Local Impedance Research Articles

Biophysical Tissue Characterization of Ventricular Tachycardia Substrate With Local Impedance Mapping to Predict Critical Sites

BackgroundNew tools are needed to improve ventricular tachycardia (VT) substrate characterization and optimize outcomes. LI provides biophysical tissue characterization. ObjectivesThe purpose of this study was to test local impedance (LI)-based mapping to predict critical ventricular tachycardia components after myocardial infarction (MI). MethodsOne month after a nonreperfused anterior MI, endo-epicardial high-density electroanatomic mapping and endocardial LI mapping were performed in 23 Landrace Large X White pigs. LI thresholds were set using the blood pool value to define a 10 Ω range: low (<blood pool −1Ω), intermediate (≥blood pool −1Ω and ≤blood pool +9Ω), and high (normal) tissue resistance (>blood pool +9Ω). ResultsLow LI was detected in low-voltage areas in 100% of cases, but intermediate LI was found in both core (87%) and border zone (12.5%) voltage areas. A total of 17 VTs were induced (VT isthmus identified in 9 animals). VT inducibility was associated with the size of intermediate LI area (OR: 1.19 [95% CI: 1.0-1.4]; P = 0.039) and the presence of specific LI patterns: LI corridor (OR: 15.0 [95% CI: 1.3-169.9]; P = 0.029); LI gradient (OR: 30.0 [95% CI: 2.1-421.1]; P = 0.012), high LI heterogeneity (OR: 21.7 [95% CI: 1.8-260.6]; P = 0.015), and presence of ≥2 low LI regions (OR: 11.3 [95% CI: 1.0-130.2]; P = 0.053). Potential VT isthmuses were in areas of intermediate LI and colocalized to LI patterns associated with VT inducibility in all cases (LI corridors or LI gradient). Low LI regions did not actively participate in the VT circuit (0%). ConclusionsLI mapping is feasible and may add useful characterization of the VT substrate. Specific LI patterns (ie, corridors, gradients) were associated with VT inducibility and colocalized with the VT isthmus, thus representing a potential new target for ablation in substrate-based procedures.

Ultra‐Broadband and Wide‐Angle Metamaterial Absorber with Carbon Black/Carbonyl Iron Composites Fabricated by Direct‐Ink‐Write 3D Printing

This study proposes the fabrication of an asymmetric woodpile metamaterial absorber using direct‐ink‐writing 3D printing technology. The prepared inks are compounded using two loss fillers: carbon black and carbonyl iron powder. The synergistic effect enhances the electromagnetic loss performance and the synergistic mechanism is analyzed. The designed asymmetric woodpile absorber has a wider bandwidth than a simple tetragonal woodpile, and the advantage presented by the asymmetric woodpile arrangement overcomes the local impedance mismatch. A simulation is then performed, which demonstrates that the designed asymmetric woodpile metamaterial with a thickness of 8.6 mm can achieve a −10 dB absorbing bandwidth in the frequency range of 3.9–18 GHz, and the maximum reflection loss reaches up to −39 dB. Additionally, the absorber exhibits excellent angular performance and the absorption bandwidth of the transverse electric polarization or transverse magnetic polarization waves can reach more than 10 GHz with incident angles from 0° to 50°. Furthermore, the manufacturing process of the absorber is simple, efficient, and inexpensive, which presents considerable potential for its widespread implementation in practical engineering applications.

Perfect-Lens Theory Enables Metasurface Reflectors for Subwavelength Focusing

Breaking the so-called diffraction limit on the resolution of optical devices and achieving subwavelength focusing requires tailoring the evanescent spectrum of wave fields. There are several possible approaches, all of which have limitations, such as the generation of strong additional scattering, limited focusing power, issues at the implementation step, and the need for a drain at the focal point. This paper presents a feasible strategy based on the concepts of the perfect lens and power flow-conformal metasurfaces. Desired fields for subwavelength focusing are integrated using double-negative media and then the surface profile of a focusing reflector is designed to be tangential to the desired power flow, so that the metasurface can be modeled as a local impedance boundary, and can be easily implemented using passive and lossless elements. Full-wave simulations demonstrate that an example reactive metasurface is able to break the diffraction limit and provide near-field focusing with subwavelength hotspot size. We expect that the outcome will find applications in antennas, beam-shaping devices, nonradiative wireless power transfer systems, microscopy, and lithography.

