title: Relationship between roll-off occurrence and spatial distribution of dehydrated tissue during RF ablation with cooled electrodes.
abstract: OBJECTIVE
  To study the relationship between roll-off (sudden increase in impedance) and spatial distribution of dehydrated tissue during RF ablation using a cooled electrode (temperatures around 100°C).
  
  
  METHODS
  We used a double approach: (1) theoretical modelling based on the finite element method, and (2) 20 ablations using an experimental study on ex vivo excised bovine liver in which we measured impedance progress and temperature at three points close to the electrode surface: 0.5 (T1), 1.5 (T2) and 2.5 (T3) mm from the tip. T2 was located exactly at the centre of the 30 mm long electrode.
  
  
  RESULTS
  Temperatures at T1 and T3 quickly rose to 100°C (at ≈20 and 40 s, respectively), while at the rise at T2 was somewhat slower, stabilized around 50 s and reached a maximum value of 99°C at about 60 s. Impedance reached a minimum of 65 Ω (plateau), began increasing at 50 s and continued rising throughout the procedure, reaching a value equal to the initial value at 70 s. Likewise, computed impedance dropped to ≈73 Ω (plateau), began increasing at 50 s and reached an impedance value equal to the initial value at ≈78 s, which approximately coincided with the time when the entire zone surrounding the electrode was within the 100°C isotherm.
  
  
  CONCLUSIONS
  There is a close relationship between the moment at which roll-off occurs and the time when the entire electrode is completely encircled by the dehydrated tissue. The mid-electrode zone is the last in which tissue desiccation occurs.
authors.affiliation: Instituto Universitario de Matemática Pura y Aplicada, Universitat Politècnica de València, Spain.
authors.forename: Macarena
authors.initials: M
authors.lastname: Trujillo
authors.forename: José
authors.initials: J
authors.lastname: Alba
authors.forename: Enrique
authors.initials: E
authors.lastname: Berjano
mesh_terms: D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation*; D002417:Cattle; D003890:Desiccation; D004553:Electric Conductivity; D004566:Electrodes; D008099:Liver / Q000473:pathology / Q000601:surgery*; D008962:Models, Theoretical; D013696:Temperature