Bimodal electric tissue ablation (BETA) — in-vivo evaluation of the effect of applying direct current before and during radiofrequency ablation of porcine liver

Aim

To examine the effect of applying increasing amounts of direct current (DC) before and during alternating current radiofrequency ablation of porcine liver.

Materials and methods

Using a Radiotherapeutics RF3000 generator, a 9V AC/DC transformer and a 16 G plain aluminium tube as an electrode, a control group of 24 porcine hepatic radiofrequency ablation zones was compared with 24 zones created using a bimodal electric tissue ablation (BETA) technique in three pigs. All ablations were terminated when tissue impedance rose to greater than 999 Ω or radiofrequency energy input fell below 5W on three successive measurements taken at 1min intervals. BETA ablations were performed in two phases: an initial phase of variable duration DC followed by a second phase during which standard radiofrequency ablation was applied simultaneously with DC. During this second phase, radiofrequency power input was regulated by the feedback circuitry of the RF3000 generator according to changes in tissue impedance. The diameters (mm) of each ablation zone were measured by two observers in two planes perpendicular to the plane of needle insertion. The mean short axis diameter of each ablation zone was subjected to statistical analysis.

Results

With increased duration of prior application of DC, there was a progressive increase in the diameter of the ablation zone (p<0.001). This effect increased sharply up to 300s of pre-treatment after which a further increase in diameter occurred, but at a much lesser rate. A maximum ablation zone diameter of 32mm was produced (control diameters 10–13mm).

Conclusion

Applying a 9V DC to porcine liver in vivo, and continuing this DC application during subsequent radiofrequency ablation, results in larger ablation zone diameters compared with radiofrequency ablation alone.