INVESTIGAÇÃO DA ATIVIDADE ELETROQUÍMICA DE LIGA Al-Cu-Li APÓS PROCESSO DE SOLDAGEM POR FRICÇÃO E MISTURA

INVESTIGATION OF THE ELECTROCHEMICAL ACTIVITY OF AN Al-Cu-Li ALLOY AFTER FRICTION STIR WELDING PROCESS. In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding (FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS – Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).

Nonlinear Electrochemical Impedance Spectroscopy for Lithium-Ion Battery Model Parameterization

In this work we analyze the local nonlinear electrochemical impedance spectroscopy (NLEIS) response of a lithium-ion battery and estimate model parameters from measured NLEIS data. The analysis assumes a single-particle model including nonlinear diffusion of lithium within the electrode particles and asymmetric charge transfer kinetics at their surface. Based on this model and assuming a moderately-small excitation amplitude, we systematically derive analytical formulae for the impedances up to the second harmonic response, allowing the meaningful interpretation of each contribution in terms of physical processes and nonlinearities in the model. The implications of this for parameterization are explored, including structural identifiability analysis and parameter estimation using maximum likelihood, with both synthetic and experimentally measured impedance data. Accurate fits to impedance data are possible, however inconsistencies in the fitted diffusion timescales suggest that a nonlinear diffusion model may not be appropriate for the cells considered. Model validation is also demonstrated by predicting time-domain voltage response using the parameterized model and this is shown to have excellent agreement with measured voltage time-series data (11.1 mV RMSE).

Nanoscale electrochemical charge transfer kinetics investigated by electrochemical scanning microwave microscopy.

We show how microwave microscopy can be used to probe local charge transfer reactions with unprecedented sensitivity, visualizing surface reactions with only a few hundred molecules involved. While microwaves are too fast under classical conditions to interact and sense electrochemical processes, this is different at the nanoscale, where our heterodyne microwave sensing method allows for highly sensitive local cyclic voltammetry (LCV) and local electrochemical impedance spectroscopy (LEIS). LCV and LEIS allow for precise measurement of the localized charge transfer kinetics, as illustrated in this study for a ferrocene self-assembled monolayer immersed in an electrolyte. The theoretical analysis presented here enables a consistent mapping of the faradaic kinetics and the parasitic contributions (nonfaradaic) to be spectrally resolved and subtracted. In particular, this methodology reveals an undistorted assessment of accessible redox site density of states associated with faradaic capacitance, fractional surface coverage and electron transfer kinetics at the nanoscale. The developed methodology opens a new perspective on comprehending electrochemical reactivity at the nanoscale.

A Reproducible Bioimpedance Transducer for Insulin Noninvasive Measurement

A bioimpedance transducer is proposed for non-invasive monitoring of insulin bioavailability after subcutaneous injection. The insulin bioavailability is assessed indirectly by measuring the local impedance variation due to the drug disappearance from the injection volume. The instrument allows to manage the extreme variability in insulin response by diabetic patients due to skin conditions and/or alterations such as lipodystrophy. In this way, the transducer can also be considered as a key component for new generation of artificial pancreas. The instrument achieves state of art accuracy and uncertainty. Intra-individual reproducibility also resulted improved with respect to previous studies. Moreover, the feasibility of an absorption measurement is proved. After presenting the concept design and the prototype, the metrological characterization during (i) laboratory (on passive electrical components), (ii) in-vitro (on eggplants), and (iii) in-vivo (on an human subject) experiments is reported. In laboratory tests, typical percentage deterministic errors of 1 % on magnitude and phase were obtained. The mean 1-σ repeatability of 0.05 % was obtained for both impedance magnitude and phase. The in-vitro tests were aimed to improve the reproducibility by comparing the electrical behavior of insulin and vehicle in eggplants. During the in-vivo tests, a decrease in percentage 1-σ intra-individual reproducibility was reported with respect to the state of art (from more than 200 % to 36 %), as the impedance magnitude is concerned. In a clinical application framework, an accuracy of 9 μl was obtained by means of a second-order polynomial model. The uncertainty resulted 4.2 μl, well below the typical volume of one insulin unit (10.0 μl).

