Biventricular pacing and transmural dispersion of the repolarization.

In 2003, Medina-Ravell et al. 1 published a study that suggested that biventricular pacing could be arrhythmogenic in a subset of patients because of the reversal of the normal endocardial-to-epicardial activation sequence by left-ventricular epicardial pacing. As epicardial action potentials are briefer than endocardial action potentials, transmural dispersion of the repolarization (TDR) is larger with an epicardial-to-endocardial activation sequence than with an endocardial-to-epicardial activation sequence. Medina-Ravell et al. demonstrated this in an isolated arterially perfused rabbit left-ventricular wedge preparation. They also showed, in a quasi-ECG derived from this preparation, that TDR was faithfully reflected by the T peak-end interval and that T peak-end was larger with epicardial pacing than with endocardial pacing of the preparation. Their conclusion that a similar effect occurs in intact hearts in humans was substantiated by the observation that in 29 heart failure patients with a biventricu-lar pacemaker, the T peak-end interval was larger during left-ventricular epicardial pacing than during right-ventricular endo-cardial pacing. However, no T peak-end values with sinus rhythm and with biventricular pacing were reported, due to measurement difficulties. With interest, we read the recently published study by Santangelo et al. 2 They describe how left-ventricular, right-ventricular, and bi-ventricular pacing in heart failure patients influences a number of ECG indexes of ventricular dispersion of the repolarization, among others the T peak-end interval. Compared with sinus rhythm, the T peak-end interval increased with left-ventricular epicardial and with right-ventricular endocardial pacing, but it decreased with bi-ventricular pacing. The observations by Santangelo et al. confirm nicely the findings of our recent study 3 in which we evaluated, in a similar way, the effect of left-, right-, and bi-ventricular pacing on a set of ECG indexes thought to represent ventricular dispersion of repolari-zation, among which was T peak-end. We also found the briefest T peak-end interval to occur with biventricular pacing. What should be the conclusion from these observations? Medina-Ravell et al. 1 conclude that, in their patients, epicardial left-ventricular pacing increases TDR with respect to right-ventricular pacing, because the T peak-end interval is the largest with left-ventricular pacing. Santangelo et al. 2 conclude, among others, on the basis of the behaviour of the T peak-end interval, that left-ventricular and right-ventricular pacing increase TDR with respect to sinus rhythm, whereas bi-ventricular pacing decreases TDR. The implications of such a conclusion would be that any single-lead ventricular pacing, be it sole endocardial right-ventricular or sole epicardial left-ventricular pacing, would …