Interelectrode Impedance Research Articles

Characterising Skin Electrical Impedance Using Tape Stripping Methods: A Bioelectrical Study of a Porcine Model.

Background Recent advancements in ultra-low power electronics and wireless devices have facilitated the widespread adoption of wearable technology for fitness and health monitoring, paving the way for personalized medicine. Microneedle-based devices, comprising small epidermal patches that penetrate the skin's stratum corneum to potentially access biomarkers in the extracellular fluid of the viable epidermis, represent a promising innovation in this field. Objectives This project aimed to develop and validate a novel method to evaluate microneedle engagement in the skin in real-time. To our knowledge, there are no studies published to date that have characterized the electrical impedance of stratum corneum and epidermis using the tape stripping method to selectively remove cell layers. Additionally, no studies have been published comparing the electrical impedance of fresh to frozen-thawed porcine skin. The objective of this study was to develop and validate a novel method to evaluate microneedle engagement in skin, in real-time, that does not require processing of the tissue. Methods A tape stripping technique was employed to selectively remove the stratum corneum from fresh and frozen-thawed porcine skin samples which were then electrically characterized using an excitation frequency of 5 kHz with a peak Voltage of 1 V. Results This study demonstrated a mean impedance reduction of 97.08 ± 1.3 % for fresh porcine skin, and 98.04 ± 0.3 % for frozen-thawed porcine skin when transitioning from the surface stratum corneum to the viable epidermis. The correlation between the reduction of impedance and the number of tape strips across all 18 test sites was significant (r = 0.98, p < 0.00001). However, comparing the skin impedance of the fresh and frozen-thawed specimens showed poor equivalence, with the frozen-thawed sites approximately 5.5 times the impedance of the fresh sites before any tape stripping, and 4.19 times greater after 30 tape strips. Conclusions These findings suggest that monitoring for an interelectrode impedance decrease of greater than 95% between two projections of a microneedle device could provide a rapid and effective evaluation of skin engagement, crucial for advancing the development and clinical application of microneedle-based technologies in personalized medicine. The study also underscores the impact of the freeze-thaw process on the mechanical and electrical properties of skin, which is crucial for standardizing testing protocols.

Long-term impedance dynamics of cochlear implant electrodes in children

Background. Nowadays in Ukraine, there are about 3 thousand cochlear implant users, and their number is constantly increasing. The internal part of the implant remains in the cochlea throughout the patient’s life, but current data on the state of the electrodes in the long-term period are contradictory. The purpose was to study the impedance dynamics of cochlear implant electrodes during 5 years after surgery in children. Materials and methods. A retrospective study of 58 children with deafness after cochlear implantation was conducted. The changes in the interelectrode impedance and the relationship between them in the different parts of the electrode were evaluated and analyzed 1, 2, 3, and 5 years after the start of electrical stimulation. Results. At 1 year after the connection of the speech processor, an increase in the impedance was recorded in the basal part of the electrode (9–12 channels) relative to the medial and apical part of the cochlea. Over the next year, according to the electric field telemetry data, a significant (p &lt; 0.05) downward trend was noted in the resistance in the basal part of the implant (9–12 electrodes). Within 2–5 years, a gradual decrease in the impedance in the medial and apical parts of the electrode occurred without statistically significant differences. In 29.3 % of cases, there was a tendency to a gradual increase in the impedance on 11–12 electrodes within 3–5 years after surgery. In another 8 patients (13.8 %), a critical increase in the impedance (&gt; 15 kilohm) was detected on one of the contacts in the basal part of the electrode, which required their disconnection or correcting the settings of the speech processor. Conclusions. Regular monitoring of electrode impedance and electrical stimulation levels is recommended, especially during the first 2 years of implant use. This is necessary to improve the performance of the implant, to determine the most comfortable levels and thresholds of volume more accurately, which will improve the sound perception in children after cochlear implantation.

