Low Radio Frequencies 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.

The radio properties of z&gt;3.5 quasars: Are most high-redshift radio-loud active galactic nuclei obscured?

We explore the radio properties of powerful (rest-frame luminosity $ at 500 MHz) high-redshift ($z 3.5$) quasars. The aim of this study is to gain a better understanding of radio-loud sources at the epoch when they reach the highest space density. We selected 29 radio-loud quasars at low radio frequencies (76 MHz). Their radio spectra, covering the range from 76 MHz to 5 GHz, are generally well reproduced by a single power law. We created samples that were matched in radio luminosity at lower redshift (from $z to $z to investigate any spectral evolution. We find that the fraction of flat-spectrum radio quasars (FSRQs) strongly increases with redshift (from $ 8&lt;!PCT!&gt;$ at z=1.2 to $ 45&lt;!PCT!&gt;$ at z$&gt;$3.5). This effect is also observed in quasars with lower luminosities (down to $ The increase in the fraction of FSRQs with redshift corresponds to a decrease in the steep- spectrum radio quasars. This result can be explained when we assume that the beaming factor and the slope of the luminosity function do not change with redshift and if high-redshift radio-loud sources can be recognized as quasars only when they are seen at a small viewing angle ($ but most of them, about 90&lt;!PCT!&gt; are obscured in the UV and optical bands. We also found a trend for the size of radio sources to decrease with increasing redshift. Because projection effects are insufficient to cause this trend, we suggest that the large amount of gas causing the nuclear obscuration also hampers the growth of the more distant sources.

Low-frequency Absorption and Radio Recombination Line Features of the Galactic Center Lobe

The Galactic center lobe (GCL) is a ∼1° object located north of the Galactic center. In the mid-infrared, the GCL appears as two 8.0 μm filaments that roughly define an ellipse. There is strong 24 μm and radio continuum emission in the interior of the ellipse. Due to its morphology and location in the sky, previous authors have argued that the GCL is created by outflows from star formation in the central molecular zone or by activity of the central black hole Sgr A*. We present images of the GCL from the GaLactic and Extragalactic All-sky Murchison Widefield Array survey in radio continuum that show thermal absorption against the Galactic center, incompatible with an interpretation of synchrotron self-absorption. Estimates of the cosmic-ray emissivity in this direction allow us to place a distance constraint on the GCL. To be consistent with standard emissivity assumptions, the GCL would be located 2 kpc away. At a distance of 8 kpc, the synchrotron background emissivity is enhanced by ∼75% in the direction of the GCL. We also present radio recombination line data from the Green Bank Telescope that constrain the electron temperature and line widths in this region, which are also more explicable if the GCL lies relatively close.

A 100 kpc ram pressure tail trailing the group galaxy NGC 2276

We present the discovery of a $100\ kpc $ low-frequency radio tail behind the nearby group galaxy, NGC 2276. The extent of this tail is a factor of ten larger than previously reported from higher-frequency radio and X-ray imaging. The radio morphology of the galaxy disc and tail suggest that the tail was produced via ram-pressure stripping, cementing NGC 2276 as the clearest known example of ram-pressure stripping in a low-mass group. With multi-frequency imaging, we extract radio continuum spectra between $ sim MHz $ and $1.2\ GHz $ as a function of projected distance along the tail. All of the spectra are well fit by a simple model of spectral ageing due to synchrotron and inverse-Compton losses. From these fits we estimate a velocity of $870\ $ for the stripped plasma across the plane of the sky, and a three-dimensional orbital velocity of $970\ $ for NGC 2276. The orbital speed that we derive is in excellent agreement with the previous estimates from an X-ray shock analysis, despite the completely independent methodology.

