Introduction The aim of this study was to investigate the influence of different VV intervals on QRS duration of surface ECG after cardiac resynchronisation therapy (CRT).

Methods 54 patients after CRT treatment due to congestive heart failure (CHF) in our hospital were enrolled in this study, of which 43 cases with the QRS duration of surface ECG >120 ms and 11 cases with QRS duration ≤120 ms (Tissue doppler ultrasound showed the existence of ventricular asynchrony), all patients were appropriate for CRT or CRT-D implantation with type I or IIa indication. After CRT implantation, the VV durations were programed by the pacemaker programme at 9 different settings: simultaneous left and right ventricle pacing, left ventricle pre-excitation (left ventricle+20, 40, 60 and 80 ms, respectively), and right ventricle pre-excitation (right ventricle+20, 40, 60 and 80 ms, respectively). During these VV intervals, the aortic velocity time integral (VTI) was measured by echocardiography, and we defined the VV intervals with the highest VTI as the best VV interval, QRS duration of surface ECG was recorded at the same time.

Results There is no significant difference of QRS durations among different VV intervals. In the simultaneous pacing of LV and RV model, the best VV interval was 12.96% of all the 54 patients, it was 37.02% in left ventricle pre-excitation and 49.98% in right ventricle pre-excitation. This was suggested that sequential pacing of the two ventricles was superior to the synchronously pacing. There was no significant correlation between the best VV interval and the width of QRS wave (r=0.205, p=0.136), and the width of QRS wave were the smallest in 9 patients (9/54, 16%) in the best VV interval, but that of the other 45 patients were not the smallest, so it was inaccurate for assessing the best VV interval merely by the width of QRS wave, and we'd better to optimise VV intervals with the help of echocardiography.

Conclusions There were no significant changes of the QRS durations during different VV intervals after CRT treatment. The sequential pacing of the two ventricles could bring 87% patients better haemodynamic effects. There was no significant correlation between the best VV interval and the width of QRS wave, and the width of QRS duration of most patients in the best VV interval was not the smallest. The effect of CRT could be improved more by optimisation of the VV interval individually.