Nonthermal irreversible electroporation: fundamentals, applications, and challenges

Effects of Parallel Contact Cooling on Pulsed-Type, Bipolar Radiofrequency-Induced Tissue Reactions in an in vivo Porcine Model

Background

Skin cooling during laser or radiofrequency (RF) treatments is a method to minimize thermal damage to the epidermis, reduce pain, and decrease post-treatment downtime. We evaluated the effect of parallel contact cooling (PCC) on RF-induced thermal reactions in minipig skin in vivo after bipolar microneedling RF treatment.

Methods

RF treatments were administered at frequencies of 0.5, 1, and 2 MHz with single (500 ms), six (1000 ms), and ten (5000 ms) sub-pulse packs to minipig skin with or without PCC. Subsequently, thermometric imaging and histology were used to analyze skin reactions to RF.

Results

Thermometric images showed that PCC promptly lowered skin temperature in the RF-treated area, with this effect persisting for over 60s. Regardless of the PCC, RF treatments lasting for 500 ms with a single pulse pack resulted in peri-electrode coagulative necrosis (PECN) zones and inter-electrode non-necrotic thermal reaction (IENT) zones in the dermis. In contrast, treatment lasting 5000 ms with 10 sub-pulse packs produced distinct IENT without notable PECN over a wide dermal area. Skin specimens obtained at 1 h and 3, 7, and 14 days after PCC-assisted RF treatments showed a higher degree of thermal tissue reactions in the deeper dermal regions compared to those after RF treatments without PCC.

Conclusion

PCC-assisted RF treatment, utilizing an invasive bipolar microneedling device, enhanced RF-induced skin reactions in the mid to deep dermis while preserving the epidermis and upper papillary dermis from excessive thermal tissue injury.

Development of Ferroelectric P(VDF-TrFE) Microparticles for Ultrasound-Driven Cancer Cell Killing

Current breast cancer treatments involve aggressive and invasive methods, leaving room for new therapeutic approaches to emerge. In this work, we explore the possibility of using piezoelectric [P(VDF-TrFE)] microparticles (MPs) as a source of inducing irreversible electroporation (IRE) of 4T1 breast cancer cells. We detail the MP formation mechanism and size control and subsequent characterizations of the as-synthesized MPs which confirms the presence of piezoelectric β-phase. Production of the necessary piezoelectric output of the MPs is achieved by ultrasound agitation. We confirm the primary factor of the IRE effect on 4T1 breast cancer cells to be the local electric field produced from the MPs by using confocal imaging and an alamarBlue assay. The results show a 52.6% reduction in cell viability, indicating that the MP treatment can contribute to a reduction of live cancer cells. The proposed method of ultrasound-stimulated P(VDF-TrFE) MPs may offer a more benign cancer treatment approach.

Engineering high post-electroporation viabilities and transfection efficiencies for elongated cells on suspended nanofiber networks

The impact of cell shape on cell membrane permeabilization by pulsed electric fields is not fully understood. For certain applications, cell survival and recovery post-treatment is either desirable, as in gene transfection, electrofusion, and electrochemotherapy, or is undesirable, as in tumor and cardiac ablations. Understanding of how morphology affects cell viability post-electroporation may lead to improved electroporation methods. In this study, we use precisely aligned nanofiber networks within a microfluidic device to reproducibly generate elongated cells with controlled orientations to an applied electric field. We show that cell viability is significantly dependent on cell orientation, elongation, and spread. Further, these trends are dependent on the external buffer conductivity. Additionally, we see that cell survival for elongated cells is still supported by the standard pore model of electroporation. Lastly, we see that manipulating the cell orientation and shape can be leveraged for increased transfection efficiencies when compared to spherical cells. An improved understanding of cell shape and pulsation buffer conductivity may lead to improved methods for enhancing cell viability post-electroporation by engineering the cell morphology, cytoskeleton, and electroporation buffer conditions.

Enhancing electroporation-induced liposomal drug release in suspension and solid phases

When exposed to an external electric field, lipid bilayer membranes are subject to increased permeability through the generation of pores. Combining this phenomenon, known as electroporation, with liposomal drug delivery offers the added benefit of on-demand release of the liposomal cargo. In previous studies, the maximum percent drug release when exposing liposomes to a pulsed electric field has not surpassed 30%, indicating most of the drug is still retained in the liposomes. Here we showed that by modulating the fluidity of the liposome membrane through appropriate selection of the primary lipid, as well as the addition of other fluidity modulating components such as cholesterol and biotinylated lipid, the electroporation-induced percent release could be increased to over 50%. In addition to improved induced release from liposomes in suspension, biomaterial scaffold-bound liposomes were developed. Electroporation-induced protein release from this solid phase was verified after performing further optimization of the liposome formulation to achieve increased stability at physiological temperatures. Collectively, this work advances the ability to achieve efficient electroporation-induced liposomal drug delivery, which has the potential to be used in concert with other clinical applications of electroporation, such as gene electrotransfer and irreversible electroporation (IRE), in order to synergistically increase treatment efficacy.

Decellularized Extracellular Matrix for Remodeling Bioengineering Organoid's Microenvironment

Over the past decade, stem cell- and tumor-derived organoids are the most promising models in developmental biology and disease modeling, respectively. The matrix is one of three main elements in the construction of an organoid and the most important module of its extracellular microenvironment. However, the source of the currently available commercial matrix, Matrigel, limits the application of organoids in clinical medicine. It is worth investigating whether the original decellularized extracellular matrix (dECM) can be exploited as the matrix of organoids and improving organoid construction are very important. In this review, tissue decellularization protocols and the characteristics of decellularization methods, the mechanical support and biological cues of extraccellular matrix (ECM), methods for construction of multifunctional dECM and responsive dECM hydrogel, and the potential applications of functional dECM are summarized. In addition, some expectations are provided for dECM as the matrix of organoids in clinical applications.

Ablative Therapy in Non-HCC Liver Malignancy

Surgical extirpation of liver tumors remains a proven approach in the management of metastatic tumors to the liver, particularly those of colorectal origin. Ablative, non-resective therapies are an increasingly attractive primary therapy for liver tumors as they are generally better tolerated and result in far less morbidity and mortality. Ablative therapies preserve greater normal liver parenchyma allowing better post-treatment liver function and are particularly appropriate for treating subsequent liver-specific tumor recurrence. This article reviews the current status of ablative therapies for non-hepatocellular liver tumors with a discussion of many of the clinically available approaches.

Effect of Pulse Widths and Cycles on Invasive, Bipolar, and Gated Radiofrequency-Induced Thermal Reactions in ex vivo Bovine Liver Tissue

Background

Radiofrequency (RF) oscillations generate thermal tissue reactions, the patterns of which vary depending on the mode and efficiency of energy delivery. The aim of our study was to analyze patterns of RF-induced thermal tissue reactions according to the modes of RF delivery, including continuous and gated modes, using an alternating current, invasive bipolar RF device.

