Radiofrequency Current Research Articles

Valvular leaflets and epicardial fat have a significant effect on lesion size in RF ablation

Abstract Introduction Radiofrequency (RF) current is the classic ablation technology in the EP lab. Underlying RF ablation parameters, such as RF power, impedance, duration and contact force are used to calculate expected lesion size. Furthermore, lesion indices (LSI, AI) are applied to estimate expected lesion durability and contiguity. Purpose The aim of this ex-vivo study was to assess the influence of valvular tissue and epicardial fat on RF lesion creation. Methods An ex-vivo porcine model was created to create RF lesions under standardized conditions. Temperature was constantly kept at 37°C using a thermostat and a circulation pump was used to imitate blood flow. A contact force sensing ablation catheter (ST SF) was used to create RF lesions using predefined RF parameters (30W/50W, CF 10g, 30sec). Lesions using the same RF parameters were created above and right next to mitral valve leaflets as well as on epicardial fat tissue (figure 1). Lesions were then dissected, and lesion depths and diameters were measured using a digital precision caliper. Results A total of 210 lesions were created. RF lesions ablated on valvular leaflets showed significantly smaller lesion depth and lesion diameter when compared to RF lesions ablated right next to valvular (diameter 8.0±2.0mm vs 10.8±1.8mm; depth 4.4±1.2 vs 7.7±1.6mm, p<0.01). Lesions ablated on epicardial fat were significantly smaller in diameter (9.2±1.5) and depth (6.5±1.8) than purely endocardial lesions (p<0.01). Examples are depicted in figure 1. Conclusions Valvular leaflets as well as epicardial fat tissue have a significant influence on RF lesion creation. RF ablation performed on valvular leaflets or epicardial fat results in significantly (p<0.01) smaller lesions when compared to RF ablations directly on endocardial tissue. This should be considered in ablations of accessory pathways and epicardial procedures.Figure 1

Observation of nonthermal electrons further acceleration and long-lasting associated with magnetic reconnection and turbulence bursting in tokamak plasma

Abstract Vital to magnetized plasma performance, the acceleration of nonthermal electrons significantly influences the current drive of radio frequency (RF) waves in plasma. In EAST, we observed nonthermal electrons initially <215 keV in energy, being locally accelerated to 600 keV within 100 milliseconds, which corresponds to the total growth time of the magnetic island. Surprisingly, these fast electrons (FE) lasted for 1.4 seconds, several times longer than the estimated relaxation time of 0.26 seconds, and exceeded 1/10 of the discharge length. Turbulence generation at island’s X point is attributed to the unexpected confinement and repopulation of FEs. This phenomenon may have positive implications for the steady-state long pulse H mode operation in EAST, especially regarding non-inductive current sustainment. For future RF electron heating-dominant devices, the mechanisms elucidated in this study have immediate implications for optimizing RF current drive efficiency.

Radiofrequency Currents Modulate Inflammatory Processes in Keratinocytes.

Keratinocytes play an essential role in the inflammatory phase of wound regeneration. In addition to migrating and proliferating for tissue regeneration, they produce a large amount of cytokines that modulate the inflammatory process. Previous studies have shown that subthermal treatment with radiofrequency (RF) currents used in capacitive resistive electric transfer (CRET) therapy promotes the proliferation of HaCat keratinocytes and modulates their cytokine production. Although physical therapies have been shown to have anti-inflammatory effects in a variety of experimental models and in patients, knowledge of the biological basis of these effects is still limited. The aim of this study was to investigate the effect of CRET on keratinocyte proliferation, cytokine production (IL-8, MCP-1, RANTES, IL-6, IL-11), TNF-α secretion, and the expression of MMP9, MMP1, NF-κB, ERK1/2, and EGFR. Human keratinocytes (HaCat) were treated with an intermittent 448 kHz electric current (CRET signal) in subthermal conditions and for different periods of time. Cell proliferation was analyzed by XTT assay, cytokine and TNF-α production by ELISA, NF-κB expression and activation by immunofluorescence, and MMP9, MMP1, ERK1/2, and EGF receptor expression and activation by immunoblot. Compared to a control, CRET increases keratinocyte proliferation, increases the transient release of MCP-1, TNF-α, and IL-6 while decreasing IL-8. In addition, it modifies the expression of MMPs and activates EGFR, NF-κB, and ERK1/2 proteins. Our results indicate that CRET reasonably modifies cytokine production through the EGF receptor and the ERK1/2/NF-κB pathway, ultimately modulating the inflammatory response of human keratinocytes.

