Evolving technology in bipolar perfused radiofrequency ablation:: assessment of efficacy, predictability and safety in a pig liver model

Bipolar radiofrequency (RF) ablation, especially with perfusion of saline, has been shown to increase volume over monopolar conventional methods. The aims of this study are to study whether this method is linked to too flattened thermal lesions and premature rise of impedance and to elucidate some safety concerns. Eighteen RF ablations were performed using a 1.8-mm-diameter bipolar applicator in the liver of nine healthy pigs through laparotomy with or without temporary vascular occlusion [ the Pringle maneuver (PGM)]: group A ( n= 9), without PGM; group B ( n= 9), with PGM. Hypertonic saline solutions (3% and 20%) were injected through the applicator at a rate of 400 ml/h during the procedure. The pigs were followed up and they were euthanased on the 15th day. Impedance, current, power output, energy output, temperatures, diameters of thermal lesion, volume, sphericity ratio of thermal lesion were correlated among groups. Impedance at the end of the procedure (50.00 Omega +/- 28.39 and 52.88 Omega +/- 26.77, for groups A and B, respectively) was very similar to the starting impedance ( 50 Omega). In a median of 1 ( range, 0 - 6) time per RF ablation procedure a reduction of 30 W from the selected power supply was observed during the RF ablation procedure linked to a slight increase of impedance. Volume and short diameter of thermal lesion were 21.28 cm(3) +/- 11.78 and 2.85 cm +/- 0.87 for group A, 87.51 cm(3) +/- 25.20 and 4.31 cm +/- 0.65 for group B. Continuous thermal between both electrodes were described with a global sphericity ratio of 1.91. One major complication ( thermal injury to the stomach) was encountered in a case of cross-sectional necrosis of the targeted liver and attributed to heat diffusion after the procedure. This method has been shown to determine: ( 1) the relative control of impedance during the procedure; ( 2) ovoid and relatively large thermal lesions with less dependence upon closest vessels.