Impact of contact force on local impedance measurements in different atrial locations
Authors: Martinez Anton C , Unger LA , Haas A , Schmidt K , Jaeger C , Doessel O , Luik A 
Published: May 2022

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860974
Regions with pathologically altered substrate have been identified as potentially responsible for atrial fibrillation and atrial flutter maintenance. Also, real time feedback on lesion formation especially in those critical areas is a challenge. The LOCALIZE trial has shown significant value of the usage of the local impedance (LI) drop as a real time indicator during ablation for durable lesion formation. In these procedures, a decrease of 10-20% of the initial LI value is used as a marker of successful ablation. Also known is the fact that low electrode-tissue contact force is associated with ineffective lesion formation, whereas a high value can lead to an increased risk of steam pop. The IntellaNavSTABLEPOINT catheter offers both, LI and contact force, as a novel combined technique to characterize the process of lesion formation. Additionally, LI values are expected to distinguish between healthy and scar tissue independently from the atrial rhythm, which can improve the understanding of underlying substrate, even more, when corrected for an eventual lack of contact by combining it with contact force.
This study aims to: (1) evaluate the relationship between contact force and LI; (2) characterise the contact force during local impedance mapping depending on the wall region of the left atrium (LA).
Patients undergoing LA ablation with the STABLEPOINT catheter were included in this analysis. Contact force and LI data were recorded in four different healthy anatomical points in the LA, two in the anterior wall, and two in the posterior wall, using manually controlled contact force values between 0 g and the saturation point (70 g). When possible, additional points in scar regions were recorded. Data were exported and processed to correlate each LI measurement with the corresponding contact force. Due to the susceptibility of raw LI recordings to oscillations, moving average approach was considered. The clinical cohort comprised ten patients with a mean age of 61 years, one female. De-Novo ablations as well as redo procedures were included. Measurements at different contact force values yielded a non-linear relationship between contact force and LI. Median value of the difference between the moving average LI measurement and the LI bloodpool value were calculated at the anterior and posterior walls of the LA at contact force values from 5 to 40 g (5 g step size). Comparing the LI values at each segment, measurements differ significantly (Mann-Whitney U-test for unpaired samples) between the anterior and the posterior wall of the LA, with an ascending trend. Scar points showed a globally lower curve.
Results from this preliminary study showed that LI and contact force are non-linearly dependent and it differs between anterior and posterior atrial walls, as well as between healthy and pathological substrate. Further investigations in a larger clinical cohort will analyse the LI variability to set an optimal contact force technique during LI mapping.