Irreversible electroporation ablation: creation of large-volume ablation zones in in vivo porcine liver with four-electrode arrays

Electrolysis products, reactive oxygen species and ATP loss contribute to cell death following irreversible electroporation with microsecond-long pulsed electric fields

Membrane permeabilization and thermal injury are the major cause of cell death during irreversible electroporation (IRE) performed using high electric field strength (EFS) and small number of pulses. In this study, we explored cell death under conditions of reduced EFS and prolonged pulse application, identifying the contributions of electrolysis, reactive oxygen species (ROS) and ATP loss. We performed ablations with conventional high-voltage low pulse (HV-LP) and low-voltage high pulse (LV-HP) conditions in a 3D tumor mimic, finding equivalent ablation volumes when using 2000 V/cm 90 pulses or 1000 V/cm 900 pulses respectively. These results were confirmed by performing ablations in swine liver. In LV-HP treatment, ablation volume was found to increase proportionally with pulse numbers, without the substantial temperature increase seen with HV-LP parameters. Peri-electrode pH changes, ATP loss and ROS production were seen in both conditions, but LV-HP treatments were more sensitive to blocking of these forms of cell injury. Increases in current drawn during HV-LP was not observed during LV-HP condition where the total ablation volume correlated to the charge delivered into the tissue which was greater than HV-LP treatment. LV-HP treatment provides a new paradigm in using pulsed electric fields for tissue ablation with clinically relevant volumes.

Investigation of lethal thresholds of nanosecond pulsed electric field in rabbit VX2 hepatic tumors through finite element analysis and verification with a single-needle bipolar electrode: A prospective strategy employing three-dimensional comparisons

Pulsed electric field has emerged as a promising modality for the solid tumor ablation with the advantage in treatment planning, however, the accurate prediction of the lesion margin requires the determination of the lethal electric field (E) thresholds. Herein we employ the highly repetitive nanosecond pulsed electric field (RnsPEF) to ablate the normal and VX2 tumor-bearing livers of rabbits. The ultrasound-guided surgery is operated using the conventional double- and newly devised single-needle bipolar electrodes. Finite element analysis is also introduced to simulate the E distribution in the practical treatments. Two- and three-dimensional investigations are performed on the image measurements and reconstructed calcification models on micro-CT, respectively. Specially, an algorithm considering the model surface, volume and shape is employed to compare the similarities between the simulative and experimental models. Blood vessel injury, temperature and synergistic efficacy with doxorubicin (DOX) are also investigated. According to the three-dimensional calculation, the overall E threshold is 4536.4 ± 618.2 V/cm and the single-needle bipolar electrode is verified to be effective in tissue ablation. Vessels are well preserved and the increment of temperature is limited. Synergy of RnsPEF and DOX shows increased apoptosis and improved long-term tumor survival. Our study presents a prospective strategy for the evaluation of the lethal E threshold, which can be considered to guide the future clinical treatment planning for RnsPEF.

Interventional Radiology in the Treatment of Pancreatic Adenocarcinoma: Present and Future Perspectives

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease; patients' long-term survival is strictly linked to the surgical resection of the tumor but only a minority of patients (2-3%) have a resectable disease at diagnosis. In patients with surgically unresectable disease, interventional radiology is taking on an increasing role in treatment with the application of loco-regional percutaneous therapies. The primary purposes of this narrative review are to analyze the safety and efficacy of ablative techniques in the management of borderline resectable and locally advanced diseases and to underline the role of the interventional radiologist in the management of patients with distant metastases. The secondary purpose is to focus on the synergy between immunotherapy and ablative therapies.

Histological Response to 5 kHz Irreversible Electroporation in a Porcine Liver Model

Unlike necrosis by thermal ablation, irreversible electroporation (IRE) is known to induce apoptosis by disrupting plasma membrane integrity with electric pulses while preserving the structure of blood vessels and bile ducts in liver tissue without a heat sink effect. This study aimed to investigate thermal damage and histopathological effects in the porcine liver by high-frequency electric pulses (5 kHz) which is much higher than the widely used 1 Hz. The electric field and thermal distributions of 5 kHz electric pulses were compared with those of 1 Hz in numerical simulations. 5 kHz-IRE was applied on pigs under ultrasound imaging to guide the electrode placement. The animals underwent computed tomography (CT) examination immediately and 1 day after IRE. After CT, IRE-treated tissues were taken and analyzed histologically. CT revealed that hepatic veins were intact for 1-day post-IRE. Histopathologically, the structure of the portal vein was intact, but endothelial cells were partially removed. In addition, the hepatic artery structure from which endothelial cells were removed were not damaged, while the bile duct structure and cholangiocytes were intact. The thermal injury was observed only in the vicinity of the electrodes as simulated in silico. 5 kHz-IRE generated high heat due to its short pulse interval, but the thermal damage was limited to the tissue around the electrodes. The histopathological damage caused by 5 kHz-IRE was close to that caused by 1 Hz-IRE. If a short-time treatment is required for reasons such as anesthesia, high-frequency IRE treatment is worth considering. Our observations will contribute to a better understanding of the IRE phenomena and search for advanced therapeutic conditions.

The Influence of Irreversible Electroporation Parameters on the Size of the Ablation Zone and Thermal Effects: A Systematic Review

Introduction: The aim of this study was to review the effect of irreversible electroporation parameter settings on the size of the ablation zone and the occurrence of thermal effects. This insight would help to optimize treatment protocols and effectively ablate a tumor while controlling the occurrence of thermal effects. Methods: Various individual studies report the influence of variation in electroporation parameters on the ablation zone size or occurrence of thermal effects. However, no connections have yet been established between these studies. With the aim of closing the gap in the understanding of and personalizing irreversible electroporation parameter settings, a systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A quality assessment was performed using an in-house developed grading tool based on components of commonly used grading domains. Data on the electroporation parameters voltage, number of electrodes, inter-electrode distance, active needle length, pulse length/number/protocol/frequency, and pulse interval were extracted. Ablation zone size and temperature data were grouped per parameter. Spearman correlation and linear regression were used to define the correlation with outcome measures. Results: A total of 7661 articles were screened, of which 18 preclinical studies (animal and phantom studies) met the inclusion criteria. These studies were graded as moderate (4/18) and low (14/18) quality. Only the applied voltage appeared to be a significant linear predictor of ablation zone size: length, surface, and volume. The pulse number was moderately but nonlinearly correlated with the ablation zone length. Thermal effects were more likely to occur for higher voltages (≥2000 V), higher number of electrodes, and increased active needle length. Conclusion: Firm conclusions are limited since studies that investigated and precisely reported the influence of electroporation parameters on the ablation zone size and thermal effects were scarce and mostly graded low quality. High-quality studies are needed to improve the predictability of the combined effect of variation in parameter combinations and optimize irreversible electroporation treatment protocols.

Irreversible electroporation for colorectal cancer liver metastasis: a review

Irreversible electroporation (IRE) ablation is gaining popularity over the last decade as a nonthermal alternative to thermal ablation technologies such as radiofrequency ablation (RFA) and Microwave ablation (MWA). This review serves as a practical guide for applying IRE to colorectal cancer liver metastases (CRLM) for interventional radiologists, oncologists, surgeons, and anesthesiologists. It covers patient selection, procedural technique, anesthesia, imaging, and outcomes.

