The influence of electrode-tissue-coverage on RF lesion formation and local impedance: Insights from an ex vivo model

Background: The influence of power, duration and contact force (CF) on radiofrequency (RF) lesion formation is well known, whereas data on local impedance (LI) and electrode-tissue-coverage (ETC) is scarce. The objective was to investigate their effect on lesion formation in an ex vivo model.Methods and Results: An ex vivo model was developed utilizing cross-sections of porcine heart preparations and a force-sensing, LI-measuring catheter. N = 72 lesion were created systematically varying ETC (minor/full), CF (1-5 g, 10-15 g, 20-25 g) and power (20 W, 30 W, 40 W, 50 W). In minor ETC, the distal tip of the catheter was in electric contact with the tissue, in full ETC the whole catheter tip was embedded within the tissue. Lesion size and all parameters were measured once per second (n = 3320). LI correlated strongly with lesion depth (r = -0.742 for Delta LI; r = 0.781 for %LI-drop). Lesions in full ETC were significantly wider and deeper compared to minor ETC (p < .001) and steam pops were more likely. Baseline LI, Delta LI, and %LI-drop were significantly higher in full ETC (p < .001). In lesions resulting in steam pops, baseline LI, and Delta LI were significantly higher. The influence of CF on lesion size was higher in minor ETC than in full ETC.Conclusions: ETC is a main determinant of lesion size and occurrence of steam pops. Baseline LI and LI-drop are useful surrogate parameters for real-time assessment of ETC and Delta LI correlates strongly with lesion size.