Electrical and mechanical components of dyssynchrony in heart failure patients with normal QRS duration and left bundle-branch block: impact of left and biventricular pacing

Background— Resynchronization pacing is an effective symptomatic treatment for heart failure patients with prolongation of the QRS duration (QRSd). Dyssynchronous contraction of the left ventricle is also observed with normal QRSd. We set out to determine how electrical activation of the left ventricular (LV) free wall differed between patients with left bundle-branch block (LBBB) and normal QRSd and if synchrony improved during pacing in patients with normal QRSd. Methods and Results— Twenty-two patients were implanted with resynchronization pacemakers, 13 with LBBB (mean QRS, 171 ms) and 9 with normal QRSd