Chemotherapy plus concurrent irreversible electroporation improved local tumor control in unresectable hilar cholangiocarcinoma compared with chemotherapy alone

INTRODUCTION

Unresectable hilar cholangiocarcinoma (UHC) is a malignant tumor and has a poor prognosis. IRE is a novel non-thermal ablative therapy that causes cellular apoptosis via electrical impulses. To compare the curative effect for UHC, chemotherapy plus concurrent IRE and chemotherapy alone were set up.

MATERIALS AND METHODS

From July 2015 to May 2019, 47 patients with UHC were analyzed to chemotherapy + IRE group (n = 23) or chemotherapy alone group (n = 24) in this study. Treatment response was assessed with computed tomography (CT) or magnetic resonance imaging (MRI) 1 month after treatment and every 3 months thereafter. Local tumor progression (LTP), time to LTP, overall survival (OS) and procedure-related complications were compared between the two groups.

RESULTS

Chemotherapy plus concurrent IRE group showed a tendency toward a decreased rate of LTP (16.7% vs. 39.5%; p = 0.039) and an increased complete response rate (52.2% vs. 12.5%; p = 0.011) compared with chemotherapy alone group. Time to LTP was significantly longer in the chemotherapy plus concurrent IRE group compared to chemotherapy alone group (11.2 months vs. 4.2 months; p = 0.001). Median OS was significantly longer in the chemotherapy plus concurrent IRE group compared to chemotherapy alone group (19.6 months vs. 10.2 months; p = 0.001).

CONCLUSIONS

Chemotherapy plus concurrent IRE improved local control and prolonged time to LTP and OS in patients with UHC.

Experimental model of occluded biliary metal stent recanalization using irreversible electroporation via a tubular catheter

PURPOSE

To demonstrate the feasibility of irreversible electroporation (IRE) for treating biliary metal stent occlusion in an experimental liver model.

METHODS AND MATERIALS

IRE was performed using an expandable tubular IRE-catheter placed in nitinol stents in the porcine liver. A 3-electrode IRE-catheter was connected to an IRE-generator and one hundred 100μs pulses of constant voltage (300, 650, 1000, and 1300 V) were applied. Stent occlusion was simulated by insertion of liver tissue both ex vivo (n = 94) and in vivo in 3 pigs (n = 14). Three scenarios of the relationship between the stent, electrodes, and inserted tissue (double contact, single contact, and stent mesh contact) were studied. Electric current was measured and resistance and power calculated. Pigs were sacrificed 72 h post-procedure. Harvested samples (14 experimental, 13 controls) underwent histopathological analysis.

RESULTS

IRE application was feasible at 300 and 650 V for the single and double contact setup in both ex vivo and in vivo studies. Significant differences in calculated resistance between double contact and single contact settings were observed (ex-vivo p ˂ 0.0001, in-vivo p = 0.02; Mann-Whitney). A mild temperature increase of the surrounding liver parenchyma was noted with increasing voltage (0.9-5.9 °C for 300-1000 V). The extent of necrotic changes in experimental samples in vivo correlated with the measured electric current (r² = 0.39, p = 0.01). No complications were observed during or after the in-vivo procedure.

CONCLUSION

Endoluminal IRE using an expandable tubular catheter in simulated metal stent occlusion is feasible. The relationship of active catheter electrodes to stent ingrowth tissue can be estimated based on resistance values.

Cell death due to electroporation - A review

Exposure of cells to high voltage electric pulses increases transiently membrane permeability through membrane electroporation. Electroporation can be reversible and is used in gene transfer and enhanced drug delivery but can also lead to cell death. Electroporation resulting in cell death (termed as irreversible electroporation) has been successfully used as a new non-thermal ablation method of soft tissue such as tumours or arrhythmogenic heart tissue. Even though the mechanisms of cell death can influence the outcome of electroporation-based treatments due to use of different electric pulse parameters and conditions, these are not elucidated yet. We review the mechanisms of cell death after electroporation reported in literature, cell injuries that may lead to cell death after electroporation and membrane repair mechanisms involved. The knowledge of membrane repair and cell death mechanisms after cell exposure to electric pulses, targets of electric field in cells need to be identified to optimize existing and develop of new electroporation-based techniques used in medicine, biotechnology, and food technology.

Clinical Phase I/II Study: Local Disease Control and Survival in Locally Advanced Pancreatic Cancer Treated with Electrochemotherapy

Objective. To assess local disease control rates (LDCR) and overall survival (OS) in locally advanced pancreatic cancer (LAPC) treated with electrochemotherapy (ECT). Methods. Electrochemotherapy with bleomycin was performed in 25 LAPC patients who underwent baseline Magnetic Resonance Imaging (MRI) and/or Computed Tomography (CT) and Position Emission Tomography (PET) scans before ECT and 1 and 6 months post ECT. LDCR were assessed using Response Evaluation Criteria in Solid Tumors (RECIST 1.1) and Choi criteria. Needle electrodes with fixed linear (N-30-4B) or fixed hexagonal configurations (N-30-HG or I-40-HG or H-30-ST) or variable geometry (VGD1230 or VGD1240) (IGEA S.p.A., Carpi, Italy) were used to apply electric pulses. Pain evaluation was performed pre-ECT, after 1 month and after 6 months with ECT. Overall survival estimates were calculated by means of a Kaplan-Meier analysis. Results. At 1 month after ECT, 76% of patients were in partial response (PR) and 20% in stable disease (SD). Six months after ECT, 44.0% patients were still in PR and 12.0% in SD. A LDCR of 56.0% was reached six months after ECT: 13 patients treated with fixed geometry had a LDCR of 46.1%, while for the 12 patients treated with variable geometry, the LDCR was 66.7%. The overall survival median value was 11.5 months: for patients treated with fixed geometry the OS was 6 months, while for patients treated with variable geometry it was 12 months. Electrochemotherapy was well-tolerated and abdominal pain was rapidly resolved. Conclusions. Electrochemotherapy obtained good results in terms of LDCR and OS in LAPC. Multiple needle insertion in a variable geometry configuration optimized by pre-treatment planning determined an increase in LDCR and OS compared to a fixed geometry configuration.

Multi-Tissue Analysis on the Impact of Electroporation on Electrical and Thermal Properties

OBJECTIVE

Tissue electroporation is achieved by applying a series of electric pulses to destabilize cell membranes within the target tissue. The treatment volume is dictated by the electric field distribution, which depends on the pulse parameters and tissue type and can be readily predicted using numerical methods. These models require the relevant tissue properties to be known beforehand. This study aims to quantify electrical and thermal properties for three different tissue types relevant to current clinical electroporation.

METHODS

Pancreatic, brain, and liver tissue were harvested from pigs, then treated with IRE pulses in a parallel-plate configuration. Resulting current and temperature readings were used to calculate the conductivity and its temperature dependence for each tissue type. Finally, a computational model was constructed to examine the impact of differences between tissue types.

RESULTS

Baseline conductivity values (mean 0.11, 0.14, and 0.12 S/m) and temperature coefficients of conductivity (mean 2.0, 2.3, and 1.2 % per degree Celsius) were calculated for pancreas, brain, and liver, respectively. The accompanying computational models suggest field distribution and thermal damage volumes are dependent on tissue type.

