Measurement, interpretation and clinical potential of QT dispersion

Abstract

QT dispersion was originally proposed to measure spatial dispersion of ventricular recovery times. Later, it was shown that QT dispersion does not directly reflect the dispersion of recovery times and that it results mainly from variations in the T loop morphology and the error of QT measurement. The reliability of both automatic and manual measurement of QT dispersion is low and significantly lower than that of the QT interval. The measurement error is of the order of the differences between different patient groups. The agreement between automatic and manual measurement is poor. There is little to choose between various QT dispersion indices, as well as between different lead systems for their measurement. Reported values of QT dispersion vary widely, e.g., normal values from 10 to 71 ms. Although QT dispersion is increased in cardiac patients compared with healthy subjects and prognostic value of QT dispersion has been reported, values are largely overlapping, both between healthy subjects and cardiac patients and between patients with and without adverse outcome. In reality, QT dispersion is a crude and approximate measure of abnormality of the complete course of repolarization. Probably only grossly abnormal values (e.g. > or =100 ms), outside the range of measurement error may potentially have practical value by pointing to a grossly abnormal repolarization. Efforts should be directed toward established as well as new methods for assessment and quantification of repolarization abnormalities, such as principal component analysis of the T wave, T loop descriptors, and T wave morphology and wavefront direction descriptors.

Multivariate associates of QT interval parameters in diabetic patients with arterial hypertension: importance of left ventricular mass and geometric patterns

“…If the increased QT interval dispersion in the subgroup of hypertensives with the concentric hypertrophy geometric pattern is related to a greater susceptibility to serious ventricular arrhythmias, then it could explain the greater cardiovascular mortality associated with this left ventricular geometry, 25 although this point remains controverse. 40 QT interval dispersion is no longer believed to represent spatial inhomogeneity of repolarization throughout the ventricular myocardium, 13 as originally proposed. 1 Several recent studies 41,42 have demonstrated that it probably indicates a global ventricular repolarization abnormality, reflected by an altered, more complex, spatial vectorcardiographic T-wave loop, as would be expected to occur in the hypertrophied myocardium with increased interstitial fibrosis.…”

“…Another aspect is that, as our patients were all type 2 diabetics as well, possibly our results could not be applied to the general population of hypertensives without diabetes mellitus. Finally, the well-recognized poor reproducibility and lack of standardization, particularly important in QT interval dispersion measurements, 13 do not need to be overemphasized.…”

“…Indeed, many reports had evaluated QT interval parameters as cardiovascular mortality predictors in several pathological conditions, such as long-QT syndromes, 2 coronary artery disease, 3,4 heart failure of different etiologies, 5,6 other cardiopathies, 7,8 diabetes mellitus 9,10 and in population-based studies, 11,12 with controverse results. 13 In patients with arterial hypertension, QT interval parameters have mainly been associated with left ventricular mass (LVM), [14][15][16][17][18] although a recent report suggested that they are no better than simple electrocardiographic voltage criteria for detection of left ventricular hypertrophy (LVH). 19 In diabetic patients, QT parameters have been correlated not only with the presence of cardiac dysautonomia, 20 coronary artery disease, 21 diabetic degenerative complications 22 and microalbuminuria, 23 but also with the presence of arterial hypertension and LVH.…”

Prolongation of the corrected QT interval in adult patients with anti‐Ro/SSA–positive connective tissue diseases

“…QTc dispersion was defined as the difference between the minimum and maximum heart rate-adjusted QT interval among the 12 EKG leads. QTc dispersion was considered abnormal if it was longer than 50 msec (19).…”

Light phase-restricted feeding slows basal heart rate to exaggerate the type-3 long QT syndrome phenotype in mice

“…Thus the slope of the linear relationship between the log-transformed QT and RR 100 defined the exponent to which the RR interval ratio should be raised to QTc. As a second method, we used an automated threshold approach so that we could compute an hourly average for the QT interval over several days (3,13,15,22). Briefly, the ECG traces recorded for each hour were aligned to the peak of R wave to generate an average trace, the Q point was defined as the base of the QRS complex (where the slope of the profile changed from negative to positive), and the T point was defined to where the ECG returned 75% of the way from the minima of the T wave to the isoelectric level.…”