Repercussions of cardiac resynchronization therapy on the ventricular repolarization of heart failure patients as assessed by body surface potential mapping.

Objective: Cardiac resynchronization therapy (CRT) is an adjunct treatment for heart failure (HF) which associates with left bundle-branch block (LBBB) and is refractory to medical therapy. However, nearly 1/3 of the patients still do not respond, the reasons for which have yet to be determined. Additionally, experimental studies proved that epicardial left ventricle (LV) pacing yields reversed electrical activation sequence, increasing QT interval duration and dispersion of the ventricular repolarization, and leaving patients at greater risk for ventricular arrhythmias.

Methods: In this study, a series of 60 patients (61.7% male, mean age 59.2+/-11.54 years) in NYHA functional class III-IV heart failure and LBBB, who received CRT through implantation of atrial-biventricular pacemakers, were assessed by 87-lead body surface potential mapping (BSPM). The BSPM, noninvasive technique with semi-automatic readings, allowed analysis of variables associated with the cardiac ventricular repolarization QT intervals, maximal, minimum and mean Tpeak-end, and QT dispersion (QTmax - min), in addition to transmural dispersion of repolarization (Tpeak-end max - Tpeak-end min), in two different moments: baseline rhythm and during atrial-biventricular pacing.

Results: QT dispersion showed a significant 19.6% reduction (p=0.0009) under CRT, as compared with baseline measurements (85.58+/-26.63 msec vs. 68.83+/-25.16 msec). The transmural dispersion of repolarization (Tpeak-end max - Tpeak-end min) showed smaller statistical significance (p=0.0343); however, its values were similarly decreased (55.50+/-15.45 msec vs 49.41+/-14.11 msec) during CRT.

Conclusion: These results may corroborate findings from major randomized clinical trials. We consider that the electrocardiographic variables obtained with the use of the BSPM, namely, the QT and Tpeak-end intervals, are appropriate for analysis and study of the effects of cardiac resynchronization therapy on the improved electrical dispersion as characterizing the improvement of homogeneity of cardiac ventricular repolarization.