Correlation between Lesions Size Index (LSI) and impedance dynamics during radiofrequency ablation for atrial fibrillation: impact of lesion duration and contact force

Abstract Introduction Impedance drop has been employed as a surrogate marker for lesion formation with its magnitude correlated to lesion size in in-vitro studies. The Lesion Size Index (LSI), and algorithm from Abbott Medical, serves as a predictor for lesion formation during radiofrequency (RF) ablation. While this formula integrates contact force (CF), lesion duration and power, it currently leaks impedance information. The new module of Ensite Cardiac Mapping system (Abbot) is capable of measuring the "filtered" impedance during each RF lesion, effectively eliminating artifacts from cardiac and respiratory oscillations. The objective of this study is to examine the correlation between the LSI and the average impedance drop during RF lesion formation. Methods We included a total of 18 consecutive patients who underwent catheter ablation for atrial fibrillation (AF) with Ensite Mapping System (Abbot). In all cases, 40 watts (W) were applied and the target LSI was set as 5 for the posterior wall and 6 for the anterior wall. For each lesion, the software automatically annotated the initial impedance, final impedance, average impedance drop (filtered), lesion duration and average contact forced (CF). The correlation between LSI, impedance drop and CF was assessed. Results A total of 1300 RF lesions delivered during AF ablation were analyzed. Mean LSI was 5.3 ± 0.8, mean average impedance drop was 10.9± 5 ohms and mean CF 12.3±6 grams (g). The LSI showed a weak but statistically significant correlation with the impedance drop (Person correlation=0.3; p<0.001). When ablation lesions were grouped by duration (<20 seconds, 21-40, 41-60, >60 seconds), the correlation between LSI and impedance drop remained weak but statistically significant for lesions shorter than 20 seconds (p<0.001) and lesions between 21 and 40 seconds (p<0.001). However, there was no longer correlation for lesions between 40-60 seconds and those longer than 60 seconds (Figure1). Mean CF for each group (from <20 to >60 seconds) was 15 ±7 g vs 11 ±5 g vs 9 ± 3 g vs 7± 3g respectively (p<0.001) (Figure 2), suggesting that the CF is key to improve the predictive value of LSI. Conclusions The LSI shows a weak correlation with the average impedance drop during AF ablation. This correlation is influenced by lesion duration, which is ultimately dependent on CF. These findings emphasize the ongoing need to optimize predictive models for RF lesion formation in the ever-evolving landscape of AF treatment.Figure 1Table 1