LOFAR Deep Fields: Probing the sub-mJy regime of polarized extragalactic sources in ELAIS-N1. I. The catalog

Quantifying the number density and physical characteristics of extragalactic polarized sources is important for the successful planning of future studies based on Faraday rotation measure (RM) grids of polarized sources to probe foreground Galactic and intergalactic magnetic fields. However, it is proving very hard to detect polarized signal from the population of very faint (sub-mJy) polarized sources at low radio frequencies, and their properties are mostly unknown. LOFAR can play an important role in such studies thanks to its sensitivity and angular resolution, combined with the precision on the inferred RM values that can be achieved through low-frequency broad-band polarimetry. The aim of this study is to probe the sub-mJy polarized source population with LOFAR. In this first paper, we present the method used to stack LOFAR polarization datasets, the resulting catalog of polarized sources, and the derived polarized source counts. The European Large Area ISO Survey-North 1 (ELAIS-N1) field, one of the deepest of the LOFAR Two-Metre Sky Survey (LoTSS) Deep Fields so far, was selected for a polarimetric study at 114.9–177.4 MHz. A total area of 25 deg$^2$ was imaged at 6"-resolution in the Stokes $Q$ and $U$ parameters. Alignment of polarization angles was done both in frequency and in Faraday space before stacking datasets from 19 eight-hour-long epochs taken in two different LOFAR observing cycles. A search for polarized sources was carried out in the final, stacked dataset, and the properties of the detected sources were examined. The depolarization level of sources known to be polarized at 1.4 GHz was quantified. A one-sigma noise level, $ QU $, of 19 mu Jy/beam was reached in the central part of the field after stacking. Twenty-five polarized sources were detected above 8$ QU $, five of which had not been detected in polarization at any other radio frequencies before. Seven additional polarized components were found by lowering the threshold to 6$ QU $ at positions corresponding to sources known to be polarized at 1.4 GHz. In two radio galaxies, polarization was detected from both radio lobes, so the final number of associated radio continuum sources is 31. The detected sources are weakly polarized, with a median degree of polarization of 1.75&lt;!PCT!&gt; for the sample of sources detected in polarized emission. For the 10 polarized sources previously identified in a pilot LOFAR study of the ELAIS-N1 field at 20"-resolution, the RM values are consistent but the degrees of polarization are higher in the 6"-resolution data. The sources previously detected in polarization at 1.4 GHz are significantly depolarized at 150 MHz. The catalog is used to derive the polarized source counts at 150 MHz. This is the deepest and highest-resolution polarization study at 150 MHz to date. A full characterization of the sources and an analysis of the catalog will be presented in Paper II.

Assessing the radiofrequency shielding effect of titanium mesh on diffusion-weighted imaging: a comparative study of the twice-refocused spin-echo and Stejskal-Tanner sequences.

This study compared twice-refocused spin-echo sequence (TRSE) and Stejskal-Tanner sequence (ST) to evaluate their respective effects on the image quality of magnetic resonance (MR) diffusion-weighted imaging in the presence of radiofrequency (RF) shielding effect of titanium mesh in cranioplasty. A 1.5-T MR scanner with a Head/Neck coil 20 channels and a phantom simulating the T2 and apparent diffusion coefficient (ADC) value of the human brain were used. Imaging was performed with and without titanium mesh placed on the phantom in TRSE and ST, and normalized absolute average deviation (NAAD), Dice similarity coefficient (DSC), and ADC values were calculated. The NAAD values were significantly lower for TRSE than for ST in the area below the titanium mesh, and the drop rates due to titanium mesh were 14.1% for TRSE and 9.8% for ST. The DSC values were significantly lower for TRSE than for ST. The ADC values were significantly higher for TRSE than for ST without titanium mesh. The ADC values showed no significant difference between TRSE and ST with titanium mesh. The ST had a lower RF shielding effect of titanium mesh than the TRSE.

A 1 bit Raw Voltage-recording System for Dedicated Observations of Transients at Low Radio Frequencies

Recently we had reported commissioning of a prototype for pulsar observations at low radio frequencies (<100 MHz) using log-periodic dipole antennas in the Gauribidanur Radio Observatory (≈77°E, 14°N) near Bangalore in India (https://www.iiap.res.in/?q=centers/radio). The aforementioned system (the Gauribidanur Pulsar System) is currently being augmented to directly digitize the radio-frequency signals from the individual antennas in the array. Our initial results using a 1 bit raw voltage-recording system indicate that such a back-end receiver offers distinct advantages like (i) simultaneous observations of any set of desired directions in the sky with multiple offline beams and smaller data rate/volume, and (ii) archival of the observed data with minimal resources for reanalysis in the future, either in the same or a different set of directions in the sky.

