title: Effectiveness of impedance monitoring during radiofrequency ablation for predicting popping.
abstract: OBJECTIVE
  To retrospectively evaluate the effectiveness of impedance monitoring for predicting popping during radiofrequency ablation (RFA) using internally cooled electrodes.
  
  
  METHODS
  We reviewed 140 patients (94 males, 46 females; age range 73.0 ± 11.1 year) who underwent RFA between February 2006 and November 2008 with a modified protocol using a limited power delivery rather than a conventional one to avoid popping. All the patients provided their written informed consent, and the study was approved by the institutional review board. Intraprocedural impedances were measured for the study subjects, and the tumors were classified into three types according to the characteristics of their impedance curves: increasing, flat, or decreasing. The tumors were further sorted into seven subtypes (A-G) depending on the curvature of the impedance curve's increase or decrease. Relative popping rates were determined for the three types and seven subtypes. A chi-square test was performed to estimate statistical significance.
  
  
  RESULTS
  A total of 148 nodules treated by RFA were analyzed. The study samples included 132 nodules of hepatocellular carcinoma, 14 nodules of metastatic liver cancer, and two nodules of intrahepatic cholangiocarcinoma. The numbers of nodules with each impedance curve type were as follows: 37 increasing-type nodules, 43 flat-type nodules, and 68 decreasing-type nodules. Popping occurrence rates were 24.3%, 46.5% and 64.7%, respectively. Flat-type nodules exhibited a significantly higher rate of popping compared to increasing-type nodules (P = 0.039). Decreasing-type nodules exhibited a significantly higher rate of popping compared to increasing-type nodules (P < 0.0001). Notably, nodules that showed a sharp decrease in impedance in the latter ablation period (subtype E) exhibited a significantly higher rate of popping compared to other subtypes.
  
  
  CONCLUSIONS
  Intraprocedural impedance monitoring can be a useful tool to predict the occurrence of popping during liver tumor RFA performed with internally cooled electrodes.
authors.affiliation: Department of Surgery, Meiwa Hospital, 4-31 Agenaruo-cho, Nishinomiya, Hyogo 663-8186, Japan. hiroya0001@mac.com
authors.forename: Hiroya
authors.initials: H
authors.lastname: Iida
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Aihara
authors.forename: Shinichi
authors.initials: S
authors.lastname: Ikuta
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamanaka
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001650:Bile Duct Neoplasms; D001653:Bile Ducts, Intrahepatic; D006528:Carcinoma, Hepatocellular / Q000473:pathology / Q000601:surgery*; D017115:Catheter Ablation / Q000009:adverse effects; D016009:Chi-Square Distribution; D018281:Cholangiocarcinoma / Q000473:pathology / Q000601:surgery*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology / Q000556:secondary / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
keywords: Complication; Internally cooled electrode; Liver; Popping; Radiofrequency ablation