We present a pilot study on the long term effects of irreversible electroporation (IRE) on a large blood vessel. The study was motivated by the anticipated use of IRE for treatment of cancer tumors abutting large blood vessels. A sequence of 10 direct current IRE pulses of 3800 V/cm, 100µs each, at a frequency of 10 pulses per second, were applied directly to the carotid artery in six rats. Measuring tissue conductivity during the procedure showed, as predicted, an increase in conductivity during the application of the pulse, which suggests that this measurement can be used to control the application of IRE. All the animals survived the procedure and showed no side effects. Histology performed 28 days after the procedure showed that the connective matrix of the blood vessels remained intact and the number of vascular smooth muscle cells (VSMC) in the arterial wall decreased with no evidence of aneurysm, thrombus formation or necrosis. Average VSMC density was significantly lower following IRE ablation compared with control (24 ± 11 vs. 139 ± 14, P<0.001), with no apparent damage to extra cellular matrix components and structure. In addition to the relevance of this study to treatment of cancer near large blood vessels these findings tentatively suggest that IRE has possible applications to treatment of pathological processes in which it is desired to reduce the proliferation of VSMC population, such as restenosis and for attenuating atherosclerotic processes in clinical important locations such as coronary, carotid and renal arteries. IntroductionIrreversible electroporation (IRE) is a modality in which microsecond electrical pulses are applied across the cell to generate a destabilizing electric potential across cell outer membrane and cause formation of permanent nanoscale defects in the lipid bilayer. The permanent permeabilization of cell membrane leads to changes in cell homeostasis and cell death (1-3). A recent theoretical study has found that irreversible electroporation could ablate substantial volumes of tissue without thermal effects (4). Subsequent studies have demonstrated the ability of irreversible ablation pulses to completely ablate cancer cells, as a function of the electrical fields (5). The validity of the theoretical study was demonstrated in vivo in the rat liver (6). The first long term IRE in vivo study was performed in the pig liver. Among the many findings with clinical relevance the study has shown the ability of irreversible electroporation to ablate tissue to the margin of a large blood vessel, while the vessel remained patent after the treatment (7). This finding is of major importance in the treatment of cancer, where tumors near large blood vessels are often either untreatable or the treatment fails. The difficulty with surgical treatment of tumors near large blood vessels is evident. In minimally ablation thermal treatment of tumors, the thermal effect of blood flow in the large blood vessels has an opposing effect to the applied thermal treatment, either cold or heat, and residu...

The four-electrode method was used to measure the ex vivo complex electrical impedance of tissues from 14 hepatic tumors and the surrounding normal liver from six patients. Measurements were done in the frequency range 1-400 kHz. It was found that the conductivity of the tumor tissue was much higher than that of the normal liver tissue in this frequency range (from 0.14 +/- 0.06 S m(-1) versus 0.03 +/- 0.01 S m(-1) at 1 kHz to 0.25 +/- 0.06 S m(-1) versus 0.15 +/- 0.03 S m(-1) at 400 kHz). The Cole-Cole models were estimated from the experimental data and the four parameters (rho(0), rho(infinity), alpha, f(c)) were obtained using a least-squares fit algorithm. The Cole-Cole parameters for the cancerous and normal liver are 9 +/- 4 Omega m(-1), 2.2 +/- 0.7 Omega m(-1), 0.5 +/- 0.2, 140 +/- 103 kHz and 50 +/- 28 Omega m(-1), 3.2 +/- 0.6 Omega m(-1), 0.64 +/- 0.04, 10 +/- 7 kHz, respectively. These data can contribute to developing bioelectric applications for tissue diagnostics and in tissue treatment planning with electrical fields such as radiofrequency tissue ablation, electrochemotherapy and gene therapy with reversible electroporation, nanoscale pulsing and irreversible electroporation.

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Electroporation is the phenomenon in which cell membrane permeability is increased by exposing the cell to short high-electric-field pulses. Reversible electroporation treatments are used in vivo for gene therapy and drug therapy while irreversible electroporation is used for tissue ablation. Tissue conductivity changes induced by electroporation could provide real-time feedback of the treatment outcome. Here we describe the results from a study in which fibrosarcomas (n = 39) inoculated in mice were treated according to different electroporation protocols, some of them known to cause irreversible damage. Conductivity was measured before, within the pulses, in between the pulses and for up to 30 min after treatment. Conductivity increased pulse after pulse. Depending on the applied electroporation protocol, the conductivity increase after treatment ranged from 10% to 180%. The most significant conclusion from this study is the fact that post-treatment conductivity seems to be correlated with treatment outcome in terms of reversibility.

BackgroundNon thermal Irreversible electroporation (NTIRE) is a new tissue ablation method that induces selective damage only to the cell membrane while sparing all other tissue components. Our group has recently showed that NTIRE attenuated neointimal formation in rodent model. The goal of this study was to determine optimal values of NTIRE for vascular smooth muscle cell (VSMC) ablation.Methods and Results33 Sprague-Dawley rats were used to compare NTIRE protocols. Each animal had NTIRE applied to its left common carotid artery using a custom-made electrodes. The right carotid artery was used as control. Electric pulses of 100 microseconds were used. Eight IRE protocols were compared: 1–4) 10 pulses at a frequency of 10 Hz with electric fields of 3500, 1750, 875 and 437.5 V/cm and 5–8) 45 and 90 pulses at a frequency of 1 Hz with electric fields of 1750 and 875 V/cm. Animals were euthanized after one week. Histological analysis included VSMC counting and morphometry of 152 sections. Selective slides were stained with elastic Van Gieson and Masson trichrome to evaluate extra-cellular structures. The most efficient protocols were 10 pulses of 3500 V/cm at a frequency of 10 Hz and 90 pulses of 1750 V/cm at a frequency of 1 Hz, with ablation efficiency of 89±16% and 94±9% respectively. Extra-cellular structures were not damaged and the endothelial layer recovered completely.ConclusionsNTIRE is a promising, efficient and simple novel technology for VMSC ablation. It enables ablation within seconds without causing damage to extra-cellular structures, thus preserving the arterial scaffold and enabling endothelial regeneration. This study provides scientific information for future anti-restenosis experiments utilizing NTIRE.