An electrode-impedance-aware neurostimulator IC that achieves low-power consumption and fast charge balance

Implantable neural stimulation is becoming increasingly popular for treating neurologically impaired patients, restoring neural functions which would otherwise be lost due to diseases or injuries. The charge balance of the stimulus pulses is of paramount importance for the long-term safety of the electrode-tissue interface. This paper presents a novel neurostimulator integrated circuit in which two novel charge balancing schemes are proposed. One is based on acquiring the access resistance part (RS) of the inter-electrode impedance. Thanks to its adaptive anodic phase, the RS-based charge balance circuit does not require an additional discharge phase, achieving faster charge balance than most existing stimulator ICs. The other scheme is based on acquiring the double-layer capacitance part (CDL) of the inter-electrode impedance and the entire charge balancing process (inc. monitoring, computation and compensation) is performed in the analog domain. This is in sharp contrast to the existing electrode-impedance-aware charge balancing schemes which require ADCs and compute the net charge in the digital domain. Hence the new impedance-aware charge-balancing scheme is faster and more power friendly. The impedance-aware stimulator ASIC has been implemented using X-FAB’s 180-nm CMOS process. The post-layout simulation results suggest a good charge balance is achieved as the voltage deviation from the electrode offset voltage on the electrode after the charge compensation reduces to 2.64 mV and –1.39 mV under the RS-based and CDL-based charge balancing schemes, respectively. The additional power overhead due to the proposed CDL-based charge balancer circuit is 2.46 μW at a stimulation rate of 400 Hz.

Research on micro-EDM discharge state detection technology based on inter-electrode impedance variation characteristics

To address the difficulty in detecting the discharge state of a narrow pulse width and small duty cycle pulse, in this study, we investigate the variation characteristics of the inter-electrode impedance in the micro-EDM process and propose a detection method to distinguish different discharge states in micro-EDM based on the change in electrical signal caused by the change characteristics. The influence of the pulse width and duty cycle on the quality of micro-EDM is summarised. The results show that the workpiece surface machining quality can be considerably improved by compressing the pulse width of the pulse power supply. A micro-EDM discharge state detection system based on the variation characteristics of the inter-electrode impedance is designed, and experiments verify the detection method. The control strategy of the discharge state detection system is analysed, and a control strategy based on the forward direction and discharge state is proposed. The machining effect of the control strategy is tested through a trial-machining experiment. According to the machining control strategy, the control signal is outputted, which can realise a stable and efficient micro-EDM process.

Аудиологические особенности ведения пациентов, перенесших хирургические вмешательства на структурах среднего уха, во время использования системы кохлеарной имплантации

This article presents a clinical case of monitoring a patient with chronic bilateral sensorineural hearing loss and chronic otitis media on the same side, using a cochlear implant system for 12 years. The complexity of managing this patient, which required a multidisciplinary approach to their resolution, is described. The errors of the patient's auditory-speech rehabilitation are presented and analyzed. This experience can be used in the practice of ENT doctors and audiologists. This article emphasizes the need for hard monitoring by an audiologist of persons who have undergone cochlear implantation, in accordance with the terms specified in the clinical guidelines. In addition, the audiologist should regularly evaluate the parameters of the cochlear implantation system: interelectrode impedance, neural response measurement, which is especially important if there is a history of chronic otitis media or previous surgical interventions on the structures of the middle ear, on the side of the cochlear implant. If there are doubts about adequate sound perception, it is necessary to perform computed tomography of the pyramids of the temporal bones with an assessment of the localization of the elements of the cochlear implant.

Investigation of Terahertz 3D EM Simulation on Device Modeling and A New InP HBT Dispersive Inter-Electrode Impedance Extraction Method

In this paper, a new 3-D electromagnetic (EM) simulation approach for heterojunction bipolar transistor (HBT) parameter extraction in terahertz band is presented. We introduce an inter-electrode impedance equivalent-circuit model with the concept of dispersive parameters and a more rigorous 3-D EM simulation parameter extraction method to avoid serious discrepancies between the simulated EM field distribution and the real EM field distribution of the device. Terahertz parasitic effects, including the EM field discretization and multi-finger device field sharing, are observed. Compared with the previous 3-D EM simulation-assisted model, the new model in this paper demonstrates better results for multi-finger indium phosphide HBTs.