Methods

RF energies at frequencies of 1 and 2 MHz were delivered at respective experimental settings into ex vivo bovine liver tissue at a 0.5-mm microneedle penetration depth. The tissue samples were then evaluated thermometrically. A histologic study was performed to evaluate RF-induced thermal tissue reactions at a 3.0-mm microneedle penetration depth.

Results

Thermal imaging study revealed homogenous, well-demarcated, square-shaped zones of RF-induced thermal reactivity on the treated area. Multivariate linear regression analysis revealed that higher temperature elevations immediately after RF treatment (∆T₁) were positively associated with RF frequency, power, conduction time/pulse pack, and off-time between pulse packs and negatively associated with total off time. In the 1-MHz experimental setting, higher ∆T₁ showed a positive association with power, conduction time/pulse pack, and off-time between pulse packs and a negative association with the number of pulse packs. In the 2-MHz setting, however, higher ∆T₁ was positively associated with only total treatment time.

Conclusion

Thermometric effects during bipolar and gated RF treatments are significantly associated with the frequency, power, and pulse widths and cycles of pulse packs.

Immediate and Late Effects of Pulse Widths and Cycles on Bipolar, Gated Radiofrequency-Induced Tissue Reactions in in vivo Rat Skin

Background

Single to multiple pulse packs of bipolar, alternating current radiofrequency (RF) oscillations have been used for various medical purposes using invasive microneedle electrodes. This study was designed to evaluate the effects of pulse widths and cycles of RF pulse packs on immediate and delayed thermal tissue reactions in in vivo rat skin.

Methods

RF energy at the frequency of 1 MHz and power of 70 W was delivered at each experimental setting into in vivo rat skin at 1.5-mm microneedle penetration, and then, tissue samples were obtained after 1 h and 3, 7, 14, and 21 days and histologically analyzed.

Results

A single-pulse-pack RF treatment generated coagulative necrosis zones in the dermal peri-electrode area and zones of non-necrotic thermal reactions in the dermal inter-electrode area. Multiple pulse-pack, RF-treated rat skin specimens revealed that the number and size of peri-electrode coagulative necrosis were markedly decreased by increasing the number of pulse packs and accordingly decreasing the conduction time of each pulse pack. The microscopic changes in RF-induced non-necrotic thermal reaction in the inter-electrode area were more remarkable in specimens treated with RF of 7 or 10 pulse packs than in specimens treated with RF of 1-4 pulse packs.

Conclusion

The gated delivery of multiple RF pulse packs using a bipolar, alternating current, 1-MHz RF system using insulated microneedle electrodes efficiently generates non-necrotic thermal tissue reactions over the upper, mid, and deep dermis and subcutaneous fat in the inter-electrode areas.

The Enlargement of Ablation Area by Electrolytic Irreversible Electroporation (E-IRE) Using Pulsed Field with Bias DC Field

Irreversible electroporation (IRE) by high-strength electric pulses is a biomedical technique that has been effectively used for minimally invasive tumor therapy while maintaining the functionality of adjacent important tissues, such as blood vessels and nerves. In general, pulse delivery using needle electrodes can create a reversible electroporation region beyond both the ablation area and the vicinity of the needle electrodes, limiting enlargement of the ablation area. Electrochemical therapy (EChT) can also be used to ablate a tumor near electrodes by electrolysis using a direct field with a constant current or voltage (DC field). Recently, reversible electroporated cells have been shown to be susceptible to electrolysis at relatively low doses. Reversible electroporation can also be combined with electrolysis for tissue ablation. Therefore, the objective of this study is to use electrolysis to remove the reversible electroporation area and thereby enlarge the ablation area in potato slices in vitro using a pulsed field with a bias DC field (constant voltage). We call this protocol electrolytic irreversible electroporation (E-IRE). The area over which the electrolytic effect induced a pH change was also measured. The results show that decreasing the pulse frequency using IRE alone is found to enlarge the ablation area. The ablation area generated by E-IRE is significantly larger than that generated by using IRE or EChT alone. The ablation area generated by E-IRE at 1 Hz is 109.5% larger than that generated by IRE, showing that the reversible electroporation region is transformed into an ablation region by electrolysis. The area with a pH change produced by E-IRE is larger than that produced by EChT alone. Decreasing the pulse frequency in the E-IRE protocol can further enlarge the ablation area. The results of this study are a preliminary indication that the E-IRE protocol can effectively enlarge the ablation area and enhance the efficacy of traditional IRE for use in ablating large tumors.

Advances of Electroporation-Related Therapies and the Synergy with Immunotherapy in Cancer Treatment

Electroporation is the process of instantaneously increasing the permeability of a cell membrane under a pulsed electric field. Depending on the parameters of the electric pulses and the target cell electrophysiological characteristics, electroporation can be either reversible or irreversible. Reversible electroporation facilitates the delivery of functional genetic materials or drugs to target cells, inducing cell death by apoptosis, mitotic catastrophe, or pseudoapoptosis; irreversible electroporation is an ablative technology which directly ablates a large amount of tissue without causing harmful thermal effects; electrotherapy using an electric field can induce cell apoptosis without any aggressive invasion. Reversible and irreversible electroporation can also activate systemic antitumor immune response and enhance the efficacy of immunotherapy. In this review, we discuss recent progress related to electroporation, and summarize its latest applications. Further, we discuss the synergistic effects of electroporation-related therapies and immunotherapy. We also propose perspectives for further investigating electroporation and immunotherapy in cancer treatment.

Liver tissue remodeling following ablation with irreversible electroporation in a porcine model

Irreversible electroporation (IRE) is a method of non-thermal focal tissue ablation characterized by irreversibly permeabilizing the cell membranes while preserving the extracellular matrix. This study aimed to investigate tissue remodeling after IRE in a porcine model, especially focusing on the extracellular matrix and hepatic stellate cells. IRE ablation was performed on 11 female pigs at 2,000 V/cm electric field strength using a versatile high-voltage generator and 3 cm diameter parallel-plate electrodes. The treated lobes were removed during surgery at 1, 3, 7, 14, and 21 days after IRE. Tissue remodeling and regeneration were assessed by histopathology and immunohistochemistry. Throughout the treated area, IRE led to extensive necrosis with intact collagenous structures evident until day 1. From then on, the necrosis progressively diminished while reparative tissue gradually increased. During this process, the reticulin framework and the septal fibrillar collagen remained in the necrotic foci until they were invaded by the reparative tissue. The reparative tissue was characterized by a massive proliferation of myofibroblast-like cells accompanied by a complete disorganization of the extracellular matrix with the disappearance of hepatic architecture. Hepatic stellate cell markers were associated with the proliferation of myofibroblast-like cells and the reorganization of the extracellular matrix. Between 2 and 3 weeks after IRE, the lobular architecture was almost completely regenerated. The events described in the present study show that IRE may be a valid model to study the mechanisms underlying liver regeneration after extensive acute injury.