Edge of Chaos Explains Prigogine’s Instability of the Homogeneous

One of the complex phenomena, which most attracted the attention of the scientific community over the past few decades, is the emergence of diffusion-driven instabilities in homogeneous cellular media. Explaining this symmetry-breaking process, which the Russian luminary Ilya Prigogine referred to as the Instability of the Homogeneous, is only possible upon invoking the Physics Law of the Edge of Chaos. While the emergence of inhomogeneous static or dynamic periodic solutions in biological reaction-diffusion systems was recently reproduced in two-cell networks, leveraging the Negative Differential Resistance of certain volatile memristors, so far, to the best of our knowledge, no cellular array was ever found to undergo dissipation-induced dynamical phenomena of higher complexity, including a route to chaos, or an uncontrollable upsurge in the respective physical variables. This manuscript determines all the possible sets of conditions on the parameters of a one-port, extracted from the classical Chua circuit, enabling to poise it on some stable and locally-active operating point, employing a deep mathematical analysis, focusing on the properties of its local impedance. The polarisation of the one-port on some Edge of Chaos operating point is the Conditio Sine Qua Non for the Destabilisation of the Homogeneous Solution, resulting in the steady-state appearance of high-order dynamical phenomena, as outlined above, in a simple Reaction-Diffusion Cellular Nonlinear Network, where a linear and passive resistor, interposed between two identical copies of the one-port, lets them interact by means of a diffusion process. Notably, as demonstrated here, whether or not the dissipative coupling path may truly succeed in moving each of the two one-ports of the two-cell array, under study, away from the respective common Edge of Chaos operating point, depends critically upon the satisfaction of the logical disjunction between three inequalities, which enforces the instability of the denominator polynomial of the rational function associated to the local input impedance of the cellular array, as seen across either of the two one-ports.

Corrosion characteristics of simulated reheated heat-affected-zone of X80 pipeline steel in carbonate/bicarbonate solution

A simulated reheated heat-affected-zone sample of X80 pipeline steel was obtained via Gleeble processing. Microstructure and corrosion behaviors in different regions were studied by optical microscope, electron backscatter diffraction, conventional electrochemical polarization and local electrochemical impedance spectroscopy. The results showed that microstructure gradients were generated in different regions. Microstructures with severely coarse martensite/austenite constituents had the most negative corrosion potential. Localized corrosion at the grain boundaries was more likely to occur in the region with more high-angle grain boundaries. Corrosion resistance in the center portions converged as the immersion process progressed and the difference from the base metal increased.

Optimal local impedance parameters for successful pulmonary vein isolation in patients with atrial fibrillation.

Local impedance (LI) parameters of IntellaNav STABLEPOINT for successful pulmonary vein isolation (PVI) of atrial fibrillation (AF) remain unclear. The purpose of this study was to seek LI data achieving successful PVI. Consecutive AF patients who underwent catheter ablation with STABLEPOINT were prospectively enrolled in two centers. PVI was performed under a constant 35-or 40-watt power, 20-sduration, and >5-gcontact force. The operators were blinded to the LI data. The characteristics of all ablation points with/without conduction gaps (Unsuccess or Success tags) after the first-attempt PVI were evaluated for the right/left PVs and anterior/posterior wall (RPV/LPV and AW/PW, respectively), and cutoff values of LI data were calculated for successful lesion formation. A total of 5257 ablation points in 102 patients (65 [58-72] years old, 65.7% male) were evaluated. The LI drop values were higher in the Success tags than Unsuccess tags on the LPV-AW and RPV-AW/PW (p < .001), except for the LPV-PW (p = .105). The %LI drop values (LI drop/initial LI) were higher for the Success tags in all areas (15.8 [12.2%-19.6%] vs. 11.6 [9.7%-15.6%] in LPV-AW: p < .001, 15.0 [11.5%-19.3%] vs. 11.4 [8.7%-17.3%] in LPV-PW: p = .035, 15.3 [11.5%-19.4%] vs. 9.9 [8.1%-13.7%]in RPV-AW: p < .001, and 13.3 [10.1%-17.4%] vs. 8.1 [6.3%-9.5%]in RPV-PW, p < .001). The LI drop and %LI drop cutoff values were 20.0 ohms and 11.6%, respectively. An insufficient LI drop with STABLEPOINT was associated with a gap formation during PVI, and the best cutoff values for the LI drop and %LI drop were 20.0 ohms and 11.6%, respectively.

