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At least 37 records · Page 2Linked to original sources
PubMed2005

A trial of self-adhesive patch electrodes and hand-held paddle electrodes for external cardioversion of atrial fibrillation (MOBIPAPA).

AIMS: External electrical cardioversion is the method of choice to terminate persistent atrial fibrillation. Whether the type of shock electrode affects cardioversion success is not known. We tested whether hand-held steel electrodes improve cardioversion outcome with monophasic or biphasic shocks when compared with adhesive patch electrodes. METHODS AND RESULTS: Two hundred and one consecutive patients with persistent atrial fibrillation (147 male, mean age 63+/-1 years, duration of atrial fibrillation 6.3+/-1 months) were randomly assigned to cardioversion using either a sinusoidal monophasic or a truncated exponential biphasic shock wave form. The first half of patients were cardioverted using adhesive patch electrodes, the second half using hand-held steel paddle electrodes, and all patients using an anterior-posterior electrode position. Paddle electrodes successfully cardioverted 100/104 patients (96%) and patch electrodes 85/97 patients (88%, P=0.04). This effect was comparable to that of biphasic shocks: biphasic shocks cardioverted 102/104 patients (98%) and monophasic shocks 83/97 patients (86%, P=0.001). A beneficial effect of paddle electrodes was observed for both shock wave forms. After cross-over from an ineffective monophasic to a biphasic shock, cardioversion was successful in 198/201 (98.5%) patients. Unsuccessful cardioversion after cross-over (3/201 patients) only occurred with patch electrodes (P=0.07). CONCLUSION: Hand-held paddle electrodes increase success of external cardioversion of atrial fibrillation in this trial. This increase is of similar magnitude as the increase in cardioversion success achieved with biphasic shocks. A combination of biphasic shocks, paddle electrodes, and an anterior-posterior electrode position renders outcome of external cardioversion almost always successful (104/104 patients in this trial).

Atrial Fibrillation↗
PubMed1992

[Temperature distribution and geometry of the electrodes in RF interstitial hyperthermia using circular and interstitial electrodes].

To evaluate the feasibility of clinical application of a newly developed interstitial hyperthermia system, which consists of an 8 MHz radiofrequency generator, interstitial needle electrodes, and a superficial circular electrode, we conducted preclinical experiments using an agar phantom and VX-2 carcinoma in the rabbit. In the experiment with an agar phantom, four 4 cm needle electrodes were placed in a square array at intervals of 1.0, 1.5, and 2.0 cm. Thermography demonstrated homogeneous temperature distribution at electrode intervals of 1.0 and 1.5 cm, but hot spots around the electrodes at an interval of 2.0 cm. When electrode deviation was less than 8 degrees from the parallel plane, no temperature deviation was observed. Using two 2 cm electrodes and two 4 cm electrodes in square array, thermography demonstrated a homogeneous temperature distribution in the area surrounded by the electrodes. Even if the electrodes were located at the periphery of the agar phantom, a homogeneous temperature distribution was obtained in the area surrounded by the electrodes. Using four 4 cm electrodes at intervals of 1.5 cm in VX-2 carcinoma in the rabbit, ideal heating was obtained: 42 degrees C at the periphery of the tumor and 43 degrees C at the center. These data suggest that the newly developed interstitial hyperthermia apparatus provides homogeneous heat distribution at electrode intervals of 1.5 cm or less and can be used in a Phase I study for deep-seated or superficial tumors.

Animals↗
PubMed1989

[Nonthoracotomy internal defibrillation in dogs using a body surface electrode with a transvenous catheter electrode].