Reinterpreting radio frequency heating and current drive theory in a tokamak

Quasilinear treatments are widely used for tokamaks to evaluate radio frequency (rf) heating and current drive. Even though the core of a tokamak plasma is weakly collisional, the solution of the linearized kinetic equation is evaluated using unperturbed collisionless trajectories while often treating successive poloidal circuits of the passing (and trapped) particles as uncorrelated or nearly so. In addition, the most important effect of tokamak geometry, the mirror force, is usually mistreated or ignored when obtaining the solution. These concerning aspects of rf treatments are clarified by considering lower hybrid heating and current drive to illustrate that the electrons in resonance with the applied rf are enclosed by narrow collisional boundary layers, and that tokamak geometry makes it necessary to retain poloidal variation when solving a weakly collisional linearized kinetic equation. Other aspects such as collisional boundary layers at the trapped–passing boundary, cyclotron resonances, and the limitations of quasilinear theory are also considered. The new insights lead to a fundamentally different formulation and interpretation of the solution of the linearized Fokker–Planck equation used for rf quasilinear theory in a tokamak, while retaining many of the features that have contributed to its successful application to rf heating and current drive.

Coherent spin wave excitation with radio-frequency spin–orbit torque

Spin waves, collective perturbations of magnetic moments, are both fundamental probes for magnetic physics and promising candidates for energy-efficient signal processing and computation. Traditionally, coherent propagating spin waves have been generated by radio frequency (RF) inductive Oersted fields from current-carrying electrodes. An alternative mechanism, spin–orbit torque (SOT), offers more localized excitation through interfacial spin accumulation but has been mostly limited to DC to kHz frequencies. SOT driven by RF currents, with potentially enhanced pumping efficiency and unique spin dynamics, remains largely unexplored, especially in magnetic insulators. Here, we conduct a comprehensive theoretical and computational investigation into the generation of coherent spin waves via RF-SOT in the prototypical yttrium iron garnet. We characterize the excitation of forward volume, backward volume, and surface modes in both linear and nonlinear regimes, employing single and interdigitated electrode configurations. We reveal and explain several unique and surprising features of RF-SOT compared to inductive excitation, including higher efficiency, distinct mode selectivity, and directional symmetry, a ∼3π/4 phase offset, reduced anharmonic distortion in the nonlinear regime, and the absence of second harmonic generation. These insights position RF-SOT as a promising new mechanism for future magnonic and spintronic applications.

Effect of dispersive electrode position (anterior vs. posterior) in epicardial radiofrequency ablation of ventricular wall: A computer simulation study.

An epicardial approach is often used in radiofrequency (RF) catheter ablation to ablate ventricular tachycardia when an endocardial approach fails. Our objective was to analyze the effect of the position of the dispersive patch (DP) on lesion size using computer modeling during epicardial approach. We compared the posterior position (patient's back), commonly used in clinical practice, to the anterior position (patient's chest). The model considered ventricular wall thicknesses between 4 and 8 mm, and electrode insertion depths between .3 and .7 mm. RF pulses were simulated with 20 W of power for 30 s duration. Statistically significant differences (P < .001) were found between both DP positions in terms of baseline impedance, RF current (at 15 s) and thermal lesion size. The anterior position involved lower impedance (130.8 ± 4.7 vs. 146.2 ± 4.9 Ω) and a higher current (401.5 ± 5.6 vs. 377.5 ± 5.1 mA). The anterior position created lesion sizes larger than the posterior position: 8.9 ± 0.4 vs. 8.4 ± 0.4 mm in maximum width, 8.6 ± 0.4 vs. 8.1 ± 0.4 mm in surface width, and 4.5 ± 0.4 vs. 4.3 ± 0.4 mm in depth. Our results suggest that: (1) the redirection of the RF currents due to repositioning the PD has little impact on lesion size and only affects baseline impedance, and (2) the differences in lesion size are only 0.5 mm wider and 0.2 mm deeper for the anterior position, which does not seem to have a clinical impact in the context of VT ablation.

