Radiofrequency Settings Research Articles

Combined approach of high-power and very high-power, short-duration ablation in superior vena cava isolation.

The effectiveness and safety of 50 W, high-power, short-duration (HPSD) ablation in superior vena cava isolation (SVCI) for patients with atrial fibrillation (AF) have been reported. However, the acute outcomes of SVCI combined with 90 W/4 s, very high-power, short-duration (vHPSD) ablation remain unknown. In this study, we aimed to investigate a novel approach that combines 50 W-HPSD and 90 W/4 s-vHPSD ablation in SVCI and to elucidate the characteristics, outcomes, and safety of this approach by comparing SVCI with conventional ablation index (AI)-guided middle-power, middle-duration (MPMD) ablation. Overall, 126 patients who underwent AF ablation with SVCI using the QDOT MICROTM catheter were retrospectively reviewed; one group underwent SVCI with a combined approach of HPSD and vHPSD ablation (50 W/90 W group, n = 73) and another group underwent AI-guided MPMD ablation (30-40 W group, n = 53). This study compared the procedural details, radiofrequency (RF) ablation profiles, and complications. The RF settings used in the 50 W/90 W group were 50 W/7 s for the lateral segment close to the phrenic nerve and 90 W/4 s for the nonlateral segment. The 50 W/90 W group required a significantly shorter procedural time (3.2 vs. 5.9 min, p < .001), shorter RF duration (42.0 vs. 162.0 s, p < .001), and lower RF energy (2834 vs. 5480 J, p < .001) than the 30-40 W group. Procedural success, first-pass SVCI, number of RF applications, and SVC reconnection after isoproterenol loading were comparable between the groups. The maximum tip-electrode temperature of the multi-thermocouple system was significantly higher in the 50 W/90 W group than in the 30-40 W group (50.0°C vs. 47.0°C, p < .001). No complications, such as phrenic nerve injury or bleeding requiring transfusion, were observed in either group. The combined approach of 50 W/7 s-HPSD and 90 W/4 s-vHPSD ablation resulted in successful and safe SVCI with shorter procedural time, shorter RF duration, and lower RF energy.

Incidence and impact on arrhythmia recurreces of atrial fibrillation termination during linear radiofrequency ablation in the left atrium

Abstract Atrial Fibrillation Termination During Linear Radiofrequency Ablation in the Left Atrium: Incidence and Impact on Arrhythmia Recurrences Background Termination of atrial fibrillation (AF) during persistent atrial fibrillation (peAF) ablation is infrequent and has shown no clear association with reduced recurrences during follow-up. Linear ablation, often considered to have minimal impact on efficacy, has been primarily explored through creating ablation lines from the mitral annulus to the inferior pulmonary vein or by isolating the posterior wall. Purpose This study aims to assess the incidence of AF termination using an alternative linear ablation approach and its correlation with arrhythmia recurrence during follow-up. Methods Patients enrolled in the PowerFast III trial (a multicenter randomized trial comparing high- power short-duration radiofrequency (RF) application to conventional RF application) with peAF and undergoing linear ablation were included in this sub-study. Conventional pulmonary vein isolation (PVI) was performed using two different RF settings along with a set of RF lines, including anteroseptal (AS), anterolateral (AL), posterior wall isolation between the pulmonary veins, and between the two anterior lines. Patients were categorized into two groups based on AF termination or flutter organization (Group 1) or no AF termination (Group 2) during RF application. All patients were monitored with EKG transmission for one year. Results Fifty-one consecutive patients (mean age 61 years, male 39) were included. AF terminated in 21 patients (41%) during RF application (9 converting to AF and 12 to atrial flutter). AF did not terminate during RF application for PVI, except for one patient during right PV ablation following left PVI. AF termination occurred by posterior wall lines in three patients, roof line in three, and anterior line in two. AF converted into atrial flutter during ablation by a roof line in 5 patients and by an anterior line in 7. No significant differences in atrial arrhythmia recurrence were observed between the two groups (three patients in Group 1 vs. eleven in Group 2, P = 0.11). However, Group 1 exhibited fewer AF recurrences (zero patients) than Group 2 (eight patients, P = 0.015). Conclusions Extensive linear RF ablation resulted in a substantial proportion of patients experiencing AF termination or conversion into atrial flutter. AF termination or conversion did not appear to be correlated with atrial arrhythmia freedom during follow-up but was associated with fewer AF recurrences.Any arrhythmia recurrenceAF recurrence