The efficacy of truncated exponential waveform shocks using a cardioverter-defibrillator catheter (Medtronic 6880) and body surface electrodes was examined in comparison with using a RV epicardial patch electrode and a LV epicardial patch electrode in fifteen pentobarbital-anesthetized dogs. The defibrillation thresholds (DFT) for 5 lead configurations were measured by the total energy, peak voltage and peak current: A) a body surface electrode (positioned at the right lateral chest wall) as the anode and a body surface electrode (positioned at the left lateral chest wall) as the cathode; B) a superior vena cava catheter electrode as the anode and a RV apex catheter electrode as the cathode; C1) a body surface electrode (positioned at left anterior chest wall) as the anode and a RV apex catheter electrode as the cathode; C2) a body surface electrode (positioned at the left lateral chest wall) as the anode and a RV apex catheter electrode as the cathode; and D) a RV epicardial patch electrode as the anode and a LV epicardial patch electrode as the cathode. The total energy at DFT for configurations C2 and D was lower than for configurations A, B, and C1, respectively (7.2 +/- 3.1 and 4.7 +/- 2.0 less than 18.9 +/- 3.8, 12.0 +/- 3.8 and 11.2 +/- 2.2 joules; p less than 0.05). The peak voltage at DFT for configurations C2 and D was lower than for configurations A, B, and C1, respectively (463 +/- 70 and 377 +/- 73 less than 767 +/- 85, 585 +/- 117 and 600 +/- 62 volts; P less than 0.05).

Animals↗
PubMed1999

Temperature-controlled radiofrequency ablation of cardiac tissue: an in vitro study of the impact of electrode orientation, electrode tissue contact pressure and external convective cooling.

BACKGROUND: A variety of basic factors such as electrode tip pressure, flow around the electrode and electrode orientation influence lesion size during radiofrequency ablation, but importantly is dependent on the chosen mode of ablation. However, only little information is available for the frequently used temperature-controlled mode. The purpose of the present experimental study was to evaluate the impact during temperature-controlled radiofrequency ablation of three basic factors regarding electrode-tissue contact and convective cooling on lesion size. METHODS AND RESULTS: In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Temperature-controlled ablation at 80 degrees C for 60 s was performed using a 7F 4 mm tip electrode in either perpendicular or parallel contact with the endocardium at a pressure of 10 or 20 g. Increased flow around the electrode was induced by circulating the saline in the tissue bath at a flow-velocity of 0.1 m/s. Lesion volume was determined by cutting lesions in 1 mm thick slices, staining with nitroblue tetrazolium and planimetering. A total of 107 lesions was created. Lesion size was significantly larger for perpendicular electrode orientation compared to parallel for both pressure-settings and both levels of flow around the electrode (p < 0.05). Increased flow around the electrode enlarged lesion size (p < 0.005). Electrode-tissue contact pressure had no significant impact on lesion size. CONCLUSIONS: During temperature-controlled radiofrequency ablation increased external cooling of the electrode tip due to either flow of the surrounding liquid or poor electrode tissue contact, as exemplified by perpendicular versus parallel electrode orientation, increases lesion size significantly. This is in contrast to the impact of these factors during power-controlled ablation due to the lack of increased power-delivery in the latter situation.

Animals↗
PubMed2005

A temporal bone study of insertion trauma and intracochlear position of cochlear implant electrodes. I: Comparison of Nucleus banded and Nucleus Contour electrodes.

In recent years, new designs of cochlear implant electrodes have been introduced in an attempt to improve efficiency and performance by locating stimulation sites closer to spiral ganglion neurons and deeper into the scala tympani. The goal of this study was to document insertion depth, intracochlear position and insertion trauma with the Nucleus Contour electrode and to compare results to those observed with the earlier generation Nucleus banded electrode. For this comparison eight Nuclears banded electrodes and 18 Contour electrodes were implanted in cadaver temporal bones using a realistic surgical exposure. Two experienced cochlear implant surgeons and two otology fellows with specialized training in cochlear implant surgery were selected for the study to represent a range of surgical experience similar to that of surgeons currently performing the procedure throughout the world. Following insertion of the electrodes, specimens were imaged using plain film X-ray, embedded in acrylic resin, cut in radial sections with the electrodes in place, and each cut surface was polished. Insertion depth was measured in digitized X-ray images, and trauma was assessed in each cross-section. The Contour electrode inserted more deeply (mean depth=17.9 mm or 417 degrees ) than the banded electrode (mean depth=15.3 mm or 285 degrees ). The incidence and severity of trauma varied substantially among the temporal bones studied. However, the nature and frequency of injuries observed with the two devices were very similar. The Contour electrode was clearly positioned closer to the modiolus than the banded model, and also appeared easier to use. Based on this difference in position and data from previous studies we conclude that the Contour electrode may provide lower thresholds and improved channel selectivity, but the incidence of trauma remains a problem with the newer design. The relative influences of electrode positioning and neural degeneration that may result from trauma are as yet unclear.

