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QT Interval Dispersion (qt + interval_dispersion)

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Medical Sciences	100%

Selected Abstracts

The Relationship Between Left Ventricular Shape and QT Interval Dispersion

ECHOCARDIOGRAPHY, Issue 8 2002
F.A.C.C., Kishore J. Harjai M.D.
Left ventricular geometry is suspected to affect heterogeneity of myocardial repolarization; therefore, it is plausible but unproven that increased sphericity of the left ventricle is associated with greater QT interval dispersion. In 60 patients with dilated cardiomyopathy with left ventricular ejection fraction , 30%, we found that spherical distortion of the left ventricle was associated with increased QT dispersion, implying increased heterogeneity of myocardial repolarization. [source]

QT Interval Dispersion and Cardiac Sympathovagal Balance Shift in Rats With Acute Ethanol Withdrawal

ALCOHOLISM, Issue 2 2010
Seiko Shirafuji
Background:, Dysregulation of autonomic nervous system function and impaired homogeneity of myocardial repolarization are 2 important mechanisms for the genesis of ventricular arrhythmias in nonalcoholic subjects. Our previous study suggested that acute ethanol withdrawal promoted the shift of cardiac sympathovagal balance toward sympathetic predominance and reduced the vagal tone, which were related to a higher incidence of ventricular arrhythmia and related death. However, the homogeneity of myocardial repolarization and its relation with the cardiac sympathovagal balance are unknown, especially in alcoholic subjects. The aim of the present study was to clarify these points. Methods:, Male Wistar rats were treated with a continuous ethanol liquid diet for 49 days, and then subjected to 1-day withdrawal and 1-day withdrawal with 7-day carvedilol (can block the sympathetic nervous system completely via ,1, ,2, and , adrenergic receptors) pretreatment. The cardiac sympathovagal balance and homogeneity of myocardial repolarization were evaluated based on the heart rate variability (HRV) and QT interval dispersion (QTd: dynamic changes in QT interval duration). Results:, The increase in QTd was observed only in rats at 1-day withdrawal, but not in nonalcoholic, continuous ethanol intake, and 1-day withdrawal with 7-day carvedilol pretreatment rats. At 1-day withdrawal, the low-frequency power/high-frequency power (LF/HF) ratio in HRV was elevated and correlated with the QTd. The increased QTd and elevated LF/HF ratio were normalized by the 7-day carvedilol pretreatment in rats at 1-day ethanol withdrawal. Conclusions:, In rats with an abrupt termination of the chronic continuous ethanol intake, the homogeneity of myocardial repolarization impaired and correlated with the cardiac sympathovagal balance. Carvedilol pretreatment is associated with a reduction in both the QTd and LF/HF ratio, raising the possibility that the cardiac sympathovagal balance shift may be responsible for the impaired homogeneity of myocardial repolarization, and that ,-blocker pretreatment may decrease the mortality risk during alcoholic withdrawal. [source]

The Relationship Between Left Ventricular Shape and QT Interval Dispersion

QT Interval Dispersion and Cardiac Sympathovagal Balance Shift in Rats With Acute Ethanol Withdrawal

Dispersion of QT Intervals: A Measure of Dispersion of Repolarization or Simply a Projection Effect?

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 9 2000
DIEGO DI BERNARDO
QT interval dispersion may provide little information about repolarization dispersion. Some clinical measurements demonstrate an association between high QT interval dispersion and high morbidity and mortality, but what is being measured is not clear. This study was designed to help resolve this dilemma. We compared the association between different clinical measures of QT interval dispersion and the ECG lead amplitudes derived from a heart vector model of repolarization with no repolarization dispersion whatsoever. We compared our clinical QT interval dispersion data obtained from 25 subjects without cardiac disease with similar data from published studies, and correlated these QT dispersion results with the distribution of lead amplitudes derived from the projection of the heart vector onto the body surface during repolarization. Published results were available for mean relative QT intervals and mean differences from the maximum QT interval. The leads were derived from Uijen and Dower lead vector data. Using the Uijen lead vector data, the correlation between measurements of dispersion and derived lead amplitudes ranged from 0.78 to 0.99 for limb leads, and using the Dower values ranged from 0.81 to 0.94 for the precordial leads. These results show a clear association between the measured QT interval dispersion and the variation in ECG lead amplitudes derived from a simple heart vector model of repolarization with no regional information. Therefore, measured QT dispersion is related mostly to a projection effect and is not a true measure of repolarization dispersion. Our existing interpretation of QT dispersion must be reexamined, and other measurements that provide true repolarization dispersion data investigated. [source]

Circadian Variation in QT Dispersion Determined from a 12-Lead Holter Recording: A Methodological Study of an Age- and Sex-Stratified Group of Healthy Subjects

