title: 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.
abstract: 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.
  
  
  RESULTS
  Twenty-two patients were implanted with resynchronization pacemakers, 13 with LBBB (mean QRS, 171 ms) and 9 with normal QRSd <120 ms (mean, 100 ms). LV lead electrograms and surface ECGs in sinus rhythm (unpaced) were recorded. Conventional and tissue Doppler echocardiography were performed without pacing, with LV and biventricular pacing at optimal atrioventricular delay. Lead electrograms from the LV free wall were later in the LBBB patients in absolute terms (155 ms [SD 23] versus 65.5 ms [SD 25]; P=0.05) and also relative to the surface QRS (90.5% [SD 8] versus 65.5% [SD 24]). Improved synchrony of the left and right ventricles (interventricular synchrony) and of the LV myocardial segments (intraventricular synchrony) was observed for patients with LBBB and normal QRSd. Baseline LV synchrony correlated with timing of LV free-wall electrical activation. Improved intraventricular synchrony during pacing also correlated with LV free-wall electrical activation time.
  
  
  CONCLUSIONS
  Resynchronization of systole can be achieved for patients with normal QRSd and LBBB during biventricular and LV pacing. The timing of LV free-wall electrical activation correlated with the improvement in synchrony.
authors.affiliation: Wales Heart Research Institute, Heath Park, Cardiff, UK.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Turner
authors.forename: Rob A
authors.initials: RA
authors.lastname: Bleasdale
authors.forename: Dragos
authors.initials: D
authors.lastname: Vinereanu
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Mumford
authors.forename: Vince
authors.initials: V
authors.lastname: Paul
authors.forename: Alan G
authors.initials: AG
authors.lastname: Fraser
authors.forename: Michael P
authors.initials: MP
authors.lastname: Frenneaux
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002037:Bundle-Branch Block / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000628:therapy*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D015150:Echocardiography, Doppler; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006333:Heart Failure / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000628:therapy*; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D009200:Myocardial Contraction; D013599:Systole; D013997:Time Factors; D016277:Ventricular Function, Left; D016278:Ventricular Function, Right