Wet radio-frequency ablation using multiple electrodes: comparative study of bipolar versus monopolar modes in the bovine liver

Abstract

Objective: To determine whether hypertonic saline (HS)-mediated bipolar radio-frequency (rf) application as advantages over monopolar simultaneous and alternating rf applications for creating larger areas of coagulation necrosis.

Materials and methods: A total of 60 rf ablations using double perfused-cooled electrodes and a 200 W generator (CC-3 model, Radionics) were performed in three different modes in explanted bovine livers: simultaneous monopolar mode (groups A and A′); alternating monopolar mode (groups B and B′); or bipolar mode (groups C and C′). Electrodes were placed at inter-electrode distances of 3 and 5 cm, and HS (6% NaCl solution) was instilled into tissue at a rate of 1 mL/min through the electrodes. rf was applied for 10 (3 cm distance) or 15 min (5 cm distance). During rf application, we measured the tissue temperature at the mid-point between the two electrodes. Dimensions of the thermal ablation zones, and temperatures were compared between the 3 groups using analysis of variance or the Kruskal–Wallis test. To compare configurations of the ablation zones in each group, the ratio of longitudinal diameter (Dl) to vertical diameter (Dv) was calculated.

Results: With a 3-cm inter-electrode spacing, the Dv between the electrodes of ablated lesions was 2.4 ± 1.2 cm in group A, 4.5 ± 1.0 cm in group B, and 6.1 ± 0.9 cm in group C (P < 0.05), and at a 5-cm spacing, groups B′ and C′ produced a single ablation area, but group A′ produced two separated ablation spheres: the Dvs were 1.4 ± 0.2 in group A, 2.9 ± 1.0 mm in group B, and 6.6 ± 0.4 cm in group C (P < 0.05). For both 5- and 3-cm spacings, the temperatures at the mid-point were higher in bipolar mode than in either monopolar simultaneous or alternating modes. The ratios of Dl/Dv of groups A, B, and C were 2.5 ± 0.2, 1.4 ± 0.1, and 1.1 ± 0.1, respectively, and the corresponding figures of groups A′, B′ and C′ were 4.5 ± 0.2, 2.7 ± 0.1, and 1.1 ± 0.1, respectively (P < 0.05).