 Study protocol: Eligible patients who successfully received AV junction ablation and biventricular pacing are randomised to a comparison between a strategy of RV apical pacing with delayed CRT based on clinical indications with a strategy of early optimal CRT based on an echocardiographic stratification. The optimal CRT is defined as the shortest intra-LV delay obtained with tissue-doppler echocardiography among RV, LV and BiV optimised VV interval. 