, aVR, -II, -aVF, -III, aVL. and: V1, V2, V3, V4, V5, V6, -V1 -V2, -V3, -V4, -V5, -V6. The T-wave amplitudes and QT were categorized according to QT into four groups with increasing mean QT. Results: Kruskal-Wallis nonparametric test showed that the shortest and longest QT values are measured on the T wave with the smallest amplitudes (P < 0.001). Inspection of plots of QT and T waves reveals that the shortest and longest QT values are usually measured in leads with a small difference in orientation (neighbor leads). The mechanism behind these characteristics is mainly that the shortest and longest QT values are measured on T waves that are close to a lead orientation, whereas the T waves are flat or biphasic. We also observed an almost significant (P = 0.057) decrease in the T-wave amplitude with increasing dispersion. Conclusion: The relation between T-wave morphology and QT in the same cardiac plane is highly organized. The shortest and longest QT values are measured on the T wave with the smallest amplitudes (P < 0.001). [source]