Decellularized Extracellular Matrix Scaffolds for Cardiovascular Tissue Engineering: Current Techniques and Challenges

Cardiovascular diseases are the leading cause of global mortality. Over the past two decades, researchers have tried to provide novel solutions for end-stage heart failure to address cardiac transplantation hurdles such as donor organ shortage, chronic rejection, and life-long immunosuppression. Cardiac decellularized extracellular matrix (dECM) has been widely explored as a promising approach in tissue-regenerative medicine because of its remarkable similarity to the original tissue. Optimized decellularization protocols combining physical, chemical, and enzymatic agents have been developed to obtain the perfect balance between cell removal, ECM composition, and function maintenance. However, proper assessment of decellularized tissue composition is still needed before clinical translation. Recellularizing the acellular scaffold with organ-specific cells and evaluating the extent of cardiomyocyte repopulation is also challenging. This review aims to discuss the existing literature on decellularized cardiac scaffolds, especially on the advantages and methods of preparation, pointing out areas for improvement. Finally, an overview of the state of research regarding the application of cardiac dECM and future challenges in bioengineering a human heart suitable for transplantation is provided.

Image-Guided Percutaneous Ablation for Primary and Metastatic Tumors

Image-guided percutaneous ablation methods have been further developed during the recent two decades and have transformed the minimally invasive and precision features of treatment options targeting primary and metastatic tumors. They work by percutaneously introducing applicators to precisely destroy a tumor and offer much lower risks than conventional methods. There are usually shorter recovery periods, less bleeding, and more preservation of organ parenchyma, expanding the treatment options of patients with cancer who may not be eligible for resection. Image-guided ablation techniques are currently utilized for the treatment of primary and metastatic tumors in various organs including the liver, pancreas, kidneys, thyroid and parathyroid, prostate, lung, bone, and soft tissue. This article provides a brief review of the various imaging modalities and available ablation techniques and discusses their applications and associated complications in various organs.

Muscle contractions and pain sensation accompanying high-frequency electroporation pulses

To minimize neuromuscular electrical stimulation during electroporation-based treatments, the replacement of long monophasic pulses with bursts of biphasic high-frequency pulses in the range of microseconds was suggested in order to reduce muscle contraction and pain sensation due to pulse application. This treatment modality appeared under the term high-frequency electroporation (HF-EP), which can be potentially used for some clinical applications of electroporation such as electrochemotherapy, gene electrotransfer, and tissue ablation. In cardiac tissue ablation, which utilizes irreversible electroporation, the treatment is being established as Pulsed Field Ablation. While the reduction of muscle contractions was confirmed in multiple in vivo studies, the reduction of pain sensation in humans was not confirmed yet, nor was the relationship between muscle contraction and pain sensation investigated. This is the first study in humans examining pain sensation using biphasic high-frequency electroporation pulses. Twenty-five healthy individuals were subjected to electrical stimulation of the tibialis anterior muscle with biphasic high-frequency pulses in the range of few microseconds and both, symmetric and asymmetric interphase and interpulse delays. Our results confirm that biphasic high-frequency pulses with a pulse width of 1 or 2 µs reduce muscle contraction and pain sensation as opposed to currently used longer monophasic pulses. In addition, interphase and interpulse delays play a significant role in reducing the muscle contraction and/or pain sensation. The study shows that the range of the optimal pulse parameters may be increased depending on the prerequisites of the therapy. However, further evaluation of the biphasic pulse protocols presented herein is necessary to confirm the efficiency of the newly proposed HF-EP.

Theoretical model of the influence of irreversibly electroporated cells on post pulse drug delivery to reversibly electroporated cells

This study numerically investigates the drug uptake by a population that includes both reversibly and irreversibly electroporated cells. A theoretical continuum model is developed and simulations are conducted in conditions representing low porosity (cells in tissues) and high porosity (cells in suspension). This model considers only passive diffusion following the electroporation pulse and estimates the permeability increases of reversibly electroporated cells using empirically based predictions that relate the long-lived electropore density to the electric field magnitude. A parametric study investigates whether the permeability and resealing rate of irreversibly electroporated cells influence the delivery to the surviving reversibly electroporated cells. The results show that this influence is negligible when the cell number density is low (cells in dilute suspensions). For conditions of cells in tissue when both the fraction of the total cells that are irreversibly electroporated and the permeability of the irreversibly electroporated cells are high enough, the irreversibly electroporated cells rapidly take up the drug and deplete the extracellular space of the available drug. This lowered extracellular concentration can result in less drug delivery to reversibly electroporated cells.

Non-thermal Electroporation Ablation of Epileptogenic Zones Stops Seizures in Mice While Providing Reduced Vascular Damage and Accelerated Tissue Recovery

In epilepsy, the most frequent surgical procedure is the resection of brain tissue in the temporal lobe, with seizure-free outcomes in approximately two-thirds of cases. However, consequences of surgery can vary strongly depending on the brain region targeted for removal, as surgical morbidity and collateral damage can lead to significant complications, particularly when bleeding and swelling are located near delicate functional cortical regions. Although focal thermal ablations are well-explored in epilepsy as a minimally invasive approach, hemorrhage and edema can be a consequence as the blood-brain barrier is still disrupted. Non-thermal irreversible electroporation (NTIRE), common in many other medical tissue ablations outside the brain, is a relatively unexplored method for the ablation of neural tissue, and has never been reported as a means for ablation of brain tissue in the context of epilepsy. Here, we present a detailed visualization of non-thermal ablation of neural tissue in mice and report that NTIRE successfully ablates epileptic foci in mice, resulting in seizure-freedom, while causing significantly less hemorrhage and edema compared to conventional thermal ablation. The NTIRE approach to ablation preserves the blood-brain barrier while pathological circuits in the same region are destroyed. Additionally, we see the reinnervation of fibers into ablated brain regions from neighboring areas as early as day 3 after ablation. Our evidence demonstrates that NTIRE could be utilized as a precise tool for the ablation of surgically challenging epileptogenic zones in patients where the risk of complications and hemorrhage is high, allowing not only reduced tissue damage but potentially accelerated recovery as vessels and extracellular matrix remain intact at the point of ablation.

Decellularised extracellular matrix-based biomaterials for repair and regeneration of central nervous system

The central nervous system (CNS), consisting of the brain and spinal cord, regulates the mind and functions of the organs. CNS diseases, leading to changes in neurological functions in corresponding sites and causing long-term disability, represent one of the major public health issues with significant clinical and economic burdens worldwide. In particular, the abnormal changes in the extracellular matrix under various disease conditions have been demonstrated as one of the main factors that can alter normal cell function and reduce the neuroregeneration potential in damaged tissue. Decellularised extracellular matrix (dECM)-based biomaterials have been recently utilised for CNS applications, closely mimicking the native tissue. dECM retains tissue-specific components, including proteoglycan as well as structural and functional proteins. Due to their unique composition, these biomaterials can stimulate sensitive repair mechanisms associated with CNS damages. Herein, we discuss the decellularisation of the brain and spinal cord as well as recellularisation of acellular matrix and the recent progress in the utilisation of brain and spinal cord dECM.

