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PubMed1983

Characteristics of advanced porous and textured surface pacemaker electrodes.

Reduced stimulation thresholds, improved sensing and better attachment have been claimed for totally porous and porous surfaced electrodes. In this study, the potential for clinical use of two new types of porous electrodes and a non-porous, textured high microsurface area electrode, has been evaluated by comparison with equivalent sized, smooth non-porous controls. Eighteen sintered and seven laser drilled porous electrodes, seven-non-porous textured electrodes, and sixteen controls, were implanted singly in the right ventricles of sheep. Measurements of threshold, pacing, sensing and bulk impedances were taken at regular intervals for up 180 days. At sacrifice, only three of the thirteen non-porous controls were attached. All laser porous electrodes, apart from two which were dislodged, were attached, as were eleven of fifteen sintered porous, and five of seven textured non-porous electrodes. Tissue ingrowth was found for both porous electrode types. Stimulation thresholds were not statistically different for all electrode types (p less than 0.05). Pacing and bulk impedances of the two porous and surface textured electrodes were significantly higher (p less than 0.10, p less than 0.05, respectively) than those of controls. The three new electrodes exhibited similar chronic sensing impedance values, 30% less than equivalent non-porous electrodes. The similar sensing performance of the porous and high microsurface area non-porous electrodes indicates that the nature of the external surface, rather than internal porosity, determines sensing impedance. All three new electrode types showed improved attachment and sensing compared with similar smooth electrodes. The laser porous electrode, which permits fixation by tissue ingrowth and maintains simplicity of construction, is promising for routine clinical use.

Animals↗
PubMed1991

Orthogonal electrode catheter array for mapping of endocardial focal site of ventricular activation.

Precise location of the endocardial site of origin of ventricular tachycardia may facilitate surgical and catheter ablation of this arrhythmia. The endocardial catheter mapping technique can locate the site of ventricular tachycardia within 4-8 cm2 of the earliest site recorded by the catheter. This report describes an orthogonal electrode catheter array (OECA) for mapping and radiofrequency ablation (RFA) of endocardial focal site of origin of a plunge electrode paced model of ventricular activation in dogs. The OECA is an 8 F five pole catheter with four peripheral electrodes and one central electrode (total surface area 0.8 cm2. In eight mongrel dogs, mapping was performed by arbitrarily dividing the left ventricle (LV) into four segments. Each segment was mapped with OECA to find the earliest segment. Bipolar and unipolar electrograms were obtained. The plunge electrode (not visible on fluoroscopy) site was identified by the earliest wave front arrival times of -30 msec or earlier at two or more electrodes (unipolar electrograms) with reference to the earliest recorded surface ECG (I, AVF, and V1). Validation of the proximity of the five electrodes of the OECA to the plunge electrode was performed by digital radiography and RFA. Pathological examination was performed to document the proximity of the OECA to the plunge electrode and also for the width, depth, and microscopic changes of the ablation. To find the segment with the earliest LV activation a total of 10 +/- 3 (mean +/- SD) positions were mapped. Mean arrival times at the two earlier electrodes were -39 +/- 4 msec and -35 +/- 3 msec. Digital radiography showed the plunge electrode to be within the area covered by all five electrodes in all eight dogs. The plunge electrode was within 1 cm2 area of the region of RFA in all eight dogs. The width and depth of ablation were 5 +/- 3.5 and 7 +/- 3.5 mm, respectively. Microscopic changes revealed coagulative necrosis, hemorrhage, and inflammatory changes in all RFAs. In conclusion, the OECA can map the endocardial focal site of origin of paced ventricular activation within 1 cm2 area in a canine model. RFA from the OECA can cause discrete ablations representing all five electrodes or cross-shaped ablation connecting central electrode to all four peripheral electrodes. This catheter holds promise for extending surgical and clinical catheter ablation procedures.

Animals↗
PubMed1998

Lidocaine's effect on defibrillation threshold are dependent on the defibrillation electrode system: epicardial versus endocardial.

