Unipolar Electrode Configuration Research Articles

Impulse Configuration in Hypoglossal Nerve Stimulation in Obstructive Sleep Apnea: The Effect of Modifying Pulse Width and Frequency

ObjectivesHypoglossal nerve stimulation is an effective treatment option for obstructive sleep apnea (OSA) in positive airway pressure therapy failure. Nonetheless, data regarding the functional effect of modifying stimulation parameters within each electrode configuration are limited. Materials and MethodsIn a retrospective study of 76 patients with 12 months or more follow-up, functional tongue protrusion thresholds were compared for pulse width and frequency configurations of 90 μsec 33 Hz vs 120 μsec 40 Hz. The number of tolerated voltage amplitude steps between sensation, functional, and subdiscomfort thresholds were assessed for both settings as well as impedances. ResultsThe overall cohort showed improvement in OSA metrics: median apnea–hypopnea index from 30.0/hour to 18.6/hour and Epworth Sleepiness Scale from 13.5 to 7.6. For both bipolar and unipolar electrode configurations, the stimulation amplitude required for functional tongue protrusion was significantly reduced when the pulse width and frequency were converted from 90 μsec 33 Hz to 120 μsec 40 Hz (p < 0.001). Nevertheless, the number of voltage amplitude steps from sensation, functional, to subdiscomfort thresholds did not differ between the two settings. The ratio of automatically derived impedances between bipolar and unipolar electrode configurations was relevantly correlated with the ratio of functional thresholds at these parameters. ConclusionChanging the stimulation parameters may lower the voltage requirements while maintaining the same effect on tongue protrusion. Changing these stimulation parameters does not affect the range of tolerated impulse steps between functional and subdiscomfort thresholds. Future technical appliances could help estimate functional thresholds at different electrode configurations for each patient by automatically measuring impedances.

Cardiac Pacemakers in Electric and Magnetic Fields of 400‐kV Power Lines

The cardiac pacemaker (PM) implantation rate per million is high. Earlier studies have found interference to PMs by electromagnetic fields. The aim of the study is to investigate disturbances in cardiac PM using a human-shaped phantom in electric and magnetic fields of 400-kV power lines. The phantom was used in the following manner: isolated from the ground, grounded from left or right foot, or grounded from left or right hand. Out of the tested PMs one had such a disturbance that it set the pace 60 times per minute, when the electric field was 6.7-7.5 kV/m and the magnetic field was 2.4-2.9 μT. The electrode configuration of the PM was unipolar. In bipolar configuration, the same PM had no disturbance. During the test period, other PMs only had minor disturbances or none at all. Some PMs do not record time information for minor disturbances. In such cases, it was impossible to link the disturbances to the exposure under the power line. The electric field under a 400-kV power line may disturb a PM. However, only one type out of several tested PMs showed a major disturbance and that was only with a unipolar electrode configuration. The risk of disturbances is therefore not deemed to be high.

Interference of programmed electromagnetic stimulation with pacemakers and automatic implantable cardioverter defibrillators

A commercially available magnetic therapy system, designed for clinical application as well as for private use without medical supervision, was examined with respect to its potential for causing electromagnetic interference with implantable pacemakers (PMs) and automatic implantable cardioverter defibrillators (AICDs). A sample of 15 PMs and 5 AICDs were experimentally investigated. Each of the implants was realistically positioned in a homogeneous, electrically passive torso phantom and exposed to the magnetic fields of the system's applicators (whole body mat, cushion, and bar applicator). The detection thresholds of the implants were programmed to maximum sensitivity and both unipolar as well as bipolar electrode configurations were considered. The evaluation of possible interferences was derived from the internal event storages and pacing statistics recorded by the implants during exposure. Any "heart activity" recorded by the implants during exposure was interpreted as a potential interference, because the implant obviously misinterpreted the external interference signal as a physiological signal. Only cases without any recorded "heart activity" and with nominal pacing rates (as expected from the program parameter settings) of the implants were rated as "interference-free." Exposure to the whole body mat (peak magnetic induction up to 265 microT) did not show an influence on PMs and AICD in any case. The cushion applicator at the highest field intensity (peak magnetic induction up to 360 microT) led to atrial sensing defects in four PM models with unipolar electrode configuration. Under bipolar electrode configuration no disturbances occurred. The bar applicator led to sensing problems and consecutively reduced pacing rates in all tested PM models under unipolar electrode configuration and maximum field intensity (peak magnetic induction up to 980 microT). Bipolar electrode configuration resolved the problem. The investigated AICDs did not show malfunctions under any investigated condition. In conclusion, the examined PEMF therapy system did not interfere with the investigated implantable cardiac devices with bipolar electrode configuration. However, unipolar electrode configuration in pacemakers seems to be potentially hazardous during application of the examined PEMF therapy system.