Characterization of dispersion and anisotropic-conductivity in tissue model during electroporation pulses

Electroporation occurs when biological cells are exposed to intensive, short-duration pulses, which can be used to ablate biological tumor tissues. Based on the traditional numerical models, the isotropic conductivity model with the non-dispersion effect (ICND), the anisotropic conductivity model with the dispersion effect (ACD) is developed in this study. The second-order Debye function is introduced to manifest the dielectric relaxation effect, and the two-dimensional Cartesian conductivity matrix is applied to describe the anisotropy of the tissue conductivity during the electroporation process. A monopolar pulse and a monopolar burst are applied to the breast tumor model through the two-needle electrodes configuration. The results show that taking the dispersion into account can increase the total electroporated area more than 2.31%. Considering the conductivity anisotropy, the total electroporated area increases, but the irreversible electroporation (IRE) area decreases by more than 3.99%. The ACD model can achieve a larger electroporated area but a relatively smaller IRE area than those of the ICND model, and comparably minor maximum thermal damage is evaluated in the ACD model. Our model analyzes the effects of the dielectric dispersion and anisotropic conductivity of tissue, which have strong guiding significance for making the treatment planning before clinical practice.

High-Voltage, Pulsed Electric Fields Eliminate Pseudomonas aeruginosa Stable Infection in a Mouse Burn Model

Objective: The incidence of severe infectious complications after burn injury increases mortality by 40%. However, traditional approaches for managing burn infections are not always effective. High-voltage, pulsed electric field (PEF) treatment shortly after a burn injury has demonstrated an antimicrobial effect in vivo; however, the working parameters and long-term effects of PEF treatment have not yet been investigated. Approach: Nine sets of PEF parameters were investigated to optimize the applied voltage, pulse duration, and frequency or pulse repetition for disinfection of Pseudomonas aeruginosa infection in a stable mouse burn wound model. The bacterial load after PEF administration was monitored for 3 days through bioluminescence imaging. Histological assessments and inflammation response analyses were performed at 1 and 24 h after the therapy. Results: Among all tested PEF parameters, the best disinfection efficacy of P. aeruginosa infection was achieved with a combination of 500 V, 100 μs, and 200 pulses delivered at 3 Hz through two plate electrodes positioned 1 mm apart for up to 3 days after the injury. Histological examinations revealed fewer inflammatory signs in PEF-treated wounds compared with untreated infected burns. Moreover, the expression levels of multiple inflammatory-related cytokines (interleukin [IL]-1α/β, IL-6, IL-10, leukemia inhibitory factor [LIF], and tumor necrosis factor-alpha [TNF-α]), chemokines (macrophage inflammatory protein [MIP]-1α/β and monocyte chemoattractant protein-1 [MCP-1]), and inflammation-related factors (vascular endothelial growth factor [VEGF], macrophage colony-stimulating factor [M-CSF], and granulocyte-macrophage colony-stimulating factor [G-CSF]) were significantly decreased in the infected burn wound after PEF treatment. Innovation: We showed that PEF treatment on infected wounds reduces the P. aeruginosa load and modulates inflammatory responses. Conclusion: The data presented in this study suggest that PEF treatment is a potent candidate for antimicrobial therapy for P. aeruginosa burn infections.

Irreversible Electroporation for the Treatment of Small Renal Masses: 5-Year Outcomes

Introduction: Irreversible electroporation (IRE) is a nonthermal ablative technology that applies high-voltage short-pulse electrical current to create cellular membrane nanopores and ultimately results in apoptosis. This is thought to overcome thermal limitations of other ablative technologies. We report 5-year oncologic outcomes of percutaneous IRE for small renal masses. Patients and Methods: A single-institution retrospective review of cT1a renal masses treated with IRE from April 2013 to December 2019 was performed. Those with <1 month follow-up were excluded. IRE was performed with the NanoKnife^© System (Angiodynamics, Latham, NY). Renal mass biopsy was obtained before or during ablation in most circumstances; biopsy was excluded in some patients because of concern for IRE probe displacement. Postablation guideline-based surveillance imaging was performed. Initial treatment failure was defined as persistent tumor enhancement on first post-treatment imaging. Survival analysis was performed through the Kaplan-Meier method for effectively treated tumors (SPSS; IBM, Armonk, NY). Results: IRE was used to treat 48 tumors in 47 patients. Twenty-two per 48 tumors (45.8%) were biopsy-confirmed renal cell carcinoma (RCC). No complications ≥ Clavien Grade III occurred and 36 patients (76.6%) were discharged the same day. Initial treatment success rate was 91.7% (n = 44/48); three treatment failures were managed with salvage radiofrequency ablation and one with robotic partial nephrectomy. Median follow-up was 50.4 months (interquartile range 29.0-65.5). The 5-year local recurrence-free survival was 81.4% in biopsy-confirmed RCC patients and 81.0% in all patients. Five-year metastasis-free survival was 93.3% and 97.1%, respectively, and 5-year overall survival was 92.3% and 90.6%, respectively. Five-year cancer-specific survival was 100% for both biopsy-confirmed RCC and all patient groups. Conclusions: IRE has low morbidity, but suboptimal intermediate-term oncologic outcomes compared with conventional thermal ablation techniques for small low-complexity tumors. Use of IRE should be restricted to select cases.

Generation of Tumor-activated T cells using electroporation

Expansion of cytotoxic T lymphocytes (CTLs) is a crucial step in almost all cancer immunotherapeutic methods. Current techniques for expansion of tumor-reactive CTLs present major limitations. This study introduces a novel method to effectively produce and expand tumor-activated CTLs using high-voltage pulsed electric fields. We hypothesize that utilizing high-voltage pulsed electric fields may be an ideal method to activate and expand CTLs due to their non-thermal celldeath mechanism. Tumor cells were subjected to high-frequency irreversible electroporation (HFIRE) with various electric field magnitudes (1250, 2500 V/cm) and pulse widths (1, 5, and 10 µs), or irreversible electroporation (IRE) at 1250 V/cm. The treated tumor cells were subsequently cocultured with CD4+ and CD8+ T cells along with antigen-presenting cells. We show that tumor-activated CTLs can be produced and expanded when exposed to treated tumor cells. Our results suggest that CTLs are more effectively expanded when pulsed with HFIRE conditions that induce significant cell death (longer pulse widths and higher voltages). Activated CD8+ T cells demonstrate cytotoxicity to untreated tumor cells suggesting effector function of the activated CTLs. The activated CTLs produced with our technique could be used for clinical applications with the goal of targeting and eliminating the tumor.

