Radio Frequency Ablation in the Rabbit Lung Using Wet Electrodes: Comparison of Monopolar and Dual Bipolar Electrode Mode

Objective: To compare the effect of radio frequency ablation (RFA) on the dimensions of radio frequency coagulation necrosis in a rabbit lung using a wet electrode in monopolar mode with that in dual electrode bipolar mode at different infusion rates (15 mm/hr versus 30 ml/hr) and saline concentrations (0.9% normal versus 5.8% hypertonic saline). Materials and Methods: Fifty ablation zones (one ablation zone in each rabbit) were produced in 50 rabbits using one or two 16-guage wet electrodes with a 1em active tip. The RFA system used in the monopolar and dual electrode wet bipolar RFA consisted of a 375-kHz generator (Elektrotom HiTT 106, Berchtold, Medizinelektronik, Germany). The power used was 30 watts and the exposure time was 5 minutes. The rabbits were assigned to one of five groups. Group A (n=10) was infused with 0.9% NaCl used at a rate of 30ml/hr in a monopolar mode. Groups B (n=10) and C (n=10) were infused with 0.9% NaCl at a rate of 15 and 30ml/hr, respectively in dual electrode bipolar mode; groups D (n=10) and E (n=10) were infused with 5.8% NaCl at a rate of 15 and 30ml/hr, respectively in a dual electrode bipolar mode. The dimensions of the ablation zones in the gross specimens from the groups were compared using one-way analysis of variance by means of the Scheffe test (post-hoc testing). Results: The mean largest diameter of the ablation zones was larger in dual electrode bipolar mode ($30.9{\pm}4.4$ mm) than in monopolar mode ($22.5{\pm}3.5$ mm). The mean smallest diameter of the ablation zones was larger in dual electrode bipolar mode ($22.3{\pm}2.5$ mm) than in monopolar mode ($19.5{\pm}3.5$ mm). There were significant differences in the largest and smallest dimension between the mono polar (group A) and dual electrode wet bipolar mode (groups B-E). In dual electrode bipolar mode, the mean largest diameter of the ablation zones was larger at an infusion rate of 15ml/hr ($34.2{\pm}4.0$ mm) than at 30 ml/hr ($27.6{\pm}0.1$ mm), and the mean smallest diameter of the ablation zones was larger at an infusion rate of 15ml/hr ($27.2{\pm}7.5$ mm) than at an infusion rate of 30ml/hr ($24{\pm}2.9$ mm). Conclusion: Using a wet electrode, dual electrode bipolar RFA can create a larger ablation zone more efficiently than monopolar RFA.