INTRODUCTION: Epicardial and endocardial defibrillation electrode systems affect myocardial electrophysiology and sympathetic function differently. Thus, we postulate that antiarrhythmic drugs will interact with these electrode systems differently. METHODS AND RESULTS: Defibrillation energy requirements (DER) at 20% (ED20), 50% (ED50), and 80% (ED80) success were measured at baseline and during lidocaine (10 mg/kg per hour) or D5W treatment for epicardial and endocardial electrodes. Pigs were randomized to treatment (lidocaine or D5W) and electrode system, which resulted in four experimental groups: (1) epicardial electrode + D5W; (2) epicardial electrode + lidocaine; (3) endocardial electrode + D5W; and (4) endocardial electrode + lidocaine. ED50 DER (mean +/- SEM) values at baseline for groups 1-4 were 10.6+/-1, 8.5+/-1, 12.6+/-1, and 12.3+/-1 J, respectively. DER values for groups 1 and 3 during D5W were similar to baseline. Conversely, lidocaine increased ED50 DER values from 8.5+/-1 to 13.5+/-2 J (P < 0.05) in group 2 animals (epicardial electrodes). When lidocaine was administered to group 4 animals (endocardial electrodes), however, ED50 DER values remained similar to baseline values (12.3+/-1 to 14.3+/-2 J, P = NS). Lidocaine increased ED50 DER values by 59% with the epicardial electrode system, which was significantly greater than the 16% increase with the endocardial electrode system (P < 0.05). Electrophysiologic response and electrode impedance were similar between electrode systems. CONCLUSION: Lidocaine increases DER values to a greater extent when using epicardial versus endocardial electrode system. Thus, drug-device interactions are dependent on the electrode system. These data suggest that the electrophysiologic milieu created by endocardial defibrillation mitigates the effects that lidocaine has on DER values.

Animals↗
PubMed1998

Effect of electrode length on atrial defibrillation thresholds.

INTRODUCTION: Catheter-based electrodes have been used previously to terminate episodes of atrial fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electrodes are positioned in the distal coronary sinus and in the right atrium. The purpose of this study was to evaluate the use of longer electrode lengths for atrial defibrillation. METHODS AND RESULTS: In 15 patients, two decapolar catheters were inserted, one into the distal coronary sinus and one in the right atrium. To provide longer electrodes lengths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6-cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecutive electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting 5 consecutive, nonoverlapping rings of the third catheter with the 10 rings of the initial right atrial or coronary sinus catheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations of electrode lengths. All 15 patients could be successfully converted to sinus rhythm without complications; however, one patient could be converted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 +/- 102 V, 5.9 +/- 4.0 J for the 6 cm/6 cm electrode length combination with an impedance of 72 +/- 18 omega. For the electrode combination using the 11-cm electrode in the right atrium, the defibrillation threshold was 296 +/- 107 V, 5.8 +/- 3.9 J with an impedance of 61 +/- 17 omega and was 294 +/- 91 V, 5.6 +/- 3.6 J with an impedance of 55 +/- 11 omega for the 11-cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P > 0.05) associated with the longer electrode lengths; however, the longer electrode lengths did significantly lower shock impedance (P < 0.05). CONCLUSION: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the defibrillation requirements for restoration of sinus rhythm.

Adult↗
PubMed1991

Perception of multiple electrode stimulus patterns: implications for design of an electrotactile speech processor.

Identification of multiple-electrode stimulus patterns was evaluated in nine adult subjects, to assess the feasibility of providing additional speech information through the tactual display of an electrotactile speech processor. Absolute identification scores decreased from 97.8% for single electrodes, to 61.9% for electrode pairs, and, to 31.8% for electrode triplets. Although input information increased with paired-and triple-electrode stimuli, information transmission scores were not significantly increased for either electrode pairs (2.99 bits) or triplets (2.84 bits) as compared with single electrodes (2.84 bits). These results suggest that speech coding strategies using stimulus patterns of electrode pairs or triplets would provide little improvement beyond that found for the present single-electrode scheme. However, higher absolute identification scores (73.6%), and an increase in information transmission to 3.88 bits, were recorded for test stimuli containing all combinations of paired and single electrodes. Based on this finding, two stimulus sets using a restricted number of combinations of paired and single electrodes were evaluated. The two stimulus sets simulated the spatial patterns of paired and single electrodes arising from use of alternative speech coding schemes to increase consonant voicing information. Results for the two stimulus sets showed higher electrode identification scores (79.7% and 90.4%), as compared with paired-electrode stimuli. Although electrode identification score was not as high as for single electrodes, information transmission was increased to 3.31 bits for the VF2 stimulus set. Analysis of the responses also showed that scores for identification of simulated voicing information conveyed by the two stimulus sets were 99.4 and 90.4% correct.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Catheter ablation of atrioventricular junction using radiofrequency current in 17 patients. Comparison of standard and large-tip catheter electrodes.