A Novel Low-Frequency Electromagnetic Active Inertial Sensor for Drug Detection.

The purpose of this paper is to demonstrate a new discovery regarding the interaction between materials and very low radio frequencies. Specifically, we observed a feedback response on an inertia active sensor when specific frequencies (around 2-4 kHz) are used to irradiate targeted pharmaceutical samples like aspirin or paracetamol drugs. The characteristics of this phenomenon, such as excitation and relaxation time, the relation between deceleration and a material's quantity, and signal amplitude, are presented and analyzed. Although the underlying physics of this phenomenon is not yet known, we have shown that it has potential applications in remote identification of compounds, detection, and location sensing, as well as identifying substances that exist in plants without the need for any processing. This method is fast, accurate, low-cost, non-destructive, and non-invasive, making it a valuable area for further research that could yield spectacular results in the future.

Design of a kilohertz repetition rate, low-emittance S-band photoinjector

Low-emittance photoinjector-enabled cutting-edge scientific instruments, such as free-electron lasers, inverse Compton scattering light sources, and ultrafast electron diffraction, will greatly benefit from the improved repetition rate. In this paper, we proposed a specifically designed S-band radio frequency (RF) photoinjector to obtain low emittance and kilohertz (kHz) high-repetition rates simultaneously. By lowering the gradient, much lower RF power is needed to feed the electron gun, and then the heat problem is much easier to handle. Meanwhile, by optimizing the length of the gun’s first cell from the normal case of 0.6-cell to 0.4-cell, the launch phase and the extraction field are significantly improved, thus ensuring the generation of low-emittance electron beams. In our design, the proposed 1.4-cell RF gun can work effectively under different field gradients ranging from 30 MV/m to 100 MV/m. For a standard case of 60 MV/m, 2.5 MW peak RF power with μs level pulse width is sufficient, thus offering the feasibility of improving the repetition rate to kHz level with a standard 5 MW irradiation klystron. In addition, simulated electron beams with a low emittance of 0.29 mm.mrad@200 pC can be generated by this proposed photoinjector, showing that this high-repetition rate injector holds the potential to deliver high-quality beams comparable to those of state-of-the-art S-band photoinjectors. Combining the merits of low emittance and high-repetition rate, this proposed photoinjector will provide a new possibility for future free-electron laser facilities operating at repetition rates ranging from kHz to tens of kHz.

Low-frequency Radio Interferometric Array Imaging Pipeline Optimization Based on Distributed Execution Framework

The Square Kilometre Array (SKA) project is an international collaboration to build the world’s largest radio telescope, whose sensitivity and measurement speed will be an order of magnitude higher than those of all current radio telescopes. Radio continuum survey is one of the main observation mode of the SKA, and the establishment of a standard map of the survey area based on continuum imaging will provide an important foundation for subsequent astronomical science. The GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X) is a project of the SKA pilot telescope Murchison Widefield Array (MWA) in 2018—2020. GLEAM-X is a new radio continuum survey project to be carried out with the MWA Phase II expansion array in 2018—2020. The experience of optimizing the imaging pipeline based on the distributed execution framework will help to solve the problem of massive data processing. In this paper, we describe the process steps of GLEAM-X imaging pipeline, integrate and improve it, and realize parallel processing of multiple pipelines on the China SKA Regional Centre Prototype (CSRC-P), and verify the deployment and test the correctness of the imaging pipeline system using GLEAM-X observation data. The GLEAM-X observations were used to validate the deployment of the imaging pipeline system and test its correctness. Then, to optimize the pipelines and improve the processing efficiency, the Data Activated Liu Graph Engine (DALiuGE) was used to integrate the imaging pipelines into the DALiuGE execution framework to automate the distributed parallel processing of the pipelines. Performance tests and results’ analysis show that the optimized imaging pipeline based on the DALiuGE execution framework has better performance, more flexible adaptability, and scalability than the traditional parallel approach, and can support future large-scale continuum imaging experiments during the first phase of SKA commissioning.