CONCLUSION

The three tissue types show similar electrical and thermal responses to IRE, though brain tissue exhibits the greatest differences. The results also show that tissue type plays a role in the expected ablation and thermal damage volumes.

SIGNIFICANCE

The conductivity and its changes due to heating are expected to have a marked impact on the ablation volume. Incorporating these tissue properties aids in the prediction and optimization of electroporation-based therapies.

Treatment Planning Optimization in Irreversible Electroporation for Complete Ablation of Variously Sized Cervical Tumors: A Numerical Study

Irreversible electroporation (IRE), a relatively new energy-based tumor ablation technology, has shown itself in the last decade to be able to safely ablate tumors with favorable clinical outcomes, yet little work has been done on optimizing the IRE protocol to variously sized tumors. Incomplete tumor ablation has been shown to be the main reason leading to the local recurrence and thus treatment failure. The goal of this study was to develop a general optimization approach to optimize the IRE protocol for cervical tumors in different sizes, while minimizing the damage to normal tissues. This kind of approach can lay a foundation for future personalized treatment of IRE. First, a statistical IRE cervical tumor death model was built using previous data in our group. Then, a multi-objective optimization problem model was built, in which the decision variables are five IRE-setting parameters, namely, the pulse strength (U), the length of active tip (H), the number of pulses delivered in one round between a pair of electrodes (A), the distance between electrodes (D), and the number of electrodes (N). The domains of the decision variables were determined based on the clinical experience. Finally, the problem model was solved by using nondominated sorting genetic algorithms II (NSGA-II) algorithm to give respective optimal protocol for three sizes of cervical tumors. Every protocol was assessed by the evaluation criterion established in the study to show the efficacy in a more straightforward way. The results of the study demonstrate this approach can theoretically provide the optimal IRE protocol for different sizes of tumors and may be generalizable to other types, sizes, and locations of tumors.

Predictors of Occlusion of Hepatic Blood Vessels after Irreversible Electroporation of Liver Tumors

PURPOSE

To examine predictors of midterm occlusion in portal and hepatic veins within or adjacent to the ablation zone after irreversible electroporation (IRE) of liver tumors.

MATERIALS AND METHODS

This retrospective cohort analysis included 39 patients who underwent CT-guided IRE of liver tumors. Vessels within or adjacent to the ablation zone were identified on CT images acquired immediately after the procedure, and the positional relationships with the ablation zone (within/adjacent), locations (proximal/distal), and diameters (< 4 mm or ≥ 4 mm) were evaluated. Using contrast-enhanced follow-up scans, each vessel was classified as patent, stenosed, or occluded. Associations between vessel occlusion and each variable were investigated.

RESULTS

Overall, 33 portal veins and 64 hepatic veins were analyzed. Follow-up scans showed occlusion in 12/33 (36.7%) portal veins and 17/64 (26.6%) hepatic veins. Vessels within the ablation zone were occluded significantly more frequently than vessels adjacent to the ablation zone (portal: 55.6% [10/18] vs 13.3% [2/15], P = .04; hepatic: 45.4% [15/33] vs 6.4% [2/31], P = .011). Vessels with a diameter < 4 mm were also occluded significantly more frequently than vessels with a diameter ≥ 4 mm (portal: 72.7% [8/11] vs 18.1% [4/22], P = .011; hepatic: 54.8% [17/31] vs 0% [0/33], P < .001). The respective positive and negative predictive values for occlusion of vessels categorized as both within and < 4 mm were 88% (7/8) and 82% (20/25) for portal veins and 79% (15/19) and 96% (43/45) for hepatic veins.

CONCLUSIONS

Midterm vessel occlusion after liver IRE could be predicted with relatively high accuracy by assessing ablation location and vessel diameter.

Effect of irreversible electroporation parameters and the presence of a metal stent on the electric field line pattern

The final ablation zone created with irreversible electroporation (IRE) depends on the size, shape and strength of the electric field that is influenced by several parameters. A profound understanding of the effect of IRE parameter alterations on the electric field are a prerequisite for a safe and effective treatment. Here, we demonstrate a semolina in castor oil model that enables visualization of the static electric field developed by a high-voltage generator between two needle-electrodes. We intuitively visualize the variation in electric field line pattern for selected IRE parameters; active needle length, inter-needle distance, applied voltage and presence of a nearby metal stent, by cameras in three dimensions. The observations were compared to and supported by two-dimensional numerical simulations of the electric field. Our semolina model visualizes the disturbance of the electric field by a metal stent, potentially leading to an incomplete tumour ablation between the needles. The reduction in electric field strength and the area at risk for incomplete tumour ablation are confirmed by the numerical simulations. The semolina model provides insight in the fundamental physics of the electric field, the effect of alterations in IRE parameter combinations and presence of a metal stent within the ablation zone.

Recent progress in pulsed electric field ablation for liver cancer

The number of liver cancer patients is likely to continue to increase in the coming decades due to the aging of the population and changing risk factors. Traditional treatments cannot meet the needs of all patients. New treatment methods evolved from pulsed electric field ablation are expected to lead to breakthroughs in the treatment of liver cancer. This paper reviews the safety and efficacy of irreversible electroporation in clinical studies, the methods to detect and evaluate its ablation effect, the improvements in equipment and its antitumor effect, and animal and clinical trials on electrochemotherapy. We also summarize studies on the most novel nanosecond pulsed electric field ablation techniques in vitro and in vivo. These research results are certain to promote the progress of pulsed electric field in the treatment of liver cancer.

Irreversible Electroporation for Locally Advanced Pancreatic Cancer

Several minimally invasive image guided tumor ablation techniques have been added to the treatment spectrum for locally advanced pancreatic cancer (LAPC). Irreversible electroporation (IRE) might have a significant additive value in the management of this difficult-to-treat disease. As opposed to thermal ablative techniques, IRE induces cell death by the delivery of high-voltage electrical pulses. The electrical energy disrupts the cellular membrane integrity, causes loss of cellular homeostasis and ultimately results in cell death. The extracellular matrix of connective tissue in surrounding delicate structures such as bile ducts, bowel wall, and larger blood vessels is spared. The preservation of these structures makes IRE attractive for the treatment of pancreatic cancers that are unresectable due to their anatomical location (ie, LAPC and local recurrence after surgical resection). In addition to its cytoreductive abilities, evidence is emerging on IRE's capability to induce systemic immunomodulation through active in vivo vaccination against pancreatic cancer cells. These effects in combination with immunotherapy may offer a new treatment paradigm for tumors with low immunogenic potential like pancreatic ductal adenocarcinoma (PDAC). This review discusses several practical and technical issues of IRE for LAPC: clinical evaluation, indications, patient preparations, procedural steps, imaging characteristics, clinical results, and "tricks of the trade" used to improve the safety and efficacy of the treatment. Future directions such as the combination of IRE with immunotherapy will be shortly addressed.

Intra-arterial Injection of Lidocaine as a Cell Sensitizer during Irreversible Electroporation

PURPOSE

To investigate whether intra-arterial injection of lidocaine enhances irreversible electroporation (IRE) in a liver model.