Cadaver↗
PubMed1998

Inverse relationship between electrode size and lesion size during radiofrequency ablation with active electrode cooling.

BACKGROUND: Clinical efficacy has driven the use of larger electrodes (7F, length > or =4 mm) for radiofrequency ablation, which reduces electrogram resolution and causes variability in tissue contact depending on electrode orientation. With active cooling, ablation electrode size may be reduced. The purpose of this study was to examine the effect of electrode length on tissue temperature and lesion size with saline irrigation used for active cooling. METHODS AND RESULTS: In 11 anesthetized dogs, the thigh muscle was exposed and bathed with heparinized canine blood. A 7F ablation catheter with a 2- or 5-mm irrigated tip electrode was positioned perpendicular or parallel to the thigh muscle. Radiofrequency current was delivered at constant voltage (50 V) for 30 seconds during saline irrigation (20 mL/min) to 148 sites. Tissue temperature at depths of 3.5 and 7 mm and lesion size were measured. In the perpendicular electrode-tissue orientation, radiofrequency applications at 50 V with the 2-mm electrode compared with the 5-mm electrode resulted in lower power at 50 V (26 versus 36 W) but higher tissue temperatures, larger lesion depth (8.0 versus 5.4 mm), and greater diameter (12.4 mm versus 8.4 mm). Also, in the parallel orientation, overall power was lower with the 2-mm electrode (25 versus 33 W), but tissue temperatures were higher and lesions were deeper (7.3 versus 6.9 mm). Lesion diameter was similar (11.1 versus 11.3 mm) for both electrodes. CONCLUSIONS: The smaller electrode resulted in transmission of a greater fraction of the radiofrequency power to the tissue and resulted in higher tissue temperature, larger lesions, and lower dependency of lesion size on the electrode orientation.

Animals↗
PubMedDate not supplied

Radio frequency ablation in the rabbit lung using wet electrodes: comparison of monopolar and dual bipolar electrode mode.

OBJECTIVE: To compare the effect of radio frequency ablation (RFA) on the dimensions of radio frequency coagulation necrosis in a rabbit lung using a wet electrode in monopolar mode with that in dual electrode bipolar mode at different infusion rates (15 mm/hr versus 30 ml/hr) and saline concentrations (0.9% normal versus 5.8% hypertonic saline). MATERIALS AND METHODS: Fifty ablation zones (one ablation zone in each rabbit) were produced in 50 rabbits using one or two 16-gauge wet electrodes with a 1-cm active tip. The RFA system used in the monopolar and dual electrode wet bipolar RFA consisted of a 375-kHz generator (Elektrotom HiTT 106, Berchtold, Medizinelektronik, Germany). The power used was 30 watts and the exposure time was 5 minutes. The rabbits were assigned to one of five groups. Group A (n = 10) was infused with 0.9% NaCl used at a rate of 30 ml/hr in a monopolar mode. Groups B (n = 10) and C (n = 10) were infused with 0.9% NaCl at a rate of 15 and 30 ml/hr, respectively in dual electrode bipolar mode; groups D (n = 10) and E (n = 10) were infused with 5.8% NaCl at a rate of 15 and 30 ml/hr, respectively in a dual electrode bipolar mode. The dimensions of the ablation zones in the gross specimens from the groups were compared using one-way analysis of variance by means of the Scheffe test (post-hoc testing). RESULTS: The mean largest diameter of the ablation zones was larger in dual electrode bipolar mode (30.9+/-4.4 mm) than in monopolar mode (22.5+/-3.5 mm). The mean smallest diameter of the ablation zones was larger in dual electrode bipolar mode (22.3+/-2.5 mm) than in monopolar mode (19.5+/-3.5 mm). There were significant differences in the largest and smallest dimension between the monopolar (group A) and dual electrode wet bipolar mode (groups B-E). In dual electrode bipolar mode, the mean largest diameter of the ablation zones was larger at an infusion rate of 15 ml/hr (34.2+/-4.0 mm) than at 30 ml/hr (27.6+/-0.1 mm), and the mean smallest diameter of the ablation zones was larger at an infusion rate of 15 ml/hr (27.2+/-7.5 mm) than at an infusion rate of 30 ml/hr (24+/-2.9 mm). CONCLUSION: Using a wet electrode, dual electrode bipolar RFA can create a larger ablation zone more efficiently than monopolar RFA.

