Improving the safety and efficacy of bimodal electric tissue ablation.
Introduction: Bimodal electric tissue ablation (BETA) is a new method of ablation, which combines the process of electrolysis with radiofrequency ablation (RFA) to increase the size of tissue ablations. The cathode of the electrolytic circuit is connected to the radiofrequency (RF) electrode to increase the surrounding tissue hydration. This allows the RFA process to continue for a longer period of time and therefore produce larger ablations. Previous research has shown that BETA could produce larger ablations compared to standard RFA and that it did not produce any significant short or long-term complications. The studies described here aim to increase the knowledge on how BETA works to facilitate its translation into clinical practice to treat liver tumours. Materials & Methods The first study tested whether BETA really acts by increasing the hydration of tissues around the RF electrode. This was achieved by reversing the polarity of the electrolytic circuit, which theoretically would produce smaller ablations compared to standard RFA. The second study assessed where would be the best location (skin, parietal peritoneum or liver) for the anode of the electrolytic circuit during a BETA process. The third experiment determined whether the principle of BETA could be incorporated into the Cool-Tip RF system, which uses internally-cooled electrodes (ICEs). Results The duration of ablation when the polarity of the electrolytic circuit was reversed (called reversed polarity bimodal electric ablation, or RP-BEA) were significantly shorter compared to standard RFA and BETA (48s vs. 148s and 84s respectively, p=0.004). Consequently the size of ablations in RP-BEA was significantly smaller compared to RFA and BETA (9.1mm vs. 13.4mm and 11.6mm, p=0.001). The second experiment showed that the size of ablations were significantly larger when the anode of the electrolytic circuit was placed on the peritoneum or the liver, compared to when it was placed on the skin (19.7mm and 17.9mm vs. 12.4mm, p<0.001). Lastly, the third experiment showed that the principle of BETA could be incorporated into the Cool-Tip RF system to produce significantly larger ablations compared to standard RFA alone (23.1mm vs. 20.1mm, p<0.001). Discussion The results from this study confirmed the theory that BETA increases ablation size due to the effects of increased tissue hydration around the RF electrode. The increased hydration delays tissue desiccation during an ablation, thus allowing the process to continue for longer periods of time, therefore producing larger ablations. The efficacy of BETA depends on good electrical conductivity between the cathode and the anode of the DC circuit. Results from the second study showed that BETA works best when the anode of the electrolytic circuit was placed deep to the skin as the stratum corneum consisted of a layer of anucleated cells which have high electrical resistivity. Lastly, BETA could be incorporated into the Cool-Tip RF system (Covidien, ValleyLab), which is one of the popular RFA generators in the market. This means that BETA could be readily incorporated into existing RF generators, therefore facilitating its translation into the clinical settings.
radio frequency ablation; liver cancer; liver metastases
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