Initial experience with ablation of ventricular arrhythmias using a pulsed-field system

Abstract Introduction Catheter ablation using radiofrequency (RF) current is a well-established method of treatment of ventricular arrhythmias (VA). However, RF ablation may fail to eliminate deeply located arrhythmogenic substrate. Pulsed-field (PF) is a novel energy source with a potential to create deeper lesions, especially in scar tissue. Purpose This study aims to present the data on safety and efficacy (acute outcome data) of VA ablation using PF. Methods The population consists of 15patients (5 women, age: 61 ± 19years) after previously failed RF ablation of VA. The underlying condition was nonischemic cardiomyopathy (53%), coronary artery disease (13%), and congenital heart disease (13%), respectively. No structural heart disease was present in 20% of cases. The mean left ventricular ejection fraction was 39 ± 13%. Eighty percent of patients had sustained VA, the remaining patients presented with frequent ventricular ectopy. Ablation was performed using a conventional irrigated 4-mm tip catheter in a combination with commercially available PF generator. Peripheral venous blood samples for the assessment of the plasmatic levels of high-sensitivity troponin T (hsTnT) were obtained the next day (usually 18-24hours) after the procedure. Results A mean of 17±12 PF applications (25A) per patient were delivered. In 5 patients (33%), an additional RF ablation (4±9 applications) was performed. Acute success as assessed by non-inducibility of VA or elimination of ectopic focus was achieved in all but one patient (93%). In 4 cases (27%), PF energy was applied within the great cardiac vein and subsequent coronary angiography did not reveal any abnormality. On the other hand, transient conduction system block occurred in 3 cases (20%) during PF application on the lateral LV wall remotely from the LV septum (complete AV block in one, LBBB in two patients). These events resolved in all cases within one hour. Ablation using PF did not result in excessive increase of hsTnT (657±482ng/l, with upper reference level of 14ng/l). Conclusion Initial experience with PF for the treatment of VA indicates high acute efficacy. The long-term effect is to be determined. PF applications in the ventricle may be associated with unexpected but transient conduction system damage, even when applications are performed remotely from the interventricular septum. The postprocedural increase in plasma troponin levels is only moderate.

Power transfer efficiency in an air-breathing radio frequency ion thruster

Abstract Due to a series of challenges such as low-orbit maintenance of satellites, the air-breathing electric propulsion has got widespread attention. Commonly, the radio frequency ion thruster is favored by low-orbit missions due to its high specific impulse and efficiency. In this paper, the power transfer efficiency of the radio frequency ion thruster with different gas composition is studied experimentally, which is obtained by measuring the radio frequency power and current of the antenna coil with and without discharge operation. The results show that increasing the turns of antenna coils can effectively improve the radio frequency power transfer efficiency, which is due to the improvement of Q factor. In pure N2 discharge, with the increase of radio frequency power, the radio frequency power transfer efficiency first rises rapidly and then exhibits a less steep increasing trend. The radio frequency power transfer efficiency increases with the increase of gas pressure at relatively high power, while declines rapidly at relatively low power. In N2/O2 discharge, increasing the N2 content at high power can improve the radio frequency power transfer efficiency, but the opposite was observed at low power. In order to give a better understanding of these trends, an analytic solution in limit cases is utilized, and a Langmuir probe was employed to measure the electron density. It is found that the evolution of radio frequency power transfer efficiency can be well explained by the variation of plasma resistance, which is related to the electron density and the effective electron collision frequency.

