title: Anatomic characterization of endocardial substrate for hemodynamically stable reentrant ventricular tachycardia: identification of endocardial conducting channels.
abstract: BACKGROUND
  Detailed anatomic characterization of endocardial substrate of ventricular tachycardia (VT) is limited.
  
  
  OBJECTIVE
  The purpose of this study was to determine the endocardial dimensions and local electrogram voltage characteristics of the reentrant circuit. VT-related conducting channels corresponding to zones of slow conduction may be identified.
  
  
  METHODS
  Electroanatomic mapping was performed in 26 patients with uniform VT. Entrainment mapping was performed in 53 VTs, of which 19 entrance, 37 isthmus, 48 exit, and 32 outer loop sites were identified. The color display of voltage maps was adjusted to identify conducting channels associated with VT circuits. A conducting channel was defined as a path of multiple orthodromically activated sites within the VT circuit that demonstrated an electrogram amplitude higher than that of surrounding areas as evidenced by voltage color differences.
  
  
  RESULTS
  Forty-seven (84%) of 56 entrance or isthmus sites were located within dense scar (<0.5 mV). Nearly all exits (92%) were located in abnormal endocardium (<1.5 mV), with more than half (54%) located in the border zone (0.5-1.5 mV). VT-related conducting channels was identified in 18 of 32 VTs with detailed mapping (average length 32 +/- 22 mm). The voltage threshold in the conducting channels ranges from 0.1 to 0.7 mV (mean 0.33 +/- 0.15 mV).
  
  
  CONCLUSIONS
  (1) Most entrance and isthmus sites of hemodynamically stable VT are located in dense scar, whereas exits are located in the border zone. (2) VT-related conducting channels may be identified by careful voltage threshold adjustment. These findings have important implications regarding strategies for substrate-based VT ablation.
authors.affiliation: Cardiovascular Medicine Division, Stanford University, Stanford, California 94305-5233, USA. hhsia@cvmed.stanford.edu
authors.forename: Henry H
authors.initials: HH
authors.lastname: Hsia
authors.forename: David
authors.initials: D
authors.lastname: Lin
authors.forename: William H
authors.initials: WH
authors.lastname: Sauer
authors.forename: David J
authors.initials: DJ
authors.lastname: Callans
authors.forename: Francis E
authors.initials: FE
authors.lastname: Marchlinski
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018780:Body Surface Potential Mapping; D017115:Catheter Ablation; D017147:Defibrillators, Implantable; D022062:Electrophysiologic Techniques, Cardiac; D004699:Endocardium / Q000473:pathology* / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D006329:Heart Conduction System / Q000473:pathology* / Q000503:physiopathology* / Q000601:surgery; D006339:Heart Rate; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D012107:Research Design; D012815:Signal Processing, Computer-Assisted; D013318:Stroke Volume; D017180:Tachycardia, Ventricular / Q000473:pathology* / Q000503:physiopathology* / Q000628:therapy; D016896:Treatment Outcome