Estimation of mechanical properties by transcatheter monitoring using local impedance and contact force

The mechanical properties of the myocardium in the left ventricle and right atrium were estimated by simultaneously measuring the local impedance (LI) and contact force (CF) using an ablation catheter. Radiofrequency catheter ablation (RFCA) is a well-established arrhythmia treatment. Monitoring the RF power, CF and properties of myocardium during RFCA are necessary to estimate the effect of ablation. Indices, such as CF, lesion size index and ablation index, do not include the myocardium mechanical properties. Therefore, there is the risk of side effects, such as cardiac tamponade, by excessive catheter indentation into vulnerable areas. We propose the simultaneous measurement of LI and CF for estimating the myocardial mechanical properties to reduce the side effects. In this study, an in vitro experimental system was constructed to measure LI and CF via the catheter. The relationship between the porcine myocardial tissue thickness and CF–LI curve was investigated using the left ventricle and right atrium. Power function coefficients approximating the CF–LI curve increased with thicker left ventricle. The thickness of the myocardium can be estimated by simultaneously measuring LI and CF. Intraoperative measurement of the myocardial mechanical properties can be used to determine the ablation conditions at each site.

Designing a novel GO@AAP reinforced epoxy coating for achieving the long-term corrosion protection of steel substrate

In this study, 4-amino-antipyrine (AAP) was grafted on graphene oxide (GO) via the hydrothermal strategy (GO@AAP) to improve the corrosion resistant property of epoxy coating. Transmission electron microscope (TEM), scanning probe microscope (SPM) and Raman techniques were employed to investigate the morphology and structure of GO@AAP nanohybrid, which also effectively confirmed the successful AAP grafted on GO surface. Electrochemical and salt spray results indicated that incorporating as-synthesized GO@AAP into epoxy coating powerfully enhanced the anti-corrosion property, which was greatly consistent with the mild steel morphology after corrosion experiment. Besides, after 60 days of immersion, the |Z|0.01 Hz was 3.7 × 108 Ω·cm2, which was two order of magnitude higher than that of pure epoxy coating. Local electrochemical impedance spectroscopy (LEIS) was visually demonstrated the synergistic effect of physical shielding and corrosion inhibition of GO@AAP in 3.5 wt% NaCl solution. This work provides a new method to achieve the barrier and inhibition activities of epoxy coatings, which are suitable for heavy corrosion resistant application in harsh environment.

Investigating local corrosion processes of magnesium alloys with scanning probe electrochemical techniques: A review

The study of corrosion of magnesium and its alloys has emerged a hot topic in the applications of lightweight structural materials. The inherently high electrochemical activity of bare magnesium surfaces still lacks a convincing mechanism to describe the observed experimental characteristics, and it has prompted the development of various types of protective coatings with the aim of slowing metal dissolution. In recent years, new instruments and techniques have been developed to study with spatial resolution the local corrosion processes that occur in metallic materials in general, and for magnesium and its alloys in particular, both for bare surfaces and coated. Scanning microelectrochemical techniques, such as local electrochemical impedance spectroscopy (LEIS), scanning electrochemical microscopy (SECM), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET) and scanning Kelvin probe (SKP) can provide information about the local electrochemical activity of metallic surfaces. In the present work, the applications of these techniques in corrosion studies of magnesium and its alloys are reviewed. Assessment of corrosion mechanisms, barrier properties of conventional coatings and active corrosion behavior of self-healing coatings are examined. Limitations and future developments in this area are discussed.

Interaction mechanism of ferrate(VI) with arsenopyrite surface and its effect on flotation separation of chalcopyrite from arsenopyrite

Potassium ferrate (K2FeO4) was used as a novel environmental-friendly depressant, and its inhibition effect on flotation performance of arsenopyrite and chalcopyrite using potassium ethyl xanthate (PEX) as a collector was investigated by flotation experiments, contact angle measurements, adsorption measurements, localized electrochemical impedance spectroscopy (LEIS) measurements, and X-ray photoelectron spectroscopy (XPS) analyses. The results showed that K2FeO4 strongly depressed arsenopyrite in a pH range of 4—11, and the flotation separation of chalcopyrite from arsenopyrite could be realized in the presence of 5×10—4 mol/L K2FeO4 and 5×10—5 mol/L PEX at pH 8 or 10. In the presence of K2FeO4 and PEX, the contact angle and the xanthate adsorption capacity of arsenopyrite decreased significantly. LEIS measurements showed that the addition of ferrate could significantly increase the impedance of the arsenopyrite surface. XPS analyses further confirmed that ferrate accelerated the oxidation of arsenopyrite surface.

