title: Factors determining the magnitude of the pre-ejection leftward septal motion in left bundle branch block.
abstract: OBJECTIVE
  An abnormal large leftward septal motion prior to ejection is frequently observed in left bundle branch block (LBBB) patients. This motion has been proposed as a predictor of response to cardiac resynchronization therapy (CRT). Our goal was to investigate factors that influence its magnitude.
  
  
  RESULTS
  Left (LVP) and right ventricular (RVP) pressures and left ventricular (LV) volume were measured in eight canines. After induction of LBBB, LVP and, hence, the transmural septal pressure (PLV-RV= LVP-RVP) increased more slowly (P < 0.01) during the phase when septum moved leftwards. A biventricular finite-element LBBB simulation model confirmed that the magnitude of septal leftward motion depended on reduced rise of PLV-RV. The model showed that leftward septal motion was decreased with shorter activation delay, reduced global or right ventricular (RV) contractility, septal infarction, or when the septum was already displaced into the LV at end diastole by RV volume overload. Both experiments and simulations showed that pre-ejection septal hypercontraction occurs, in part, because the septum performs more of the work pushing blood towards the mitral valve leaflets to close them as the normal lateral wall contribution to this push is lost.
  
  
  CONCLUSIONS
  Left bundle branch block lowers afterload against pre-ejection septal contraction, expressed as slowed rise of PLV-RV, which is a main cause and determinant of the magnitude of leftward septal motion. The motion may be small or absent due to septal infarct, impaired global or RV contractility or RV volume overload, which should be kept in mind if this motion is to be used in evaluation of CRT response.
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, 0372 Oslo, Norway espen.remme@medisin.uio.no.|Centre for Cardiological Innovation, Oslo University Hospital, Oslo, Norway.|Department of Cardiology, Oslo University Hospital, Oslo, Norway.|KG Jebsen Cardiac Research Centre, University of Oslo, Oslo, Norway.
authors.forename: Espen W
authors.initials: EW
authors.lastname: Remme
authors.affiliation: Department of Imaging Sciences and Biomedical Engineering, King's College London, London, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Niederer
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, 0372 Oslo, Norway.|Department of Cardiology, Oslo University Hospital, Oslo, Norway.
authors.forename: Ola
authors.initials: O
authors.lastname: Gjesdal
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, 0372 Oslo, Norway.|Department of Cardiology, Oslo University Hospital, Oslo, Norway.
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Russell
authors.affiliation: Department of Imaging Sciences and Biomedical Engineering, King's College London, London, UK.
authors.forename: Eoin R
authors.initials: ER
authors.lastname: Hyde
authors.affiliation: Department of Imaging Sciences and Biomedical Engineering, King's College London, London, UK.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Smith
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, 0372 Oslo, Norway.|Centre for Cardiological Innovation, Oslo University Hospital, Oslo, Norway.|Department of Cardiology, Oslo University Hospital, Oslo, Norway.|KG Jebsen Cardiac Research Centre, University of Oslo, Oslo, Norway.
authors.forename: Otto A
authors.initials: OA
authors.lastname: Smiseth
mesh_terms: D000818:Animals; D002037:Bundle-Branch Block / Q000503:physiopathology*; D058406:Cardiac Resynchronization Therapy; D004195:Disease Models, Animal; D004285:Dogs; D004452:Echocardiography; D004562:Electrocardiography; D006352:Heart Ventricles / Q000503:physiopathology*; D008943:Mitral Valve / Q000503:physiopathology*; D008955:Models, Cardiovascular; D013318:Stroke Volume; D016277:Ventricular Function, Left; D054088:Ventricular Septum / Q000503:physiopathology*
keywords: Computer modelling; Dyssynchrony; Left bundle branch block; Septal beaking; Ventricular function