title: Radiofrequency ablation: simultaneous application of multiple electrodes via switching creates larger, more confluent ablations than sequential application in a large animal model.
abstract: OBJECTIVE
  To compare radiofrequency (RF) ablations created by using a sequential technique to those created simultaneously by using a switching algorithm in ex vivo and in vivo liver models.
  
  
  METHODS
  RF ablation was performed by using either sequential or switched application of three cooled electrodes in a 2-cm triangular array in ex vivo bovine liver (28 total ablations) and in vivo swine liver (12 total ablations) models. For sequential ablations, electrodes were powered for 12 minutes each with a 5-minute rest interval between activations to simulate electrode repositioning. Switched ablations were created by using a multiple-electrode switching system for 12 minutes. Temperatures were measured during ex vivo experiments at four points in the ablation zone. Ablation zones were measured for minimum and maximum diameter, cross-sectional area, and isoperimetric ratio. Mann-Whitney and Wilcoxon matched pairs tests were used to identify differences between groups.
  
  
  RESULTS
  The switched application created larger and more circular zones of ablation than did the sequential application, with mean (+/-standard deviation) ex vivo cross-sectional areas of 25.4 cm(2) +/- 5 .3 and 18.8 cm(2) +/- 6.6 (P = .001), respectively, and mean in vivo areas of 17.1 cm(2) +/- 5.1 and 13.2 cm(2) +/- 4.2 (P < .05). Higher temperatures and more rapid heating occurred with the switched application; switched treatments were 74% faster than sequential treatments (12 vs 46 minutes). In the sequential group, subsequent ablations grew progressively larger due to local ischemia.
  
  
  CONCLUSIONS
  Switched application of three electrodes creates larger, more confluent ablations in less time than sequential application. Thermal synergy and ablation-induced ischemia both substantially influence multiple-electrode ablations.
authors.affiliation: Department of Radiology, University of Wisconsin, Clinical Sciences Center, Madison, WI 53792, USA. clbrace@wisc.edu
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Brace
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Sampson
authors.forename: J Louis
authors.initials: JL
authors.lastname: Hinshaw
authors.forename: Neil
authors.initials: N
authors.lastname: Sandhu
authors.forename: Fred T
authors.initials: FT
authors.lastname: Lee
mesh_terms: D000465:Algorithms; D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation / Q000379:methods*; D002417:Cattle; D003080:Cold Temperature; D004566:Electrodes; D004867:Equipment Design; D005260:Female; D007511:Ischemia / Q000473:pathology; D008099:Liver / Q000098:blood supply / Q000473:pathology / Q000601:surgery*; D023421:Models, Animal; D034421:Sus scrofa; D013997:Time Factors