title: Characterization of the infarct substrate and ventricular tachycardia circuits with noncontact unipolar mapping in a porcine model of myocardial infarction.
abstract: BACKGROUND
  Conventional mapping of ventricular tachycardia (VT) after myocardial infarction is limited in patients with hemodynamically untolerated or noninducible VT.
  
  
  OBJECTIVE
  The purpose of this study was to develop a unique strategy using noncontact unipolar mapping to define infarct substrate and VT circuits.
  
  
  METHODS
  Dynamic substrate mapping (DSM) was performed in seven pigs with healed anterior myocardial infarction. This technique defined substrate as the intersection of low-voltage areas identified in sinus rhythm and during pacing around the infarct. Pacing was also performed within the substrate to determine exit sites.
  
  
  RESULTS
  Anteroapical transmural scar was identified in all animals. A mean of three pacing sites was used for substrate definition. The mean area (+/- SD) was 18.4 +/- 8.8 cm2 by DSM and 15.4 +/- 6.9 cm2 by pathology (P >.5). A mean of 4.5 sites was paced within substrate. Ten of 18 paced wavefronts exited substrate adjacent to the pacing area, seven exited at distant areas, and one had two exits. VT was induced in five animals (1.6 morphologies per animal). Except for one VT, circuit exit sites were identified at substrate borders on the endocardium. VT exit sites were at (n = 6) or near (n = 3) a pacing exit site. Electrogram voltages differed significantly between substrate, border, and nonsubstrate areas in infarcted animals and in comparison with control animals. No substrate was identified in two control animals.
  
  
  CONCLUSIONS
  DSM is a reliable method for infarct substrate localization in this model. Pacing within substrate can predict VT exit sites and may prove useful for ablation of unmappable VT after myocardial infarction.
authors.affiliation: Division of Cardiovascular Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Jason T
authors.initials: JT
authors.lastname: Jacobson
authors.forename: Valtino X
authors.initials: VX
authors.lastname: Afonso
authors.forename: Gregory
authors.initials: G
authors.lastname: Eisenman
authors.forename: John R
authors.initials: JR
authors.lastname: Schultz
authors.forename: Sorin
authors.initials: S
authors.lastname: Lazar
authors.forename: John J
authors.initials: JJ
authors.lastname: Michele
authors.forename: Mark E
authors.initials: ME
authors.lastname: Josephson
authors.forename: David J
authors.initials: DJ
authors.lastname: Callans
mesh_terms: D000818:Animals; D002304:Cardiac Pacing, Artificial; D002921:Cicatrix / Q000503:physiopathology*; D004195:Disease Models, Animal; D022062:Electrophysiologic Techniques, Cardiac; D006329:Heart Conduction System / Q000503:physiopathology; D009203:Myocardial Infarction / Q000503:physiopathology*; D018709:Statistics, Nonparametric; D013552:Swine; D017180:Tachycardia, Ventricular / Q000503:physiopathology*