Comparison of ablation index versus time‐guided radiofrequency energy dosing using normal and half‐normal saline irrigation in a porcine left ventricular model

Abstract

Background Ablation Index (AI) is a multiparametric quality marker to assess the durability of radiofrequency (RF) lesions. The comparative effectiveness and safety of AI versus time‐based energy dosing for ablation of ventricular arrhythmias are unknown. Objective We compared AI and time‐based RF dosing strategies in the left ventricles (LVs) of freshly harvested porcine hearts. Methods Ablation was performed in vitro with an open‐irrigated ablation catheter (Thermocool ST/SF), 40 W, contact force 10–15 g. Tissue samples were stained in triphenyltetrazolium chloride for the measurement of lesion dimensions. Results A total of 560 lesions were performed (AI‐group: [n = 360]; time‐group: [n = 200]). Using normal saline (NS) (n = 280), growth in lesion depth slowed after 30 s and AI > 550 in comparison to width, volume, and magnitude of impedance drops which continued to increase with longer RF duration. Risk of steam pop (SP) was higher for RF > 30 s (RF < 30 s:1 SP [2.5%] vs. RF > 30 s: 15 SP [25%]; p = .002) or AI targets >550 (AI: 350–550: 2 SP [2%] vs. AI 600–750: 15 SP [19%]; p = .001). Using half‐normal saline (HNS) (n = 280), lesion dimension and impedance drops were larger and growth in lesion depth slowed earlier (AI: 500). Risk of SPs was higher above AI 550 (AI: 350–550: 7 [7%] SPs vs. AI 600–750: 28 [35%] SPs; p < .00001). While codependent variables, correlation between AI and time was modest‐to‐strong but decreased with longer RF duration. Conclusion In this ex vivo study, AI was a better predictor of lesion dimensions than ablation time and magnitude of impedance drop in the LV using NS and HNS irrigation. AI targets above 550 led to a higher risk of SPs. Future trials are required to verify these findings.

Ablation index to guide radiofrequency ablation in the left ventricle: Are we there yet?

“…In this context, Gasperetti ventricular outflow tract when using the AI to guide ablation (target values 590 in the free wall and 610 in the septum). 19 Of interest, Gasperetti et al reported no SP despite target AI values substantially higher than those shown to increase the risk of SP in the present study by Larsen et al 18 The reasons for this apparent discrepancy warrant further investigation, although they may be related to the…”

“…In this context, Gasperetti et al have recently shown improved long‐term outcomes of catheter ablation of premature ventricular complexes from the right ventricular outflow tract when using the AI to guide ablation (target values 590 in the free wall and 610 in the septum) 19 . Of interest, Gasperetti et al reported no SP despite target AI values substantially higher than those shown to increase the risk of SP in the present study by Larsen et al 18 The reasons for this apparent discrepancy warrant further investigation, although they may be related to the specific experimental conditions tested by Larsen et al (i.e., stable contact force and catheter orientation, fixed power) which may not be reproducible or obtainable in the clinical setting. Additional limitations that have been highlighted also by the authors include the lack of generalizability to RF lesions within abnormal substrates and the potential analytical bias due to collinearity between AI and lesion duration, particularly considering that the other variables included in the AI calculation such as contact force and power were maintained constant per study protocol.…”

“…In this issue of the Journal of Cardiovascular Electrophysiology, Larsen et al provide important new data comparing AI-guided ablation versus a time-guided approach under uniform experimental conditions in a porcine left ventricular ex vivo model. 18 Ablation lesions were delivered using an open-irrigated Thermocool ST-SF ablation catheter (Biosense-Webster) with the power of 40 W and contact force maintained between 10 and 15 g. In the AI-based group, a total of 360 lesions were delivered, and in the time-based group, a total of 200 lesions were delivered. AI was found to be a better predictor of the final lesion dimensions than time and magnitude of impedance drop.…”

Impact of electrode tip shape on catheter performance in cardiac radiofrequency ablation

“…Available clinical and experimental data also support that the type of irrigation, be it a discrete number of pores or a surround flow designs, has no significant impact on lesion size. (2,3,10,18,19,20) Our study also suggests that the incidence of steam pops is not directly related to the amount of irrigation. Whether the type of irrigation, discrete vs surround flow, has an impact on pop occurrence remains unclear.…”

“…Available clinical and experimental data also support that the type of irrigation (ie, discrete number of pores or surround flow designs) has no significant impact on lesion size. 2 , 3 , 10 , 18 , 19 , 20 …”