Background P-wave dispersion (PWD) is a useful predictor of paroxysmal atrial fibrillation (AF).The effect of cardiac resynchronization therapy (CRT) on PWD and the prognostic implications of the improvement in PWD remain undefined.The aim of the study was to explore the clinical significance of the improvement of PWD after CRT.Methods Electrocardiographic studies were performed before and three months after CRT in 81 patients (57 men and 24 women; age (60.5±11.2) years) with standard CRT indication but no history of AF.A significant improvement of PWD (PWD responder) was defined as a relative decrease ≥20％ from baseline PWD.The primary endpoints were new-onset AF detected by electrocardiogram (ECG) or CRT.Results After (30.6±7.5) months of follow-up,PWD responders (n=-43) had a significantly lower incidence of AF than did PWD nonresponders,12％ vs.29％ (P ＜0.001).In Cox proportional hazard analysis,PWD responders was the only predictor of lower risk of new-onset AF (HR 0.33,95％ confidence interval 0.12-0.96,P=0.033).Conclusion Improvement of P-wave dispersion after CRT was associated with a lower incidence of AF,which may be related to the significant improvement in left ventricular systolic function and the reverse modeling of the left atrium.