Animals↗
PubMed1991

The importance of the orientation of the electrode plates in recording the external anal sphincter EMG by non-invasive anal plug electrodes.

Two non-invasive anal plug electrodes of similar size have been compared, one with the electrode plates orientated circularly in the anal canal and the other with the plates in the long axis of the anal canal. There was a significant increase in the amplitude in the EMG signals recorded at rest and during squeeze from the external anal sphincter with a longitudinally placed electrode in 117 patients. Inappropriate contraction of the external anal sphincter when straining at stool was more readily detected using the longitudinal electrode in 52 patients investigated for intractable constipation. The longitudinal electrode detected the amplitude of the response to the elicitation of a pudeno-anal reflex more readily than the circular electrode. When in 12 of the 117 the pudeno-anal reflex EMG signal was either absent or not detected with the circumferential plug electrode, the longitudinal electrode detected the presence of a low amplitude response in 11 of these. When the non-invasive longitudinal electrode was compared to invasive fine wire stainless steel electrodes, a correlation was found for external anal sphincter resting EMG (r = 0.99, p less than 0.01), voluntary squeeze EMG (r = 0.99, p less than 0.001) and strain EMG (r = 0.91, p less than 0.01). The longitudinal anal plug electrode thus facilitates surface acquisition of EMG activity.

Adult↗
PubMed1991

Impedance plethysmography in human limbs. Part 1. On electrodes and electrode geometry.

Electrode design and electrode positioning are important factors in blood flow measurements using impedance plethysmography. Optimal electrode type and accurate positioning will decrease measurement errors and improve the signal-to-noise-ratio. Disk electrodes were found to be superior to tape electrodes because of their better skin-electrode stability and because they prevent limb compression. The distance between current electrodes and potential electrodes should be greater than 2.3 R (disk electrodes) and 1.5 R (tape electrodes) to avoid the influence of the so-called diffusion resistance (R is the radius of the limb at the electrode site).

Adult↗
PubMed1993

Muscle contractile properties by surface electrodes compared with those by needle electrodes.

We measured the contractile properties of the first dorsal interosseous muscle by surface electrodes and needle electrodes during submaximal voluntary contraction. Twenty-seven single motor units were recorded from 5 volunteers by surface electrodes, which were confirmed by subsequent needle electrode recordings. Twitch tension ranged from 0.6 to 10.0 g with a mean of 3.7 g based on an averaging method triggered by surface myoelectric signals, and the tension calculated from the needle myoelectric signals ranged from 0.8 to 11.7 g with a mean of 3.6 g. Rise time ranged from 33.9 to 81.6 msec with a mean of 49.4 msec for the surface electrode recordings, and from 33.0 to 73.2 msec with a mean of 50.8 msec for the needle electrode recordings. The obtained data of surface electrode recordings indicated a high correlation with that of the needle electrode recordings, r = 0.92 (P < 0.001) for twitch tension and r = 0.91 (P < 0.001) for rise time. We also found a positive correlation between threshold force and twitch tension (by surface electrodes: r = 0.71, P < 0.05; by needle electrodes: r = 0.77, P < 0.05). Our studies indicate that it is possible to record single motor units by non-invasive surface electrodes provided that the unit has a threshold force of less than 2 kg.

