title: Effects of biventricular pacing and scar size in a computational model of the failing heart with left bundle branch block.
abstract: OBJECTIVE
  To study the impact of biventricular pacing (BiV) and scar size on left ventricular (LV) regional and global function using a detailed finite element model of three-dimensional electromechanics in the failing canine heart.
  
  
  BACKGROUND
  Cardiac resynchronization therapy (CRT) clinical trials have demonstrated that up to 30% of patients may be classified as non-responders. The presence of a scar appears to contribute to those that do not respond to CRT. A recent study in patients with myocardial scar showed that LV dyssynchrony was the sole independent predictor of reverse remodeling, and not scar location or size.
  
  
  METHODS
  Two activation sequences were simulated: left bundle branch block (LBBB) and acute simultaneous BiV (with leads in the left and right ventricle) in hearts with chronic scars of various sizes. The dependence of regional function (mean fiber ejection strain, variance of fiber isovolumic strain and fraction of tissue stretched during ejection) and global function (left ventricular dP/dt(max), ejection fraction, stroke work) on scar size and pacing protocol was tested.
  
  
  RESULTS
  Global function and regional function averaged over the whole LV during LBBB and BiV decreased as a function of scar size. In the non-scarred regions, however, regional function was largely independent of scar size for a fixed pacing site.
  
  
  CONCLUSIONS
  The model results suggest that uniformity of mechanical contraction in non-scarred regions in the failing heart during biventricular pacing is independent of scar size for a fixed pacing site.
authors.affiliation: Department of Bioengineering, The Whitaker Institute for Biomedical Engineering, University of California, San Diego, La Jolla, CA 92093-0412, USA. roy@bioeng.ucsd.edu
authors.forename: Roy C P
authors.initials: RC
authors.lastname: Kerckhoffs
authors.forename: Andrew D
authors.initials: AD
authors.lastname: McCulloch
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Omens
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Mulligan
mesh_terms: D000818:Animals; D002037:Bundle-Branch Block / Q000150:complications / Q000503:physiopathology* / Q000517:prevention & control*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D002921:Cicatrix / Q000503:physiopathology*; D003198:Computer Simulation; D004285:Dogs; D055119:Elastic Modulus; D054459:Elasticity Imaging Techniques / Q000379:methods; D006333:Heart Failure / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control*; D006801:Humans; D008955:Models, Cardiovascular; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control