Measuring brain beats: Cardiac-aligned fast functional magnetic resonance imaging signals.

Blood and cerebrospinal fluid (CSF) pulse and flow throughout the brain, driven by the cardiac cycle. These fluid dynamics, which are essential to healthy brain function, are characterized by several noninvasive magnetic resonance imaging (MRI) methods. Recent developments in fast MRI, specifically simultaneous multislice acquisition methods, provide a new opportunity to rapidly and broadly assess cardiac-driven flow, including CSF spaces, surface vessels and parenchymal vessels. We use these techniques to assess blood and CSF flow dynamics in brief (3.5min) scans on a conventional 3T MRI scanner in five subjects. Cardiac pulses are measured with a photoplethysmography (PPG) on the index finger, along with functional MRI (fMRI) signals in the brain. We, retrospectively, align the fMRI signals to the heartbeat. Highly reliable cardiac-gated fMRI temporal signals are observed in CSF and blood on the timescale of one heartbeat (test-retest reliability within subjects R2 > 50%). In blood vessels, a local minimum is observed following systole. In CSF spaces, the ventricles and subarachnoid spaces have a local maximum following systole instead. Slower resting-state scans with slice timing, retrospectively, aligned to the cardiac pulse, reveal similar cardiac-gated responses. The cardiac-gated measurements estimate the amplitude and phase of fMRI pulsations in the CSF relative to those in the arteries, an estimate of the local intracranial impedance. Cardiac aligned fMRI signals can provide new insights about fluid dynamics or diagnostics for diseases where these dynamics are important.

Electrochemical Corrosion Behavior of CrFeCoNi and CrMnFeCoNi Coatings in Salt Solution

CrFeCoNi and CrMnFeCoNi coatings were prepared by laser remelting method. The grain boundary characteristics distribution of both coatings was investigated by electron backscattered diffraction technique. The results showed that the CrFeCoNi coating exhibited higher fraction of low angle grain boundaries and Σ3 boundaries compared to the CrMnFeCoNi coating. The corrosion properties of the CrFeCoNi and CrMnFeCoNi coatings in 3.5 wt% NaCl solution were identified by electrochemical method and localized electrochemical impedance spectroscopy technique. The results indicated that the CrFeCoNi coating had a higher corrosion resistance than the CrMnFeCoNi coating. The better corrosion resistance of the CrFeCoNi coating could be attributed to the high fraction of Σ3 boundaries and low fraction of the high angle boundaries.

Combined contact force and local impedance dynamics during repeat atrial fibrillation catheter ablation.

Background: Optimal lesion formation during catheter-based radiofrequency current (RFC) ablation depends on electro-mechanical tip-tissue coupling measurable via contact force (CF) and local impedance (LI) monitoring. We aimed to investigate CF and LI dynamics in patients with previous atrial fibrillation (AF) ablation who frequently present with heterogenous arrhythmia substrate. Methods: Data from consecutive patients presenting for repeat AF or atrial tachycardia ablation using a novel open-irrigated single-tip ablation catheter were studied. RFC applications were investigated regarding CF, LI and the maximum LI drop (∆LI) for evaluation of ablation efficacy. ∆LI > 20 Ω was defined as a successful RFC application. Results: A total of 730 RFC applications in 20 patients were analyzed. Baseline CF was not associated with baseline LI (R = 0.06, p = 0.17). A mean CF < 8 g during ablation resulted in lower ∆LI (<8 g: 13 Ω vs. ≥ 8 g: 16 Ω, p < 0.001). Baseline LI showed a better correlation with ∆LI (R = 0.35, p < 0.001) compared to mean CF (R = 0.17, p < 0.001). Mean CF correlated better with ∆LI in regions of low (R = 0.31, p < 0.001) compared to high (R = 0.21, p = 0.02) and intermediate voltage (R = 0.17, p = 0.004). Combined CF and baseline LI predicted ∆LI > 20 Ω (area under the receiver operating characteristic curve (AUC) 0.75) better compared to baseline LI (AUC 0.72), mean CF (AUC 0.60), force-time integral (AUC 0.59) and local bipolar voltage (0.55). Conclusion: Combination of CF and LI may aid monitoring real-time catheter-tissue electro-mechanical coupling and lesion formation within heterogenous atrial arrhythmia substrate in patients with repeat AF or atrial tachycardia ablation.

