Dual Switching Monopolar Radiofrequency Ablation Using a Separable Clustered Electrode: Comparison with Consecutive and Switching Monopolar Modes in Ex Vivo Bovine Livers

Objective: To compare the in-vitro efficiency of dual-switching monopolar (DSM) radiofrequency ablation (RFA) using a separable clustered electrode (Octopus$^{(R)}$ electrodes) with consecutive monopolar (CM) and switching monopolar (SM) RFA techniques to create an ablative zone in the explanted bovine liver. Materials and Methods: For DSM-RFA, we used a prototype, three-channel, dual generator RFA Unit and Octopus$^{(R)}$ electrodes with three, 17 gauge internally cooled electrodes. The RFA Unit allowed simultaneous radiofrequency (RF) energy delivery to two electrodes of the Octopus$^{(R)}$ electrodes as well as automatic switching among the three electrode pairs according to the impedance changes. RF energy was sequentially applied to one of the three electrodes for 24 minutes (group A; CM mode, n = 10) or alternatively applied for 12 minutes (group B; SM mode, n = 10) or concurrently applied to a pair of electrodes for 12 minutes (group C; DSM mode, n = 10) in explanted bovine livers. Changes in the impedance and current during RFA as well as the dimensions of the thermal ablative zones were compared among the three groups. Results: The mean, delivered RF energy amounts in groups A, B, and C were 63.15 ${\pm}$ 8.6 kJ, 72.13 ${\pm}$ 5.4 kJ, and 106.08 ${\pm}$ 13.4 kJ, respectively (p < 0.001). The DSM mode created a significantly larger ablation volume than did the other modes, i.e., 68.1 ${\pm}$ 10.2 $cm^3$ (group A), 92.0 ${\pm}$ 19.9 $cm^3$ (group B), and 115.1 ${\pm}$ 14.0 $cm^3$ (group C) (p < 0.001). The circularity in groups A, B, and C were 0.84 ${\pm}$ 0.06, 0.87 ${\pm}$ 0.04 and 0.90 ${\pm}$ 0.03, respectively (p = 0.03). Conclusion: DSM-RFA using Octopus$^{(R)}$ electrodes can help create large ablative zones within a relatively short time.