MATERIALS AND METHODS

Conventional IRE (C-IRE) and lidocaine-enhanced IRE (L-IRE) were performed in 8 pig livers. Protocol 1 (tip exposure and electrode distance of 2.0 cm each) and protocol 2 (increased tip exposure and electrode distance 2.5 cm each) were used. Animals were sacrificed 3 hours after IRE. Study goals included electrical tissue properties (eg, current, conductivity) during IRE, geometry of IRE zones analyzed using computed tomography and magnetic resonance imaging (eg, volume and sphericity index), degree of acute liver damage, and irreversible cell death analyzed using microscopy (hematoxylin and eosin staining and terminal deoxynucleotidyl transferase deoxyuridine 5-triphosphate nick end labeling). Statistical comparisons were performed using the paired t test and Wilcoxon test.

RESULTS

All treatments were performed without adverse events. Electrical tissue properties were not significantly different between C-IRE and L-IRE. For protocol 1, the diameter of the largest sphere within the IRE zone was significantly larger for L-IRE than for C-IRE (25.0 ± 4.7 mm vs 18.4 ± 3.1 mm [P = .013]). For protocol 2, the volume of IRE zone was significantly larger for L-IRE compared with C-IRE (46.0 ± 5.4 cm³ vs 22.6 ± 6.4 cm³ [P = .018]), as well as the diameter of the largest sphere within the IRE zone (27.1 ± 2.2 mm vs 19.8 ± 2.3 mm [P = .020]). For protocol 1, a significantly higher degree of irreversible cell death was noted for L-IRE than for C-IRE (1.8 ± 1.0 vs 0.8 ± 1.0 [P = .046]).

CONCLUSIONS

Intra-arterial injection of lidocaine can enhance IRE in terms of larger IRE zones and an increase of irreversible cell death.

Irreversible Electroporation: Background, Theory, and Review of Recent Developments in Clinical Oncology

Irreversible electroporation (IRE) has established a clinical niche as an alternative to thermal ablation for the eradication of unresectable tumors, particularly those near critical vascular structures. IRE has been used in over 50 independent clinical trials and has shown clinical success when used as a standalone treatment and as a single component within combinatorial treatment paradigms. Recently, many studies evaluating IRE in larger patient cohorts and alongside other novel therapies have been reported. Here, we present the basic principles of reversible electroporation and IRE followed by a review of preclinical and clinical data with a focus on tumors in three organ systems in which IRE has shown great promise: the prostate, pancreas, and liver. Finally, we discuss alternative and future developments, which will likely further advance the use of IRE in the clinic.

Simplified Non-Thermal Tissue Ablation With a Single Insertion Device Enabled by Bipolar High-Frequency Pulses

OBJECTIVE

To demonstrate the feasibility of a single electrode and grounding pad approach for delivering high frequency irreversible electroporation treatments (H-FIRE) in in-vivo hepatic tissue.

METHODS

Ablations were created in porcine liver under surgical anesthesia by adminstereing high frequency bursts of 0.5-5.0 μs pulses with amplitudes between 1.1-1.7 kV in the absence of cardiac synchronization or intraoperative paralytics. Finite element simulations were used to determine the electric field strength associated with the ablation margins (E_Lethal) and predict the ablations feasible with next generation electronics.

RESULTS

All animals survived the procedures for the protocol duration without adverse events. E_Lethal of 2550, 1650, and 875 V/cm were found for treatments consisting of 100x bursts containing 0.5 μs pulses and 25, 50, and 75 μs of energized-time per burst, respectively. Treatments with 1 μs pulses consisting of 100 bursts with 100 μs energized-time per burst resulted in E_Lethal of 650 V/cm.

CONCLUSION

A single electrode and grounding pad approach was successfully used to create ablations in hepatic tissue. This technique has the potential to reduce challenges associated with placing multiple electrodes in anatomically challenging environments.

SIGNIFICANCE

H-FIRE is an in situ tumor ablation approach in which electrodes are placed within or around a targeted region to deliver high voltage electrical pulses. Electric fields generated around the electrodes induce irrecoverable cell membrane damage leading to predictable cell death in the relative absence of thermal damage. The sparing of architectural integrity means H-FIRE offers potential advantages compared to thermal ablation modalities for ablating tumors near critical structures.

Image-Guided Thyroid Ablation: Proposal for Standardization of Terminology and Reporting Criteria

Background: Image-guided tumor ablation is commonly performed in clinical practice. Trying to standardize terminology and data collection to enable a more reliable comparison among the different studies, in 2003, a document entitled "Image-Guided Tumor Ablation: Proposal for Standardization of Terms and Reporting Criteria" was published by the International Working Group on Image-Guided Tumor Ablation. Since then, ablations have evolved significantly, with the development of new technology and techniques and applications. This has included benign thyroid nodules, and their ablation has become increasingly accessible, not only among radiologists but also among other specialists involved in thyroid care, including endocrinologists and surgeons. This has resulted in further inhomogeneity in how data are presented and reported among different studies, resulting in a need for standardization to homogenize language and data reporting on the topic. Summary: In February 2018 in Milano, Italy, a meeting involving specialists concerned with minimally invasive treatments of thyroid lesions was organized, and the Italian Working Group on Minimally Invasive Treatments of the Thyroid was founded with the aim of establishing a collaborative network among all clinicians working in this field. The first work of this group is to present a proposal for standardization of terminology and reporting criteria on image-guided ablations to treat benign thyroid nodules. Conclusion: This proposal was drafted with the goal of providing guidance for standardized reporting of results in studies regarding image-guided thyroid ablations. We encourage adoption of this terminology worldwide, anticipating that this will facilitate improved communication and understanding within the field and stimulate further discussion on the topic over the next years.

Safety and Short-Term Efficacy of Irreversible Electroporation and Allogenic Natural Killer Cell Immunotherapy Combination in the Treatment of Patients with Unresectable Primary Liver Cancer

PURPOSE

This study aimed to investigate the safety and short-term efficacy of irreversible electroporation (IRE) combined with allogenic natural killer (NK) cell immunotherapy in the treatment of patients with unresectable primary liver cancer.

MATERIALS AND METHODS

Between October 2015 and December 2016, 40 patients were enrolled and randomly allocated to either the IRE group (n = 22) or the IRE-NK group (n = 18). All adverse events experienced by the patients were recorded; the changes in tumor biomarkers [AFP, CA 19-9, circulating tumor cells (CTCs)], lymphocyte number and function, quality of life, clinical response, progression-free survival (PFS) and overall survival (OS) were assessed.

RESULTS

Patients who received combination therapy exhibited significantly longer median PFS and OS than who just received IRE (PFS 15.1 vs. 10.6 months, P < 0.05, OS 17.9 vs. 23.2 months, P < 0.05). The combination therapy of IRE and NK cell immunotherapy significantly reduced CTCs and increased immune function and Karnofsky performance status.

CONCLUSION

Our data suggest a novel, promising combination therapy using IRE and allogenic NK cell immunotherapy. Larger clinical trials are required to confirm these conclusions.

