Bimodal electric tissue ablation (BETA) — in-vivo evaluation of the effect of applying direct current before and during radiofrequency ablation of porcine liver

Bimodal electric tissue ablation (BETA)--effect of reversing the polarity of the direct current on the size of ablation

BACKGROUND

Bimodal electric tissue ablation (BETA) is a new technique that uses the direct current in electrolysis to improve the efficacy of radio frequency (RF) ablation. It was hypothesized that attaching the cathode of the electrolytic circuit to the RF electrode will increase the tissue hydration, therefore delaying tissue desiccation during ablation. Consequently, the ablation process can continue for a longer period of time and produce larger ablations. This hypothesis was tested by reversing the polarity of the electrolytic circuit, which theoretically would cause tissue desiccation and therefore produce smaller ablations. This new setup is called reversed polarity bimodal electric ablation (RP-BEA).

MATERIALS AND METHODS

Three types of ablations standard radiofrequency ablation (RFA), BETA, and RP-BEA) were tested in a pig liver model. In BETA and RP-BEA, 9 V of direct current were provided for 10 min, after which the rf generator were switched on and both electrical circuits allowed to run concurrently. In all three setups, ablations were continued until "roll-off." The size of ablation was measured and compared with each other.

RESULTS

The duration of ablation was significantly shorted in RP-BEA compared with standard RFA and BETA (48 s verus 148 s and 84 s, respectively, P = 0.004). The sizes of ablations in RP-BEA were also significantly smaller compared with standard RFA and BETA-skin.

CONCLUSION

RP-BEA caused tissue desiccation resulting in a shorter duration of ablation and smaller ablations. Therefore, the theory that BETA increases ablation size due to the effects of increased tissue hydration around the rf electrode is correct.

Intrahepatic radiofrequency ablation versus electrochemical treatment ex vivo

BACKGROUND

Radiofrequency ablation (RFA) and electrochemical treatment (ECT) are two methods of local liver tumor ablation. A reproducible perfusion model allowed us to compare these methods when applied in proximity to vascular structures.

MATERIAL AND METHODS

In a porcine liver perfusion model, we used RFA (group A) and ECT (group B) to perform ablations under ultrasound guidance within 10 mm of a vessel and examined the induced necrosis macroscopically and histologically.

RESULTS

We created 83 lesions (RFA: 59, ECT: 24) in 27 livers. In group A (mean liver weight: 2046 g), perfusion was macroscopically found to limit necrosis in 52.5% of the procedures. Histology demonstrated the destruction of only 30.4% of the vessel walls within the ablation areas. In group B (mean liver weight: 1885 g), we detected reproducible and sharply demarcated ablation areas both macroscopically and histologically. Necrosis was unaffected by nearby vessels. No viable cells were found perivascularly. Histology showed destruction of the vascular endothelium without any discontinuities. We measured pH values of 0.9 (range: 0.6-1.8) at the anode and 12.2 (range: 11.4-12.6) at the cathode. Treatment time was 100 min when a charge of 300 coulombs was delivered.

CONCLUSIONS

Electrochemical treatment is a method of ablation that creates reproducible and predictable volumes of necrosis. It produces sharply demarcated areas of complete necrosis also in perivascular sites. ECT, however, requires much longer treatment times than RFA. In our model, the effects of RFA were considerably limited by perfusion, which caused incomplete areas of necrosis in proximity to vessels.

Bimodal electric tissue ablation (BETA) compared with the Cool-Tip RFA system

BACKGROUND

Bimodal electric tissue ablation (BETA) incorporates the process of electrolysis into radiofrequency ablation (RFA) to increase the size of tissue ablation. This study investigated whether BETA could increase the efficacy of the Cool-Tip RF system (Covidien, Boulder, CO, USA) to produce larger ablations. It also investigated whether applying electrolysis only during the pretreatment phase (called electrochemical treatment (ECT)/RFA group) is as effective as BETA (where electrolysis was used during both the pretreatment and RFA phases).

METHODS

A Cool-Tip RF system (Covidien) was used to test three types of ablations (RFA, BETA, and ECT/RFA) in a pig liver model. In BETA, 9 V of direct current was provided for 10 min, after which the RF generator was started and both electrical circuits were allowed to run concurrently. In ECT/RFA, however, the direct current circuit was switched off after 10 min of pretreatment and only RFA was performed as described above. Ablation sizes were measured in three dimensions.