High and dry? Comparing active dry EEG electrodes to active and passive wet electrodes.

Dry electrodes are becoming popular for both lab-based and consumer-level electrophysiological-recording technologies because they better afford the ability to move traditional lab-based research into the real world. It is unclear, however, how dry electrodes compare in data quality to traditional electrodes. The current study compared three EEG electrode types: (a) passive-wet electrodes with no onboard amplification, (b) actively amplified, wet electrodes with moderate impedance levels, and low impedance levels, and (c) active-dry electrodes with very high impedance. Participants completed a classic P3 auditory oddball task to elicit characteristic EEG signatures and event-related potentials (ERPs). Across the three electrode types, we compared single-trial noise, average ERPs, scalp topographies, ERP noise, and ERP statistical power as a function of number of trials. We extended past work showing active electrodes' insensitivity to moderate levels of interelectrode impedance when compared to passive electrodes in the same amplifier. Importantly, the new dry electrode system could reliably measure EEG spectra and ERP components comparable to traditional electrode types. As expected, however, dry active electrodes with very high interelectrode impedance exhibited marked increases in single-trial and average noise levels, which decreased statistical power, requiring more trials to detect significant effects. This power decrease must be considered as a trade-off with the ease of application and long-term use. The current results help set constraints on experimental design with novel dry electrodes, and provide important evidence needed to measure brain activity in novel settings and situations.

No Effect of 2 mA Anodal tDCS Over the M1 on Performance and Practice Effect on Grooved Pegboard Test and Trail Making Test B

Previous studies suggest that transcranial direct current stimulation (tDCS) can facilitate motor performance and learning. In this double-blind experiment, 60 healthy human subjects (29 females) were randomized into three groups (active tDCS, sham tDCS, and no-treatment control group) in order to investigate the effect of a 20 min session of 2 mA tDCS over the motor cortex contralateral to the dominant hand on practice effect and performance on the Grooved Pegboard Test (GPT) and Trail Making Test (TMT). Performance was operationalized as the time to complete the tests before, during, and after stimulation. The practice effect was termed as the difference in time to complete the tests from pretest to post-test. Data on body mass index (BMI), head circumference, sleep status, interelectrode impedance, and caffeine and nicotine use were sampled to control for the influence of individual differences on the effect of tDCS. Adverse effects were registered using a standardized form. The results indicated no effect of tDCS on performance and practice effects on the GPT and TMT. For all groups, BMI was a predictor for a practice effect on the TMT. In the active tDCS group, high caffeine intake and low impedance predicted a practice effect on the GPT for the dominant hand. The present results suggest that impedance levels in tDCS studies should be routinely reported in future studies, as it might not only provide valuable information on the efficacy of the blinding conditions and participant discomfort, but also correlate with individual differences that are relevant to the outcome of the stimulation.

Accelerated soak performance of BPDA-PPD polyimide for implantable MEAs

To mature toward real-world applications biomedical sensors should maintain long-term functionality under relatively harsh in-vivo conditions. Microelectrode arrays (MEAs) rely on thin films, such as parylene C or polyimide, the water-barrier of which is crucial for the long-term stability. This work reports on the high water-barrier of BPDA-PPD polyimide. This material was spin-coated on interdigitated microstructures and immersed in saline@60°C for 170 days. The interdigitated impedance remained stable, higher than parylene C. Curing was crucial for the water-barrier of this polyimide: only long-cured microelectrode arrays remained unchanged in their inter-electrode impedances as compared to short-cured devices when soaked in saline@60°C for 140 days. Subjecting BPDA-PPD polyimide foils to water-vapour penetration revealed higher performance than parylene C. These results disclose BPDA-PPD polyimide as a promising insulation for implantable MEAs.

