title: Ablation effect indicated by impedance fall is correlated with contact force level during ablation for atrial fibrillation.
abstract: BACKGROUND
  Previous studies have validated the use of impedance fall as a measure of the effects of ablation. We investigated whether catheter-to-tissue contact force correlated with impedance fall during atrial fibrillation ablation.
  
  
  RESULTS
  A total of 394 ablation points from 35 patients who underwent atrial fibrillation ablation were selected and analyzed in terms of the presence of stable catheter contact in non-ablated areas in the left atrium. A fixed power output (30 W) was applied for 60 seconds. Contact force, impedance fall, and force-direction angle were retrieved and exported for off-line analysis. Qualified points were divided into 5 groups according to the level of contact force (1-5 g, 6-10 g, 11-15 g, 16-20 g, and >20 g). An acute impedance fall was observed in the first 10 seconds followed by a plateau in group I and by a further fall in the other groups. Group V showed a rise in impedance during the last 20 seconds of ablation. Levels of impedance fall at each time point were significantly different among all the groups (P<0.001) except between groups III and IV. There was a significant correlation between contact force and maximum impedance fall (rho = 0.54, P<0.01). Lesions with a force-direction angle of 0-30° had significantly lower contact force and maximum impedance fall than those with angles of 30-60° and 60-135° (P<0.01).
  
  
  CONCLUSIONS
  Under stable catheter conditions, contact force correlates with impedance fall during 60 seconds of ablation. Contact force exceeding 5 g produces greater impedance fall, which probably indicates adequate lesion formation. A contact force greater than 20 g may lead to late tissue overheating.
authors.affiliation: Department of Heart Disease, Haukeland University Hospital and Department of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Alessandro
authors.initials: A
authors.lastname: De Bortoli
authors.forename: Li-Zhi
authors.initials: LZ
authors.lastname: Sun
authors.forename: Eivind
authors.initials: E
authors.lastname: Solheim
authors.forename: Per Ivar
authors.initials: PI
authors.lastname: Hoff
authors.forename: Peter
authors.initials: P
authors.lastname: Schuster
authors.forename: Ole-Jørgen
authors.initials: OJ
authors.lastname: Ohm
authors.forename: Jian
authors.initials: J
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D001281:Atrial Fibrillation / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D062906:Cardiac Catheters; D017115:Catheter Ablation / Q000295:instrumentation; D017097:Electric Impedance; D004566:Electrodes; D004867:Equipment Design; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013314:Stress, Mechanical; D007507:Therapeutic Irrigation / Q000295:instrumentation; D013997:Time Factors; D016896:Treatment Outcome
keywords: atrial fibrillation; catheter ablation; contact force; impedance