RESULTS

The size of ablations (transverse diameter A and B) produced by BETA and ECT/RFA was significantly larger compared with standard RFA (P < 0/001). BETA also created larger ablations compared with ECT/RFA (P < 0.001).

CONCLUSION

BETA could improve the efficacy of the Cool-Tip RF system (Covidien) to achieve larger ablations. The increased tissue hydration improved delivery of electrical energy to the tissues and delayed the process of desiccation, thus allowing the ablation process to continue for longer periods of time to produce larger ablations. BETA could be used to treat larger liver tumours more effectively than standard RFA.

Bimodal electric tissue ablation (BETA): a study on ablation size when the anode is placed on the peritoneum and the liver

BACKGROUND

In bimodal electric tissue ablation (BETA), the cathode of the DC circuit is attached to the radiofrequency (RF) electrode to increase the surrounding tissue hydration. This will delay tissue desiccation and allowing the ablation process to continue for a longer period of time before "roll-off" occurs, resulting in larger ablations compared with standard radiofrequency ablation (RFA). Previous research showed that attaching the anode to the skin using electrosurgical grounding pads would reduce the efficacy of BETA because of the high electrical resistivity of the skin. This study investigated the ablation size produced when the anode was attached to the peritoneum (BETA-peritoneum) and the liver (BETA-liver) respectively.

MATERIALS AND METHODS

The anode of the DC circuit in BETA was attached to the peritoneum and the liver in a pig model using ECG dots. In BETA, 9 V of DC was provided for 10 min, after which the radiofrequency generator were switched on and both electrical circuits allowed to run concurrently until "roll-off." The size of ablations produced was compared to when the anode attached to the skin (BETA-skin) and standard RFA, respectively. The sites of anode placement were examined for local tissue injury.

RESULTS

The transverse diameters in BETA-peritoneum and BETA-liver were significantly larger compared with BETA-skin and standard RFA, respectively (P < 0.001). The axial diameter in the BETA-peritoneum and BETA-liver groups were also larger compared with the BETA-skin and RFA groups, although the differences did not reach statistical significance (P = 0.09). Hematoxylin and eosin (H and E) examination of the peritoneum and the liver where the anode was attached showed coagulation necrosis involving the superficial epithelium and the liver capsule, respectively.

CONCLUSIONS

BETA can be used to treat larger liver tumors more effectively and may reduce the tumor recurrence rates compared with standard RFA. The efficacy of BETA depends on ensuring good electrical conductivity between the cathode and the anode of the DC circuit. Research so far has shown that BETA works best when the anode is placed deep to the skin as the stratum corneum consisted of a layer of a-nucleated cells, which have high electrical resistivity. The liver could be the ideal location to place the anode as it has excellent electrical conductivity, therefore ensuring maximum tissue hydration around the cathode to produce the largest ablations possible.

Direct current combined with bipolar radiofrequency ablation: an ex vivo feasibility study

The combination of radiofrequency ablation (RFA) with direct current (DC) is a promising strategy to improve the efficiency of RFA. However, DC-enhanced monopolar RFA is limited by electrolytic injury at the positive-electrode site. The aim of this study was to investigate the feasibility of the DC-enhanced bipolar RFA. To obviate the need for the subcutaneous positive electrode, the DC circuit was combined with a commercially available bipolar RFA system, in which both poles of the DC circuit are connected to a single RF probe. DC was applied for 15 min and followed by RFA in bovine livers using the following various DC currents: (1) no DC (control), (2) 3V continued until the end of RFA, (3) 5V continued until the end of RFA, (4) 10V continued until the end of RFA, (5) 5V continued in the circuit with reversed pole, (6) 3V stopped after initiation of RFA, and (7) 5V stopped. Coagulation volume, temperatures at a distance of 5, 10, and 15 mm from the RF probe, mean amperage, ablation duration, applied energy, minimum impedance, and degree of tissue charring were assessed and compared (analysis of variance, Student-Newman-Keuls test). All combined DC and RFA groups did increase coagulation volume. The 10V continued group showed significantly lower applied energy, shortest ablation duration, highest minimum impedance, and highest degree of charring with the lowest coagulation volume (p<0.05). DC-enhanced bipolar RFA with both poles of the DC circuit on a single probe appears to be ineffective.

