Paired data were collected on 22 patients ( aged 67.5 8.3 years , 16 male ) with refractory heart failure , NYHA class III/IV symptoms , sinus rhythm , LBBB and a broad QRS complex > 120 ms. All patients underwent implantation of a biventricular pacemaker and were randomised to eight weeks of factory pacing mode ( Mode 1 ) or echocardiographically-guided pacing mode ( Mode 2 ) , followed by eight weeks in the alternate mode , in a randomised blinded crossover design .