BACKGROUND: Two catheter electrode systems were compared for delivering radiofrequency current for ablation of the atrioventricular junction. Seventeen patients with drug-resistant supraventricular tachyarrhythmias were studied. METHODS AND RESULTS: A 6F or 7F catheter with six or eight standard electrodes (1.25 mm wide, 2.5-mm spacing) was used in the first seven patients (group 1). A 7F quadripolar catheter with a large-tip electrode (4 mm long; surface area, 27 mm2) was used in the final 10 patients (group 2). Both ablation catheters were positioned to record a large atrial potential and a small but sharp His bundle potential from the distal bipolar electrode pair. Radiofrequency current was applied between a large skin electrode on the left posterior chest and either 1) each individual electrode on the standard-tip electrode catheter at 40 V (group 1) or 2) the large-tip electrode at 50-60 V (group 2). Radiofrequency current was limited to 40 V in group patients because of the strong potential for an early impedance rise when higher voltage is applied through standard electrodes. Complete atrioventricular block was achieved in six of seven group 1 patients and all 10 group 2 patients. A junctional escape rhythm followed ablation in five or six group 1 patients (mean cycle length, 1,066 +/- 162 msec) and eight of 10 group 2 patients (mean cycle length, 1,281 +/- 231 msec). Atrioventricular block was produced in a mean of 4.7 +/- 4.6 radiofrequency current applications delivered over a period of 42 +/- 45 minutes using the large-tip electrode (group 2) compared with 46 +/- 22 applications using standard electrodes (15.9 +/- 10.2 applications delivered through the standard-tip electrode) over a period of 147 +/- 59 minutes (group 1). For the application producing atrioventricular block, the large-tip electrode used higher voltage (58 +/- 17 versus 38 +/- 5 V, p less than 0.03) and had lower impedance (103 +/- 22 versus 148 +/- 40 omega, p less than 0.01), resulting in greater power (33.0 +/- 13.0 versus 10.2 +/- 0.6 W, p less than 0.003) and shorter time to block (8 +/- 3 versus 22 +/- 3 seconds, p less than 0.001). Current delivery through standard electrodes was limited by an impedance rise occurring 7 +/- 7 seconds after the onset of one or more radiofrequency current applications at 10 +/- 1 W in six of seven patients. Using the large-tip electrode, an impedance rise occurred in five of 10 patients, but at 25 +/- 10 W and after 21 +/- 9 seconds. Atrioventricular block occurred before the impedance rise in three of these five patients. Complete atrioventricular block persisted in 15 of 16 patients at a mean follow-up of 8.7 months. Atrioventricular conduction returned at 1 month in one group 2 patient and was successfully ablated by a second procedure. Three group 1 patients died 0.5-2 months after ablation, and a fourth patient underwent cardiac transplantation after 10 months. Pathological examination of the heart in two of these patients showed necrosis of the atrioventricular node and origin of the His bundle, without injury to the middle or distal His bundle. All 10 group 2 patients are alive and subjectively improved after ablation. CONCLUSIONS: We conclude that catheter-delivered radiofrequency current effectively produces complete atrioventricular block (94%) without requiring general anesthesia or the risk of ventricular dysfunction or cardiac perforation. The large-tip electrode allows a threefold increase in delivered power and markedly decreases the number of pulses and time required to produce atrioventricular block.

Atrioventricular Node↗
PubMed1998

Comparison of concentric needle versus hooked-wire electrodes in the canine larynx.