Time dependency in the radiofrequency lesion formation for a local impedance guided catheter in an ex vivo experimental model.

The local impedance (LI) is an emerging technology that monitors tissue-catheter coupling during radiofrequency (RF) ablation. The relationships between the LI, RF delivery time, and lesion formation remain unclear. Using an LI-enabled RF catheter in an ex vivo experimental model, RF lesions were created combined with various steps in the power (40 and 50 W), CF (10g, 30 g, and 50 g), and time (10s, 20s, 30s, 40s, 50s, and 60s at 40 W and 5s, 10s, 20s, 30s, 40s, 50s, and 60s at 50 W). The correlations between the LI drop, lesion size, and RF delivery time were evaluated. The rate of change in the time-dependent gain in the LI, depth, and diameter and the time to reach 90% decay of the peak dY/dT (time to 90% decay) were assessed. The correlation between the LI drop and ablation time revealed non-linear changes. The time to a 90% decay in the LI drop differed depending on the RF ablation setting and was always shorter with the 50 W setting than 40 W setting. The LI drop always correlated with the lesion formation under all ablation power settings. Deeper or wider lesions were predominantly created within the time to 90% decay of the LI drop. The LI drop was useful for predicting lesion sizes. Deeper or wider lesions cannot be obtained with a longer ablation than the 90% decay time of the LI drop. A shorter ablation than the 90% decay time of the LI drop would be preferable for an effective ablation.

Local Impedance Measurement by Direct Detection of Oscillating Electrostatic Potential Using Kelvin Probe Force Microscopy

Local Impedance Measurement by Direct Detection of Oscillating Electrostatic Potential Using Kelvin Probe Force Microscopy

Limitations of Baseline Impedance, Impedance Drop and Current for Radiofrequency Catheter Ablation Monitoring: Insights from In silico Modeling.

Background: Baseline impedance, radiofrequency current, and impedance drop during radiofrequency catheter ablation are thought to predict effective lesion formation. However, quantifying the contributions of local versus remote impedances provides insights into the limitations of indices using those parameters. Methods: An in silico model of left atrial radiofrequency catheter ablation was used based on human thoracic measurements and solved for (1) initial impedance (Z), (2) percentage of radiofrequency power delivered to the myocardium and blood (3) total radiofrequency current, (4) impedance drop during heating, and (5) lesion size after a 25 W–30 s ablation. Remote impedance was modeled by varying the mixing ratio between skeletal muscle and fat. Local impedance was modeled by varying insertion depth of the electrode (ID). Results: Increasing the remote impedance led to increased baseline impedance, lower system current delivery, and reduced lesion size. For ID = 0.5 mm, Z ranged from 115 to 132 Ω when fat percentage varied from 20 to 80%, resulting in a decrease in the RF current from 472 to 347 mA and a slight decrease in lesion size from 5.6 to 5.1 mm in depth, and from 9.2 to 8.0 mm in maximum width. In contrast, increasing the local impedance led to lower system current but larger lesions. For a 50% fat–muscle mixture, Z ranged from 118 to 138 Ω when ID varied from 0.3 to 1.9 mm, resulting in a decrease in the RF current from 463 to 443 mA and an increase in lesion size, from 5.2 up to 7.5 mm in depth, and from 8.4 up to 11.6 mm in maximum width. In cases of nearly identical Z but different contributions of local and remote impedance, markedly different lesions sizes were observed despite only small differences in RF current. Impedance drop better predicted lesion size (R2 > 0.93) than RF current (R2 < 0.1). Conclusions: Identical baseline impedances and observed RF currents can lead to markedly different lesion sizes with different relative contributions of local and remote impedances to the electrical circuit. These results provide mechanistic insights into the advantage of measuring local impedance and identifies potential limitations of indices incorporating baseline impedance or current to predict lesion quality.