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.

A retrospective study of CT-guided percutaneous irreversible electroporation (IRE) ablation: clinical efficacy and safety

Background

To evaluate the clinical efficacy and safety of ablating renal cell carcinoma (RCC) by irreversible electroporation (IRE).

Methods

Fifteen patients (19 lesions) with RCC who underwent IRE were retrospectively reviewed. Seven patients had solitary kidneys. Two lesions were located in the renal hilus. One patient had chronic renal insufficiency. Percutaneous biopsy for histopathology was performed. The best puncture path plan was evaluated before CT-guided IRE. The estimated glomerular filtration rate (eGFR) was compared vs baseline at 1–2 months after the ablation. Contrast-enhanced computed tomography imaging changes were evaluated immediately after IRE. Contrast-enhanced computed tomography/magnetic resonance was performed 1 month, 3 months, 6 months, 12 months and every year thereafter. The complications after treatment were also reviewed.

Results

The success rate of the procedure was 100%. The median tumor size was 2.4 (IQR 1.3–2.9) cm, with an median score of 6 (IQR 5.5–8) per R.E.N.A.L. criteria (radius, exophytic/endophytic, nearness to collecting system or sinus, anterior/posterior, and location relative to polar lines). Two cases (3 lesions) were punctured through the liver. In other cases, puncture was performed through the perirenal space. There were no severecomplications in interventional therapy. Transient gross hematuria occurred in 2 patients (centrally located). Self-limiting perinephric hematomas occurred in 1 patient. Needle puncture path metastasis was found in 1 patient 2.5 years after IRE. The subcutaneous metastasis was surgically removed, and there was no evidence of recurrence. There was no significant change in eGFR levels in terms of short- term clinical outcomes (t = 0.348, P = 0.733). At 6 months, all 15 patients with imaging studies available had no evidence of recurrence. At 1 year, 1 patient (1 of 15) was noted to have experienced needle tract metastasis and accepted salvage radiofrequency ablation (RFA) therapy.

Conclusions

IRE appears to be a safe and effective treatment for RCC that may offer a tissue-sparing method and complete ablation as an alternative therapy for RCC.

Anatomical targets and expected outcomes of catheter-based ablation of atrial fibrillation in 2020

Anatomical-based approaches, targeting either pulmonary vein isolation (PVI) or additional extra PV regions, represent the most commonly used ablation treatments in symptomatic patients with atrial fibrillation (AF) recurrences despite antiarrhythmic drug therapy. PVI remains the main anatomical target during catheter-based AF ablation, with the aid of new technological advances as contact force monitoring to increase safety and effective radiofrequency (RF) lesions. Nowadays, cryoballoon ablation has also achieved the same level of scientific evidence in patients with paroxysmal AF undergoing PVI. In parallel, electrical isolation of extra PV targets has progressively increased, which is associated with a steady increase in complex cases undergoing ablation. Several atrial regions as the left atrial posterior wall, the vein of Marshall, the left atrial appendage, or the coronary sinus have been described in different series as locations potentially involved in AF initiation and maintenance. Targeting these regions may be challenging using conventional point-by-point RF delivery, which has opened new opportunities for coadjuvant alternatives as balloon ablation or selective ethanol injection. Although more extensive ablation may increase intraprocedural AF termination and freedom from arrhythmias during the follow-up, some of the targets to achieve such outcomes are not exempt of potential severe complications. Here, we review and discuss current anatomical approaches and the main ablation technologies to target atrial regions associated with AF initiation and maintenance.

Intratumoral STING Agonist Injection Combined with Irreversible Electroporation Delays Tumor Growth in a Model of Hepatocarcinoma

BACKGROUND/AIM

Irreversible electroporation (IRE) showed promising results for small-size tumors and very early cancers. However, further development is needed to evolve this procedure into a more efficient ablation technique for long-term control of tumor growth. In this work, we show that it is possible to increase the antitumor efficiency of IRE by simmultaneously injecting c-di-GMP, a STING agonist, intratumorally.

MATERIALS AND METHODS

Intratumoral administration of c-di-GMP simultaneously to IRE was evaluated in murine models of melanona (B16.OVA) and hepatocellular carcinoma (PM299L).

RESULTS

The combined therapy increased the number of tumor-infiltrating IFN-γ/TNF-α-producing CD4 and CD8 T cells and delayed tumor growth, as compared to the effect observed in groups treated with c-di-GMP or IRE alone.

CONCLUSION

These results can lead to the development of a new therapeutic strategy for the treatment of cancer patients refractory to other therapies.

Irreversible Electroporation for Renal Ablation Does Not Cause Significant Injury to Adjacent Ureter or Bowel in a Porcine Model

Objective: To evaluate the safety of irreversible electroporation (IRE) for renal ablation adjacent to the ureter or bowel. Materials and Methods: Six adult pigs each underwent bilateral IRE of the kidney. To simulate adjacence, the left proximal ureter and duodenum were secured onto the left and right kidney capsule, respectively. Two IRE probes were placed into the renal parenchyma and configured to bridge the ureter and bowel. Therapeutic IRE was delivered at 2000 V/cm for 70 pulses in both forward and reverse polarity. The animal was survived and euthanized at 1, 3, or 14 days. Histopathology was obtained for all potentially injured bowel and ureteral segments. Retrograde pyelogram (RPG) was performed on each left-sided ureter. Results: Histologic analysis of the ureter identified reactive changes at the level of the periureteral adipose tissue, which progressed from acute inflammation on day 1 to focal fibrosis by day 14. Urothelial mucosa and surrounding smooth muscle layers were unaffected at all time points. RPGs did not show any abnormalities in all specimens. Histologic analysis of the bowel demonstrated acute inflammation in the serosa and subserosal tissue on day 1. Three days after IRE, inflammation and crypt abscesses were focally present in the deep aspects of the bowel mucosa. Inflammation in the mucosal layer resolved 14 days after IRE. Conclusions: In a porcine model of renal IRE, no significant injury was apparent after intentional ablation adjacent to the ureter and bowel. IRE may be a safe alternative to thermal ablation for tumors near the ureter or bowel.

Thermochromic Tissue Phantoms for Evaluating Temperature Distribution in Simulated Clinical Applications of Pulsed Electric Field Therapies

Background: Irreversible electroporation (IRE) induces cell death through nonthermal mechanisms, however, in extreme cases, the treatments can induce deleterious thermal transients. This study utilizes a thermochromic tissue phantom to enable visualization of regions exposed to temperatures above 60°C. Materials and Methods: Poly(vinyl alcohol) hydrogels supplemented with thermochromic ink were characterized and processed to match the electrical properties of liver tissue. Three thousand volt high-frequency IRE protocols were administered with delivery rates of 100 and 200 μs/s. The effect of supplemental internal applicator cooling was then characterized. Results: Baseline treatments resulted thermal areas of 0.73 cm2, which decreased to 0.05 cm2 with electrode cooling. Increased delivery rates (200 μs/s) resulted in thermal areas of 1.5 and 0.6 cm2 without and with cooling, respectively. Conclusions: Thermochromic tissue phantoms enable rapid characterization of thermal effects associated with pulsed electric field treatments. Active cooling of applicators can significantly reduce the quantity of tissue exposed to deleterious temperatures.

