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To the Editor:The recent article by Medina-Ravell et al1 addresses a potentially harmful effect of cardiac resynchronization therapy on ventricular repolarization. The authors found that single epicardial and biventricular pacing in patients with congestive heart failure increased the QT interval and the transmural dispersion of repolarization (interval from the peak to the end of the T wave, Tpeak-end). However, probably as a result of the ECG signal quality (the authors did not provide any details about ECG registration and analysis), Tpeak-end was not estimated at baseline and during biventricular pacing. We think that this information is of great importance.In a preliminary study of our cohort of patients with congestive heart failure, we assessed ventricular repolarization with a high-resolution 65-lead surface ECG.2 Using signal-processing techniques, such as the total 65-lead root mean square curves,3,4 even low-amplitude signals (eg, onset and offset of the P wave4) can be precisely determined. With respect to the QT duration, our findings are in accordance with those of Medina-Ravell et al1; any pacing increases QTc. However, with respect to the Tpeak-end interval, we observed a significant decrease after biventricular pacing, as compared with baseline (baseline 100%, biventricular pacing 86±17% [ P <0.05], right ventricular pacing 115±19%, left ventricular pacing 105±13%).We fully agree that the epicardial-endocardial spread of activation during biventricular pacing may be a potential risk in a subset …

Effect of Epicardial or Biventricular Pacing to Prolong QT Interval and Increase Transmural Dispersion of Repolarization