BACKGROUND: The use of a specific electrode type in laryngeal electromyography has not been standardized. Laryngeal electromyography is usually performed with hooked-wire electrodes or concentric needle electrodes. Hooked-wire electrodes have the advantage of allowing laryngeal movement with ease and comfort, whereas the concentric needle electrodes have benefits from a technical aspect and may be advanced, withdrawn, or redirected during attempts to appropriately place the electrode. OBJECTIVES: This study examines whether hooked-wire electrodes permit more stable recordings than standard concentric needle electrodes at rest and after large-scale movements of the larynx and surrounding structures. A histologic comparison of tissue injury resulting from placement and removal of the two electrode types is also made by evaluation of the vocal folds. METHODS: Electrodes were percutaneously placed into the thyroarytenoid muscles of 10 adult canines. Amplitude of electromyographic activity was measured and compared during vagal stimulation before and after large-scale laryngeal movements. Signal consistency over time was examined. Animals were killed and vocal fold injury was graded and compared histologically. RESULTS: Waveform morphology did not consistently differ between electrode types. The variability of electromyographic amplitude was greater for the hooked-wire electrode (p < 0.05), whereas the mean amplitude measures before and after large-scale laryngeal movements did not differ (p > 0.05). Inflammatory responses and hematoma formation were also similar. CONCLUSIONS: Waveform morphology of electromyographic signals registered from both electrode types show similar complex action potentials. There is no difference between the hooked-wire electrode and the concentric needle electrode in terms of electrode stability or vocal fold injury in the thyroarytenoid muscle after large-scale laryngeal movements.

Action Potentials↗
PubMed2001

Evaluation of flexible cloth electrodes for electrodermal activity recording.

BACKGROUND: Instrument selection for recording physiological data in flight studies requires careful attention to subject comfort and non-interference with aircrew activities. Several electrode types and recording sites may be used to examine electrodermal activity (EDA). Placement of electrodes on the foot minimizes interference with physical activity and reduces motion artifacts; however, use of conventional, hard-plastic-encased metal (PEM) electrodes within a flight boot can produce discomfort and pressure-induced artifacts. HYPOTHESIS: When applied with proper electrolyte gels, thin, flexible, silver-impregnated cloth electrodes should acquire EDA signals qualitatively similar to those acquired using conventional, PEM electrodes. METHODS: EDA responses evoked by light flashes, auditory stimuli and valsalva maneuvers were recorded with cloth and PEM electrodes simultaneously from both feet of 4 male subjects. Performance of cloth vs. PEM electrodes and variability of signals recorded with the same electrode type were examined by placing pairs of selected electrodes on each foot of the subjects. Placements were balanced with respect to age and handedness of the subject and the number of trials with each electrode type placed on the left or right foot. RESULTS: Qualitatively similar signals were recorded with cloth and PEM electrodes. Cloth electrodes showed more variability between electrodes of the same type. CONCLUSION: For EDA recording, cloth electrodes can perform at least as well as PEM electrodes, making it practical to take advantage of the cloth electrodes' flexibility and lower profile.

Adult↗
PubMed1990

Recording and physical characteristics of disposable concentric needle EMG electrodes.

There is currently considerable interest in using disposable concentric needle (CN) electrodes for clinical electromyography (EMG). To determine how these electrodes compare with reusable CN electrodes, we have compared signals recorded by these two electrode types from the same muscle in normal subjects. We also made similar recordings with two groups of reusable electrodes. There was no difference in the features of motor unit action potentials (MUAPs) recorded by the two groups of reusable electrodes. Disposable electrodes performed satisfactorily in conventional EMG examination. However, compared to reusable electrodes, the disposable electrodes recorded MUAPs with smaller amplitude and area but with the same area:amplitude ratio and MUAP duration. The physical and electrical properties of the CNE groups were also investigated. Disposable electrodes had lower electrical resistance and greater capacitance than reusable electrodes when measurements were made in saline. Photomicrographs showed that the disposable electrodes had smaller recording surfaces and that the central wire was frequently eccentric in the cannula. The differences in electrical recording characteristics could be due to differences in the size of the recording surface, eccentric placement of the central wire in the cannula or differences in the metal used for the central wire. We conclude that electrical and physical testing may not predict the recording characteristics of needle electrodes. Electrophysiologic testing is necessary to determine how EMG signals recorded by new types of electrodes compare with those recorded by currently used electrodes.

