Background

Local impedance (LI) drop can predict sufficient lesion formation during radiofrequency ablation (RF). Recently, a novel ablation catheter technology which is able to measure both LI and contact force has been made available for clinical use. High power short duration (HPSD) RF ablation has been shown to be feasible for atrial fibrillation (AF) ablation with short procedure time. We used LI drop and LI plateau formation to guide duration of 50 Watt RF power applications for circumferential pulmonary vein isolation (PVI).

Methods

Consecutive patients with indication for de novo AF ablation (n=20, age 66±10 years) with paroxysmal (n=10) or persistent (n=10) AF underwent ultra high density 3D mapping of the left atrium (Orion, Rhythmia, Boston Scientific) and catheter ablation (StablePoint, Boston Scientific). Low voltage areas of more than 10% of the left atrium were found in 45% of patients. Thereafter, ipsilateral PV encircling with 50 Watt RF applications targeting an interlesion distance of ≤ 6mm, a contact force of 10-30g and an LI drop >2 0Ohm was performed. Duration of HPSD RF application between 7-15s was guided by LI drop >20 Ohm and plateau formation of LI. LI drop > 50 Ohm was a cut off criteria. Further ablation strategies were left to the investigator’s discretion. Esophageal temperature measurement was performed using a three thermistor catheter with temperature cut off 39.0°C. In case of temperature rise or very near esophageal contact to the circumferential line, RF application time was shortened to 6-7s. Patients underwent adenosine testing after PVI. Previously we performed all types of AF ablation using LI-guided HPSD ablation without contact force measurement capability (IntellaNav MiFi OI, Boston Scientific) in 80 patients.

Results

Complete PVI was achieved in all 20 pts with only 13.5 ± 4.3 min cumulative RF application duration and an PVI ablation procedure duration of 46.5 ± 10.4 min with the novel LI measuring catheter (StablePoint). First-pass isolation of ipsilateral veins was achieved in 67% of circles. Recurrence of PV conduction during waiting period (20min) and adenosine testing occured in 31% of circles, and was reablated in most patients with a single spot of HPSD application. Reconnected fibers were not associated with low LI drop or low contact force, but with too large interlesion distance or instable catheter position due to breathing in case of difficult sedation of the patient. Mean procedure time was 158 ± 35 min, including 7 pts with successful additional AF ablation strategies beyond PVI (cavotricuspid isthmus ablation in 5 pts, mitral line in 3 pts, roof line in 2 pts and PV box isolation in 2 pts).  Very short esophagus temperature rise above 39.0°C occured in 25% of patients. No serious complications occurred in all 20 pts using HPSD with the novel catheter design. The former 80 pts were safely performed with HPSD with the older generation LI drop-guided catheter (IntellaNav MiFi OI) as well. Follow up will be available at presentation time.

Conclusion

Guiding of HPSD RF ablation by LI is highly efficient and safe. A novel local impedance algorithm in combination with contact force sensing enable short PVI times with low early recurrence of PV conduction. Prediction of permanent lesion seems achievable and the only limitation seems to be unstable RF catheter contact due to patients breathing. Follow up have to be waited.