• atrial fibrillation;
  • contact force;
  • catheter ablation;
  • impedance

Contact Force Correlates with Impedance Fall During Ablation


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.

Methods and 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).


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.