title: Electrically unexcitable scar mapping based on pacing threshold for identification of the reentry circuit isthmus: feasibility for guiding ventricular tachycardia ablation.
abstract: BACKGROUND
  We hypothesized that delineating electrically unexcitable scar (EUS) within low-voltage infarct regions will locate reentry circuit isthmuses by defining their borders. The pacing threshold and electrogram amplitude that best determines EUS is unknown.
  
  
  RESULTS
  The change in dimension of the virtual electrode was estimated in 11 patients and observed to increase by 4.4+/-2.5 mm as stimulus strength increases from threshold (2.9+/-1.8 mA) to 10 mA. EUS was defined as a threshold >10 mA. In 14 consecutive patients, mapping and ablation of ventricular tachycardia (VT) were performed using an electroanatomic mapping system. During sinus rhythm, unipolar pacing was performed at sites with bipolar electrogram amplitude <1.5 mV. EUS regions were marked on the maps. Reentry circuit isthmuses were identified by entrainment mapping or pace mapping, and ablation was performed. EUS was identified in the infarct in all 14 patients (11.8+/-13.9 cm2). All 20 VT circuit isthmuses identified were adjacent to EUS. Although electrogram amplitude correlated with pacing threshold (r=0.64, P<0.0001), many isthmuses had very low-amplitude electrograms, and EUS could not be identified from electrogram amplitude alone. RF ablation lines connecting selected EUS regions abolished all inducible VTs in 10 patients (71%); spontaneous VT was markedly reduced during follow-up (from 142+/-360 to 0.9+/-2.0 episodes per month, P=0.002).
  
  
  CONCLUSIONS
  This new method of identifying EUS provides complimentary information to the electrogram amplitude in delineating potential reentry circuit paths, potentially facilitating ablation during sinus rhythm.
authors.affiliation: Cardiovascular Division, Department of Internal Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Mass, USA. ksoejima@partners.org
authors.forename: Kyoko
authors.initials: K
authors.lastname: Soejima
authors.forename: William G
authors.initials: WG
authors.lastname: Stevenson
authors.forename: William H
authors.initials: WH
authors.lastname: Maisel
authors.forename: John L
authors.initials: JL
authors.lastname: Sapp
authors.forename: Laurence M
authors.initials: LM
authors.lastname: Epstein
mesh_terms: D000368:Aged; D018780:Body Surface Potential Mapping / Q000379:methods*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D017115:Catheter Ablation / Q000379:methods; D002921:Cicatrix / Q000503:physiopathology*; D017147:Defibrillators, Implantable; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D005500:Follow-Up Studies; D006329:Heart Conduction System / Q000473:pathology / Q000503:physiopathology; D006339:Heart Rate; D006352:Heart Ventricles / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D009203:Myocardial Infarction / Q000150:complications / Q000503:physiopathology; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D012684:Sensory Thresholds / Q000502:physiology; D017180:Tachycardia, Ventricular / Q000150:complications / Q000503:physiopathology* / Q000601:surgery