An elusive brain death diagnosis: You can't get there from here.

I read with great interest the case report by Story and Winter.1 Their patient was brain dead clinically but confirmatory testing in the form of CT angiography and EEG was requested, which failed to document whole-brain death. One might argue that they would not have encountered this medical, ethical, and legal quandary if the concept of brain stem death was adopted and accepted universally as opposed to whole-brain death, which is the currently accepted criterion in the United States. Electrocerebral inactivity or electrocerebral silence in a brain death EEG is defined as no EEG activity over 2 uV when recording from scalp electrode pairs 10 or more cm apart with interelectrode impedances under 10,000 Ohms (10 KOhms) but over 100 Ohms. It is a well-known fact that pockets of brain activity may persist in a patient who is clinically (all brain stem reflexes absent and apnea test positive) brain dead. These islands of brain activity may yield a …

Atrial fibrillation as a consequence of tuberculous pericardial effusion

in the current study for low-energy internal cardioversion of AF. Compared to the conventional lead configurations, the proposed electrode placement strategy achieves lower inter-electrode impedance and delivers more intense electric field thorough atrial myocardium while only having minimum amounts of myocardium subject to damage. We would like to thank Minnesota Supercomputing Institute for providing the computation resources. The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [16].

947 Evaluation of Paroxysmal Activity on Aeeg and Eeg Tracings During Cool Cap Treatment of Asphyxiated Newborns with Hie

Aims: To evaluate the incidence, type and duration of paroxysmal activity on aEEG and simultaneous EEG activity during therapeutic cranio-cerebral hypothermia in term severely and moderately asphyxiated newborns. Methods: aEEG tracings of 23 newborn infants with severe and moderate HIE undergoing therapeutic cranio-cerebral hypothermia were studied. Singlechannel aEEG together with regular EEG were obtained with OLYMPIC GFM 6000 monitor. Bifrontal placement of electrodes was used. An interelectrode impedance was maintained at the level of 5 kOhm. aEEG was monitored continuously from the moment of diagnosis of HIE to the 15-th day of life. All the aEEG tracings during the entire period of aEEG monitoring were reviewed together with regular EEG tracings in zones of concern. Results: There were “saw tooth” patterns or episodes of elevation of the lower margin of band of aEEG activity detected in the tracings of all 23 babies undergoing cool cap treatment with simultaneous paroxysmal activity on EEG. In all the patients these encephalographic changes were treated with phenobarbital. In 14 cases aEEG seizures were observed together with clinically apparent seizures, at least before cooling. In majority of patients aEEG seizures were observed throughout and beyond the period of head cooling despite the phenobarbital treatment. Conclusions: Electroencephalographic seizures are common in asphyxiated newborn undergoing neuroprotective hypothermia, in many cases without clinical manifestations. aEEG monitoring may be helpful in evaluation of CNS condition and indicates that the anticonvulsive treatment probably needs to be enhanced during cranio-cerebral hypothermia.

Ordinary surface ECG electrodes accurately reflect cardiac electric activity at hypothermia

It has been claimed that needle electrodes can be a useful means to detect weak ECG signals in cases of accidental hypothermia. Four pigs were cooled by immersion in ice water, followed by direct cooling of the blood through an extracorporeal circulation system until the core temperature was lowered to 12 degrees C and surface-measured ECG indicated asystole. Following cooling, the pigs were rewarmed and weaned from extracorporeal circulation if possible. ECG and interelectrode impedance were measured between surface electrodes, needle electrodes and electrodes sewn to the epicardium during the cooling and rewarming procedure. Needle and surface electrodes showed exactly the same ECG whatever the temperature of the skin or the core was. The impedance varied only slightly with temperature and could not explain the disappearance of surface ECG. The QRS wave amplitude showed the greatest sensitivity to temperature, disappearing completely before the P-wave disappeared. The P-wave showed the least sensitivity, and was the last wave to disappear, indicating that the sinus node is the most resistant part of the heart to cooling. Between 19 and 17 degrees C, a commercial monitor indicated asystole although P-waves could be seen in the ECG and atrial contractions could be visually observed on the heart. Surface electrodes had a similar high accuracy to indicate electric activity as needle electrodes. Higher amplification and reduction of the timebase made it possible to detect ECG in a situation where asystole was indicated by commercial monitors.

