GastrointestinalBimodal Electric Tissue Ablation-Modified Radiofrequency Ablation with a Le Veen Electrode in a Pig Model
Introduction
It has been well established that patients with hepatomas or colorectal liver metastases have their best chance of long term survival where surgical resection is possible [1, 2]. Unfortunately, only 20% of patients are amenable to this form of treatment [2]. This has resulted in the development of ablative techniques that offer these patients an alternative treatment. Of these, radiofrequency ablation is currently one of the most popular. It works by delivering a high frequency, alternating electrical current through the tumor that causes oscillation of ions as they follow the alternating current [3]. This in turn leads to frictional heating of the tumor cells and this heating of the tumor induces coagulative necrosis [3, 4]. Previous reports have shown it to be safe and efficacious and it can be performed percutaneously or surgically [5, 6, 7, 8].
Reports are now emerging which suggest that the rates of local recurrence after treatment with radiofrequency ablation are unacceptably high and these have been reported to be as high as 47% [9, 10, 11, 12, 13, 14]. There are many associated factors with local recurrence but the most profound risk factor for local recurrence is the size of the tumor being ablated [9]. Tumors greater than 3 cm in diameter have been shown to have much greater rates of local recurrence [9, 12, 15, 16].
In a trial of four commonly used needle electrodes, the authors concluded that theoretically, the largest tumor that is able to be ablated with a 1 cm safety margin is 3 cm in diameter [17]. Larger tumors require multiple ablations to treat the one tumor [18]. This has the potential to lead to incomplete ablation of the tumor treated and, as a result, can lead to local recurrence [19].
The limiting factor for all electrodes is tissue desiccation and localized charring that occurs around the electrode itself [18]. Charring prevents further conduction of the electrical current [18]. It is hypothesized that if desiccation and charring could be prevented or at least delayed, the size of the ablation zone could be increased. Experiments with preinjecting the tissue to be ablated with hypertonic saline and the development of perfusion needle electrodes that allow infusion of saline through them into the tissues have shown modest improvements in the size of the ablative zones [20, 21].
Previous experimental work has shown that direct electrical currents have water attracted to the cathode or negative electrode [22, 23, 24]. It was therefore hypothesized that if a direct current could be combined with an alternating radiofrequency current, then potentially water could be drawn into the region where the electrode is performing an ablation and charring could be prevented. Consequently, a bimodal electrical circuit that combined the two electrical modalities was created and the hypothesis was tested in a pig model using a standard 35 mm multitine Le Veen electrode.
Section snippets
Materials and Methods
This study was performed using white female domestic pigs at The Queen Elizabeth Hospital campus of the University of Adelaide. Ethical approval for the study was gained from the combined Central North Adelaide Health Service and Institute of Medical and Veterinary Service animal ethics committee and the University of Adelaide animal ethics committee. The study conformed with the Code of Practice for the Care and Use of Animals for Scientific Purposes 2004 and the South Australian Prevention of
Results
Four female domestic white pigs were used for this study. From these pigs, 14 controls and 12 bimodal electrical tissue ablation (BETA) zones were produced. Four controls and two BETA zones were produced in the first pig, three controls and three BETA zones were produced in the second pig, four controls and four BETA zones were produced in the third pig. Three controls and three BETA zones were produced in the fourth pig. The large BETA zones performed in the first pig took up considerable room
Discussion
This study has shown that the combination of a direct current and an alternating radiofrequency current, the ablation zones produced are significantly larger in size than those produced by radiofrequency ablation alone. This is most likely as a result of the target liver becoming less desiccated, thus leading to a delay in charring of the tissues. This hydrating effect was illustrated by the way in which the liver became congested and secreted fluid from its surface. The lack of resistance from
Acknowledgments
The authors thank Dr. Catriona Brennan from the Department of Pathology at The Queen Elizabeth Hospital for her assistance in reviewing the histology slides, Dr. John Field from Biostats SA for statistical support, Mr. Adrian Hines from The Queen Elizabeth Hospital animal house for his assistance in providing anesthesia, and Ms. Lisa Leopardi from the Department of Surgery at The Queen Elizabeth Hospital for her assistance in providing clerical support for this project.
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2012, Journal of Surgical ResearchCitation Excerpt :Numerous modifications have been made to both the radiofrequency generator and the electrode design to increase the size of tissue ablation achievable. One recent discovery is bimodal electric tissue ablation (BETA) which combines the cathode of a DC circuit to the radiofrequency (RF) electrode to increase the size of tissue ablation [7–10]. The cathode will increase the hydration of the tissues around it which will delay tissue desiccation and “roll-off” during an ablation.
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2012, Journal of Surgical ResearchCitation Excerpt :It was this “hydrating” property of the cathode that forms the underlying principle in bimodal electric tissue ablation (BETA). Cockburn et al. and Dobbins and colleagues postulated that increasing the hydration of the liver tissues around the active RF electrode would reduce the tissue temperature during ablation [21–24]. This would delay tissue desiccation and allows the ablation process to continue for a longer period of time and therefore produce larger ablations.
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2012, Journal of Surgical ResearchCitation Excerpt :In summary, it is doubtful that RFA can induce adequate and complete perivascular necrosis at a distance of 10 mm from a vessel. The effect of RFA can theoretically be increased by a Pringle maneuver or, as was reported by a number of authors, larger ablations can be produced by RFA with the addition of a low level of direct electrical current [23, 24]. Whereas radiofrequency ablation is a thermal procedure that induces tissue necrosis mainly through protein denaturation, a number of different mechanisms of destruction are believed to play a role in electrochemical treatment.
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2011, Surgical OncologyCitation Excerpt :Similar results were confirmed in two other studies (BETA = 3.0 ± 0.3 cm and 2.5 ± 0.1 cm) [15,16]. Larger diameters were achieved with a LeVeen electrode and, even in this case, those obtained with the combined BETA modality were significant larger than with RFA alone (RFA = 2.9 ± 0.3 cm; BETA = 5.0 ± 0.3 cm) [14,49]. BETA lesions had the same temporal evolution as EA alone with a proliferation of fibroblasts and bile ducts progressively replaced the necrotic zones [15].