Validation of predictive models for lesion transmurality and steam-pop using ex-vivo porcine bipolar ablation model

Abstract Introduction Bipolar ablation has been reported to create deeper myocardial ablation lesion as compared to unipolar ablation, however, there is currently no standardized strategy for bipolar ablation settings such as energy and ablation time. Purpose The aim of the present study is to test our hypothesis that both transmural lesion creation and steam-pop occurrence during bipolar ablation can be predicted by the settings of bipolar ablation and the myocardial tissue characteristics such as tissue thickness and initial impedance prior to RF. Methods Using porcine cardiac tissues, we conducted ex-vivo ablation experiments. Commercially available radiofrequency (RF) ablation catheters were utilized for the procedures. Each ablation catheter was positioned bilaterally on the myocardial slices at a 45-degree angle, maintaining a targeted contact force of 10g. We documented the occurrence of steam-pop under various conditions, modulating tissue thickness (5-20 mm), RF power (20, 30, 40, 50 Watt) and ablation duration (20 sec, 40 sec, 60 sec, 180 sec). Generalized linear models (GLM) were developed to forecast the creation of transmural lesion and steam-pop incidents, drawing on the bipolar ablation settings and myocardial tissue characteristics. Subsequently, we engaged in an additional series of experiments to validate the models. Results In total, 194 bipolar applications were utilized as training data. Transmural lesions and steam-pops were observed in 95 (49%), and 11 applications (5.7%), respectively. We constructed GLM using the RF energy (Watt), tissue thickness (mm), initial bipolar impedance (Ohm), impedance drop during the first 5 seconds of application (Ohm), and RF duration (seconds). For transmurality prediction the model validation was conducted with another independent 111 RF applications (102 transmural, and 25 steam-pops). The GLM, which utilized RF energy, tissue thickness, initial bipolar impedance, and RF duration, performed the best performance in predicting transmural lesion creation (AUC 0.94 [0.90-0.99], sensitivity 86 %, specificity 100 %). However, the exclusion of ‘tissue thickness’ from this model led to a significant decrease in its predictive performance (AUC 0.69 [0.48-0.89], sensitivity 47%, specificity 100%, P=0.0057). For pop prediction in validation data, the GLM utilizing RF energy, initial bipolar impedance and impedance drop showed the best performance (AUC 0.90 [0.83-0.97], sensitivity 76 %, specificity 92 %). Conclusion Our data show that accurate assessment of tissue thickness is pivotal for predicting transmural lesion creation. To predict lesion transmurality and steam-pop incidents through RF parameters and tissue characteristics within a beating heart, further research is warranted. This could facilitate the calibration of RF settings, potentially enhancing the safety of bipolar ablation procedures.

Development of a field-reversed configuration device using radio frequency antennas to produce E × B for current-drive

A unique field-reversed configuration (FRC) experiment is presently being assembled at the Plasma Technology Research Institute, KFE. It is a compact small-scale FRC device, which uses a set of radio frequency (RF) antennas to produce an internal E × B that drives the electrons for current-drive, in which E is the electric field and B is the magnetic field. This is very similar to the rotating magnetic field (RMF) current-drive, where the horizontal and vertical antennas are driven 90° out of phase. For this device, the RF antennas are arranged differently than the RMF. The RF antennas, being two separate sets, are positioned inside the vacuum chamber. Each set consists of 8 coils, for a total of 16 coils, where 80~100 kHz sine and cosine waveform currents are applied. One set of coils generates a radial B-field, while the other set provides an E-field in the z-direction. As the phase changes, the E and B fields are switched by these two sets. Nevertheless, E × B propagates in the same θ-direction so that this allows the electrons to rotate around the circumference of the device. The FRC device will test wave heating by launching 2.45 GHz microwaves. Also, passive stabilizers are positioned at each end to provide extra stability while preventing tilt instability. The experiment is expected to produce its first plasma in 2025.

