Introduction: Insufficient lesion depth and discontinuity of lesion lines are reasons for reconnections after point-by-point pulmonary vein isolation (PVI). A novel technology for the measurement of local tissue impedance (LI) may allow to define the optimal duration of radiofrequency ablation at each point.

Purpose: To evaluate the LI parameters during PVI and their relationship to gap formation and pulmonary vein reconnections.

Methods: A total of 14 continuous patients with paroxysmal atrial fibrillation underwent a first antral PVI using the novel ablation catheter with local tissue impedance measurement. LI from the catheter, generator impedance (GI) and maximum electrogram amplitude were recorded before, during and after ablation. Each ablation was performed using 40 W at the anterior segments and 30 W at the posterior, roof and bottom segments with inter-lesion distance of < 5 mm and stopped as soon as LI-drop plateau was reached. If first-pass PVI did not occur, gap-mapping and touch-up ablation were performed along the index ablation circle. Remapping and adenosine infusion were performed after 30 min waiting time to reveal acute reconnections (AR) and dormant conduction (DC).  

Results: All 28 PV antra of 14 patients were successfully isolated. RF ablation time per circle was 15.1 ± 3.7 min. First-pass PVI was achieved in 17 circles. First-pass gaps (n=11), AR (n=8) and DC (=1) were registered in 16 circles and 48 adjacent ablation points defined as an unsuccessful lesion, which were compared with 650 successful lesions. The median LI-drop for successful lesions was 12.1 Ω (7.2-19.3 Ω), which was larger than for unsuccessful lesions (4.0 Ω [2.0-7.8 Ω], P < 0.001). On receiver operating characteristic curve analysis, the optimal LI-drop threshold was 6,1 Ω (sensitivity, 81 %; specificity, 71 %). The LI-drop of <5.0 Ω predicted an unsuccessful ablation with a high sensitivity 90%, but low specificity 56 %. 

Conclusions: Sufficient local impedance drop can indicate successful transmural ablation in the atrium. Local impedance drop <5 Ω predicted a gap formation with high sensitivity but low specificity. However, the clinical significance of those findings needs to be investigated in future and larger studies.