The methodology for endoluminal irreversible electroporation in porcine models

The aim of this study was to describe the methodology of the surgical technique for endoluminal irreversible electroporation in the biliary tract performed within the perihilar region in porcine models. Endoluminal irreversible electroporation of the common bile duct was performed on eight porcine models using an endoluminal device inserted during laparotomy. The endoluminal device consisted of three electrodes 1 cm in length, attached at 120 degrees around the balloon catheter. The procedure was conducted with the following parameters: number of pulses 90, voltage of 1500 V between each couple of electrodes. Cross sectional imaging and histopathological assessment were employed for evaluations of the ablation zone. Models were sacrificed 24 h and 96 h after ablation. The treatment was successful in all porcine models. All animals survived the defined study period. Peri-ablation oedema within the hepatoduodenal ligament and adjacent liver tissue could be measured on post-procedural MRI or CT. Perforation in the site of ablation developed in one model. Histopathological examination showed heavy regressive changes of the ablated tissue. The elastic membranes of the adjacent portal vein were preserved in all models. In our experience, this novel endoluminal modality used within the perihilar region in porcine models is a feasible and well predictable procedure. Further studies should explore the optimal protocol of catheter-based ablation to limit complications.

Tumor Ablation Enhancement by Combining Radiofrequency Ablation and Irreversible Electroporation: An In Vitro 3D Tumor Study

We hypothesized and demonstrated for the first time that significant tumor ablation enhancement can be achieved by combining radiofrequency ablation (RFA) and irreversible electroporation (IRE) using a 3D cervical cancer cell model. Three RFA (43, 50, and 60 °C for 2 min) and IRE protocols (350, 700, and 1050 V/cm) were used to study the combining effect in the 3D tumor cell model. The in vitro experiment showed that both RFA enhanced IRE and IRE enhanced RFA can lead to a significant increase in the size of the ablation zone compared to IRE and RFA alone. It was also noted that the sequence of applying ablation energy (RFA → RE or IRE → RFA) affected the efficacy of tumor ablation enhancement. The electrical conductivity of 3D tumor was found to be increased after preliminary RFA or IRE treatment. This increase in tumor conductivity may explain the enhancement of tumor ablation. Another explanation might be that there is repeat injury to the transitional zone of the first treatment by the second one. The promising results achieved in the study can provide us useful clues about the treatment of large tumors abutting large vessels or bile ducts.

Electrochemotherapy of cholangiocellular carcinoma at hepatic hilum: A feasibility study

AIM

We evaluated feasibility, safety and efficacy of Electrochemotherapy (ECT) in a prospective series of patients with unresectable Perihilar-Cholangiocarcinoma (PHCCA).

PATIENTS AND METHODS

Five patients with PHCCA underwent ECT. Three patients underwent percutaneous ECT of a single PHCCA nodule. One patient underwent resection of a nodule in the IV segment and intraoperative ECT of a large PHCCA in the VIII segment. Another patient underwent percutaneous ECT of a large PHCCA recurrence after left lobectomy and RF ablation of a synchronous metastasis in the VI segment. ECT was performed under US guidance. Efficacy was evaluated by contrast-enhanced multiple-detector-computed-tomography (MDCT) 4 weeks after treatment. Follow-up entailed MDCT every 6 months thereafter.

RESULTS

No major complication occurred. Follow-up ranges from 10 to 30 months. Four weeks post-treatment CT showed complete response in 3 cases. These patients are still alive, and follow-up CT controls demonstrated no local or distant intrahepatic recurrences and no biliary duct dilation in 2 cases and local recurrence at 18 months follow-up control in 1 patient. In the remaining 2 cases, 4-weeks-post-treatment CT showed incomplete response (>90%). In these patients follow-up CT demonstrated local progression of the disease at 6 months. One of them had bilateral external biliary drainages and died because of tumor progression at 16-months-follow-up. The other patient, died at 10 months follow-up for cardiovascular failure not related to the hepatobiliary disease.

CONCLUSIONS

ECT is feasible, safe and effective therapy to improve prognosis and quality of life of patients with unresectable PHCCA.

Clinically applicable irreversible electroporation for eradication of micro-organisms

Irreversible electroporation (IRE) damages cell membranes and is used in medicine for nonthermal ablation of malignant tumours. Our aim was to evaluate the antimicrobial effect of IRE. The pathogenic micro-organisms, Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, Pseudomonas aeruginosa and Candida albicans were subjected to IRE. Survival was measured as a function of voltage and the number of pulses applied. Combined use of IRE and oxacillin for eradication of Staph. aureus was also tested. Log10 reduction in micro-organisms positively correlated with the number of applied pulses. The colony count of Strep. pyogenes and E. coli declined by 3·38 and 3·05 orders of magnitude, respectively, using an electric field of 2000 V and 100 pulses. Killing of Staph. aureus and P. aeruginosa was achieved with a double cycle of IRE (2000, 1500 V and repeated 1250 V respectively) of 50-100 IRE pulses. The addition of subclinical inhibitory concentrations of oxacillin to the Staph. aureus suspension prior to IRE led to total bacterial death, demonstrating synergism between oxacillin and IRE. Our results demonstrate that using IRE with clinically established parameters has a marked in vitro effect on pathogenic micro-organisms and highlights the potential of IRE as a treatment modality for deep-seated infections, particularly when combined with low doses of antibiotics.

SIGNIFICANCE AND IMPACT OF THE STUDY

Irreversible electroporation (IRE) is utilized in interventional radiology to treat cancer patients. In this study we evaluated in vitro the antimicrobial effect of IRE. We demonstrated that using IRE with clinically established parameters has a marked effect on pathogenic micro-organisms and is synergistic to antimicrobials when both are combined. Our results point to the potential of IRE as a treatment modality for deep-seated infections.

Conductivity Rise During Irreversible Electroporation: True Permeabilization or Heat?

Purpose

Irreversible electroporation (IRE) induces apoptosis with high-voltage electric pulses. Although the working mechanism is non-thermal, development of secondary Joule heating occurs. This study investigated whether the observed conductivity rise during IRE is caused by increased cellular permeabilization or heat development.

Methods

IRE was performed in a gelatin tissue phantom, in potato tubers, and in 30 patients with unresectable colorectal liver metastases (CRLM). Continuous versus sequential pulsing protocols (10-90 vs. 10-30-30-30) were assessed. Temperature was measured using fiber-optic probes. After temperature had returned to baseline, 100 additional pulses were delivered. The primary technique efficacy of the treated CRLM was compared to the periprocedural current rise. Seven patients received ten additional pulses after a 10-min cool-down period.

Results

Temperature and current rise was higher for the continuous pulsing protocol (medians, gel: 13.05 vs. 9.55 °C and 9 amperes (A) vs. 7A; potato: 12.70 vs. 10.53 °C and 6.0A vs. 6.5A). After cooling-down, current returned to baseline in the gel phantom and near baseline values (Δ2A with continuous- and Δ5A with sequential pulsing) in the potato tubers. The current declined after cooling-down in all seven patients with CRLM, although baseline values were not reached. There was a positive correlation between current rise and primary technique efficacy (p = 0.02); however, the previously reported current increase threshold of 12–15A was reached in 13%.

Conclusion

The observed conductivity rise during IRE is caused by both cellular permeabilization and heat development. Although a correlation between current rise and efficacy exists, the current increase threshold seems unfeasible for CRLM.

Electronic supplementary material

The online version of this article (10.1007/s00270-018-1971-7) contains supplementary material, which is available to authorized users.