Optimal Transvenous Coil Position on Active-can Single-coil ICD Defibrillation Efficacy: A Simulation Study

The implantable cardioverter defibrillator with an active can and a single coil lead is effective in treating ventricular fibrillation, but the lead placement associated with the high defibrillation efficacy is still controversial and remains largely empirical. In this study, an anatomically realistic finite difference model of the thorax was developed based on MRI cross-sectional images of a human thorax to examine the effect of transvenous coil placement on defibrillation efficacy. Four electrode configurations with the coil was placed, respectively, in the right ventricular (RV) apex, in the middle of RV cavity, along the free wall in RV, or along the septal wall in RV, were simulated and their defibrillation efficacies were evaluated based on a set of metrics including voltage defibrillation threshold, current defibrillation threshold, interelectrode impedance, potential gradient distribution uniformity, current density distribution, and myocardium damage. It was found that the optimal electrode configuration is to position the coil in the middle of the RV cavity. The results were compared with the results from a simplified thoracic model. The comparison indicates that for a given electrode configuration a simplified representation of the thorax may overestimate defibrillation efficacy.

Bioimpedance skin condition monitoring during therapeutic and cosmetic procedures

Engineering and technological problems of bioimpedance skin surface mapping are considered. A typical design of a device based on a PIC 16F microcontroller is suggested. It includes a keyboard, LCD indicator, probing current generator with programmed frequency tuning, and units for probing current monitoring and bioimpedance measurement. The electrode matrix of the device is constructed using nanotechnology. A microcontroller-controlled multiplexor provides scanning of interelectrode impedance, which makes it possible to obtain the impedance image of the skin surface under the electrode matrix. The microcontroller controls the probing signal generator frequency and allows layer-by-layer images of skin under the electrode matrix to be obtained. This makes it possible to use reconstruction tomography methods for analysis and monitoring of the skin condition during therapeutic and cosmetic procedures.

The neuropsychological basis of the Chinese mental lexicon: An ERP study using LORETA

Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, Graduate school of CAS, Beijing 100101, ChinaAccepted 6 July 2006IntroductionThe aim of this study was to investigate the event-related potentialsinvolved in the processing of orthography, phonology and meaning duringChinese character recognition. Event-related potentials (ERPs) are thesummed activity of synchronized post-synaptic EEG potentials recordedon the scalp. ERPs can illuminate the temporal dynamics of the cognitiveactivity underlying lexical access and semantic integration in word recog-nition because of excellent temporal resolution (Curran, Tucker, & Kutas,1993). The neural sources of each ERP component can also be localizedwith low-resolution electromagnetic tomography (LORETA). Topo-graphic mapping is a means to display electrical activity in the brain onthe basis of multi-channel EEG recordings using temporal resolution thatis recorded in milliseconds. LORETA is an algorithm that solves theinverse problem of EEG and is performed on averaged ERPs to isolatethe spatial distribution of the components by finding the smoothest ofall possible solutions consistent with the scalp distribution (Pascual-Mar-qui, Michel, & Lehmann, 1994). The LORETA procedure calculates cur-rent densities in 2394 pre-selected brain voxels based on the scalpdistribution of potentials. The spatial reference used for this procedureis the Talairach brain atlas (Talairach & Tournoux, 1988). The spatial res-olution is 7 mm and the maximal error is within 10 mm (Pascual-Marqui,1999). Topographic mapping is shown as a distribution of colour-codedvalues on the head surface. The head surface is used to associate surfacenormal orientations to electrodes and also to compute radial and tangen-tial current density components. The distribution of topographic valuescan be interpreted as the distribution of the local radial current densityfrom just underneath the skull layer. Thus, topographic mapping givesan approximate image of cortical processes. If positive and negative topo-graphic values of high magnitude are found in any one scalp area, it can beconcluded that superficial brain activity occurred under this area (Pascual-Marqui, 1999). Very few studies have used EEG methods to examine Chi-nese character recognition (Liu, Perfetti, & Hart, 2003; Valdes-Sosa et al.,1993). All models of lexical access in Chinese (e.g. Perfetti, Liu, & Tan,2005) assume three independent cognitive stages—orthographic, phono-logical and semantic. In the present study, we used LORETA to examinetopographic values associated with these cognitive processing stages thatwe assume are necessary in character identification. We predicted thattasks designed toisolate theseprocesses would activate differentERP com-ponents and brain regions for orthographic, phonological and semanticprocessing.Participants and methodsTwenty right-handed native Chinese speaking students from the Agri-cultural University of China (10 males and 10 females) aged between 20and 23 years (Mean=22, SD=1.12) with no history of neurological or psy-chiatric illness, drug or alcohol abuse, current medication and normal orcorrected-to-normal vision. In the first task, participants performed anorthographic judgement task (OJT) requiring a decision about visual sim-ilarity of a pair of characters. In the second task, participants performed ahomophone judgement task (HJT) requiring a decision about the phono-logical similarity of a pair of characters. In the third task, participants per-formed a synonym judgement task (SJT) requiring a decision about themeaning of a pair of characters. Subjects were seated in a comfortablechair in a darkened, sound-attenuated room. EEG was recorded from64 sites using tin electrodes mounted in an elastic cap (NeuroScan) withreferences on the left and right mastoids. The vertical electrooculagram(EOG) was recorded with electrodes above and below the left eye. Inter-electrode impedance was maintained below 5 kX. EEG and EOG wereamplified using a 0.3–40 Hz band-pass and continuously sampled at512 Hz/channel for off-line analysis. Trials with EOG artefacts (meanEOG voltage > ± 100 lV) and artefacts due to amplifier clipping, burstsof electromyographic activity, or peak-to-peak deflection exceeding±100 lV were excluded from averaging.Results and conclusionsTwo ERP components (N1 and N400) were quantified as peak ampli-tude and latency and subjected to repeated measures ANOVA. There wasan effect of hemisphere on the amplitude of N1 F(1,30) = 16.73, p .05). Post hoc analyses using LSD test for multiple compar-ison showed a significant difference between tasks on the amplitude ofN400 F(1,30) = 62.92, p < 0.001 but not N1. Comparisons showed signif-icantly lower amplitude and significantly later N400 for semantic thandoi:10.1016/j.bandl.2006.06.109

P‐113: Rigorous Calculation of Pixel and Inter‐electrode Impedances of TFT‐LCDs Using three‐dimensional Simulation

AbstractWe have rigorously calculated for the first time all the inter‐electrode and the pixel impedances of thin‐film transistor liquid crystal displays using the total electrostatic energy and the total power dissipation inside a liquid crystal cell. The electrostatic energy and the power dissipation were obtained from the three‐dimensional profiles of the potential distribution and the molecular director profiles. The effects of the lateral fields generated by multiple electrodes of finite sizes were taken into account in the simulation. As a result, we confirmed that the pixel capacitance and the pixel resistance obtained from the three‐dimensional simulation are about 40% larger and about 15% smaller than those obtained from the conventional approach.

Electrical circuit model for thermionic converters

An electrical circuit model which accounts for the internal electrical characteristics of a real vacuum thermionic converter (VTC) is presented. Using this model, the expected theoretical behavior of the VTC was determined in its equilibrium state. Besides this, its dynamic behavior was found when the VTC was operated under transient conditions. It is shown that the theoretical asymptotic tendency defined by the electrical model approaches the experimental behavior when an adequate choice is made for fitting the employed values of the internal elements in the circuit model. In this study, we also included theoretical results obtained by the electrical model by variation of the temperature and work function of the emitter and also by variation of the interelectrode impedance.