Action Potentials↗
PubMed1992

The impedance of a spherical monopolar electrode.

The impedance of a monopolar electrode immersed in an environmental volume conductor consists of two parts; the impedance of the active electrode-electrolyte interface, and the resistance of the environmental conductor. Two studies were carried out to quantitate these components. First, impedance-frequency data were collected for five spherical stainless-steel electrodes (ranging from 0.473 to 1.11 cm in diameter) immersed in 0.9% saline (p = 70 omega-cm). Impedance measurements were made from 100 Hz to 100 kHz and two sets of data were obtained; one before and one after each electrode was polished with fine emery paper. At low frequency, the measured impedances were high and varied with electrode surface preparation. However, above a transition frequency, the impedances were resistive, independent of the electrode surface preparation, and equal to rho/2 pi d as predicted from the theory. This study indicates that the low frequency impedance of a monopolar electrode is dominated by the impedance of the electrode-electrolyte interface. Above a transition frequency, the resistance of the environmental conductor dominates, the value of this resistance depending on the electrode geometry and the resistivity (rho) of the environmental conductor. A second study was conducted, to examine the effect of the distance to the indifferent electrode. A frequency (100 kHz) above the transition frequency was used and impedance data were collected for various distances between the monopolar and indifferent electrodes. The measured resistance increased asymptotically as the distance between the electrodes was increased. When the indifferent electrode diameter was at least 10 times the diameter of the spherical monopolar electrode, the measured resistance was within 5% of the value predicted for an indifferent electrode at infinity.

Electric Impedance↗
PubMed2006

Intraoperative radiofrequency ablation using a loop internally cooled-perfusion electrode: in vitro and in vivo experiments.

OBJECTIVE: We sought to validate the efficiency of intraoperative radiofrequency ablation (RFA) using a prototype loop internally cooled-perfusion (LICP) electrode to induce coagulation in the subcapsular portion of the liver. MATERIALS AND METHODS: In in vitro experiments, 30 ablation regions were created using a 200-W generator and a LICP electrode featured simultaneous intraelectrode cooling and continuous flow of hypertonic saline along the shaft in explanted bovine liver. In the in vivo experiments, 26 ablation zones were created according to one of the five protocols in 10 dogs: group A, RFA using a cooled-tip electrode (n = 6); group B, RFA using a LICP electrode with 2 cm loop tip (n = 6); group C, RFA using a LICP electrode with a 3-cm loop tip (n = 6); group D, RFA using a cooled-tip electrode and Pringle maneuver (n = 4); and group E, RFA using a LICP electrode with 2 cm loop tip and Pringle maneuver (n = 4). The dimensions of the coagulation parameters were compared between the groups. RESULTS: In the in vitro experiments, RFA using a 2- or 3-cm diameter LICP electrode (3.6 +/- 0.3 cm, 3.4 +/- 0.5 cm, respectively) created deeper dimensions of coagulation than did a 4-cm electrode (2.3 +/- 0.2 cm; P < 0.05). In the in vivo experiments, the RFA using the LICP electrodes in porcine liver with normal perfusion induced wider but superficial ablation regions when compared to standard RFA using an internally cooled electrode (P < 0.05). However, using a Pringle maneuver, RFA with a LICP electrode created a larger volume of ablation area when compared to RFA using an internally cooled electrode with a similar range of axial diameter along the electrode axis: 30.0 +/- 6.1 cm3 (group D) versus 68.5 +/- 14.0 cm3 (group E; P < 0.05) CONCLUSIONS: Intraoperative RFA using the LICP electrode induced a well-defined semicircular coagulation with a 3.5-cm axial diameter in the subcapsular region of the liver. This device appears to be promising for the treatment of superficial tumors during intraoperative RFA.