Effect of a negative DC bias on a capacitively coupled Ar plasma operated at different radiofrequency voltages and gas pressures

The effect of a negative DC bias, |V dc|, on the electrical parameters and discharge mode is investigated experimentally in a radiofrequency (RF) capacitively coupled Ar plasma operated at different RF voltage amplitudes and gas pressures. The electron density is measured using a hairpin probe and the spatio-temporal distribution of the electron-impact excitation rate is determined by phase-resolved optical emission spectroscopy. The electrical parameters are obtained based on the waveforms of the electrode voltage and plasma current measured by a voltage probe and a current probe. It was found that at a low |V dc|, i.e. in α-mode, the electron density and RF current decline with increasing |V dc|; meanwhile, the plasma impedance becomes more capacitive due to a widened sheath. Therefore, RF power deposition is suppressed. When |V dc| exceeds a certain value, the plasma changes to α–γ hybrid mode (or the discharge becomes dominated by the γ-mode), manifesting a drastically growing electron density and a moderately increasing RF current. Meanwhile, the plasma impedance becomes more resistive, so RF power deposition is enhanced with |V dc|. We also found that the electrical parameters show similar dependence on |V dc| at different RF voltages, and α–γ mode transition occurs at a lower |V dc| at a higher RF voltage. By increasing the pressure, plasma impedance becomes more resistive, so RF power deposition and electron density are enhanced. In particular, the α–γ mode transition tends to occur at a lower |V dc| with increase in pressure.

Contemporary catheter ablation of complex atrial tachycardias after prior atrial fibrillation ablation: pulsed field vs. radiofrequency current energy ablation guided by high-density mapping.

Catheter ablation (CA) of post-ablation left atrial tachycardias (LATs) can be challenging. So far, pulsed field ablation (PFA) has not been compared to standard point-by-point radiofrequency current (RFC) energy for LAT ablation. To compare efficacy of PFA vs. RFC in patients undergoing CA for LAT. Consecutive patients undergoing LAT-CA were prospectively enrolled (09/2021-02/2023). After electro-anatomical high-density mapping, ablation with either a pentaspline PFA catheter or RFC was performed. Patients were matched 1:1. Ablation was performed at the assumed critical isthmus site with additional ablation, if necessary. Right atrial tachycardia (RAT) was ablated with RFC. Acute and chronic success were assessed. Fifty-six patients (n = 28 each group, age 70 ± 9 years, 75% male) were enrolled.A total of 77 AT (n = 67 LAT, n = 10 RAT; 77% macroreentries) occurred with n = 32 LAT in the PFA group and n = 35 LAT in the RFC group. Of all LAT, 94% (PFA group) vs. 91% (RFC group) successfully terminated to sinus rhythm or another AT during ablation (P = 1.0). Procedure times were shorter (PFA: 121 ± 41 vs. RFC: 190 ± 44 min, P < 0.0001) and fluoroscopy times longer in the PFA group (PFA: 15 ± 9 vs. RFC: 11 ± 6 min, P = 0.04). There were no major complications. After one-year follow-up, estimated arrhythmia free survival was 63% (PFA group) and 87% (RFC group), [hazard ratio 2.91 (95% CI: 1.11-7.65), P = 0.0473]. Pulsed field ablation of post-ablation LAT using a pentaspline catheter is feasible, safe, and faster but less effective compared to standard RFC ablation after one year of follow-up. Future catheter designs and optimization of the electrical field may further improve practicability and efficacy of PFA for LAT.

Adipose Tissue Impacts Radiofrequency Ablation Lesion Size: Results of an Ex Vivo Poultry Model