Comparison of very high-power short-duration, high-power short-duration, and low-power long-duration radiofrequency ablation for atrial fibrillation: A systematic review and network meta-analysis.

The optimal power and duration settings for radiofrequency (RF) atrial fibrillation (AF) ablation to improve efficacy and safety is unclear. We compared low-power long-duration (LPLD), high-power short-duration (HPSD), and very HPSD (vHPSD) RF settings for AF ablation. This network meta-analysis (NMA) was structured according to the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines. Medline, Scopus and Cochrane Central Register of Controlled Trials were systematically searched to identify relevant studies. Observational and randomized studies were included. Eligible studies compared outcomes in AF patients who underwent first-time RF ablation with the following settings: vHPSD (70-90W, 3-10 s), HPSD (45-60W, 5-10 s), or LPLD (20-40W, 20-60 s). Thirty-six studies comprising 10,375 patients were included (33% female). Frequentist NMA showed LPLD tended toward a lower odds of freedom from arrhythmia (FFA) versus HPSD (OR 0.93, 95% CI 0.86-1.00). There was no difference in FFA between vHPSD versus HPSD. Splitwise interval estimates showed a lower odds of FFA in LPLD versus vHPSD on direct (OR 0.78, 95% CI 0.65-0.93) and network estimates (OR 0.85, 95% CI 0.73-0.98). Frequentist NMA showed less total procedural (TP) time with HPSD versus LPLD (generic variance 1.06, 95% CI 0.83 to 1.29) and no difference between HPSD versus vHPSD. This NMA shows improved procedural times in HPSD and vHPSD versus LPLD. Although HPSD tended toward improved odds of FFA compared to LPLD, the overall result was not statistically significant. The odds of FFA in LPLD was lower versus vHPSD on direct and network estimates on splitwise interval analysis. Large prospective head-to-head randomized trials are needed to validate HPSD and vHPSD settings.

Abstract 15070: Predicting Steam-Pop Incidence Using Ex-Vivo Bipolar Ablation Model of Porcine Ventricular Myocardium

Introduction: Bipolar ablation has been reported to be able to create deep myocardial ablation lesion as compared to unipolar ablation, however, the incidence of steam-pop can lead to undesirable periprocedural complication. Hypothesis: Steam-pop occurrence during bipolar ablation can be predicted by the settings of bipolar ablation and the myocardial tissue characteristics such as tissue thickness and initial impedance prior to RF. Methods: Using porcine cardiac tissues ex-vivo ablation experiments were conducted. We adopted the commercially available radiofrequency (RF) ablation catheters. Each ablation catheter was placed on both sides of the myocardial slice at an angle of 45 degrees under targeted contact force of 10g. We recorded the occurrence of steam-pop under the multiple settings of tissue thickness, RF power and ablation duration. We created a generalized linear model (GLM) to predict steam-pop based on the bipolar ablation settings and the myocardial tissue characteristics. Results: In total 194 bipolar applications were analyzed. Steam-pops were observed in 11 out of 194 applications (5.7%). In the applications with steam-pop, the RF energy was higher (median 40W [q1-q3: 30-50] vs 30W [20-40], P=0.017), the initial impedance was lower (88 [86.75 - 91.5] vs 93 Ohm [89.75 - 95.75], P=0.0042) and the tissue thickness was thinner (9.4 [8.43 - 9.89] vs 12.9 mm [10.06 - 15.47], P&lt;0.0001) as compared to the applications without steam-pop. Using tissue thickness, RF energy and initial impedance, the constructed GLM achieved sensitivity of 100%, specificity of 93% and the area under the receiver-operator-characteristics curve of 0.969. Conclusion: Our data showed that the steam-pop occurrence during bipolar ablation may be predicted based on the initial RF settings and the tissue characteristics in the ex-vivo porcine myocardial model. Further studies are necessary to validate the feasibility of predicting steam-pops using the RF and tissue characteristics in the beating heart and human heart, which may enable us to titrate the RF settings and lead to safer bipolar ablation.

