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 drop 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 drop plateau formation to guide duration of 50 Watt RF applications for AF ablation.

Methods

Consecutive patients (pts) with indication for de novo AF ablation (n=100, 65±9 years) with paroxysmal (n=43), persistent (n=57) AF underwent high density 3D mapping of the left atrium (Orion, Rhythmia, Boston Scientific) and RF catheter ablation (StablePoint, Boston Scientific). Low voltage areas of more than 5% of the left atrium were found in 40 pts, of more than 20% in 19 pts. Thereafter, ipsilateral PV encircling with 50 Watt RF applications targeting an interlesion distance of ≤ 6mm, a contact force of 5-30g and a LI drop >15 Ohm in the first 7s was performed. Application of HPSD RF application between 5-15s was terminated in case of LI drop plateau formation or a maximum duration of 15s. For safety reasons, a LI drop > 50 Ohm was a cut off criteria. Further ablation strategies were dependent on the amount and distribution of left atrial fibrosis leading to linear left atrial ablation in 19 pts (roof line and/or anterior mitral line) or posterior PV box isolation in 6 pts. Esophageal temperature measurement was performed and in case of temperature rise or very near esophageal contact to the circumferential line, RF application time was shortened to 3-7s. In case of failing first pass isolation of encircled PVs, either a more antral RF application near the PV ostium or a conventional unlimited 35 Watt RF application was performed.

Results

Complete PVI was achieved with 16.3 ± 2.8 min cumulative RF application duration requiring PVI duration of 58 ± 13 min. First-pass isolation of ipsilateral veins was achieved in 86% on the right side and in 74% of the left side with the HPSD protocol. Conventional RF applications with unlimited 35 Watt pulses were added in 7 pts predominately at the anterior border of the LIPV and the carina between LSPV and LIPV and in 4 pts anterior the right PVs. Left atrial ablation lines, tested by high density activation mapping, were completed in all patients, however, required a higher percentage of conventional unlimitied 35 Watt RF applications. Mean procedure time was 139 ± 32 min in pts only PVI was performed, overall mean procedure time of all patients accounted for 161 ± 42 min. No serious complications occurred in all 100 pts using HPSD. In the limited follow up of 3-12 months, median 7 months, 84% of pts remained in stable sinus rhythm, 9% had recurrence of AF and 7% recurrence of atrial flutter. In up to now three reablated pts, all PV isolation were approved to be permanent.

Conclusion

Guiding of HPSD RF ablation by LI drop plateau formation is highly efficient and safe, and may ensure permanent PVI, however, unmask the limitations of short 50 Watt RF-applications in the free wall of the left atrium and corresponding thicker atrial tissue at the carina between pulmonary veins. A novel local impedance algorithm in combination with contact force sensing enable short PVI times and accelerate linear ablation in case of left atrial fibrosis. Prediction of permanent lesions seems to be achievable.