Lesion formation in irrigated RF-ablation is not linear, but monoexponential

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: Radiofrequency ablation remains one of the most important ablation techniques in the EP lab. Creating durable lesion is difficult, as progression of lesion formation cannot be observed directly. Surrogate parameters, as force-time-integral and indices, as the ablation index or lesion size index, help distinguishing the efficacy of a RF-application, but several deficiencies are known. The aim of this study was to further investigate dynamic changes in ablation parameters and lesion growth in RF-ablation. METHODS: RF-lesions were created using an ex vivo porcine cardiac model with a force and local impedance sensing catheter. A second catheter was used for lesions up to 70 Watts. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and electrode tissue coupling. RF power of 20W, 30W, 40W, and 50W was used in the local impedance sensing catheter, while RF power of 30W, 40W, 50W, 60W, and 70W were used in the second catheter. All parameters (power, temperature, global impedance, ETC, lesion diameter and lesion depth) were measured once per second during application of RF-current, enabling real-time correlation of RF parameters and lesion size. In case of an audible steam pop, RF application was stopped. RESULTS: In total, 61 lesions were included in the analysis. Due to at least 60 measurements per lesion, 3321 data points with all ablation parameters (power, temperature, global impedance, lesion diameter and lesion depth) were collected and analyzed. Throughout the application, lesion progression was highest in the first seconds of RF application and showed a slowing approximation to a maximum (Figure 1 and 2). Potential maximum lesion size seems to be defined by selected power level (s. Figure 3). Interestingly, these findings were seen in all power levels from 20 – 70 W (s. Figure 3). 75 % of final lesion size was achieved after 12-25 seconds, depending on selected power levels (s. Figure 4). In high power ablation (> 50 W), 75% of final lesion size was reached significantly earlier compared to lower power levels (20-40 W, s. Figure 4). CONCLUSION: In RF-ablation, lesion growth is not linear. A slowing approximation of lesion diameter and depth to a maximum is observed. This finding should be considered in clinical settings to avoid steam pops and collateral damage due to a long RF duration despite little changes in lesion size. Further investigation is needed for a surrogate parameter, which is able to assess declining lesion growth after the first seconds of RF-application. [Figure: see text] [Figure: see text]