1322Impact of system impedance in ablation-index guided lesion formation in an in vitro model
Authors: Lozano-Granero C , Moreno Planas J , Matia Frances R , Hernandez Madrid A , Sanchez Perez I , Zamorano Gomez J L , Franco Diez E 
Published: June 2020

Abstract

Funding Acknowledgements
Beca de la Sección de Electrofisiología y Arritmias para formación en investigación post-residencia en centros españoles
INTRODUCTION
Ablation Index and Lesion Size Index are novel markers of ablation lesion quality that incorporate power (W), contact force (CF), and time (T) in a weighted formula to accurately estimate lesion size. While LSI includes system impedance (I) in the formula, this parameter is not considered for AI calculation.
PURPOSE
The aim of our study was to analyse the impact of I in lesion formation.
METHODS
Radiofrequency (RF) lesions were created on porcine myocardial slabs by using an open-tip irrigated catheter with real-time monitoring of CF (a TactiCath™ Quartz Contact Force Ablation Catheter for LSI-guided lesions and a ThermoCool® SmartTouch® Catheter for AI-guided lesions). Catheters were mounted in an articulated arm and manually maneuvered over a platform placed within a tank filled with either a low impedance medium (saline solution) or a high impedance medium (running water) with a heating pump to produce non-pulsatile flow directed perpendicularly to the myocardium surface at a rate of 5 l/min and a temperature of 37ºC. For each catheter and medium, ten lesions were performed with a CF of 20 grams and a W of 25, 30, 35 and 40 watts aiming at a LSI of 5 or a AI of 400 (recommended targets for posterior wall pulmonary vein isolation for each index). After RF delivery, the myocardium was cross-sectioned at the level of each lesion and its blanched zone was measured with a dial calliper with a 0.1 mm resolution (image, panel A). Lesion volume was calculated using width and depth, according to a validated formula (image, panel B).
RESULTS
No difference in application time was noted in the AI-guided lesions depending on the medium (23.8 ± 1.6s, 17.2 ± 1.4s, 13.7 ± 0.8s and 12.2 ± 0.7s for 25W, 30W, 35W and 40W, respectively) while a significant reduction in application time was noted in the LSI-guided lesions performed in a low I medium (93.8 ± 6.6 ohms; 17.9 ± 1.9s, 11.3 ± 3.7s, 9.1 ± 0.9s and 7.3 ± 0.5s for 25W, 30W, 35W and 40W) compared with those performed in a high impedance medium (132.4 ± 6.6 ohms; 27.3 ± 1.4s, 17.9 ± 2.5s, 15.5 ± 1.4 and 13 ± 1.2 for the same programmed W (p &lt; 0.0001 for all comparisons).
Both catheters showed differences in lesion size according to the I, with lower lesion volumes in the low I medium and higher lesion volumes in the high I medium. Although globally smaller in size, higher lesion volumes were noted in the AI-guided lesions compared to LSI-guided lesions in a low I medium (image, panel C). On the contrary, a better performance of the LSI-guided lesions was observed in the high I medium (image, panel D).
CONCLUSIONS
System impedance affected lesion size both in LSI-guided an AI-guided ablation lesions, with smaller lesions seen in a lower I medium. Further studies are needed to assess the clinical relevance of this findings in an in-vivo scenario.
Abstract Figure.