Baseline local impedance and changes in local impedance are predictors of electrode tissue coupling in RF-ablation

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Background Radiofrequency (RF) current remains the most ablation technology in the electrophysiologic laboratory. Durable lesion formation without collateral tissue damage is key for obtaining efficient and safe procedures. RF power, duration and contact force are considered as main determinants of lesion size. Recently published data show that electrode tissue coupling (ETC) is another important parameter of lesion formation. This ex vivo model was created to investigate local impedance changes and lesion size when alternating ETC-levels. Methods RF-lesions were created using a force and local impedance sensing catheter in an ex vivo porcine cardiac model. 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. A RF power of 20W, 30W, 40W, and 50W was used. The ETC levels were 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 8654 measurements of lesion depth and diameter were analyzed after creating 72 lesions. Lesion depth and diameter in full ETC-level were significantly higher compared to minor ETC-level (s. Table 1). Interestingly, lesions in lower power levels (20-30 Watt), but full ETC-level became wider and deeper than lesions in high power levels (40-50 Watts), but minor ETC-level (s. Figure 1). These observations were made despite shorter RF-duration (54.00 ± 13.07 s vs. 47.11 ± 17.57 s, p=0.032) in lesions with full ETC-level due to higher incidence of steam pops (14 vs. 6 steam pops, p = 0.032). Baseline LI and LI-drop were significantly higher in full ETC-level (Figure 2), but no relevant difference was observed in baseline GI. Conclusion Baseline LI and LI changes during ablation provide information about ETC-levels and interaction of the RF ablation catheter with cardiac tissue. ETC-levels, as predicted by LI, had a significantly higher impact on RF lesion size than RF power or RF-duration. Therefore, LI should be monitored during RF ablation for estimating ETC-levels and lesion formation.