Irreversible electroporation in patients with liver tumours: treated-area patterns with contrast-enhanced ultrasound

BACKGROUND

Familiarity with post-IRE imaging interpretation is of considerable importance in determining ablation success and detecting recurrence. CEUS can be used to assess the tumour response and characteristics of the ablation zone. It is of clinical interest to describe the ultrasonographic findings of liver tumours after irreversible electroporation (IRE) percutaneous ablation.

METHODS

A prospective study of 24 cases of malignant liver tumours (22 cases of primary liver tumours and 2 cases of liver metastases) treated by IRE ablation was conducted. Two inspectors evaluated the ablation zone in a consensus reading performed immediately, 1 day, and 1 month after IRE ablation. The gold standard method, magnetic resonance imaging (MRI), was used to evaluate the effectiveness of the treatment at 1 month.

RESULTS

Immediately after IRE ablation and up to 1 month later, the ablation zones gradually changed from hypo-echogenicity to hyper-echogenicity on conventional ultrasound and showed non-enhancement on contrast-enhanced ultrasound (CEUS). One month after IRE ablation, CEUS and MRI results were highly consistent (κ = 0.78, p < 0.05).

CONCLUSIONS

We conclude that CEUS may be an effective tool for assessing post-IRE ablation changes after 1 month. CEUS enables the depiction of tumour vascularity in real time and serves as an easy, repeatable method.

Analysis on reversible/irreversible electroporation region in lung adenocarcinoma cell model in vitro with electric pulses delivered by needle electrodes

Irreversible electroporation (IRE) is a minimally invasive tumor therapy using pulsed electric field with high intensity while the important tissues such as blood vessel, bile duct, and nerve are preserved. In addition to ablation area, reversible electroporation (RE) region is also generated using needle electrodes for pulse delivery. The goal of this work is to study the generation of RE region and ablation region on a 2D lung adenocarcinoma cell model in vitro. The tumor model is exposed to electric pulses with various number. The calcium AM and propidium iodide (PI) are examined to detect the ablation area and electroporation area, respectively. The results show that electroporation area firstly tends to plateau after approximately 50 pulses, while the ablation area continues to increase. The percentage of IRE area in total electroporation area increases with additional pulses, which means that RE region could be gradually turned into ablation area with increased pulse number. However, the percentage of IRE area only achieves to 54% for 200 pulses, which indicates that RE region still cannot be completely removed. RE and IRE thresholds appear to converge as the number of pulses increases. An equation between pulse number and the electric field threshold of ablation including the electric field threshold of RE is also provided for lung adenocarcinoma cell ablation. This work may have the value for the optimization of IRE protocols on tumor ablation.

Algorithmically Controlled Electroporation: A Technique for Closed Loop Temperature Regulated Pulsed Electric Field Cancer Ablation

OBJECTIVE

To evaluate the effect of a closed-loop temperature based feedback algorithm on ablative outcomes for pulsed electric field treatments.

METHODS

A 3D tumor model of glioblastoma was used to assess the impact of 2 μs duration bipolar waveforms on viability following exposure to open and closed-loop protocols. Closed-loop treatments evaluated transient temperature increases of 5, 10, 15, or 22 °C above baseline.

RESULTS

The temperature controlled ablation diameters were conditionally different than the open-loop treatments and closed-loop treatments generally produced smaller ablations. Closed-loop control enabled the investigation of treatments with steady state 42 °C hyperthermic conditions which were not feasible without active feedback. Baseline closed-loop treatments at 20 °C resulted in ablations measuring 9.9 ± 0.3 mm in diameter while 37 °C treatments were 20% larger (p < 0.0001) measuring 11.8 ± 0.3 mm indicating that this protocol induces a thermally mediated biological response.

CONCLUSION

A closed-loop control algorithm which modulated the delay between successive pulse waveforms to achieve stable target temperatures was demonstrated. Algorithmic control enabled the evaluation of specific treatment parameters at physiological temperatures not possible with open-loop systems due to excessive Joule heating.

SIGNIFICANCE

Irreversible electroporation is generally considered to be a non-thermal ablation modality and temperature monitoring is not part of the standard clinical practice. The results of this study indicate ablative outcomes due to exposure to pulses on the order of one microsecond may be thermally mediated and dependent on local tissue temperatures. The results of this study set the foundation for experiments in vivo utilizing temperature control algorithms.

Differential Cell Death and Regrowth of Dermal Fibroblasts and Keratinocytes After Application of Pulsed Electric Fields

Background: High-powered pulsed electric fields (PEF) may be used for tissue debridement and disinfection, while lower PEF intensities may stimulate beneficial cellular responses for wound healing. We investigated the dual effects of nonuniform PEF on cellular death and stimulation. Methods: Dermal fibroblast or keratinocyte monolayers were exposed to PEF induced by two needle electrodes (2 mm apart). Voltages (100-600 V; 1 Hz; 70 micros pulse width; 90 pulses/cycle) were applied between the two electrodes. Controls consisted of similar monolayers subjected to a scratch mechanical injury. Results: Cell growth and closure of the cell-free gap was faster in PEF-treated cell monolayers versus scratched ones. Media conditioned from cells pre-exposed to PEF, when applied to responder cells, stimulated greater proliferation than media from scratched monolayers. Conclusions: PEF treatment causes the release of soluble factors that promote cell growth, and thus may play a role in the accelerated healing of wounds post PEF.

Development of a Multi-Pulse Conductivity Model for Liver Tissue Treated With Pulsed Electric Fields

Pulsed electric field treatment modalities typically utilize multiple pulses to permeabilize biological tissue. This electroporation process induces conductivity changes in the tissue, which are indicative of the extent of electroporation. In this study, we characterized the electroporation-induced conductivity changes using all treatment pulses instead of solely the first pulse as in conventional conductivity models. Rabbit liver tissue was employed to study the tissue conductivity changes caused by multiple, 100 μs pulses delivered through flat plate electrodes. Voltage and current data were recorded during treatment and used to calculate the tissue conductivity during the entire pulsing process. Temperature data were also recorded to quantify the contribution of Joule heating to the conductivity according to the tissue temperature coefficient. By fitting all these data to a modified Heaviside function, where the two turning points (E₀, E₁) and the increase factor (A) are the main parameters, we calculated the conductivity as a function of the electric field (E), where the parameters of the Heaviside function (A and E₀) were functions of pulse number (N). With the resulting multi-factor conductivity model, a numerical electroporation simulation can predict the electrical current for multiple pulses more accurately than existing conductivity models. Moreover, the saturating behavior caused by electroporation can be explained by the saturation trends of the increase factor A in this model. The conductivity change induced by electroporation has a significant increase at about the first 30 pulses, then tends to saturate at 0.465 S/m. The proposed conductivity model can simulate the electroporation process more accurately than the conventional conductivity model. The electric field distribution computed using this model is essential for treatment planning in biomedical applications utilizing multiple pulsed electric fields, and the method proposed here, relating the pulse number to the conductivity through the variables in the Heaviside function, may be adapted to investigate the effect of other parameters, like pulse frequency and pulse width, on electroporation.

