Sequential activation of ground pads reduces skin heating during radiofrequency ablation: initial in vivo porcine results

Abstract

Purpose: Radiofrequency (RF) ablation is a common treatment modality for inoperable liver cancer. Skin burns below ground pads during RF ablations are increasingly prevalent, hindering the development of higher-power RF generators capable of creating larger ablation zones.

Materials and methods: 9 RF ablations (n=4 simultaneous, n=5 sequential) were performed with 300 W for 12 min via two internally cooled cluster electrodes placed in the gluteus maximus of domestic swine. Three ground pads placed on the animal's abdomen were activated either simultaneously, or sequentially where activation timing was adjusted to equilibrate skin temperature below each pad. Temperature rise at each pad was compared. Ablation zone dimensions were determined via MRI.

Results: Maximum temperature rise was significantly higher with simultaneous activation than with sequential activation (21.4 vs 8.1 degress C, p<0.01). Ablation zone diameters during simultaneous and sequential activation were 6.9+/-0.3 and 5.6+/-0.3, respectively.

Conclusion: Sequential activation of multiple ground pads resulted in significantly lower skin temperatures during highpower RF ablation.

Figure 3

Timing diagram for sequential activation algorithm. During power application, skin heating occurs primarily at the leading edge of the activated ground pad that is nearest to the active RF electrode (ie, the proximal pad during t₁, the middle pad during t₂, and the distal pad during t₃).

Figure 4

Diagram of ground pad activation control system. A control algorithm on the PC regulated the generator output power P. A digital multimeter/DAQ measured the applied voltage V and relayed it to the control algorithm for calculation of current and impedance. A second data acquisition device recorded the temperatures (T₁, T₂, T₃) at the leading edge of each ground pad. During the group 1 procedures, all 3 ground pads were activated for the entire ablation. During the group 2 ablations, the control algorithm adjusted the switching periods (t₁, t₂, and t₃) via the digital multimeter/DAQ to keep leading edge temperatures equal between pads.