Local impedance changes are a suitable real time surrogate for lesion formation in RF-ablation

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Background Radiofrequency current remains one of the most important techniques for catheter ablation. Creating durable lesions is key for sufficient and safe procedures. Several possibilities were tested for estimating the progress of lesion formation. For instance, force-time-integral, ablation index and lesion size index are used to assess quality of RF-application and, therefore, lesion size and durability. Nevertheless, recovered conduction after acute conduction block remains an issue in RF-ablation. The aim of this study was to evaluate local impedance (LI) changes as real time surrogate for lesion formation. Methods RF-lesions were created using an ex vivo porcine cardiac model and a force and local impedance sensing catheter. 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 contact force. RF power (20W, 30W, 40W, 50W) and level of electrode-tissue-coupling were also systematically varied between minor and full coupling. In minor ETC-level, only the distal end of the catheter is in contact with the tissue. In full ETC-level, the whole catheter tip is in contact with the tissue. All parameters (power, temperature, global and local impedance, contact force, ETC, lesion size) were measured constantly 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 Including a total of 8654 measurements into the analysis, maximum diameter and depth were 9.51 ± 1.91 mm and 7.29 ± 2.50 mm in average. Local impedance correlated well with lesion depth (r= 0,78, p<0,001), as well as lesion diameter (r=0,652, p<0,001, Figure 1). After significant declines of LI at the beginning of RF-application, it slowly approximates a minimum. Lesion size on the other hand, rises exponentially in first seconds and gets closer to a maximum after more than 25 seconds. This relationship is illustrated in Figure 2. With decreasing lesion growth at the end of RF-application, LI changes decrease to low level (Figure 3). Conclusion Lesion formation in RF-ablation is not linear during application of RF current. Local impedance changes seem to be a suitable real-time surrogate for assessing changes in lesion size during ablation.