Abstract 13783: Tissue Thickness is an Essential Factor of Higher Risk of Steam Pop During Bipolar Ablation - Ex-Vivo Assessment

Introduction/Backgrounds: For ventricular arrhythmias originating deep within the myocardium, bipolar ablation can be employed. However, there is currently no standardized strategy for bipolar ablation settings such as energy and ablation time. Hypothesis and Aims: We intended to test a hypothesis that the target tissue thickness may determine the optimal bipolar ablation settings of power and duration. Methods: Using porcine cardiac tissues ex-vivo ablation experiments were conducted. Each radiofrequency (RF) ablation catheter was placed on both sides of the myocardial slice at an angle of 45 degrees and 10g contact. We investigated the depth of ablation lesions and the occurrence of steam-pop under the multiple settings of myocardial tissue thickness, energy and ablation duration. Results: We analyzed in total 194 bipolar RF applications. For myocardial slices of 10-, 15- and 20-mm thickness, we performed 60-second RF ablation of 20, 30, 40 and 50W energy settings. No transmural lesion creation was noted on the 20-mm thickness tissues even by 50W RF energy ( Figure 1 ). Transmural lesion was observed with RF energy of 30W or more on the most of the 10-mm thickness tissues. Prolonged duration of 180 seconds with 30W or more accomplished the transmural lesion on the 15-mm thickness tissues. We observed steam-pop in 11 out of 194 applications (5.7%). Steam-pops were exclusively observed on the 10mm tissue with 30W or more. Conclusion: Our data showed that (1) transmural lesion creation for 10-mm tissue is feasible under 30W or more and 60 seconds bipolar ablation, (2) for thicker tissue even 50W application of 60 seconds may not generate transmural lesion, (3) prolonged RF duration enables transmural lesion for thicker tissues, (4) steam-pop can occur on thinner tissues under higher wattage. These results suggest that we should adapt the bipolar RF settings, particularly the power and duration depending on the target tissue thickness.

Commissioning Results and Electron Beam Characterization with the S-Band Photoinjector at SINBAD-ARES

Over the years, the generation and acceleration of ultra-short, high quality electron beams has attracted more and more interest in accelerator science. Electron bunches with these properties are necessary to operate and test novel diagnostics and advanced high-gradient accelerating schemes, such as plasma accelerators and dielectric laser accelerators. Furthermore, several medical and industrial applications require high-brightness electron beams. The dedicated R&amp;D facility ARES at DESY (Deutsches Elektronen-Synchrotron) will provide such probe beams in the upcoming years. After the setup of the normal-conducting, radio-frequency (RF) photoinjector and linear accelerating structures, ARES successfully started the beam commissioning of the RF gun. This paper gives an overview of the ARES photoinjector setup and summarizes the results of the gun commissioning process. The quality of the first electron beams is characterized in terms of charge, momentum, momentum spread and beam size. Additionally, the dependencies of the beam parameters on RF settings are described. All measurement results of the characterized beams fulfill the requirements for operating the ARES linac with this RF photoinjector.

High Precision Monitoring of Radiofrequency Ablation for Liver Using Hyperspectral Imaging.

