A role for Local Impedance in CF guided PVI: initial results from the LOCALIZE CF Trial
Authors: Garcia-Bolao I , Schillaci V , Ramos P , Luik A , Ince H , Ewerston N C , Das M , Raybuck J , Canepa S , Okeson B , Polster P , Solimene F 
Published: May 2024

Abstract

Background
Contact force catheters (CF) in combination with high-resolution 3D mapping are the gold standard for treatment of complex arrhythmias. Stable CF and catheter position increase both the safety and effectiveness of energy delivery. To date, local impedance (LI) is the only established parameter for real-time measure of lesion quality. Other methods tend to use surrogate parameters. Catheter ablation may be further improved by combining CF and LI.

Purpose
LOCALIZE CF assessed the utility of LI in addition to CF in predicting lesion durability during RF PVI procedures for paroxysmal atrial fibrillation (PAF).

Methods
LOCALIZE CF is an international, multicenter non-randomized trial consisting of an index PVI and invasive redo mapping procedure at 3 months. Patients (pts) with PAF underwent de novo PVI using a combined CF/LI catheter and 3D mapping system. Operators could use CF but were blinded to LI. Power settings and ablation duration were at operator discretion. PVI was performed with point-by-point circumferential ablation. The procedural endpoint was confirmation of entry block for all pulmonary veins (PV) after a 20-minute wait. Secondary endpoints included: safety events, procedural characteristics, and the correlation between LI-values and gaps. Gaps at 3-month remap were analysed by anatomical segment (8/ipsilateral PVI circle, 16/pt).

Results
This study enrolled 60 pts across 4 European centers, 54 pts completed 3-month remap. On average, pts (25% female) were 61 years of age, BMI 27kg/m2, LVEF 64%, LA diameter 38mm, and CHA2DS2-VASc score 1. High-power (40-45W) short duration was used by 3 of 4 sites (32 patients), with standard power (&lt;40W) in the remainder. First pass isolation, assessed after 20min wait, was achieved in 73% of pts. Acute isolation of all PVs was achieved in all pts. At the 3-month re-map procedure, 92 of 845 segments were found to be reconnected.
3,980 point-to-point index ablations were analysed with respect to gap vs blocked segments. The median CF in gap segments was 11g compared to 13.9g in blocked segments (p&lt;0.0001). Gap segments had significantly lower median LI drop (13Ω) than blocked segments (19Ω; p&lt;0.001). In multivariate analysis, lesion spacing, CF and LI drop all independently predicted block. In ROC curve analysis (&gt;9.5g CF, &gt;20Ω LI), a model including all 3 factors had a significantly greater area under the curve than spacing and CF alone (p&lt;0.0001).

Conclusions
Real-time measurements such as LI and CF are important for improving the quality and durability of ablations. While CF represents the stability of the catheter, LI reflects real-time lesion formation. The combination of both is important and may improve ablation and avoid gaps. This study suggests that CF &gt;9.5g and LI drop &gt;20Ω are predictors of durable lesion. Thus, LI, when used alongside CF, potentially offers a distinctive measure of ablation effectiveness, complementing the data provided by CF.