BACKGROUND: Radiofrequency ablation (RFA) is a common treatment in which radiofrequency (RF) is used to heat neural tissue and reduce pain. The impact of adipose content in tissue on the lesion size may impact efficacy, and to date, there is little, if any, data comparing its influence on RFA. OBJECTIVES: We evaluated the influence of adipose tissue on RF lesion size. STUDY DESIGN: Controlled, ex vivo study. SETTING: Academic institution in a procedural setting. METHODS: RF lesions were created using 20-G 10-mm protruding electrode (PE) needles inserted into unbrined chicken breasts and thighs at 21°C. RF current was applied for 90 seconds at 80°C. Chicken breasts were used as the control group and chicken thighs were used as the high adipose variant. Four different groups were examined: 1- Standard 20 g RFA needle, 2- 20 g RFA PE needle, 3- Standard RFA needle with lidocaine 2% injectate, and 4- Standard RFA needle with iohexol 240 mg injectate. There were 12 lesions performed in each group; length, width, and depth were measured. RESULTS: The control group had significantly deeper lesions in all 4 cohorts. Lesions’ lengths were smaller in the fat-rich group. The control and PE cohorts showed a significant difference in width between the 2 fat-rich and nonfatty groups. LIMITATIONS: Radiofrequency ablation was performed at room temperature and not heated to physiological temperature. This was an ex vivo study, thus factors of human anatomy and physiology could not be evaluated. CONCLUSIONS: Adipose tissue content was inversely related to lesion size in all samples. This factor should be considered when assessing methods of enhancing lesion size in human models. KEY WORDS: Radiofrequency, ablation, lesion size, injection, adipose tissue, tissue modeling, interventional pain, education

Output Current and Efficacy of Pulsed Radiofrequency of the Lumbar Dorsal Root Ganglion in Patients With Lumbar Radiculopathy: A Prospective, Double-blind, Randomized Pilot Study

BACKGROUND: Lumbar radicular pain (LRP) is a common but challenging clinical symptom. Pulsed radiofrequency (PRF), a neuromodulation technique that uses short pulses of radiofrequency current, is effective in treating various pain disorders. However, few studies have been conducted on the effects of PRF and its modifying parameters. OBJECTIVES: Our study aimed to determine the intraoperative parameters of PRF of the lumbar dorsal root ganglion (DRG) that are related to clinical effects in patients with LRP unresponsive to transforaminal epidural steroid injections (TFESI). STUDY DESIGN: Prospective double-blind randomized controlled trial, pilot study. SETTING: Single medical center in the Republic of Korea. METHODS: Patients were allocated to one of 2 groups, high-voltage (60 V) or standard-voltage (45 V), according to the preset maximum voltage at which the active tip temperature does not exceed 42°C. Intraoperative parameters, such as output current, sensory threshold, and impedance, were measured. The primary outcomes were radicular pain intensity, physical functioning, global improvement and satisfaction with treatment, and adverse events. The assessments were performed up to 3 months postprocedure. RESULTS: The patients in the standard-voltage group showed significant improvements in the Numeric Rating Scale pain score (P = 0.007) and Oswestry Disability Index (ODI) (P = 0.008) scores at 3 months post-PRF; however, no difference was observed in the high-voltage group. Among the intraoperative parameters, the output current showed a significant negative linear relationship with analgesic efficacy. The output current also showed a significant association with pain intensity (P = 0.005, R2 = 0.422) and ODI score (P = 0.004, R2 = 0.427) at 3 months postprocedure in a multiple regression analysis. The optimal cut-off value of the output current to lower pain intensity after 3 months was 163.5 mA with a sensitivity of 87.5%, specificity of 100%, and an area under the receiver operating characteristic curve value of 0.92 (95% CI. 0.76 – 1.00). LIMITATIONS: Limitations of our study include an imbalance of baseline characteristics, small sample sizes, and short follow-up periods CONCLUSIONS: Lower output currents during PRF application to the lumbar DRG were associated with greater analgesic effects in patients who did not respond to therapeutic TFESI. KEY WORDS: Lumbar radicular pain, pulsed radiofrequency, dorsal root ganglion

Catheter Ablation of Atrial Fibrillation with Short Duration Radiofrequency Current using Non-Irrigated Catheters

