The recent article by Medina-Ravell et al 1 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, T peak-end ). However, probably as a result of the ECG signal quality (the authors did not provide any details about ECG registration and analysis), T peak-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 wave 4 ) can be precisely determined. With respect to the QT duration, our findings are in accordance with those of Medina-Ravell et al 1 ; any pacing increases QTc. However, with respect to the T peak-end interval, we observed a significant decrease after biventricular pacing, as compared with baseline (baseline 100%, biventricular pacing 86Ϯ17% [PϽ0.05], right ventricular pacing 115Ϯ19%, left ventricular pacing 105Ϯ13%).We fully agree that the epicardial-endocardial spread of activation during biventricular pacing may be a potential risk in a subset of these quite sick patients and that risk stratification is important. However, with respect to the presented QRST analysis, further refinements in methodology in addition to the correlation with the excellent animal experiment, especially assessment of T peak-end 5 at baseline and during biventricular pacing, may be warranted.
Franz
To the Editor:In their recent article, Medina-Ravell et al 1 investigated changes in QT interval and transmural dispersion of repolarization in surface ECG in patients after implantation of a resynchronization device under right, left, and biventricular stimulation.Pacing-site-dependent changes in a rabbit left ventricular wedge preparation were also examined.On the basis of individual observations and supported by a surface ECG (Figure 4 of their article 1 ), the authors suggest that epicardial pacing might lead to the development of torsade des pointes (TdP) in a subset of patients.Critical review of Figure 4 in their article 1 identifies a potentially different mechanism of TdP induction. None of the premature ventricular beats shown fulfill the definition of an R-on-T phenomenon according to the literature. [2][3][4] Because of an unexplainable left ventricular asynchronous stimulation (VOO mode), left ventricular premature beats (almost the same morphology as left ventricular-paced beats) are upcoming, and the stimulus is delivered several times into the T wave (beats 46, 48, 50, and 54) before catching the vulnerable period of the premature ventricular beat following beat ...