Tissue Damage, Temperature, and pH Induced by Different Electrode Arrays on Potato Pieces (Solanum tuberosum L.)

One of the most challenging problems of electrochemical therapy is the design and selection of suitable electrode array for cancer. The aim is to determine how two-dimensional spatial patterns of tissue damage, temperature, and pH induced in pieces of potato (Solanum tuberosum L., var. Mondial) depend on electrode array with circular, elliptical, parabolic, and hyperbolic shape. The results show the similarity between the shapes of spatial patterns of tissue damage and electric field intensity, which, like temperature and pH take the same shape of electrode array. The adequate selection of suitable electrodes array requires an integrated analysis that involves, in a unified way, relevant information about the electrochemical process, which is essential to perform more efficiently way the therapeutic planning and the personalized therapy for patients with a cancerous tumor.

Optimization of Electrode Configuration and Pulse Strength in Irreversible Electroporation for Large Ablation Volumes Without Thermal Damage

The aim of this study was to analyze five factors that are responsible for the ablation volume and maximum temperature during the procedure of irreversible electroporation (IRE). The five factors used in this study were the pulse strength (U), the electrode diameter (B), the distance between the electrode and the center (D), the electrode length (L), and the number of electrodes (N). A validated finite element model (FEM) of IRE was built to collect the data of the ablation volume and maximum temperature generated in a liver tissue. Twenty-five experiments were performed, in which the ablation volume and maximum temperature were taken as response variables. The five factors with ranges were analyzed to investigate their impacts on the ablation volume and maximum temperature, respectively, using analysis of variance. Response surface method (RSM) was used to optimize the five factors for the maximum ablation volume without thermal damage (the maximum temperature ≤ 50 °C for 90 s). U and L were found with significant impacts on the ablation volume (P < 0.001, and P = 0.009, respectively) while the same conclusion was not found for B, D and N (P = 0.886, P = 0.075 and P = 0.279, respectively). Furthermore, U, D, and N had the significant impacts on the maximum temperature with P < 0.001, P < 0.001, and P = 0.003, respectively, while same conclusion was not found for B and L (P = 0.720 and P = 0.051, respectively). The maximum ablation volume of 2952.9960 mm3 without thermal damage can be obtained by using the following set of factors: U = 2362.2384 V, B = 1.4889 mm, D = 7 mm, L = 4.5659 mm, and N = 3. The study concludes that both B and N have insignificant impacts (P = 0.886, and P = 0.279, respectively) on the ablation volume; U has the most significant impact (P < 0.001) on the ablation volume; electrode configuration and pulse strength in IRE can be optimized for the maximum ablation volume without thermal damage using RSM.

Focused Transhepatic Electroporation Mediated by Hypersaline Infusion through the Portal Vein in Rat Model. Preliminary Results on Differential Conductivity

Background

Spread hepatic tumours are not suitable for treatment either by surgery or conventional ablation methods. The aim of this study was to evaluate feasibility and safety of selectively increasing the healthy hepatic conductivity by the hypersaline infusion (HI) through the portal vein. We hypothesize this will allow simultaneous safe treatment of all nodules by irreversible electroporation (IRE) when applied in a transhepatic fashion.

Material and methods

Sprague Dawley (Group A, n = 10) and Athymic rats with implanted hepatic tumour (Group B, n = 8) were employed. HI was performed (NaCl 20%, 3.8 mL/Kg) by trans-splenic puncture. Deionized serum (40 mL/Kg) and furosemide (2 mL/Kg) were simultaneously infused through the jugular vein to compensate hypernatremia. Changes in conductivity were monitored in the hepatic and tumour tissue. The period in which hepatic conductivity was higher than tumour conductivity was defined as the therapeutic window (TW). Animals were monitored during 1-month follow-up. The animals were sacrificed and selective samples were used for histological analysis.

Results

The overall survival rate was 82.4% after the HI protocol. The mean maximum hepatic conductivity after HI was 2.7 and 3.5 times higher than the baseline value, in group A and B, respectively. The mean maximum hepatic conductivity after HI was 1.4 times higher than tumour tissue in group B creating a TW to implement selective IRE.

Conclusions

HI through the portal vein is safe when the hypersaline overload is compensated with deionized serum and it may provide a TW for focused IRE treatment on tumour nodules.

The role of the irreversible electroporation in the hepato-pancreatico-biliary surgery

Irreversible electroporation is a novel technique growing in popularity over the last years among the ablative modalities. Its unique action mechanism produces irreversible nanopores in the membrane of the cell leading to apoptosis; therefore irreversible electroporation can be used to ablate substantial volumes of tissue without the undesirable thermal effects as the "heat sink effect". Moreover the extracellular matrix is left unperturbed, thus sparing the structural architecture of surrounding structures such as bile ducts and blood vessels. In the last years its use has been widespread in both liver and pancreatic ablation. Irreversible electroporation has shown its safety with however some caution, feasibility and favorable outcomes in clinical settings such as unresectable locally advanced disease in which the surgical and therapeutic options are very limited.

Irreversible electroporation of hepatocellular carcinoma: patient selection and perspectives

Irreversible electroporation (IRE) is a novel form of tissue ablation that uses high-current electrical pulses to induce pore formation of the cell lipid bilayer, leading to cell death. The safety of IRE for ablation of hepatocellular carcinoma (HCC) has been established. Outcome data for ablation of HCC by IRE are limited, but early results are encouraging and suggest equivalency to the outcomes obtained for thermal ablation for appropriately selected, small (<3 cm) tumors. Long-term oncologic efficacy and histopathologic response data have not been published, and therefore, application of IRE for the treatment of HCC should still be viewed with caution.

Percutaneous electrochemotherapy in the treatment of portal vein tumor thrombosis at hepatic hilum in patients with hepatocellular carcinoma in cirrhosis: A feasibility study

AIM

To treated with electrochemotherapy (ECT) a prospective case series of patients with liver cirrhosis and Vp3-Vp4- portal vein tumor thrombus (PVTT) from hepatocellular carcinoma (HCC), in order to evaluate the feasibility, safety and efficacy of this new non thermal ablative technique in those patients.

METHODS

Six patients (5 males and 1 female), aged 61-85 years (mean age, 70 years), four in Child-Pugh A and two in Child-Pugh B class, entered our study series. All patients were studied with three-phase computed tomography (CT), contrast enhanced ultrasound (CEUS) and ultrasound-guided percutaneous biopsy of the thrombus before ECT. All patients underwent ECT treatment (Cliniporator Vitae^®, IGEA SpA, Carpi, Modena, Italy) of Vp3-Vp4 PVTT in a single session. At the end of the procedure a post-treatment biopsy of the thrombus was performed. Scheduled follow-up in all patients entailed: CEUS within 24 h after treatment; triphasic contrast-enhanced CT and CEUS at 3 mo after treatment and every six months thereafter.

RESULTS

Post-treatment CEUS showed complete absence of enhancement of the treated thrombus in all cases. Post-treatment biopsy showed apoptosis and necrosis of tumor cells in all cases. The follow-up ranged from 9 to 20 mo (median, 14 mo). In 2 patients, the follow-up CT and CEUS demonstrated complete patency of the treated portal vein. Other 3 patients showed a persistent avascular non-tumoral shrinked thrombus at CEUS and CT during follow-up. No local recurrence was observed at follow-up CT and CEUS in 5/6 patients. One patient was lost to follow-up because of death from gastrointestinal hemorrage 5 wk after ECT.