Introduction. The use of high-power radiofrequency current is considered to be a promising alternative to the currently used technique of catheter ablation of atrial fibrillation (AF) with radiofrequency current of normal power. To date, there are no studies on the application of this technique using catheters without external irrigation.&#x0D; The aim. To study direct results of application of high-power radiofrequency current in AF catheter ablation using non-irrigated catheters.&#x0D; Materials and methods. We analyzed 30 consecutive patients who underwent primary catheter ablation (12 women and 18 men, mean age of the patients was 57.6 ± 11.7 years). Concomitant pathology (coronary heart disease, hypertension, diabetes mellitus) was observed in 19 (63.3%) patients.&#x0D; Wide isolation of pulmonary veins was performed, and in nonparoxysmal forms, applications were added in the places where fragmented activity was registered or in the line of applications between ipsilateral pulmonary veins and inferior left pulmonary vein and mitral valve annulus. The applications were made with a 4 mm electrode without irrigation function with wiping it after every 30 applications. Application parameters were 40-45 Watt power, application time 10 seconds, target temperature 55°C.&#x0D; Results. The mean left atrial catheter dwelling time was 1.6 ± 0.3 hours. The mean time of X-ray exposure was 8.2 ± 2.3 minutes. The average number of applications was 127.8 ± 23.6. It was not possible to isolate 3 pulmonary veins in three patients: one superior left pulmonary vein and two inferior right pulmonary veins (2.5% of all pulmonary veins).&#x0D; No complications related to the procedure were observed. The occurrence of AF in the early postoperative period was observed in 4 (13.3%) patients.&#x0D; Conclusions. The immediate results of applying the radiofrequency current of 40-45 W with the application duration of 10 seconds and the target temperature of 55°C during AF catheter ablation using non-irrigated catheters indicate the safety of this technique. It is necessary to study a larger contingent of patients and long-term results.

Full-Endoscopic Transforaminal Approach for Lumbar Discectomy.

With technical advancements, the full-endoscopic transforaminal approach for lumbar discectomy (ETALD) is gaining popularity. This technique utilizes various tools and instruments, including a dilator, a beveled working sleeve, and an endoscope with a 20-degree angle and 177 mm length, equipped with a 9.3-diameter oval shaft and a 5.6 mm diameter working channel. Additionally, the procedure involves using a Kerrison punch (5.5 mm), rongeur (3-4 mm), punch (5.4 mm), tip control radioablator applying a radiofrequency current of 4 MHz, fluid control irrigation and suction pump device, 5.5 mm oval burr with lateral protection, burr round, and the diamond round. During the surgery, it is essential to identify significant landmarks, including the caudal pedicle, ascending facet, annulus fibrosis, posterior longitudinal ligament, and the exiting nerve root. The steps of the technique are relatively easy to follow, especially when utilizing the appropriate instruments and having a good understanding of the anatomy. Research studies have demonstrated comparable outcomes to open microdiscectomy techniques. ETALD presents itself as a safe option for lumbar discectomy, as it minimizes tissue disruption, results in low postoperative surgical site pain, and allows for early mobilization.

Prolonged sinus pauses after the paroxysms of atrial tachycardia in children, to pace or to ablate? Case report

Background. The presence of prolonged sinus pauses is quite rare in children and adolescents with structural normal heart. The decision of the optimal therapeutic tactics is always challenging. Case report. The 16-years-old girl addressed with complains of palpitations and dizziness after the palpitations end. A Holter ECG monitoring was performed with the detection of prolonged sinus pauses after the paroxysm of atrial tachycardia. We decided to perform an electrophysiological study to diagnose the tachycardia type. The presence of atrial tachycardia originating from the ostium of the coronary sinus was demonstrated. We decided to manage the tachyarrhythmia with catheter ablation. During the application of the radiofrequency currents, the tachycardia stopped, and the sinus rhythm was restored. The ablation was preferred over medication taking into consideration the potential risk of worsening of the bradycardia by antiarrhythmic therapy. Conclusions. The optimal therapeutic solution in similar pediatric cases should be directed towards the supraventricular tachycardia treatment and not to the bradyarrhythmia. The majority of supraventricular tachycardias could be cured by catheter ablation.

How the new technologies and tools will change the electrophysiology of the future.