Implantable cardioverter/defibrillator: long-term stability of the defibrillation threshold with a unipolar electrode configuration (active-can")

The majority of cardioverter/defibrillator (ICD) implantations are currently performed with a non-thoracotomy approach. From November 1993 to January 1995, 46 patients underwent implantation of a PCD 7219C with an "active-can" lead configuration at our institution. While the chronic stability of the defibrillation threshold (DFT) for an epicardial lead system is well established, the results are still inconsistent for non-thoracotomy lead systems. Accordingly, the aim of the present study was to compare the acute and chronic defibrillation thresholds of the ICDs implanted with an "active-can" lead system in order to assess the chronic stability of these systems. The defibrillation energy requirements were measured at implant, prior to hospital discharge, three, six and twelve months after implantation of the defibrillator. The patient group consisted of 8 females and 38 males with a mean age of 57.2 years. The mean left ventricular ejection fraction was 43.8%. The most frequent underlying heart disease was coronary artery disease in 31 of 46 patients. Eight patients had idiopathic dilated cardiomyopathy. In 39 of 46 patients, the defibrillation threshold could be successfully determined at all 4 time points after implantation. The mean defibrillation energy requirement at the time of implantation was 9.2 +/- 5.9 Joules (J). The subsequent mean energy requirements were 7.6 +/- 4.8 J at pre-hospital discharge, 8.6 +/- 5.7 J at the 3 month, 8.1 +/- 6.0 J at the 6 month and 8.6 +/- 5.8 J at the 12 month follow-up visits. The mean defibrillation threshold was lowest at the time of prehospital discharge, significantly lower than at the time of initial implantation (p = 0.021). However, at all later time points up to one year, there was no significant difference in the DFT as compared with the time of initial implantation. Comparing the DFT at the time of implantation and the DFT at all other time points, there were no significant differences (9.23 vs. 8.56 J, p = 0.291). Although there was an initial decrease in the DFT at seven to ten days, the long-term stability of the DFT up to one year remained stable in the devices with the "active-can" lead system.

Radiofrequency coagulation of ventricular myocardium: improved prediction of lesion size by monitoring catheter tip temperature.

To assess the importance of voltage, current, impedance and catheter tip temperature for the prediction of the size of tissue injury induced by transcatheter radiofrequency application, radiofrequency pulses (500 kHz) were delivered both in vitro and in vivo to isolated ventricular preparations and the intact canine heart, respectively. Radiofrequency coagulations were performed using unipolar electrode configuration. Besides measurements of current and voltage which were used to calculate the delivered power and tissue impedance, the catheter tip temperature was monitored during each application using specially designed 6F USCI catheters with a built-in nickel/chromium-nickel thermoelement. Lesion dimensions were measured and the correlation between lesion volume and delivered radiofrequency energy, maximum changes in catheter tip temperature and the integral of the temperature curve were calculated. First, in a pilot in vitro investigation, 50 radiofrequency coagulations (3.2 W-22.4 W, pulse duration 10 s) were performed in ventricular preparations from freshly excised dog hearts. The correlation between applied radiofrequency energy and lesion volume was 0.87; the correlation between maximal catheter tip temperature and lesion volume was 0.82; the correlation between temperature integral and lesion volume was 0.9. In the intact dog heart, 44 radiofrequency pulses were delivered to the left and right ventricular endocardium in 12 anaesthetized dogs (exposure time: 10 s). Delivered power ranged between 5.6 W and 24.6 W; tissue impedance varied between 92 omega and 364 omega; lesion volume measured 0-273 mm3; developed peak temperatures ranged from 16.25 degrees C to 196 degrees C. The calculated integral beneath temperature curves measured 126-1971 degrees C.s. The correlation between applied radiofrequency energy and lesion volume was 0.32; the correlation between maximal catheter tip temperature and lesion volume was 0.61. Temperature integral correlated best with the assessed volume of myocardial necrosis (r = 0.7). No significant arrhythmogenic or haemodynamic side-effects were observed. Macroscopic examination showed a central depression surrounded by a zone of homogeneous coagulation. Vaporization and crater formation up to a depth of 4 mm were observed following three radiofrequency discharges. In two of these cases, rapid changes and oscillation of catheter tip temperature were observed. Thus, monitoring of catheter tip temperature during radiofrequency energy application improves the prediction of lesion size. In addition, temperature monitoring might improve the safety of the procedure with respect to the risk of perforation.

Effect of electrode parameters on the bandwidth of the surface e.m.g. power-density spectrum

The effect of the electrode configuration (unipolar against bipolar), the electrode separation, the electrode position and the electrode contact area on the bandwidth of the power density spectrum of the surface e.m.g. has been studied. The dependence of the half-power point bandwidthB on the interelectrode distanced can be described by the regression function BHz=810/dmm+58. The unipolar electrode configuration yields an e.m.g. signal with the smallest bandwidth. Neither a variation of the electrode position nor a variation of the electrode contact area has a significant effect on the bandwidth of the e.m.g.