Optimization of direct current-enhanced radiofrequency ablation: an ex vivo study

The purpose of this study was to investigate the optimal setting for radiofrequency (RF) ablation combined with direct electrical current (DC) ablation in ex vivo bovine liver. An electrical circuit combining a commercially available RF ablation system with DC was developed. The negative electrode of a rectifier that provides DC was connected to a 3-cm multitined expandable RF probe. A 100-mH inductor was used to prevent electrical leakage from the RF generator. DC was applied for 15 min and followed by RF ablation in freshly excised bovine livers. Electric current was measured by an ammeter. Coagulation volume, ablation duration, and mean amperage were assessed for various DC voltages (no DC, 2.2, 4.5, and 9.0 V) and different RF ablation protocols (stepwise increase from 40 to 80 W, 40 W fixed, and 80 W fixed). Results were compared using Kruskal-Wallis and Mann-Whitney U test. Applying DC with 4.5 or 9.0 V, in combination with 40 W fixed or a stepwise increase of RF energy, resulted in significantly increased zone of ablation size compared with 2.2 V or no DC (P = 0.009). At 4.5 V DC, the stepwise increase of RF energy resulted in the same necrosis size as a 40 W fixed protocol (26.6 +/- 3.9 vs. 26.5 +/- 4.0 ml), but ablation duration was significantly decreased (296 +/- 85 s vs. 423 +/- 104 s; P = 0.028). Mean amperage was significantly lower at 4.5 V compared with 9.0 V (P = 0.028). Combining a stepwise increase of RF energy with a DC voltage of 4.5 V is most appropriate to increase coagulation volume and to minimize procedure time.

Experimental application of electrolysis in the treatment of liver and pancreatic tumours: principles, preclinical and clinical observations and future perspectives

BACKGROUND

Electrolytic ablation (EA) is a treatment that destroys tissues through electrochemical changes in the local microenvironment. This review examined studies using EA for the treatment of liver and pancreatic tumours, in order to define the characteristics that could endow the technique with specific advantages compared with other ablative modalities.

METHODS

Literature search of all studies focusing on liver and pancreas EA.

RESULTS

A specific advantage of EA is its safety even when conducted close to major vessels, while a disadvantage is the longer ablation times compared to more frequently employed techniques. Bimodal electric tissue ablation modality combines radiofrequency with EA and produced significant larger ablation zones compared to EA or radiofrequency alone, reducing the time required for ablation. Pancreatic EA has been investigated in experimental studies that confirmed similar advantages to those found with liver ablation, but has never been evaluated on patients. Furthermore, few clinical studies examined the results of liver EA in the short-term but there is no appropriate follow-up to confirm any survival advantage.

CONCLUSIONS

EA is a safe technique with the potential to treat lesions close to major vessels. Specific clinical studies are required to confirm the technique's safety and eventually demonstrate a survival advantage.

Bimodal electric tissue ablation-long term studies of morbidity and pathological change

BACKGROUND

Radiofrequency ablation is a popular method of treating unresectable liver tumors but tumors greater than 3 cm in diameter have a much greater risk of local recurrence after treatment. Bimodal electric tissue ablation is a modified form of radiofrequency ablation that creates significantly larger ablations by the addition of extra direct current circuitry. This may help to reduce the risk of local recurrence in these larger tumors. Prior to use in a clinical setting, a long term study was performed to assess associated morbidity and the pathological changes in the ablations.

METHODS

In eight pigs, six ablations were performed in each liver. Pigs were euthanized at 2 d, 2 wk, 2 mo, and 4 mo, and the ablations were assessed macroscopically and microscopically for pathological change. Regular blood tests were performed to assess changes in liver function. At death, any other abnormalities detected were reported.

RESULTS

Histopathological examination of ablation zones revealed tissue death by coagulative necrosis and healing by fibrotic scarring. Transient rises in serum liver enzymes were seen in the postoperative period. Skin necrosis was noted at the site of the positive electrode of the direct electrical current but no other form of morbidity was seen associated with the procedure.

CONCLUSIONS

Although the positive electrode placement requires further consideration, bimodal electric tissue ablation appears to be safe and behaves in a similar fashion to other thermal therapies such as standard radiofrequency ablation.