Effect of Electrode Position and Gel-Application Technique on Predicted Transcardiac Current During Transthoracic Defibrillation

Study objective: In transthoracic defibrillation, the American Heart Association (AHA) recommends wide separation of electrodes and avoidance of gel smearing between electrodes. Few data support this recommendation. Our objective was to determine the importance of electrode placement and gel-application technique on transcardiac defibrillation current and the effect of changes caused by postexercise vasodilation and sweating. Methods: Our subjects were 10 normal adults, 5 men and 5 women, who ranged in age from 22 to 48 years. We determined interelectrode impedance (Z) using a validated test-pulse method that does not require shock delivery. Electrode placement/gel-application techniques were varied among four types: (1) AHA-recommended technique (apex-to-anterior electrode placement, no smearing of gel between electrodes); (2) parasternal-to-anterior placement, electrodes within 2 cm of each other, no smearing of gel between electrodes; (3) parasternal-to-anterior placement, electrodes within 2 cm of each other with smearing of gel between electrodes (worst-case scenario); and (4) apex-to-anterior placement, smearing of gel between electrodes. To assess the effect of cutaneous vasodilation and sweating on interelectrode impedance, we repeated these measurements after the subjects performed 12 to 18 minutes of treadmill exercise. The ratio of predicted transcardiac current of the AHA technique to that of the nonstandard technique was estimated with this formula: √Z, non-standard technique ÷ √Z, AHA technique. Results: Resting interelectrode impedance declined 38% from 58±10.3 Ω (AHA-recommended technique) to 36±7.6 Ω (electrode paddles adjacent, gel smeared between) (P<.01). Predicted transcardiac current ratio was reduced to .78±.09 ( P <.01), a 22% reduction. We noted no change in the results after exercise. Conclusion: Adjacent placement of electrodes and smearing of gel between electrodes creates a low-impedance pathway along the chest wall, which shunts current away from the heart. Thus improper application of electrodes and gel substantially degrades transcardiac current and may result in failed defibrillation. Sweating and vasodilation did not cause a similar problem. [Caterine MR, Yoerger DM, Spencer KT, Miller SG, Kerber RE: Effect of electrode position and gel-application technique on predicted transcardiac current during transthoracic defibrillation. Ann Emerg Med May 1997; 29:588-595.]

Simulated internal defibrillation in humans using an anatomically realistic three-dimensional finite element model of the thorax.

Determination of the optimal electrode configuration during implantable cardioverter defibrillator (ICD) implantation remains largely an empirical process. This study investigated the feasibility of using a finite element model of the thorax to predict clinical defibrillation metrics for internal defibrillation in humans. Computed defibrillation metrics from simulations of three common electrode configurations with a monophasic waveform were compared to pooled metrics for similar electrode and waveform configurations reported in humans. A three-dimensional finite element model was constructed from CT cross-sections of a human thorax. Myocardial current density distributions for three electrode configurations (epicardial patches, right ventricular [RV] coil/superior vena cava [SVC] coil, RV coil/SVC coil/subcutaneous patch) and a truncated monophasic pulse with a 65% tilt were simulated. Assuming an inexcitability threshold of 25 mA/cm2 (10 V/cm) and a 75% critical mass criterion for successful defibrillation, defibrillation metrics (interelectrode impedance, defibrillation threshold current, voltage, and energy) were calculated for each electrode simulation. Values of these metrics were within 1 SD of sample-size weighted means for the corresponding metrics determined for similar electrode configurations and waveforms reported in human clinical studies. Simulated myocardial current density distributions suggest that variations in current distribution and uniformity partially explain differences in defibrillation energy requirements between electrode configurations. Anatomically realistic three-dimensional finite element modeling can closely simulate internal defibrillation in humans. This may prove useful for characterizing patient-specific factors that influence clinically relevant properties of current density distributions and defibrillation energy requirements of various ICD electrode configurations.