Adult↗
PubMed2002

Determination of standard electrode potential E(o) for chronic platinum and gold electrodes in rat muscle: implications for biosensors and the "anode" of bipolar pacing.

Pacemaker electrode surface modification by organosilane and organic self-assembled monolayer strategies creates a possible new variable in pacemaker electrode behavior. Because all of these chemical surface coatings are unstable at extremes of potential, the potential to which the electrode relaxes (between pacing pulses) becomes extremely important. The authors measured this potential for platinum (Pt) and gold (Au) relevant for their use as anode (or cathode) in a bipolar pacing system and from this potential the standard electrode potential, E(o) was determined. Thirty-Four determinations were made by a null current three-electrode potentiostatic technique of 2.45 mm2 platinum or gold electrodes implanted chronically in blood perfused muscle in a spontaneously breathing rat. Linear voltage sweeps were performed while monitoring current with voltage at null current determined repeatedly at varying scan rates and limits. Electrode potential varied between -388 +/- 19 mV (vs Ag/Ag+) for platinum and -388 +/- 55 mV for gold electrodes. Hysteresis was observed in all sweeps (P < 0.008, Fisher's exact) and measured 61 +/- 17 mV (anodic) and 25 +/- 3 mV (cathodic) with steep dependence on polarity (P < 0.001, t-test). The findings were independent of the materials' electronic work function. E(o) versus normal hydrogen electrode (NHE) were thus -166 mV (platinum) and -166 mV (gold). Because the most common bipolar system, uses platinum as anode, these results are directly applicable to current pacing technology. Provided low thresholds are achievable with novel surface modified electrodes, the small range of variation of E(o), and the particular mean value observed, are both compatible with function, provided care is used during electrode testing to avoid surface disruption. These results are significant also for biosensors that use similar surface modification methodologies.

Animals↗
PubMed1995

Electrode polarity does not alter the initial ventricular activation sequence during pacing with extracardiac electrodes.

Ventricular epicardial mapping was performed in six closed-chest anesthetized dogs to investigate the cardiac electrical response to external pacing. A right thoracotomy was performed, complete AV block was produced by formaldehyde injected into the AV node and a sock electrode array, comprised of 127 unipolar electrodes, was placed over the ventricles. Isopotential and isochronal epicardial maps were generated by computer from the unipolar electrograms. Unipolar stimulation pulses were applied between pairs of different types of cutaneous (metal, carbon) and esophageal (metal) electrodes, and recordings were performed at maximum lung inflation. Isopotential maps recorded during the stimulation artifacts showed that the epicardial electrical field was little affected by the type of electrode but depended mostly on electrode position. A reproducible and relatively uniform apex-to-base potential gradient was regularly produced with anteroposterior and anteroesophageal electrode configurations. This uniform potential gradient induced ventricular activation sequences that showed interindividual differences. Thus, for each dog, the areas of initial activation observed on the isochronal maps during pacing tended to remain the same (i.e., apical, lateral, and anterior) despite changes in the stimulation protocol. Inverting the polarity of the electrodes did not appreciably change the site of origin of activation (81% remained the same) and activation never originated from the area showing the most negative potential during the stimulation artifact. In conclusion, since electrode polarity does not seem to alter the ventricular activation sequence during cardiac pacing with extracardiac electrodes, the standard nomenclature for cutaneous patches, which defines the negative electrode as the "active" electrode, may have to be revised.

Animals↗
PubMed2005

Spinal cord stimulation electrode design: a prospective, randomized, controlled trial comparing percutaneous with laminectomy electrodes: part II-clinical outcomes.

