title: Comparison of epicardial and endocardial linear ablation using handheld probes.
abstract: BACKGROUND
  The optimal technique for producing linear radiofrequency thermal lesions in myocardial tissue is unclear. We compared epicardial ablation on the beating heart with endocardial ablation after cardioplegia.
  
  
  METHODS
  Radiofrequency lesions were produced using a multielectrode malleable handheld probe in ovine myocardium with three wall thicknesses. Detailed analysis of lesion dimensions was used to assess the effects of site of ablation, muscle thickness, and duration of ablation.
  
  
  RESULTS
  After epicardial atrial ablation, myocardial lesions were detected in all sections without macroscopically visible epicardial fat (n = 10), but only 43% (6/14) of sections with epicardial fat. Three of 24 atrial epicardial sections (13%) and 92% (23/25) of endocardial atrial lesion sections were clearly transmural. In thicker tissues lesion depth was independent of endocardial (right ventricle: 3.9 +/- 1.1 mm, left ventricle: 3.8 +/- 0.7 mm) or epicardial (right ventricle: 3.4 +/- 0.6 mm, left ventricle: 4.3 +/- 0.9 mm) ablation site. Epicardial lesions are less deep in thinner areas of myocardium (p = 0.003). Lesions were all wider than they were deep. There was no significant increase in lesion depth with the increase in ablation duration from 1 to 2 minutes.
  
  
  CONCLUSIONS
  Lesions were unlikely to be transmural with either technique when the wall thickness was greater than about 4 mm. Epicardial fat has an important negative effect on epicardial lesion formation. Where epicardial fat is absent epicardially produced lesions penetrate less deeply when the wall thickness is small, possibly due to endocardial cooling by circulating blood. Prolongation of the duration of ablation from 1 to 2 minutes does not significantly increase lesion depth.
authors.affiliation: Department of Cardiology, Westmead Hospital, Westmead, New South Wales, Australia. stuartpt@yahoo.com
authors.forename: Stuart P
authors.initials: SP
authors.lastname: Thomas
authors.forename: Duncan J R
authors.initials: DJ
authors.lastname: Guy
authors.forename: Anita C
authors.initials: AC
authors.lastname: Boyd
authors.forename: Vicki E
authors.initials: VE
authors.lastname: Eipper
authors.forename: David L
authors.initials: DL
authors.lastname: Ross
authors.forename: Richard B
authors.initials: RB
authors.lastname: Chard
mesh_terms: D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation / Q000379:methods*; D006329:Heart Conduction System / Q000473:pathology / Q000601:surgery*; D023421:Models, Animal; D009206:Myocardium / Q000473:pathology; D012756:Sheep