Novel technologies and therapies are evolving rapidly in the field of electrophysiology and cardiac ablation, particularly with the aim of improving the management of atrial fibrillation (AF) where pharmacologic treatment fails. High-power short-duration radiofrequency (RF) ablation, in association with the optimized cooling process of the electrode-tissue interface, is one of the most promising approaches for treating durable lesions and pulmonary vein isolation (PVI). Cryo energy, laser, and RF current are examples of novel tools used by competitive balloon catheter platforms and these tools are specifically created to properly promote an effective PVI. Specific mention deserves to be made on the linear array ablation with ultra-low temperature cryoablation that appears promising for durable lesions. It is needless to remind here about the novel evolving energy source in the form of pulsed electrical field (PFA), which results in an irreversible electroporation of myocardial tissue, sparing the surrounding tissue, and thus, apparently with a significant reduction of potential untoward effects. Furthermore, intensive research is in place to specifically investigate the activation pattern of AF so as to devise a patient-('tailored') target ablation, although with inhomogeneous results. Overall, it seems that technologies and therapies are evolving so rapidly than ever with the hope of achieving better long-term clinical results and an improved quality of life for our patients.

On power and fundamental resistance relations in symmetric RF CCPs by simulating simplified nonlinear circuits

Voltage and current measured from radio frequency (RF) capacitively coupled plasmas (CCPs) are basic data, from which various powers and impedances are subsequently calculated via fast Fourier transform to gain deep insight into RF CCPs. The specific values of these parameters depend on the nonlinearity of RF CCPs and the interaction with the external circuit, but the relation between harmonic powers and that among the fundamental resistances are not known. These questions are investigated via Multisim software by simplifying the symmetric RF CCP with the nonlinear circuit consisting of a linear resistor and a nonlinear capacitor. The results show that the calculated total RF power is accurately equal to that dissipated by the resistor in discharge. However, it is not true for the fundamental power and harmonic one. The fundamental resistance calculated at the external electrode, which was previously proposed as the plasma resistance, is higher than the latter. The conversion between the fundamental and harmonic powers in the nonlinear ideal capacitor of RF CCPs is the origin of the obtained abnormal feature. In comparison, the plasma resistance calculated from the total RF power and current is unaffected by harmonics and is, thus, more credible, despite that this method requires an assumption of constant transient plasma resistance.

Assessment of Inflammation in 3D Reconstructed Human Skin Exposed to Combined Exposure to Ultraviolet and Wi-Fi Radiation.

In the human environment, the increasing exposure to radiofrequency (RF) radiation, especially that emitted by wireless devices, could be absorbed in the body. Recently, mobile and emerging wireless technologies (UMTS, DECT, LTE, and Wi-Fi) have been using higher frequencies than 2G GSM systems (900/1800 MHz), which means that most of the circulating RF currents are absorbed into the skin and the superficial soft tissue. The harmful genotoxic, cytotoxic, and mutagenic effects of solar ultraviolet (UV) radiation on the skin are well-known. This study aimed at investigating whether 2422 MHz (Wi-Fi) RF exposure combined with UV radiation in different sequences has any effect on the inflammation process in the skin. In vitro experiments examined the inflammation process by cytokines (IL-1α, IL-6, IL-8) and MMP-1 enzyme secretion in a 3D full-thickness human skin model. In the first study, UV exposure was immediately followed by RF exposure to measure the potential additive effects, while in the second study, the possible protective phenomenon (i.e., adaptive response) was investigated when adaptive RF exposure was challenged by UV radiation. Our results suggest that 2422 MHz Wi-Fi exposure slightly, not significantly increased cytokine concentrations of the prior UV exposure. We could not detect the adaptive response phenomenon.