OBJECTIVE: Spinal cord stimulation, in use for more than 30 years, has evolved into an easily implemented technique involving percutaneous or laminectomy electrode placement. In a randomized comparison of four-contact percutaneous and four-contact insulated laminectomy electrodes placed at the same level in the dorsal, epidural midline, quantitative measures of stimulator performance revealed significant technical advantages for the laminectomy electrodes. Our prospective, randomized, controlled trial compares clinical results in these same patients. METHODS: Impartial third parties followed our series of 24 patients with failed back surgery syndrome to gather clinical outcome data. We defined "success" as at least 50% sustained relief of pain and patient satisfaction with the result of treatment. RESULTS: At a mean follow-up of 1.9 years, 10 of 12 patients receiving the laminectomy electrode and 5 of 12 patients receiving the percutaneous electrode reported a successful outcome (P < 0.05). Follow-up at a mean of 2.9 years showed that this result was maintained in 5 of 12 patients with the laminectomy electrode and 3 of 12 with the percutaneous electrode (not statistically significant). Many patients reported improvements in most activities of daily living, and loss of function was rare. In addition, 9 patients with laminectomy electrodes and 4 with percutaneous electrodes reducted or eliminated analgesic intake (P < 0.05), and 2 returned to work. No electrode migration was observed. CONCLUSION: Laminectomy electrode placement, although more invasive than percutaneous placement, yields significantly better clinical results in patients with failed back surgery syndrome at mean 1.9 years follow-up. In our small sample, however, the statistical significance of this advantage disappeared at mean 2.9 years follow-up.

Adult↗
PubMed2006

Can electrocardiogram electrodes replace bispectral index electrodes for monitoring depth of anesthesia?

BACKGROUND: Bispectral index has been introduced to provide optimal level of anesthesia. However, Bispectral index monitoring may not be cost effective in a relatively short procedures due to the high costs of the electrode. The authors conducted the present study to compare the feasibility of commercially available electrocardiogram (ECG) electrodes instead of the Bispectral index (BIS) monitoring. MATERIAL AND METHOD: The authors evaluated the difference in signal quality index (SQI) and BIS values collected from two BIS monitors, using ECG electrodes and BIS electrodes on the same patients before anesthesia, during light anesthesia, deep anesthesia and the emergence period Both sets of electrodes were placed at bifrontal areas throughout the procedure. Statistical analysis was evaluated by mean difference 95% confidence limits of agreement and visualized by Bland-Altman plot. A parametric analysis was analyzed using paired t-test. RESULTS: There were 390 parallel signal quality index and BIS values recorded in the present study. During anesthesia the mean BIS values were 58.63 +/- 18.77 in the ECG electrode group and 56.99 +/- 19.84 in the BIS electrode group, which were not statistically different. The mean SQI values were 79.2 +/- 24.8 and 82.8 +/- 21.6 using ECG electrodes and BIS electrodes, respectively. The mean difference between BIS values was 1.65 with 95% confidence limits of agreement between 0.91 and 2.38. CONCLUSION: Commercial ECG electrodes could be used for monitoring depth of anesthesia with clinically acceptable mean bias and 95% confidence limits of agreement of BIS value obtained from BIS electrode.

Anesthesia, General↗
PubMed1992

Comparison of colloidal gold electrode fabrication methods: the preparation of a horseradish peroxidase enzyme electrode.

In order to prepare biosensing electrodes which respond to hydrogen peroxide, horseradish peroxidase has been adsorbed to colloidal gold sols and electrodes prepared by deposition of these enzyme-gold sols onto glassy carbon using three methods: evaporation, electrodeposition and electrolyte deposition. In the latter method the enzyme-gold sol is applied to the surface of a glassy carbon disk electrode followed by an equal volume of 2 mM CaCl2. The electrolyte causes the sol to precipitate on the electrode surface, producing an immobilized enzyme electrode. Satisfactory electrodes which gave an electrochemical response to hydrogen peroxide in the presence of the electron transfer mediator ferrocenecarboxylic acid were produced by all three methods. Evaporation of horseradish peroxidase-gold sols produced electrodes with the best reproducibility and the widest linear amperometric response range. These electrodes can also easily be stored in a dry state. Although not as good as evaporation, electrodeposition also produced satisfactory electrodes. Electro-deposition provides the added advantage that it lends itself to the preparation of multi-enzyme/multi-analyte electrodes by the adsorption of different enzymes to separate gold sols, followed by sequential electrodeposition onto discrete areas of a multichannel electrode.