Phase transformation and plasmonic damping study for semi-solid ionic polymeric hydrogel system at higher temperature and low radio frequency

This article represents the findings regarding the phase transitions exhibited by a polymeric hydrogel material composed of sodium polyphosphate-polyethylene glycol. These transitions play a crucial role in the generation of ionic plasmons and the manifestation of surface plasmon resonance (SPR) with dielectric permittivity damping within the polymer electrolyte system of the hydrogel. Usually, SPR has been observed in electron-conducting systems within an optical frequency range. However, here SPR is observed in an ionic system within a lower radio frequency range of 104-10 (Parwati et al., 2024) 77 Hz for temperatures exceeding 80 °C. The mechanism responsible for permittivity damping can be elucidated by considering the accumulation of ionic charges at the interface between the electrode and the electrolyte, coupled with a high degree of charge absorption following the Drude model. A power law has been used to describe the resonance that occurs between the applied DC frequency and the motion of charge carrier ions, thus confirming the presence of free ionic motion within the hydrogel matrix. tan δ shows significant energy absorption further substantiating permittivity damping, which transitions from positive to negative values.

Redeveloping a CLEAN Deconvolution Algorithm for Scatter-broadened Radio Pulsar Signals

Broadband radio waves emitted from pulsars are distorted and delayed as they propagate toward the Earth due to interactions with the free electrons that compose the interstellar medium (ISM), with lower radio frequencies being more impacted than higher frequencies. Multipath propagation in the ISM results in both later times of arrival for the lower frequencies and causes the observed pulse to arrive with a broadened tail described via the pulse broadening function. We employ the CLEAN deconvolution technique to recover the pulse broadening timescale and by proxy the intrinsic pulse shape. This work expands upon previous descriptions of CLEAN deconvolution used in pulse broadening analyses by parameterizing the efficacy on simulated data and developing a suite of tests to establish which of a set of figures of merit leads to an automatic and consistent determination of the scattering timescale and its uncertainty. We compare our algorithm to the cyclic spectroscopy method of estimating the scattering timescale, specifically to the simulations performed in Dolch et al. (2021). We test our improved algorithm on the highly scattered millisecond pulsar J1903+0327, showing the scattering timescale to change over years, consistent with estimates of the refractive timescale of the pulsar.

Study of Wolf-Rayet Stars Using uGMRT

In recent years, systems involving massive stars with large wind kinetic power have been considered as promising sites for investigating relativistic particle acceleration in low radio frequencies. With this aim, we observed two Wolf-Rayet systems, WR 114 and WR 142, using upgraded Giant Meterwave Radio Telescope observations in Band 4 (550–950 MHz) and Band 5 (1050–1450 MHz). None of the targets was detected at these frequencies. Based on the non-detection, we report 3𝜎 upper limits to the radio flux densities at 735 and 1260 MHz (123 and 66 𝜇Jy for WR 114, and 111 and 96 𝜇Jy for WR 142, respectively). Plausible scenarios to interpret this non-detection are presented.

High-time resolution GPU imager for FRB searches at low radio frequencies

Abstract Fast Radio Bursts (FRBs) are millisecond dispersed radio pulses of predominately extra-galactic origin. Although originally discovered at GHz frequencies, most FRBs have been detected between 400 and 800 MHz. Nevertheless, only a handful of FRBs were detected at radio frequencies $\le$ 400 MHz. Searching for FRBs at low frequencies is computationally challenging due to increased dispersive delay that must be accounted for. Nevertheless, the wide field of view (FoV) of low-frequency telescopes – such as the the Murchison Widefield Array (MWA), and prototype stations of the low-frequency Square Kilometre Array (SKA-Low) – makes them promising instruments to open a low-frequency window on FRB event rates, and constrain FRB emission models. The standard approach, inherited from high-frequencies, is to form multiple tied-array beams to tessellate the entire FoV and perform the search on the resulting time series. This approach, however, may not be optimal for low-frequency interferometers due to their large FoVs and high spatial resolutions leading to a large number of beams. Consequently, there are regions of parameter space in terms of number of antennas and resolution elements (pixels) where interferometric imaging is computationally more efficient. Here we present a new high-time resolution imager BLINK implemented on modern graphical processing units (GPUs) and intended for radio astronomy data. The main goal for this imager is to become part of a fully GPU-accelerated FRB search pipeline. We describe the imager and present its verification on real and simulated data processed to form all-sky and widefield images from the MWA and prototype SKA-Low stations. We also present and compare benchmarks of the GPU and CPU code executed on laptops, desktop computers, and Australian supercomputers. The code is publicly available at https://github.com/PaCER-BLINK-Project/imager and can be applied to data from any radio telescope.

