Analysis of tissue impedance waveform reflecting in a grounding pad burn during radiofrequency ablation

We experienced a patient, 70s old male, complicated by second-degree skin burns at the grounding pad site during percutaneous radiofrequency ablation therapy (RFA). The patient underwent two sessions of RFA for two hepatocellular carcinoma nodules. Monitoring of the impedance (IMP) in the tissue during ablation showed irregular waves, differing from regular normal pattern. During the first session, he showed restlessness and needed to be restrained, and a sudden increase in IMP without bubble appearance on ultrasound was observed. At the start of the second session, IMP increased, while in normal case it would decrease. On the following day, a skin burn was observed at the grounding pad site, and it was thought that the skin burn developed as a result of increased RF current density due to the partial detachment of the grounding pad during ablation. As the increase in the amplitude of the IMP wave during ablation in this case was caused by the partial detachment of the grounding pad, monitoring of IMP wave is useful in an early detection of grounding pad detachment and prevention of skin burns during RFA.