Minimally invasive procedures are achieving better satisfaction for treating liver cancers. Energy-based techniques were studied as prospective alternatives to the gold standard of liver transplantation. Among these techniques, radiofrequency (RF) was investigated for the selective ablation of liver tissue. In addition to optimizing the RF settings for the purpose of overcoming tissue perforation or inadequate ablation, an instrument collecting quantitative data regarding the intraoperative tissue status can aid the treatment procedure. This study demonstrates an innovative noninvasive technique using hyperspectral imaging (HSI) for monitoring RF ablative therapy in ex-vivo liver tissue. The cubic data generated by HSI provides spectral as well as spatial properties of the liver tissue included in each pixel of the field of view. In our study, the applied statistical analysis saves the computational burdens of multivariate analysis techniques. For this purpose, spectral angle mapper, logistic regression algorithm, and principal component analysis were applied. Of all spectral bands captured by the HSI camera, bands centered at 760 and 960 nm were identified for predicting the ablated area. Based on statistical analysis, the threshold for predicting the ablated area of the liver samples was determined, provided that the specificity is kept at 90%.

Optimization of magnetic fluid hyperthermia with respect to nanoparticle shape-related parameters: case of magnetite ellipsoidal nanoparticles

Issues related to the optimization of heat transfer mechanisms dominated by superparamagnetic relaxation are considered in the case of AC (alternating current) magnetic field hyperthermia procedures. The key role in the conversion of electromagnetic energy to the thermal one via the superparamagnetic relaxation mechanism is played by the magnetic anisotropy of nanoparticles, easily to be controlled via the shape anisotropy component. The optimization process has been discussed in the case of magnetite (Fe3O4) ellipsoidal nanoparticles with dominant shape anisotropy dispersed in different media. Nanoparticles of different sizes and aspect ratios have been considered in correlation with those specific parameters of the actuating AC magnetic field which respect an established biological safely criterion. It has been proven that the dissipated power can be maximized for a given set of biological compatible RF (radiofrequency) field parameters (frequency and field amplitude at the sample space) only for specific pairs of particle sizes and aspect ratios. For instance, it has been shown that ellipsoidal magnetite nanoparticles with 10 nm equatorial size and aspect ratio of 2 are optimal for a maximum transferred power under radiofrequency excitations of 250 kHz and field amplitude of 20 kA/m, if high viscosity dispersion media are used. The methodology for deriving the optimal shape (geometrical) parameters of a specific type of nanoparticles in conditions of using available radiofrequency excitations, or vice versa, for deriving the optimal radiofrequency working parameters in the case of ferrofluids with specific nanoparticles (type and geometry) is described and discussed in detail.

In silico analysis of the relation between conventional and high-power short-duration RF ablation settings and resulting lesion metrics.

Use of lesion metric indices is a proposed strategy to support pulmonary vein isolation procedures and these indices show good correlations with lesion sizes. The aim of this in silico study is to provide a detailed analysis of radiofrequency (RF) settings, including high-power short-duration (HPSD) settings, and resulting lesion metric indices. A software program was designed which simulated virtual RF ablations. Lesion metric indices (Ablation index: AI, Lesion size index: LSI) were calculated based on underlying RF settings (contact force [CF], power, duration). In series of calculations, the applied settings were varied within defined ranges (CF: 1-80 g, power: 1-60 W, duration: 1-60 seconds). Overall, n = 388 000 virtual ablations were calculated. The resulting lesion metric indices were compared with each other and analyzed in relation to respective RF settings. Increasing contact force from 1 to 10 g resulted in a 4.4-fold LSI value, whilst increasing contact force from 10 to 20g resulted in a 1.5-fold value (P < .01). When RF power was increased by 10 W, lesion metric indices increased between 1.3- and 1.6-fold. A prolongation of RF duration by 10 seconds resulted in a 1.2-to-1.3-fold increase of lesion metric indices. HPSD RF applications of 50 W, 11 to 13 seconds, and 60 W, 8 to 10 seconds resulted in equivalent lesion metric indices when compared with 30 W, 30 seconds conventional ablations. The findings support the clinical use of contact forces within a 10 to 20 g range. AI is more sensitive to RF duration, whereas LSI is more sensitive to contact force. HPSD RF settings can successfully be derived from lesion metric indices.

Indoor Localiza tion

Wi-Fi-based indoor localization is a solved problem --- given a space with enough Wi-Fi access points (APs) and a set of radio frequency (RF) signal strength measurements that profile the environment, we can provide a service that can accurately locate uncalibrated devices in that space. No one would argue with this assertion, yet after more than 15 years of research, there are no pervasive products and the research community continues to work on this problem. Why?