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2007
Stig Hansen M.D.
Background: QT dispersion is considered to reflect inhomogeneity of myocardial repolarization. Method: The circadian variation of QT interval dispersion was examined in 95 healthy subjects using 24-hour Holter monitoring. Three different methods of lead selection were applied: all 12 leads (QTdisp 12), only precordial leads (QTdisp 6), and the pair of leads selected at 3 a.m. in which the longest and shortest QT intervals were found in each individual subject (QTdisp 2). Results: A preliminary methodological study including measurements from every minute in 10 subjects revealed no significant circadian variation using mean values of QTdisp 12, QTdisp 6, or QTdisp 2 obtained every hour, every 2, or every 4 hours, except in QTdisp 6, which demonstrated a significant circadian variation (P < 0.01) in 1-hour measurements. Analysis of all 95 subjects using measurements obtained every 4 hours revealed a significant circadian variation in QTdisp 12 and QTdisp 6 (P < 0.0001), whereas no circadian variation was seen in QTdisp 2. A subdivision into 10-year age groups revealed that subjects at age >50 years had a significant circadian variation in QTdisp 12 and QTdisp 6, but not in QTdisp 2. Only in males a significant circadian variation was seen in QTdisp 12 (P < 0.0001), whereas QTdisp 6 demonstrated a circadian variation both in females (P < 0.001) and in males (P < 0.0001). Conclusions: Selection of leads is of crucial importance for repetitive measurements of QT dispersion. Circadian variation was detected in subjects over 50 years of age, when all 12 or only the 6 precordial leads were taken into account. [source]

QT Dispersion and Mortality in the Elderly

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2001
Juha S. Perkiömäki M.D.
Background: The prognostic value of QT interval dispersion measured from a standard 12-lead electrocardiogram (ECG) in the general population is not well established. The purpose of the present study was primarily to assess the value of QT interval dispersion obtained from 12-lead ECG in the prediction of total, cardiac, stroke, and cancer mortality in the elderly. Methods: A random population sample of community-living elderly people (n = 330, age ,; 65 years, mean 74 ±; 6 years) underwent a comprehensive clinical evaluation, laboratory tests, and 12-lead ECG recordings. Results: By the end of the 10-year follow-up, 180 subjects (55%) had died and 150 (45%) were still alive. Heart rate corrected QT (QTc) dispersion had been longer in those who had died than in the survivors (75 ±; 32 ms vs 63 ±; 35 ms, P = 0.01). After adjustment for age and sex in the Cox proportional hazards model, prolonged QTc dispersion (,; 70 msec) predicted all-cause mortality (relative risk [RR] 1.38, 95% confidence interval [Cl] 1.02,1.86) and particularly stroke mortality (RR 2.7, 95% Cl 1.29,5.73), but not cardiac (RR 1.38, 95% Cl 0.87,2.18) or cancer (RR 1.51, 95% Cl 0.91,2.50) mortality. After adjustment for age, sex, body mass index, blood pressure, blood glucose and cholesterol concentrations, functional class, history of cerebrovascular disease, diabetes, smoking, previous myocardial infarction, angina pectoris, congestive heart failure, medication, left ventricular hypertrophy on ECG, presence of atrial fibrillation and R-R interval, increased QTc dispersion still predicted stroke mortality (RR 3.21, 95% Cl 1.09,9.47), but not total mortality or mortality from other causes. The combination of increased QTc dispersion and left ventricular hypertrophy on ECG was a powerful independent predictor of stroke mortality in the present elderly population (RR 16.52, 95% Cl 3.37,80.89). QTcmin (the shortest QTc interval among the 12 leads of ECG) independently predicted total mortality (RR 1.0082, 95% Cl 1.0028,1.0136, P = 0.003), cardiac mortality (RR 1.0191, 95% Cl 1.0102,1.0281, P < 0.0001) and cancer mortality (RR 1.0162, 95% Cl 1.0049,1.0277, P = 0.005). Conclusions: Increased QTc dispersion yields independent information on the risk of dying from stroke among the elderly and its component, QTcmin, from the other causes of death. A.N.E. 2001; 6(3):183,192 [source]

Electrocardiographic Quantitation of Heterogeneity of Ventricular Repolarization

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2000
Peter M. Okin M.D.
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 (QTod) and to T-wave peak (QTpd) dispersion and the PCA ratio to T-wave area and amplitude, heart rate, QRS axis and duration, and the QTo interval were examined in 163 asymptomatic subjects with normal resting ECGs and normal left ventricular mass and function. QTod and QTpd were measured by computer from digitized ECGs as the difference between the maximum and minimum QTo and QTp 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 < 0.001), but there was no significant correlation of the sum of T-wave area with QTod (R = 0.11, P = NS) or QTpd (R=0.09, P = NS). There were only modest correlations between QTod and QTpd (R = 0.45) and between the PCA ratio and QTod (R = 0.29) and QTpd (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), QTod correlated only with the maximum QTo0 interval (R = 0.39, P < 0.001), and QTpd 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 QTod was significantly greater than dispersion measured by QTod (23.5 ± 11.5 ms vs 18.3 ± 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 wo 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 reflection of the heterogeneity of ventricular repolarizat on. A.N.E. 2000;5(1):79,87 [source]