Electro-Thermal Therapy Algorithms and Active Internal Electrode Cooling Reduce Thermal Injury in High Frequency Pulsed Electric Field Cancer Therapies

Thermal tissue injury is an unintended consequence in current irreversible electroporation treatments due to the induction of Joule heating during the delivery of high voltage pulsed electric fields. In this study active temperature control measures including internal electrode cooling and dynamic energy delivery were investigated as a process for mitigating thermal injury during treatment. Ex vivo liver was used to examine the extent of thermal injury induced by 5000 V treatments with delivery rates up to five times faster than current clinical practice. Active internal cooling of the electrode resulted in a 36% decrease in peak temperature vs. non-cooled control treatments. A temperature based feedback algorithm (electro-thermal therapy) was demonstrated as capable of maintaining steady state tissue temperatures between 30 and 80 °C with and without internal electrode cooling. Thermal injury volumes of 2.6 cm³ were observed for protocols with 60 °C temperature set points and electrode cooling. This volume reduced to 1.5 and 0.1 cm³ for equivalent treatments with 50 °C and 40 °C set points. Finally, it was demonstrated that the addition of internal electrode cooling and active temperature control algorithms reduced ETT treatment times by 84% (from 343 to 54 s) vs. non-cooled temperature control strategies with equivalent thermal injury volumes.

Electro-thermal therapy: Microsecond duration pulsed electric field tissue ablation with dynamic temperature control algorithms

Electro-thermal therapy (ETT) is a new cancer treatment modality which combines the use of high voltage pulsed electric fields, dynamic energy delivery rates, and closed loop thermal control algorithms to rapidly and reproducibly create focal ablations. This study examines the ablative potential and profile of pulsed electric field treatments delivered in conjunction with precise temperature control algorithms. An ex vivo perfused liver model was utilized to demonstrate the capability of 5000 V 2 μs duration bipolar electrical pulses and dynamic temperature control algorithms to produce ablations. Using a three applicator array, 4 cm ablation zones were created in under 27 min. In this configuration, the algorithms were able to rapidly achieve and maintain temperatures of 80 °C at the tissue-electrode interface. A simplified single applicator and grounding pad approach was used to correlate the measured ablation zones to electric field isocontours in order to determine lethal electric field thresholds of 708 V/cm and 867 V/cm for 45 °C and 60 °C treatments, respectively. These results establish ETT as a viable method for hepatic tumor treatment with ablation profiles equivalent to other energy based techniques. The single applicator and multi-applicator approaches demonstrated may enable the treatment of complex tumor geometries. The flexibility of ETT temperature control yields a malleable intervention which gives clinicians robust control over the ablation modality, treatment time, and safety profile.

Cytoskeletal Disruption after Electroporation and Its Significance to Pulsed Electric Field Therapies

Pulsed electric fields (PEFs) have become clinically important through the success of Irreversible Electroporation (IRE), Electrochemotherapy (ECT), and nanosecond PEFs (nsPEFs) for the treatment of tumors. PEFs increase the permeability of cell membranes, a phenomenon known as electroporation. In addition to well-known membrane effects, PEFs can cause profound cytoskeletal disruption. In this review, we summarize the current understanding of cytoskeletal disruption after PEFs. Compiling available studies, we describe PEF-induced cytoskeletal disruption and possible mechanisms of disruption. Additionally, we consider how cytoskeletal alterations contribute to cell-cell and cell-substrate disruption. We conclude with a discussion of cytoskeletal disruption-induced anti-vascular effects of PEFs and consider how a better understanding of cytoskeletal disruption after PEFs may lead to more effective therapies.

Simulation of the influence of voltage level and pulse spacing on the efficiency, aggressiveness and uniformity of the electroporation process in tissues using meshless techniques

Electroporation is a widely used method consisting of application of high-voltage, short-duration electric pulses to increase cell membrane permeability, allowing cellular internalization of medications. In this work, the influence of two primary parameters, voltage level (V) and pulse spacing (N), on electroporation efficiency, uniformity and aggressiveness, as quantified by the total mass transport to viable cells, intracellular concentration gradients and an aggressiveness factor introduced here, is studied by means of numerical simulations of drug transport in electroporated tissues. The global method of approximate particular solutions (Global MAPS) is used to solve the governing equations, together with domain scaling, singular value decomposition and smoothing algorithms, to address the ill-conditioning of the final system and suppress small scale oscillations. The accuracy of Global MAPS is evaluated by comparing the initial extracellular concentration, C_e , and final intracellular concentration, C_i , with previous finite volume method results, obtaining similar behavior of C_e and C_i along the tissue domain, with some differences for C_i in high-gradient zones. According to the Global MAPS results, the influence of V and N on C_i is only significant over a certain range, within which the largest drug transport to viable cells occurs. In general, both electroporation efficiency and aggressiveness change in nonuniform manner with V and decrease with N, whereas the electroporation uniformity decreases as V increases and N decreases. The contour plots obtained here can be considered useful tools to compare electroporation-based treatments in terms of their efficiency, aggressiveness and uniformity, assisting in the selection of a suitable treatment plan for cancer.

Time-Dependent Impact of Irreversible Electroporation on Pathology and Ablation Size in the Porcine Liver: A 24-Hour Experimental Study

Irreversible electroporation causes cell death through low frequency, high voltage electrical pulses and is increasingly used to treat non-resectable cancers. A recent systematic review revealed that tissue damage through irreversible electroporation is time-dependent, but the impact of time on the ablation zone size remains unknown. Irreversible electroporation ablations were performed hourly during 24 consecutive hours in the peripheral liver of 2 anaesthetized domestic pigs using clinical treatment settings. Immediately after the 24th ablation, the livers were harvested and examined for tissue response in time based on macroscopic and microscopic pathology. The impact of time on these outcomes was assessed with Spearman rank correlation test. Ablation zones were sharply demarcated as early as 1 hour after treatment. During 24 hours, the ablation zones showed a significant increase in diameter (rs = 0.493, P = .014) and total surface (rs = 0.499, P = .013), whereas the impact of time on the homogeneous ablated area was not significant (rs = 0.172, P = .421). Therefore, the increase in size could mainly be attributed to an increase in the transition zone. Microscopically, the ablation zones showed progression in cell death and inflammation. This study assessed the dynamics of irreversible electroporation on the porcine liver during 24 consecutive hours and found that the pathological response (ie, cell death/inflammation), and ablation size continue to develop for at least 24 hours. Consequently, future studies on irreversible electroporation should prolong their observation period.