Propagation effects at low frequencies seen in the LOFAR long-term monitoring of the periodically active FRB 20180916B

ABSTRACT LOFAR (LOw Frequency ARray) has previously detected bursts from the periodically active, repeating fast radio burst (FRB) source FRB 20180916B down to unprecedentedly low radio frequencies of 110 MHz. Here, we present 11 new bursts in 223 more hours of continued monitoring of FRB 20180916B in the 110–188 MHz band with LOFAR. We place new constraints on the source’s activity window $w =4.3^{+0.7}_{-0.2}$ d and phase centre $\phi _{\mathrm{c}}^{\mathrm{LOFAR}} = 0.67^{+0.03}_{-0.02}$ in its 16.33-d activity cycle, strengthening evidence for its frequency-dependent activity cycle. Propagation effects like Faraday rotation and scattering are especially pronounced at low frequencies and constrain properties of FRB 20180916B’s local environment. We track variations in scattering and time–frequency drift rates, and find no evidence for trends in time or activity phase. Faraday rotation measure (RM) variations seen between June 2021 and August 2022 show a fractional change &amp;gt;50 per cent with hints of flattening of the gradient of the previously reported secular trend seen at 600 MHz. The frequency-dependent window of activity at LOFAR appears stable despite the significant changes in RM, leading us to deduce that these two effects have different causes. Depolarization of and within individual bursts towards lower radio frequencies is quantified using LOFAR’s large fractional bandwidth, with some bursts showing no detectable polarization. However, the degree of depolarization seems uncorrelated to the scattering time-scales, allowing us to evaluate different depolarization models. We discuss these results in the context of models that invoke rotation, precession, or binary orbital motion to explain the periodic activity of FRB 20180916B.

Use of intracardiac echocardiography in vein of Marshall ethanol infusion for ablation of persistent atrial fibrillation

BackgroundFew methods have been reported to demonstrate real-time effects during vein of Marshall (VOM) ethanol infusion in persistent atrial fibrillation (PeAF). ObjectiveThis study was to evaluate the impact of left atrial (LA) monitoring using intracardiac echocardiography (ICE) during VOM ethanol infusion. MethodsSeventy-four consecutive patients with PeAF who underwent VOM ethanol infusion followed by radiofrequency (RF) ablation were included. Patients with findings on ICE consistent with echogenic streaming in the LA and with increased myocardial local echogenicity along the VOM area were placed into one group (group A) and those without into the other group (group B). Outcomes between the 2 groups were compared. ResultsForty-six patients (62%) were placed into group A. A new ethanol-induced low-voltage area in group A was larger than that in group B (8.5 cm2 [5.5–10.2 cm2] and 4.0 cm2 (2.4–6.3 cm2]; P < .001). The RF ablation time required to achieve MI block was reduced in group A patients (263.0 seconds [196.0–351.0 seconds] vs 417.0 seconds [315.0–709.5 seconds] in group B patients; P < .001). MI block was achieved in 46 patients (100%) via an endocardial approach in group A and 27 patients (96.4%) in group B (extra coronary sinus ablation in 4 patients). One patient developed clinically significant pericardial effusions and required pericardiocentesis in group B. ConclusionPresence of increased myocardial local echogenicity at the ridge and consistent echogenic streaming in the LA detected by ICE-based imaging during VOM ethanol infusion suggests increased ablated tissue in that region and lower RF ablation time during ablation for PeAF.

