1319Local impedance on a force sensing catheter predicts volumetric lesion temperature changes

Abstract

Funding Acknowledgements Study was funded by Boston Scientific The effective delivery of RF energy is dependent on transmural tissue heating, with irreversible tissue necrosis occurring at a tissue temperature ≥ 50°C. While multi-input lesion indexing algorithms can provide some value in predicting lesion durability, no clinically available metric measures tissue heating under the endocardial surface. Temperature measured from the catheter at the tissue surface is a surrogate for intra-lesion heating, but variables such as intra-cardiac flow and catheter irrigation have the potential to make this measure unreliable. A metric that assesses volumetric tissue heating would provide a superior method of predicting RF ablation in clinical practice. This study evaluated a prototype catheter that measures local catheter impedance (LI) using ring and tip electrodes and contact force (CF) using inductive sensors with an electroanatomical mapping system. In vitro, 51µm thermocouples were placed in explanted cardiac ventricular swine tissue to measure the temperature profile during RF delivery. The correlation between the LI drop during RF and intra-lesion temperature was assessed. A total of 44 lesions were created. Intra-lesion temperature was measured using 3 51µm thermocouples placed 0mm, 2mm, and 4mm from the surface of the tissue. The probes were placed in-line, 0.5-1mm lateral to the catheter tip. Lesions were created at a constant force of 15 ± 3g at standard powers of 25W and 30W and high power of 50W for durations of 10s and 30s. LI drop correlated strongly with lesion depth (R = 0.81) while force time integral (FTI) did not correlate as strongly (R = 0.58). As seen in Figure 1A (temperature traces inverted), a characteristic temperature increase was observed, with the greatest increase at the probes located in the lesion core (2mm). Lower temperatures were observed in the probes exposed to irrigation flow/ bloodpool (0mm). Notably, the LI drop (33Ω) demonstrated a similar slope to the 2mm temperature probe recordings (maximum 78°C). There was a strong linear relationship between maximum intra-lesion temperature and LI drop (R = 0.74) (Figure 1B), while there was a very weak relationship between temperature and FTI (R = 0.36). There was a strong relationship between LI drop and maximum temperature in the first 5s across all powers (R = 0.81). At 50W, both LI drop (22 ± 5Ω) and maximum temperature (66 ± 9°C) were greater than standard power. For 30W, LI drop was 14 ± 6Ω and maximum temperature was 52 ± 7°C in the first 5 seconds. In this study, LI drop was highly correlated to intra-lesion temperature at standard and high power, demonstrating the sensitivity of the metric to volumetric heating under the tissue surface. A LI drop greater than 20Ω results in a tissue temperature >50°C, and a 30Ω LI drop likely results in a transmural temperature profile in 2mm tissue. The correlation of LI to the core lesion temperature provides a powerful, biophysical measure of tissue heating during RF ablation. Abstract Figure 1

The optimal ablation setting for a local impedance guided catheter in an in vitro experimental model

“…The LI continued to decrease under the 30 g/50 W, 50 g/50 W, and 50 g/40 W ablation settings, which indicated that the local tissue temperature continued to increase because the LI drop reflects the tissue temperature. 13 Finally steam pops occurred under during the 50 W ablation. Steam pops did not occur during the 40 W ablation in our experiment, but a longer ablation duration might have triggered a steam pop even if the ablation power was 40 W. The value of the LI might be useful to predict steam pops.…”

“…Kara et al reported that the LI drop closely reflected the tissue temperature in an in-vitro porcine experiment. 13 The tissue temperature would be increasing under a higher CF or higher ablation power and the LI drop was be less likely to reach the plateau level.…”

Catheter contact angle influences local impedance drop during radiofrequency catheter ablation: Insight from a porcine experimental study with 2 different LI-sensing catheters

“…This catheter has 3 microelectrodes incorporated into the distal tip, and a more precise LI would be detected with these microelectrodes. Since the LI would be changed by tissue contact and temperature, this parameter allows us to speculate about the CF and tissue temperature during the RF application [11] . In addition, both LI-and CF-sensing ablation catheters (INTELLANAV STABLEPOINT Boston Scientific, Maple Grove, MN, USA: STABLEPOINT) have recently become available, and they will contribute to additional improvement in the quality of RFCA.…”

Local impedance to guide focal radiofrequency ablation: there is life in the old dog yet

“…A local potential field is generated by driving a non-stimulatory current between a distal and a more proximal catheter electrode; proximity to physical structures such as myocardium causes distortions in this local field which can be measured with one or more intermediate electrodes, allowing derivation of a LI value 4 . Bench work has shown that during RF application, LI drop dynamically follows the rate of intramural temperature rise (Figure 1) 5 . The resulting tissue feedback can potentially allow operators to individualize each RF application, and several groups have already reported on their clinical experience (Table 1) with a LI-sensing catheter.…”