Biopotential as predictor of ablation zone size during radiofrequency tumor ablation

Biopotential is an electrochemical potential that has been shown to correlate well with the coagulation zone size during cardiac RF catheter ablation. We designed an in vivo experiment to test the hypothesis that a similar correlation exists during hepatic RF ablation. We created coagulation zones, in vivo, in porcine liver, with 17 gauge needle electrodes, using RF ablation (n=56n=56). The power was set constant at 30 W, controlled by impedance, and applied for 60, 120 or 180 s. We measured the biopotential between the electrode and the ground pad with low-pass filtering. The diameter and volume of the coagulation zone were measured and correlated with the change in biopotential between the beginning and end of each ablation procedure. Moderate correlation between biopotential change and both coagulation zone volume (R2=0.43R2=0.43) and diameter (R2=0.31R2=0.31) was observed. The time constant of the biopotential change was not significantly different from the time constant of the ablation zone diameter (36.6 s, p=0.93p=0.93); the biopotential may, therefore, predict the time course of the ablation zone diameter. The biopotential can potentially be used for intraprocedural monitoring of the progression of the thermal damage zone. It may also allow termination of the procedure, if it can be confirmed that the biopotential reliably correlates with the cessation of ablation zone expansion.