Low-frequency Radio Recombination Lines Away from the Inner Galactic Plane

Diffuse radio recombination lines (RRLs) in the Galaxy are possible foregrounds for redshifted 21 cm experiments. We use EDGES drift scans centered at −26.°7 decl. to characterize diffuse RRLs across the southern sky. We find that RRLs averaged over the large antenna beam (72° × 110°) reach minimum amplitudes of R.A. = 2–6 hr. In this region, the Cα absorption amplitude is 33 ± 11 mK (1σ) averaged over 50–87 MHz (27 ≳ z ≳ 15 for the 21 cm line) and increases strongly as frequency decreases. Cβ and Hα lines are consistent with no detection with amplitudes of 13 ± 14 and 12 ± 10 mK (1σ), respectively. At 108–124.5 MHz (z ≈ 11) in the same region, we find no evidence for carbon or hydrogen lines at the noise level of 3.4 mK (1σ). Conservatively assuming that observed lines come broadly from the diffuse interstellar medium, as opposed to a few compact regions, these amplitudes provide upper limits on the intrinsic diffuse lines. The observations support expectations that Galactic RRLs can be neglected as significant foregrounds for a large region of sky until redshifted 21 cm experiments, particularly those targeting cosmic dawn, move beyond the detection phase. We fit models of the spectral dependence of the lines averaged over the large beam of EDGES, which may contain multiple line sources with possible line blending, and find that including degrees of freedom for expected smooth, frequency-dependent deviations from local thermodynamic equilibrium (LTE) is preferred over simple LTE assumptions for Cα and Hα lines. For Cα we estimate departure coefficients 0.79 < b n β n < 4.5 along the inner Galactic plane and 0 < b n β n < 2.3 away from the inner Galactic plane.

The centroid speed as a characteristic of the group speed of solar coronal fast magnetoacoustic wave trains

ABSTRACT The highly filamented nature of the coronal plasma significantly influences dynamic processes in the corona such as magnetohydrodynamic waves and oscillations. Fast magnetoacoustic waves, guided by coronal plasma non-uniformities, exhibit strong geometric dispersion, forming quasi-periodic fast-propagating (QFP) wave trains. QFP wave trains are observed in extreme-ultraviolet imaging data and indirectly in microwaves and low-frequency radio, aiding in understanding the magnetic connectivity, energy, and mass transport in the corona. However, measuring the field-aligned group speed of QFP wave trains, as a key parameter for seismological analysis, is challenging due to strong dispersion and associated rapid evolution of the wave train envelope. We demonstrate that the group speed of QFP wave trains formed in plane low-β coronal plasma non-uniformities can be assessed through the propagation of the wave train’s effective centre of mass, referred to as the wave train’s centroid speed. This centroid speed, as a potential observable, is shown empirically to correspond to the group speed of the most energetic Fourier harmonic in the wave train. The centroid speed is found to be almost insensitive to the waveguide density contrast with the ambient corona, and to vary with the steepness of the transverse density profile. The discrepancy between the centroid speed as the group speed measure and the phase speed at the corresponding wavelength is shown to reach 70 per cent, which is crucial for the energy flux estimation and interpretation of observations.