Animals↗
PubMed1997

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: square root of Z, non-standard technique divided by square root of Z, AHA technique. RESULTS: Resting interelectrode impedance declined 38% from 58 +/- 10.3 omega (AHA-recommended technique) to 36 +/- 7.6 omega (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.

Adult↗
PubMed2003

An iridium oxide reference electrode for use in microfabricated biosensors and biochips.

In this paper we argue for the use of iridium oxide (IrO(x)) electrodes as quasi-reference electrodes in microfabricated biosensors and biochips that operate in buffered solutions. The simple microfabrication of these electrodes consists of a one-step electrodeposition of IrO(x) onto a microfabricated platinum (Pt) electrode. The IrO(x) electrode potential was found to vary less than 20 mV over 9 days after stabilization for 1 day in a phosphate-buffered saline (PBS) solution; this behavior of the electrode potential was found to be easily reproduced. Moreover, the electrode potential was found to vary by less than 15 mV in the initial hour of its use; this behavior of the electrode potential was also found to be reproducible. The performance of a microfabricated glucose sensor employing an IrO(x) reference electrode is characterized in this paper in order to evaluate the usefulness of this new IrO(x) electrode as a quasi-reference electrode. The glucose sensor consists of a recessed microfabricated Pt electrode array, an electrodeposited IrO(x) film, an inner layer composed of an electropolymerized poly(m-phenylenediamine)/glucose oxidase (PMPD/GOx) film, and an outer or protective layer composed of Teflon and polyurethane (PU) films. The response of this sensor was found to be equivalent to the response of the same sensor employing a commercial Ag/AgCl reference electrode. These results show that a microfabricated IrO(x) electrode can be used as a quasi-reference electrode in microfabricated biosensors and biochips operating in buffered solutions.

Biosensing Techniques↗
PubMed2001

Perimodiolar electrodes in cochlear implant surgery.

Perimodiolar-positioned cochlear implant electrodes have been developed in order to bring the electrode contacts as close as possible to the spiral ganglion cells, which are the target of electrostimulation. This results in lower electrical thresholds, higher dynamic ranges and less channel interaction when compared with normal implant electrodes which are usually located peripherally within the scala tympani. In this study we evaluated 4 different types of perimodiolar electrode: the Clarion Preformed electrode, the Clarion Preformed electrode with positioner, the Nucleus Contour electrode and the Med-El Perimodiolar Combi 40 electrode. These devices require different approaches to achieve a perimodiolar electrode position. The electrodes were inserted in fresh human temporal bones. After processing these bones with the electrodes in situ by employing a sawing, grinding and polishing technique, the inner ear structures as well as the electrode positions could be evaluated in detail. All electrode types studied had a more or less perimodiolar position; however, each type produced a certain amount of trauma to cochlear structures which is discussed in relation to mechanical properties. Further human temporal bone studies with improved perimodiolar cochlear implant electrodes are necessary in order to find an optimized type of electrode.

Cochlea↗
PubMedDate not supplied

Spatial steering with quadruple electrodes in 27 MHz capacitively coupled interstitial hyperthermia.

PURPOSE: The 27 MHz Multi Electrode Current Source (MECS) interstitial hyperthermia system uses probes consisting of multiple independent electrodes, 10-20 mm long, to steer the 3-D power deposition. Seven point thermocouples integrated into the probes provide matching 3-D temperature feedback data. To improve spatial steering the number of independent segments was increased; the feasibility and reliability of four independent electrodes integrated into a single probe were evaluated, with special attention to efficiency and to interference between separate electrodes. METHODS: The contribution of secondary coupling on the apparent electrode impedance and the dependence of cross coupling on the distance between leads, thermocouple and electrodes are computed using simple analytical models. The effect of this secondary coupling was assessed experimentally by comparing power delivery by dual and quadruple electrodes, and by quadruple electrodes in different electrode configurations (segment length 10 or 20 mm) in a nylon catheter in a muscle equivalent medium. RESULTS: Cross coupling with the thermocouple and other electrodes was computed to be of the same magnitude as the primary coupling for a quadruple electrode. Fortunately, this does not affect operation of the electrode, there was no difference in performance between quadruple and dual electrodes, and the output power was effectively independent of the electrode configuration. CONCLUSION: Quadruple MECS electrodes for improved 3-D power control are feasible.

