title: Comparison of radiofrequency ablation in normal versus scarred myocardium.
abstract: BACKGROUND
  Reentrant circuits causing ventricular tachycardia are closely associated with previously scarred myocardium. The presence of scar has been blamed for the poor success rate of radiofrequency ablation (RFA) in that context. This article investigates the in vivo effects of radiofrequency ablation in myocardium scarred from acute myocardial infarction.
  
  
  RESULTS
  Anterior myocardial infarction was induced in five dogs by ligating the left anterior descending artery. The mean left ventricular ejection fraction after infarction was 38%. At a mean of 15 weeks following myocardial infarction, 50 RFA lesions were created in random order, 25 in scarred and 25 in normal myocardium using a needle electrode (21 gauge, 5 mm in length) introduced from the epicardium of the left ventricle at thoracotomy. During unipolar temperature-controlled RFA (90 degrees C for 60 seconds), intramural temperatures were measured by thermistors at distances of 1, 2, 3, 4, and 5 mm from the ablating electrode. The margins of the lesions were clearly discernible in scar at histological examination in 64% of ablations where the scarring was patchy. There were no significant differences between lesion sizes, intramural temperatures at different distances, total energy required for ablation, or mean impedance during ablation of normal versus scarred myocardium.
  
  
  CONCLUSIONS
  Scar does not affect lesion size or intramural temperature profile during RFA if electrode size, tissue contact, and tip temperature are controlled. More radiofrequency energy is not required to maintain tip temperature at 90 degrees C in scar compared to normal myocardium.
authors.affiliation: Department of Cardiology, Westmead Hospital, Sydney, Australia. kovoor@westgate.wh.usyd.edu.au
authors.forename: Pramesh
authors.initials: P
authors.lastname: Kovoor
authors.forename: Michael P J
authors.initials: MP
authors.lastname: Daly
authors.forename: Jim
authors.initials: J
authors.lastname: Pouliopoulos
authors.forename: Karen
authors.initials: K
authors.lastname: Byth
authors.forename: Barbara I
authors.initials: BI
authors.lastname: Dewsnap
authors.forename: Vicki E
authors.initials: VE
authors.lastname: Eipper
authors.forename: Teresa
authors.initials: T
authors.lastname: Yung
authors.forename: John F B
authors.initials: JF
authors.lastname: Uther
authors.forename: David L
authors.initials: DL
authors.lastname: Ross
mesh_terms: D000818:Animals; D001831:Body Temperature; D017115:Catheter Ablation / Q000379:methods*; D004195:Disease Models, Animal; D004285:Dogs; D005260:Female; D006358:Hot Temperature; D008297:Male; D009203:Myocardial Infarction / Q000150:complications* / Q000473:pathology; D009206:Myocardium / Q000473:pathology*; D017180:Tachycardia, Ventricular / Q000150:complications / Q000473:pathology / Q000601:surgery*; D016896:Treatment Outcome