Biosensing Techniques↗
PubMed1989

ERG electrode in pediatric patients: comparison of DTL fiber, PVA-gel, and non-corneal skin electrodes.

Hard contact lens electrodes have been the type most frequently used in pediatric electroretinography but they are not well-tolerated by patients. The Dawson Trick Litzkow fiber electrode is better tolerated but it is fragile and difficult to sterilize. A new electrode made from anomalous polyvinyl alcohol gel is inexpensive, has stable electrical recording properties, and can be discarded after use. Dermal electrodes have been used for electroretinogram recording for some time; however, there are few reports that directly compare their performance against standard contact lens assemblies. We compared the DTL and the polyvinyl gel electrodes in the same group of subjects and investigated their recording characteristics along with non corneal skin electrodes placed on the infraorbital ridge. Signal-averaged electroretinogram were obtained under both scotopic and photopic stimulation conditions and the implicit time and amplitudes of the a- and b-waves were determined. Overall, dermal recordings generally had shorter implicit times and lower amplitudes than with the fiber or gel electrodes. The dermal electrodes were best tolerated and outlasted the corneal in repeated use. Since amplitude characteristics of the dermal electrodes were generally about 50% of that obtained with corneal electrodes, we feel that under standardized conditions they are acceptable for most clinical recording situations in infants and young children.

Adolescent↗
PubMedDate not supplied

Spatial potential and current distributions along transvenous defibrillation electrodes: variation of electrode characteristics.

The therapeutic efficacy of an endocardial defibrillation lead system can be improved by controlling the profile of current delivery through a suitable choice of electrode characteristics, which include the length, radius, number of conductor elements, electrode resistance, and point of connection to the voltage source. Such control will minimize tissue and lead damage during long-term use. In this study, a semianalytical model was developed to study cylindrical electrodes of different constructions in an idealized electrolytic medium. Simulations were performed to investigate the effects of varying the electrode characteristics on the spatial voltage and current distributions and interelectrode resistance for cylindrical electrodes of different constructions. The results show that, for transvenous electrodes of realistic dimensions, the current distributions are determined largely by the edge effects. The edge effects increase as the aspect ratio of the electrode (length/radius) decrease. The multiple edges resulting from wrapping conductor elements over a nonconducting base are found to increase the nonuniformity and the current density over the conductor-covered surface. The model is used to demonstrate two techniques of controlling the current distribution. The first method involve modifying the electrode resistivity profile and point of connection. In the second approach, the electrode surface is covered with a thin film having a model-computed resistance profile. By using either methods to produce isocurrent electrodes, the interelectrode resistance is found to increase.

Electric Countershock↗
PubMed2003

Evolution in impedance at the electrode-skin interface of two types of surface EMG electrodes during long-term recordings.

The evolution in impedance at the electrode-skin interface of Beckman and Red Dot electrodes was assessed during long-term recordings. Impedance was measured between each pair of electrodes, arranged in a bipolar configuration on tibialis anterior (n=13). A waveform constructed of sinusoids of known frequencies, evenly distributed on a log scale from 1-16,384 Hz, was applied through the electrodes, and the result recorded by a DAQ system. SEMG signals were recorded at 1000 Hz during isometric dorsiflexion contractions of 30 s, performed every 15 min for 2 h. Impedance data were acquired at 65,536 Hz immediately before and after SEMG recordings. Large individual differences in impedance levels were observed at low frequencies. At high frequencies, impedance values depended only on the electrode type. Impedance decreased steadily with time for Beckman electrodes (p < 0.05), but did not decrease significantly for Red Dot electrodes. The magnitude of the reduction over time varied widely between individuals, and was related to the initial impedance values. The impedance-bandwidth product remained constant for each electrode type (95% confidence intervals 146.2-148.2 and 126.1-127.8 for Beckman and Red Dot electrodes respectively). When skin impedance is electrically modelled with a simple network containing a resistor and a capacitor, the capacitance varies with the properties of the electrode used, whereas resistance is dependent on the subject. Furthermore, the EMG spectrum is unaffected by impedance provided skin preparation is sufficient to reduce the impedance below 55 komega.

Adult↗