Electrodes↗
PubMed1993

Using compound electrodes in electrical impedance tomography.

In electrical impedance tomography, we inject currents and measure voltages to estimate an object's resistivity distribution. The electrode configuration affects measured voltage data because the electrode-skin contact impedance is high and varies with electrode location. We developed a compound electrode which is composed of two electrodes: a large outer electrode to inject current and a small inner electrode to sense voltage. We used these compound electrodes to measure voltages from a physical phantom. We showed that the measured voltages from the compound electrodes are smaller in amplitude than those from conventional electrodes. This demonstrates that the compound electrode can minimize contact impedance voltage drop from the measured data. We used a finite element model for the compound electrode and incorporated the model into the regularized Newton-Raphson reconstruction algorithm. We performed a sensitivity study and showed that the reconstructed resistivity distributions are less dependent on the unknown contact resistance values for a compound electrode than a conventional electrode and that the use of a compound electrode results in improved images for the reconstruction algorithm.

Algorithms↗
PubMed1976

Pacemaker wires and electrodes. A follow-up study.

In 362 patients on permanent pacing, a follow up with regard to pacemaker electrode function time and connection to pulse-generators has been carried out. In 12 patients Elema epicardial electrode were used with an average function time of 3.8 years. 232 Elema EMT 588 endocardial electrodes were used in 216 patients. Average observation time for the electrodes was 3.3 years. Sixty-eight electrodes have been followed for more than 5 years. Early electrode complications comprise 10 per cent of displacements before implantation of the pulse-generator and another 6 per cent of electrode displacements within the first 3 months after implantation. Eleven per cent of the electrodes had to be corrected due to high threshold value before implantation and another 6 per cent during the first 3 months after implanattion of pulse-generator. On hundred and fifty-five unipolar electrodes of the types Cordis, Medtronic, Elema EMT 282, and Stanium were implanted in 149 patients. Average observation time for the electrodes were 1.2 years. During the first 3 months after pacemaker implant 7 per cent of the electrodes were dislocated, 5 per cent failed due to high threshold value. Three perforations of the right ventricle occurred, without serious complications. Late complications i.e. after 3 months, for EMT 588 electrode included 4 per cent electrode dislocations, 4.5 per cent failure due to high threshold, 3 cases of wire break and 4 defects in the insulation. Many of the late electrode complications were probably caused by replacement operations for pulse-generators. The most frequent late complications for the conventional unipolar electrode was wire break which occurred in 5 cases.

Arrhythmias, Cardiac↗
PubMed1996

Randomised evaluation of a prototype suction fetal scalp electrode.

OBJECTIVE: To compare the performance and acceptability of a prototype suction fetal scalp electrode with that of a double helix spiral electrode. SETTING: An urban academic hospital in Johannesburg, South Africa. DESIGN: Randomised, by means of sealed opaque envelopes opened consecutively. PARTICIPANTS: One hundred women in active labour with an indication for direct fetal heart rate monitoring. INTERVENTION: Application of a fetal scalp electrode to the presenting part. OUTCOME MEASURES: Performance of the electrodes with respect to application success, detachment, quality of the tracings, scalp trauma and women's preferences. RESULTS: Application of the suction electrode was unsuccessful in 15/50 (30%) compared to 1/50 (2%) with the spiral electrode. Detachment rates were similar. There were more tracings of average quality with the suction electrode (nine versus four). There were three instances of scalp bleeding at delivery with the spiral electrode. The suction electrode was preferred by more women and its application caused somewhat less discomfort. CONCLUSIONS: The lower rate of successful application with the suction electrode needs to be weighed against the advantage of avoiding fetal scalp penetration. In particular, women's concerns about pain or harm to the baby from needle electrodes, the theoretical risk of viral transmission, and the risk of serious scalp infection must be considered. These factors favour the use of a suction electrode when direct fetal heart rate monitoring is required. Needle electrodes should be considered when suction electrode application is unsuccessful. Correction of practical problems experienced with the prototype suction electrodes used in this study may result in improved success rates.

Adolescent↗