CONCLUSION

In patients with cirrhosis, ECT seems effective and safe for curative treatment of Vp3-Vp4 PVTT from HCC.

Anatomically Realistic Simulations of Liver Ablation by Irreversible Electroporation: Impact of Blood Vessels on Ablation Volumes and Undertreatment

Irreversible electroporation is a novel tissue ablation technique which entails delivering intense electrical pulses to target tissue, hence producing fatal defects in the cell membrane. The present study numerically analyzes the potential impact of liver blood vessels on ablation by irreversible electroporation because of their influence on the electric field distribution. An anatomically realistic computer model of the liver and its vasculature within an abdominal section was employed, and blood vessels down to 0.4 mm in diameter were considered. In this model, the electric field distribution was simulated in a large series of scenarios (N = 576) corresponding to plausible percutaneous irreversible electroporation treatments by needle electrode pairs. These modeled treatments were relatively superficial (maximum penetration depth of the electrode within the liver = 26 mm) and it was ensured that the electrodes did not penetrate the vessels nor were in contact with them. In terms of total ablation volume, the maximum deviation caused by the presence of the vessels was 6%, which could be considered negligible compared to the impact by other sources of uncertainty. Sublethal field magnitudes were noticed around vessels covering volumes of up to 228 mm³. If in this model the blood was substituted by a liquid with a low electrical conductivity (0.1 S/m), the maximum volume covered by sublethal field magnitudes was 3.7 mm³ and almost no sublethal regions were observable. We conclude that undertreatment around blood vessels may occur in current liver ablation procedures by irreversible electroporation. Infusion of isotonic low conductivity liquids into the liver vasculature could prevent this risk.

Time-Dependent Impact of Irreversible Electroporation on Pancreas, Liver, Blood Vessels and Nerves: A Systematic Review of Experimental Studies

Introduction

Irreversible electroporation (IRE) is a novel ablation technique in the treatment of unresectable cancer. The non-thermal mechanism is thought to cause mostly apoptosis compared to necrosis in thermal techniques. Both in experimental and clinical studies, a waiting time between ablation and tissue or imaging analysis to allow for cell death through apoptosis, is often reported. However, the dynamics of the IRE effect over time remain unknown. Therefore, this study aims to summarize these effects in relation to the time between treatment and evaluation.

Methods

A systematic search was performed in Pubmed, Embase and the Cochrane Library for original articles using IRE on pancreas, liver or surrounding structures in animal or human studies. Data on pathology and time between IRE and evaluation were extracted.

Results

Of 2602 screened studies, 36 could be included, regarding IRE in liver (n = 24), pancreas (n = 4), blood vessels (n = 4) and nerves (n = 4) in over 440 animals (pig, rat, goat and rabbit). No eligible human studies were found. In liver and pancreas, the first signs of apoptosis and haemorrhage were observed 1–2 hours after treatment, and remained visible until 24 hours in liver and 7 days in pancreas after which the damaged tissue was replaced by fibrosis. In solitary blood vessels, the tunica media, intima and lumen remained unchanged for 24 hours. After 7 days, inflammation, fibrosis and loss of smooth muscle cells were demonstrated, which persisted until 35 days. In nerves, the median time until demonstrable histological changes was 7 days.

Conclusions

Tissue damage after IRE is a dynamic process with remarkable time differences between tissues in animals. Whereas pancreas and liver showed the first damages after 1–2 hours, this took 24 hours in blood vessels and 7 days in nerves.

The Safety and Efficacy of Irreversible Electroporation for Large Hepatocellular Carcinoma

This study aimed to investigate the safety and effectiveness of irreversible electroporation ablation for unresectable large liver cancer. Fourteen patients were enrolled: 8 with large hepatocellular carcinoma (tumor diameter: 5.1-11.5 cm) and 6 with medium hepatocellular carcinoma (tumor diameter: 3.0-4.1 cm). All patients received percutaneous irreversible electroporation ablation. Ablation time and the incidence of complications were assessed by a t test. Post-irreversible electroporation and regular contrast-enhanced computerized tomography scans were performed to investigate the effect of tumor size (large vs medium) on irreversible electroporation treatment efficacy; 4-table data were assessed using a Fisher exact test. The 14 patients completed irreversible electroporation ablation successfully. In the large hepatocellular carcinoma group, no major complications occurred in the perioperative period. Minor complications comprised bloating, hypokalemia, edema, low white blood cells, and blood clotting abnormalities. All complications were mild and improved after symptomatic treatment. The frequency of minor complications was not significantly different (P > .05) compared with the medium hepatocellular carcinoma group. The average follow-up time was 2.8 ± 2.1 months and complete ablation was achieved in 25% (2/8; residual = 75%). For the patients with medium hepatocellular carcinoma, the mean follow-up time was 4.3 ± 3.2 months; the rate of complete ablation was 66.6% (4/6; residual rate = 33.3%). The complete ablation rate was not statistically different between the 2 groups (P > .05). Irreversible electroporation ablation for unresectable large hepatocellular carcinoma is safe, with no major complications. Short-term efficacy is relatively good; however, long-term efficacy remains to be explored.

Ultrasound and Contrast-Enhanced Ultrasound for Evaluation of Irreversible Electroporation Ablation: In Vivo Proof of Concept in Normal Porcine Liver

The objective of this study was to describe the performance of ultrasound (US) and contrast-enhanced ultrasound (CEUS) within 2 h after irreversible electroporation (IRE) ablation of porcine liver. Six IRE ablations were performed on porcine liver in vivo; ultrasound assessments were performed within 2 h after IRE ablation. On US images, the ablation zone appeared as a hypo-echoic area within 10 min after the ablation, and then the echo of the ablation zone gradually increased. On CEUS images, the ablation zone appeared as a non-enhanced area within 10 min after ablation and then was gradually centripetally filled by microbubbles. A hyper-echoic rim on US images and a hyper-enhanced rim on CEUS images appeared in the periphery of the ablation zone 60 min after the ablation. Characteristic and dynamic ultrasound images of the IRE ablation zone were obtained within 2 h after IRE ablation of in vivo porcine liver.

Induction of rapid, reproducible hepatic ablations using next-generation, high frequency irreversible electroporation (H-FIRE) in vivo

INTRODUCTION

Irreversible electroporation (IRE) offers an alternative to thermal tissue ablation in situ. High-frequency IRE (H-FIRE), employing ultra-short bipolar electrical pulses, may overcome limitations associated with existing IRE technology to create rapid, reproducible liver ablations in vivo.

METHODS

IRE electrodes (1.5 cm spacing) were inserted into the hepatic parenchyma of swine (n = 3) under surgical anesthesia. In the absence of paralytics or cardiac synchronization five independent H-FIRE ablations were performed per liver using 100, 200, or 300 pulses (2250 V, 2-5-2 μs configuration). Animals were maintained under isoflurane anesthesia for 6 h prior to analysis of ablation size, reproducibility, and apoptotic cell death.