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.

High-frequency irreversible electroporation for cardiac ablation using an asymmetrical waveform

Background

Irreversible electroporation (IRE) using direct current (DC) is an effective method for the ablation of cardiac tissue. A major drawback of the use of DC-IRE, however, are two problems: requirement of general anesthesia due to severe muscle contractions and the formation of bubbles containing gaseous products from electrolysis. The use of high-frequency alternating current (HF-IRE) is expected to solve both problems, because HF-IRE produces little to no muscle spasms and does not cause electrolysis.

Methods

In the present study, we introduce a novel asymmetric, high-frequency (aHF) waveform for HF-IRE and present the results of a first, small, animal study to test its efficacy.

Results

The data of the experiments suggest that the aHF waveform creates significantly deeper lesions than a symmetric HF waveform of the same energy and frequency (p = 0.003).

Conclusion

We therefore conclude that the use of the aHF enhances the feasibility of the HF-IRE method.

Veterinary Clinics: Tumor Ablation

Over the past decade, interventional oncology techniques have become integrated into the treatment plans of companion animals with cancer on a regular basis. Although procedures such as stenting are performed commonly, other less frequently utilized techniques for locoregional therapy, such as embolization and ablation, are emerging and demonstrating promise. Tumor ablation techniques are categorized into two subgroups: chemical ablation and energy-based ablation. Increased utilization of ablation will allow for the determination of specific indications and evaluation of outcomes for these techniques.

A Conceivable Mechanism Responsible for the Synergy of High and Low Voltage Irreversible Electroporation Pulses

Irreversible electroporation (IRE), is a new non-thermal tissue ablation technology in which brief high electric field pulses are delivered across the target tissue to induce cell death by irreversible permeabilization of the cell membrane. A deficiency of conventional IRE is that the ablation zone is relatively small, bounded by the irreversible electroporation isoelectric field margin. In the previous studies we have introduced a new treatment protocol that combines few short high voltage (SHV) pulses with long low-voltage (LLV) pulses. In the previous studies, we also have shown that the addition of few SHV pulses increases by almost a factor of two the area ablated by a protocol that employs only the LLV pulses. This study employs potato and gel phantom to generate a plausible explanation for the mechanism. The study provides circumstantial evidence that the mechanism involved is the production of electrolytic compounds by the LLV pulse sequence, which causes tissue ablation beyond the margin of the irreversible electroporation isoelectric field generated by the SHV pulses, presumable to the reversible electroporation isoelectric field margin generated by the SHV pulses.

High-Frequency Irreversible Electroporation for Intracranial Meningioma: A Feasibility Study in a Spontaneous Canine Tumor Model

High-frequency irreversible electroporation is a nonthermal method of tissue ablation that uses bursts of 0.5- to 2.0-microsecond bipolar electric pulses to permeabilize cell membranes and induce cell death. High-frequency irreversible electroporation has potential advantages for use in neurosurgery, including the ability to deliver pulses without inducing muscle contraction, inherent selectivity against malignant cells, and the capability of simultaneously opening the blood–brain barrier surrounding regions of ablation. Our objective was to determine whether high-frequency irreversible electroporation pulses capable of tumor ablation could be delivered to dogs with intracranial meningiomas. Three dogs with intracranial meningiomas were treated. Patient-specific treatment plans were generated using magnetic resonance imaging-based tissue segmentation, volumetric meshing, and finite element modeling. Following tumor biopsy, high-frequency irreversible electroporation pulses were stereotactically delivered in situ followed by tumor resection and morphologic and volumetric assessments of ablations. Clinical evaluations of treatment included pre- and posttreatment clinical, laboratory, and magnetic resonance imaging examinations and adverse event monitoring for 2 weeks posttreatment. High-frequency irreversible electroporation pulses were administered successfully in all patients. No adverse events directly attributable to high-frequency irreversible electroporation were observed. Individual ablations resulted in volumes of tumor necrosis ranging from 0.25 to 1.29 cm³. In one dog, nonuniform ablations were observed, with viable tumor cells remaining around foci of intratumoral mineralization. In conclusion, high-frequency irreversible electroporation pulses can be delivered to brain tumors, including areas adjacent to critical vasculature, and are capable of producing clinically relevant volumes of tumor ablation. Mineralization may complicate achievement of complete tumor ablation.

Scaling Relationship of In Vivo Muscle Contraction Strength of Rabbits Exposed to High-Frequency Nanosecond Pulse Bursts

We studied the influence of various parameters of high-frequency nanosecond pulse bursts on the strength of rabbit muscle contractions. Ten unipolar high-frequency pulse bursts with various field intensities E (1 kV/cm, 4 kV/cm, and 8 kV/cm), intraburst frequencies f (10 kHz, 100 kHz, and 1 MHz), and intraburst pulse numbers N (1, 10, and 100) were applied using a pair of plate electrodes to the surface skin of the rabbits' biceps femoris, and the acceleration signal of muscle contraction near the electrode was measured using a 3-axis acceleration sensor. A time- and frequency-domain analysis of the acceleration signals showed that the peak value of the signal increases with the increasing strength of the pulse burst and that the frequency spectra of the signals measured under various pulse bursts have characteristic frequencies (at approximately 2 Hz, 32 Hz, 45 Hz, and 55 Hz). Furthermore, we processed the data through multivariate nonlinear regression analysis and variance analysis and determined that the peak value of the signal scales with the logarithm to the base 10 of EN ^x, where x is a value that scales with the logarithm to the base 10 of intraburst frequency (f). These results indicate that for high-frequency nanosecond pulse treatment of solid tumors in or near muscles, when the field strength is relatively high, the intraburst frequency and the intraburst pulse number require appropriate selection to limit the strength of muscle contraction as much as possible.

The potential for remodelling the tumour vasculature in glioblastoma

Despite significant improvements in the clinical management of glioblastoma, poor delivery of systemic therapies to the entire population of tumour cells remains one of the biggest challenges in the achievement of more effective treatments. On the one hand, the abnormal and dysfunctional tumour vascular network largely limits blood perfusion, resulting in an inhomogeneous delivery of drugs to the tumour. On the other hand, the presence of an intact blood-brain barrier (BBB) in certain regions of the tumour prevents chemotherapeutic drugs from permeating through the tumour vessels and reaching the diseased cells. In this review we analyse in detail the implications of the presence of a dysfunctional vascular network and the impenetrable BBB on drug transport. We discuss advantages and limitations of the currently available strategies for remodelling the tumour vasculature aiming to ameliorate the above mentioned limitations. Finally we review research methods for visualising vascular dysfunction and highlight the power of DCE- and DSC-MRI imaging to assess changes in blood perfusion and BBB permeability.