Synergistic current drive of helicon wave and lower hybrid wave in HL-2M

Non-inductive current drive plays a crucial role in tokamak, especially for its steady state operations. Recently, the helicon wave (HW) has been regarded as a promising tool for driving off-axis plasma current in reactor-grade machine. The lower-hybrid wave (LHW) is the most effective radio-frequency current drive method, however, it has the drawback, which is limited by the conditions of wave accessibility in the high parameter tokamak, making the wave power usually damped at the plasma edge. HW can spiral towards the plasma centre directly under a high electron density. To obtain a long pulse steady state operation of reactor tokamak, the complementarity of HW and LHW in the aspect of driven current distribution in the high parameter tokamak is considered. The synergy current drive of the HW and the LHW is studied numerically in the steady-state scenario of HL-2M. According to the fast wave dispersion relation of plasma, the HW parameters, including its wave frequency and launched parallel refractive index, are obtained firstly. Results of GENRAY code simulation show that a single pass wave power absorption of the HW can be obtained generally through the electron Landau damping and transit time magnetic pumping effects. On the other hand, the LHW parameters are adopted from the equipped system on the machine. Results of single pass wave absorption are also obtained in the case of LHW. And then, the synergy effects of HW and LHW are studied numerically based on the GENRAY/CQL3D models. The cooperation of these two waves results in a broad plasma current distribution along the radial direction (&lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$\rho = $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231077_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231077_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;0.2－0.9) in the machine. Taking the electron distribution functions of these waves into account, it is clear that the electrons are accelerated by the HW in the parallel magnetic field direction, resulting in more electrons entering the region of LHW resonance area. As the consequence, a net plasma current appears. Furthermore, a fine-grained parametric scan is performed by changing the launched parallel refractive index of HW, and the results indicate that positive synergy effects can be generally observed once the related wave current drive profiles are overlapped. Finally, the synergy factor is shown to be proportional to this overlap and reaches its maximum value of 1.18 in HL-2M.

161 ABLATION OF EPICARDIAL VENTRICULAR TACHYCARDIA ORIGINATING IN THE AREA OF PERICARDIAL ADHESIONS INDUCED BY STEREOTACTIC RADIOABLATION IN A PATIENT WITH ISCHEMIC CARDIOMYOPATHY

Abstract This is the case of a 64-year-old male patient with prior inferior wall myocardial infarction, wearing a cardiac resynchronization therapy defibrillator and suffering from recurrent ventricular tachycardia (VT). The patient had undergone a transitory successful endocardial radiofrequency catheter ablation (RFCA) in 2013 and a stereotactic ablative body radiotherapy (SABR) in 2021, targeting the VT originating in the inferior wall myocardial scar. The patient was referred to our institution due to recurrent highly symptomatic slow-VT. A coronary angiography ruled out coronary artery disease (CAD) progression and a RFCA was rescheduled. Given the suspected epicardial origin of VT based on a 12-lead ECG, the decision was made to perform a combined epi-endocardial ablation. SABR-induced pericardial adhesions prevented posterior pericardial access, thus requiring an anterior access approach (Figure 1, Panel A, yellow star). Following epicardial and endocardial electroanatomic mapping (EAM), VT ablation relied on a substrate-based approach. Local abnormal ventricular activities (LAVAs), detected both in the accessible epicardial inferior wall of the left ventricle and at the opposite endocardial site, were eliminated by radiofrequency (RF) current. Upon completion of endocardial ablation, ventricular pacing induced hemodynamically unstable VT, exiting from the epicardial region corresponding to the SABR-induced pericardial adhesions. Mechanical adhesiolysis, using the elbow of the open-irrigated ablation catheter, was performed to disrupt SABR-induced pericardial adhesions in the inferior wall. The epicardial EAM performed with the open-irrigated catheter recorded LAVAs in the infero-posterior wall of the left ventricle, corresponding to the SABR-disrupted pericardial adhesions. A RF current was delivered, targeting LAVAs at this site (Figure 1, Panel B: the central green dot corresponds to the area of disrupted pericardial adhesions). At the end of the procedure, no sustained VT was induced by programmed ventricular stimulation. Conclusion SABR constitutes a novel and promising non-invasive radioablative treatment of VT, potentially associated with cardiac toxicity. To our knowledge, this is the first reported case of combined epicardial and endocardial RFCA of recurrent VT after SABR. Based on the first RFCA report and exclusion of CAD progression, we hypothesized that SABR might have favoured progression of the inferior low voltage area. With this case report, we would like to demonstrate that even if pericardial adhesions could be a consequence of SABR, gentle catheter-driven manoeuvres can be enough to disrupt the adhesions and to achieve full EAM. Further research is mandatory to shed light on SABR's long-term arrhythmogenic role.