Atrial fibrillation high power radiofrequency ablation: efficiency and safety

Abstract Introduction High power-ablation index (HP-AI) guided radiofrequency (RF) ablation of atrial fibrillation (AF) is increasingly being used as an alternative to conventional power (CP) ablation due to its better procedural performance and similar safety profile. Some evidence suggests that the lower RF time used in HP-AI may also have a protective effect in contact related complications. Despite this evidence, this strategy is still not widely used. Purpose Compare procedural efficiency and safety between HP-AI vs CP-AI-guided ablation in AF patients (pts). Methods Retrospective single-center study of consecutive pts submitted to AI-guided ablation, between 05/2018 and 10/2022. RF power and AI were 25W/500 and 45W/500 for the anterior wall and 20W/380 and 35W/380 for the posterior wall in CP-AI and HP-AI, respectively. Procedure related complications incidence were checked at 1 month. Results Of a total of 83 pts included in the study, mean age was 62±10y and 57.8% were males. HP-AI was performed in 61.4% (n=51). 39.2% had persistent AF (vs 25% in CP-AP, p=0.235). HP-AI was associated with significantly lower median procedure duration (150.0[140.0-180.0]min vs 192.0[180.0-235.0]min, p&amp;lt;0.001), fluoroscopy time (9.2[7.3-11.3]min vs 12.2[9.7-14.3]min, p=0.003) and RF time (26.3[20.4-28.4]min vs 34.3[30.1-39.6]min, p&amp;lt;0.001). These times were significantly reduced for both paroxysmal and persistent AF (figure 1). Electrical isolation of all the pulmonary veins was achieved in all patients. There were no early complications related to the procedure in either CP-AI or HP-AI groups. Conclusion HP-AI guided AF ablation significantly reduced procedure duration without impairing safety. It was also associated with lower RF application time, which may potentially lead to a reduction in procedure related complications. Data regarding long-term effectiveness will eventually support HP-AI as the best option for RF AF ablation.Comparison of median procedural times

Surpoint algorithm for improved guidance of ablation for ventricular tachycardia (SURFIRE-VT): a propensity-matched study

Abstract Background Ablation Index (AI) is a novel multiparametric radiofrequency (RF) ablation lesion quality metric, which incorporates contact force, time, and power in a weighted formula. AI guided strategies have been shown to be clinically effective for catheter ablation of atrial arrhythmias. The utility of AI to guide ablation of ventricular tachycardia (VT) in patients with structural heart disease is not known. Objectives To assess RF ablation and procedural characteristics, safety, and long-term clinical outcomes in patients undergoing VT ablation using either an AI guided strategy (maximum AI target value 550) or conventional approach using traditional parameters at a large tertiary medical center. Methods Consecutive patients (n=91) undergoing initial VT ablation for both ischemic (ICM) and non-ischemic (NICM) VT at single tertiary medical center between 2017 and 2022 were examined. Patients were 1:1 propensity matched for baseline characteristics, co-morbid conditions, and antiarrhythmic use depending on whether the ablation was guided by AI or traditional lesion quality parameters. Baseline categorical variables were compared using chi square test or Fisher exact test, and continuous measures were evaluated using Wilcoxon rank sum test. Linear regression was used to assess the impact of the use of AI on ablation characteristics and Cox proportional hazard model was used evaluate clinical outcomes. Results After propensity matching, baseline characteristics were well balanced between AI (n=37) and non-AI (n=37) groups (Table 1). Patients undergoing an AI guided strategy had shorter average procedure duration (-30.9 minutes, 95% CI [-60.4, -1.4], p=0.04) and average time per lesion (-13.7 seconds, 95% CI [-17.9, -9.5], p &amp;lt;0.001), as well as a trend toward significantly lower total RF ablation duration (357 seconds, 95% CI [-776, 61.9] p=0.09) and fewer steam pops (-0.19, 95% CI [-0.40, 0.02] p = 0.08). Lesion sets were similar between AI and non-AI groups (Scar homogenization: 41% vs 27%; p=0.22, Linear: 23% vs 73%; p=0.31, elimination LPs/LAVAs: 50% vs 43%; p=0.25, Scar dechanneling: 19% vs 8%; p=0.19, Core isolation: 5% vs 11%; p=0.4) as was use of epicardial mapping and ablation (11% vs 14%; p=0.73) Inducibility of VT (70% vs 67%; p=0.8) and termination of clinical VT during ablation (11% vs 16%; p=0.17) were also similar between AI and non-AI groups. When compared to a traditional strategy, patients undergoing an AI strategy had similar hazard for VT recurrence (0.97, 95% CI [0.42 – 2.2], p=0.93) and appropriate device therapy (0.79, 95% CI [0.32 – 1.95] p=0.61). Conclusions Compared to a strategy guided by traditional lesion parameters, use of AI of 550 for VT ablation in patients with structural heart disease resulted in shorter procedure time and average time of RF delivery per lesion with similar intermediate term clinical outcomes.Table 1Figure 1