Relay Selection for Simultaneous Information Transmission and Wireless Energy Transfer: A Tradeoff Perspective

In certain applications, relay terminals can be employed to simultaneously deliver information and energy to a designated receiver and a set of radio frequency (RF) energy harvesters, respectively. In such scenarios, the relay that is preferable for information transmission does not necessarily coincide with the relay that is preferable for energy transfer, since the corresponding channels fade independently. Relay selection thus entails a tradeoff between the efficiency of the information transmission to the receiver and the amount of energy transferred to the energy harvesters. The study of this tradeoff is the subject on which this work mainly focuses. Specifically, we investigate the dependence of the ergodic capacity and the outage probability of the information transmission to the receiver on the amount of energy transferred to the RF energy harvesters. We propose a relay selection policy that yields the optimal tradeoff in a maximum capacity/minimum outage probability sense, for a given energy transfer constraint. We also propose two suboptimal relay selection methods that apply to scenarios with limited availability of channel state information. Additionally, we propose a suboptimal scheme which approximates the optimal scheme for the special case of two relays and facilitates performance analysis. Interesting insights on the aforementioned tradeoffs are unveiled.

Separate-function configuration of a two-cavity debuncher system

An advantageous configuration has been devised for a debuncher system with application to a high-intensity linac envisioned. The debuncher system consists of two RF (Radio Frequency) cavities, each of which is used as a tuning knob for either of the momentum spread adjustment or the centroid momentum jitter correction. This “separate-function” nature of the configuration considerably simplifies the tuning procedure for the RF set points. In addition, this system is less sensitive to the phase error originated from the centroid momentum deviation at the linac exit. Theoretical background of the configuration is discussed with a simplified analytical model, which is followed by a particle simulation for a practical example to validate the design strategy.

Thermal profile of radiofrequency energy in the inferior glenohumeral ligament.

Currently, two different methods of applying radiofrequency (RF) energy (monopolar and bipolar) are available to the surgeon for thermal shortening of the shoulder capsule. The objective of this study was to investigate the temperature changes and the thermal conduction across the human inferior glenohumeral ligament (IGHL) during radiofrequency energy application. Thermistors were secured onto both the intra-articular and extra-articular surfaces of human IGHL. Monopolar RF energy and bipolar RF energy were delivered to the intra-articular surface at the manufacturer's recommended settings. Pre-treatment and post-treatment ligament lengths, widths, heating times, and temperatures were measured and compared. For the monopolar devices, temperature spikes to 89 degrees C were recorded for the set temperature of 67 degrees C, averaging 77 degrees C +/- 10 degrees C. Temperatures across the ligament averaged 48 degrees C +/- 3 degrees C. For both devices, the IGHL became thicker with higher RF settings. Recorded temperatures decreased as distance increased from the point of application. Maximum temperatures occurred at least 6 to 7 seconds after cessation of energy application. The bipolar and monopolar devices had similar conduction times across the ligament, suggesting that this occurs by simple diffusion of heat. Bipolar and monopolar devices were equally efficacious for capsular shrinkage if the extent of the shortening is tightly defined. The thermal probe should not rest in one position for an extended period of time during RF energy application because, as our study showed, the monitoring of temperature or the visualization of tissue change is not efficacious for determining the end point of thermal shrinkage of the shoulder capsule.

Radio Frequency-Single Electron Transistor: A Fast and Sensitive Electrometer Analogous to the Radio Frequency-Superconducting Quantum Interference Device

We describe a new mode of operation of the single electron transistor (SET). The so-called RF-SET (radio frequency-SET) is a dual of the RF-SQUID (radio frequency-superconducting quantum interference device). It has been operated at frequencies above 100 MHz with a very high charge sensitivity (1.2 × 10−5 e/√Hz. The large bandwidth, combined with a high sensitivity, will enable studies of the dynamics of mesoscopic systems on very short time scales.