RESULTS

Mean ablation time was 230 ± 31 s and no EKG abnormalities occurred during H-FIRE. In 1/15 HFIRE's minor muscle twitch (rectus abdominis) was recorded. Necropsy revealed reproducible ablation areas (34 ± 4 mm(2), 88 ± 11 mm(2) and 110 ± 11 mm(2); 100-, 200- and 300-pulses respectively). Tissue damage was predominantly apoptotic at pulse delivery ≤200 pulses, after which increasing evidence of tissue necrosis was observed.

CONCLUSION

H-FIRE can be used to induce rapid, predictable ablations in hepatic tissue without the need for intraoperative paralytics or cardiac synchronization. These advantages may overcome limitations that restrict currently available IRE technology for hepatic ablations.

Optimizing Irreversible Electroporation Ablation with a Bipolar Electrode

PURPOSE

To optimize single-insertion bipolar irreversible electroporation (IRE) by characterizing effects of electric parameters and controlling tissue electric properties in a porcine model.

MATERIALS AND METHODS

Single-insertion electrode bipolar IRE was performed in 28 in vivo pig livers (78 ablations). First, effects of voltage (2,700-3,000 V), number of pulses, repeated cycles (1-6 cycles), and pulse width (70-100 µs) were studied. Next, electric conductivity was altered by instillation of hypertonic and hypotonic fluids. Finally, effects of thermal stabilization were assessed using internal electrode cooling. Treatment effect was evaluated 2-3 hours after IRE. Dimensions were compared and subjected to statistical analysis.

RESULTS

Delivering 3,000 V at 70 µs for a single 90-pulse cycle yielded 3.8 cm ± 0.4 × 2.0 cm ± 0.3 of ablation. Applying 6 cycles of energy increased ablation to 4.5 cm ± 0.4 × 2.6 cm ± 0.3 (P < .001). Further increasing pulse lengths to 100 µs (6 cycles) increased ablation to 5.0 cm ± 0.4 × 2.9 cm ± 0.3 (P < .001) but resulted in electric spikes and system crashes in 40%-50% of cases. Increasing tissue electric conductivity via hypertonic solution instillation in surrounding tissues increased frequency of generator crashes, whereas continuous instillation of distilled water eliminated this arcing phenomenon but reduced ablation to 2.3 cm ± 0.1. Controlled instillation of distilled water when electric arcing was suspected from audible popping produced ablations of 5.3 cm ± 0.6 × 3.1 cm ±0.3 without crashes. Finally, 3.1 cm ± 0.1 short-axis ablation was achieved without system crashes with internal electrode perfusion at 37°C versus 2.3 cm ± 0.1 with 4°C-10°C perfusion (P < .001).

CONCLUSIONS

Bipolar IRE ablation zones can be increased with repetitive high voltage and greater pulse widths accompanied by either judicious instillation of hypotonic fluids or internal electrode perfusion to minimize unwanted electric arcing.

Electrochemical Effects after Transarterial Chemoembolization in Combination with Percutaneous Irreversible Electroporation: Observations in an Acute Porcine Liver Model

PURPOSE

To evaluate the effects of combined use of transarterial chemoembolization and irreversible electroporation (IRE) for focal tissue ablation in an acute porcine liver model.

MATERIALS AND METHODS

Two established interventional techniques were combined: IRE with zones of irreversible and reversible electroporation and chemoembolization with microspheres, iodized oil, and doxorubicin. IRE was performed before chemoembolization in two pigs (pigs 1 and 2; IRE/chemoembolization group), chemoembolization was performed before IRE in two pigs (pigs 3 and 4; chemoembolization/IRE group), and only IRE was performed in two pigs (pigs 5 and 6). Five study groups were defined: IRE/chemoembolization (pigs 1 and 2), chemoembolization/IRE (pigs 3 and 4), IRE only (pigs 5 and 6), chemoembolization only (tissue outside the IRE zones in pigs 1-4), and control (untreated liver tissue outside the IRE zones in pigs 5 and 6). Animals were euthanized 2 hours after intervention. Size and shape of IRE zones on contrast-enhanced computed tomography, cell death on light microscopy, and doxorubicin tissue concentrations on chromatography and fluorescence microscopy were analyzed.

RESULTS

Size and shape of IRE zones were not significantly different (eg, P = .067 for volume). A histologic marker for irreversible cell death was positive in IRE/chemoembolization, chemoembolization/IRE, and IRE groups only in the macroscopically visible IRE zones. Doxorubicin tissue concentrations were not significantly different (P = .873). However, in the reversible electroporation (RE) zones, broad areas with intense intranuclear doxorubicin accumulation were observed in IRE/chemoembolization but not in chemoembolization/IRE and chemoembolization groups.

CONCLUSIONS

IRE before chemoembolization enhances the intranuclear accumulation of doxorubicin in the RE zone.

Irreversible electroporation of the liver: is there a safe limit to the ablation volume?

Irreversible electroporation is a fast-growing liver ablation technique. Although safety has been well documented in small ablations, our aim is to assess its safety and feasibility when a large portion of liver is ablated. Eighty-seven mice were subjected to high voltage pulses directly delivered across parallel plate electrodes comprising around 40% of mouse liver. One group consisted in 55 athymic-nude, in which a tumor from the KM12C cell line was grown and the other thirty-two C57-Bl6 non-tumoral mice. Both groups were subsequently divided into subsets according to the delivered field strength (1000 V/cm, 2000 V/cm) and whether or not they received anti-hyperkalemia therapy. Early mortality (less than 24 hours post-IRE) in the 2000 V/cm group was observed and revealed considerably higher mean potassium levels. In contrast, the animals subjected to a 2000 V/cm field treated with the anti-hyperkalemia therapy had higher survival rates (OR = 0.1, 95%CI = 0.02–0.32, p < 0.001). Early mortality also depended on the electric field magnitude of the IRE protocol, as mice given 1000 V/cm survived longer than those given 2000 V/cm (OR = 4.7, 95%CI = 1.8–11.8, p = 0.001). Our findings suggest that ionic disturbances, mainly due to potassium alterations, should be warned and envisioned when large volume ablations are performed by IRE.

Electric Ablation with Irreversible Electroporation (IRE) in Vital Hepatic Structures and Follow-up Investigation

Irreversible electroporation (IRE) with microsecond-pulsed electric fields (μsPEFs) can effectively ablate hepatocellular carcinomas in animal models. This preclinical study evaluates the feasibility and safety of IRE on porcine livers. Altogether, 10 pigs were included. Computed tomography (CT) was used to guide two-needle electrodes that were inserted near the hilus hepatis and gall bladder. Animals were followed-up at 2 hours and at 2, 7 and 14 days post-treatment. During and after μsPEF ablation, electrocardiographs found no cardiovascular events, and contrast CT found no portal vein thrombosis. There was necrosis in the ablation zone. Mild cystic oedema around the gall bladder was found 2 hours post-treatment. Pathological studies showed extensive cell death. There was no large vessel damage, but there was mild endothelial damage in some small vessels. Follow-up liver function tests and routine blood tests showed immediate liver function damage and recovery from the damage, which correlated to the pathological changes. These results indicate that μsPEF ablation affects liver tissue and is less effective in vessels, which enable μsPEFs to ablate central tumour lesions close to the hilus hepatis and near large vessels and bile ducts, removing some of the limitations and contraindications of conventional thermal ablation.