Efficiency of quantification of cardiac electrical heterogeneity: via QT dispersion, transmural dispersion, or both

We read with great interest the article entitled 'A 24-hour ambulatory ECG monitoring in assessment of QT interval duration and dispersion in rowers with physiological myocardial hypertrophy' by Lutfullin IY et al. [1] published in the Biology of Sport journal. In the study, the effects of myocardial hypertrophy on cardiac repolarization parameters were investigated in endurance athletes using both 12-lead ECG and 24-hour ECG monitoring. In the conclusion of the article, it was stated that myocardial hypertrophy observed in athletes does not lead to an increase in corrected QT interval (QTIc) duration, QT dispersion (QTd) or corrected QT dispersion (QTcd). QT interval (QTI) duration was found to be increased in athletes with myo-cardial hypertrophy, but it was attributed to the increased vagal tone of the endurance athletes. Regular intensive training may lead to cardiac hypertrophy known as athlete's heart. Athlete's heart is associated with alterations in cardiac structure and electrophysiological properties [2]. As expected , heterogeneity in the duration of the ventricular repolarization phase leading to arrhythmias may also be seen in athlete's heart. As used in this study, QTd is the most frequently used parameter to detect ventricular inhomogeneity. However, as also mentioned in this article, varying results have been reported in the studies related to QTI [3]. This may be due to the technical limitations in the QTI measurement. QTI can be measured either manually or automatically. It is well known that the reproducibility of QTI measurements is low in both manual and automatic measurements [4] Additionally , in manual measurements, inter-and intra-observer variability of QTd is very high [3]. Quantifying the inhomogeneity of the myocardium, transmural dispersion of repolarization (TDR) has also been used since the beginning of the 2000s in addition to QTd [5] There are three cell types having different electrophysiological properties in the ventricu-lar myocardium: the endocardial, epicardial and midmyocardial M cells. Repolarization of these three different cell types creates the T wave of the ECG. The epicardial cells are repolarised early, which coincides with the peak of the T wave, but repolarization of M cells is the latest and coincides with the end of the T wave. Therefore, the time between the peak and end of the T wave is called the Tp-e interval, as an index of TDR. The ratio of the TDR to the total duration of repolarization (Tp-e/QT ratio) has also been used as an ECG index of ventricular arrhythmogenesis …