Background: The impact of cardiac resynchronization therapy (CRT) on dispersion of repolarization is controversial. This study aimed to determine whether CRT alters the QT interval and Tpeak-Tend interval (Tpeak-end) and whether such changes relate to the risk of developing a major arrhythmic event (MAE). Methods: Data from 67 patients (49 men; age 717 10 years) who underwent CRT device placement were analyzed retrospectively. Patients had NYHA class III or IV heart failure. Mean left

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... r ejection fraction was 25 7 9%. The electrocardiogram was recorded at baseline and during follow-up after implantation (3 days, 7 days, 1 month, and 2 months). Results: After 29-months of follow-up, 11 patients had experienced MAEs. QT interval and Tpeak-end did not change significantly immediately after CRT. However, 3 days after CRT, Tpeak-end in patients with MAE was significantly increased when compared with patients without MAE (po 0.05). We divided patients into 2 groups according to the change in Tpeak-end at 3 days (increased Tpeak-end group, n ¼27; decreased Tpeak-end group, n ¼40). The increased Tpeak-end group demonstrated a significant increase in MAEs (po 0.05). Conclusions: Increased Tpeak-end at 3 days after CRT was associated with a significant increase in MAEs. This could be a useful predictor of ventricular proarrhythmia.