A step forward parameter for the effects of transcatheter aortic valve implantation: transmural dispersion of repolarization

To the Editor We read the article " Effect of transcatheter aortic valve implantation on QT dispersion in patients with aortic stenosis " by Erkan, et al. [1] with great interest. In this study, they investigated the effect of transcatheter aortic valve implanta-tion (TAVI) on QT dispersion (QTd) in patients with symptomatic severe aortic stenosis. They reported that left ventricular mass index (LVMI) and associated QTd were both reduced by the TAVI procedure. Given the correlation of QTd with the incidence of ventricular tachyarrhythmias and sudden death, it was concluded that the TAVI procedure might have potential beneficial effects on reducing such arrhythmias beyond relieving symptoms of these patients. As mentioned by authors, it has long been known that QTd reflects inhomogeneity of ventricular repolarization which serves as a prognostic tool in the detection of future ventricular tachyarrhythmias and sudden death. [2–4] This electrical instability can be measured in the electrophysi-ologic laboratory via monophasic action potential mapping method. [5] Meanwhile, QTd is the most frequently used non-invasive method to reveal electrical regional heterogen-ity of the myocardium. However, in the literature, there are varying results due to the technical limitations of QT interval (QTI) measurement. [6] The reproducibility of QTI measurements is low both in manual and automatic measurement techniques. [5,6] Moreover, in manual measurements, inter-and intra-observer variability of QTd is very high. [6] In this study, the measurements have been performed by two independent cardiologists manually, without transferring the data to the digital platform. Additionally, standard 12-lead ECG recordings were done with a paper speed of 25 mm/ms. In order to obtain more accurate data, the measurements were recommended to be performed in digital platform. Also, the accuracy of the measurements could be increased by recording the ECGs with the paper speed of 50 mm/ms and amplitude of 20 mm/mV. Determination of the end of the T wave is one of the technical challenges of the QTI measurements. [7] Tangential, differential threshold and visual methods may be used to determine the end of the T-wave. [7] Despite all efforts, the end of the T-wave can't be determined in some leads and the number of measurable leads in the standard ECG have been shown to influence the range of QTI durations. As the number of the leads in which QTI can't be measured increases, accuracy of the QTd decreases. In order to overcome this limitation, different methods (standard deviation of the …