The Validation of the Finite Difference Method and Reciprocity for Solving the Inverse Problem in EEG Dipole Source Analysis

The performance of the finite difference reciprocity method (FDRM) to solve the inverse problem in EEG dipole source analysis is investigated in the analytically solvable three-shell spherical head model for a large set of test dipoles. The location error for a grid with 2 mm and 3 mm node spacing is in general, not larger than twice the internode distance, hence 4 mm and 6 mm, respectively. Increasing the number of scalp electrodes from 27 to 44 only marginally improves the location error. The orientation error is always smaller than 4° for all the test dipoles considered. We have also compared the sensitivity to noise using FDRM in EEG dipole source analysis with the sensitivity to noise using the analytical expression for the forward problem. FDRM is not more sensitive to noise than the method using the analytical expression.     

颅内电极脑电图监测对枕叶致痫灶的定位价值

目的：探讨颅内电极埋藏后视频脑电图（V-EEG）监测对枕叶致痫灶的定位价值。方法：对19例经无创方法难以定位致痫灶的药物难治性枕叶癫痫（OLE）病人,开顷埋置硬脑膜下条状、栅格状电极和深部电极,行V-EEG监测,记录发作间期及发作期脑电图（EEG）变化,确定发作起源区,再手术切除致痫灶。结果：16例埋置硬脑膜下电极,3例联合应用硬脑膜下电极和深部电极。颅内电极V-EEG监测36～192h（平均68h）,均记录到发作间期痫样放电及发作期EEG情况。行枕叶致痼灶切除术后,平均随访24个月,13例发作消失（EngelⅠ级）,4例偶发（EngelⅡ级）,2例发作减少75％以上（EngelⅢ级）。结论：在致痫灶定位困难的顽固性OLE中,开颅埋藏硬脑膜下电极、深部电极,行V-EEG监测,根据癫痫发作初始期异常放电的节律和范围,可精确定位致痫灶。     

长程视频脑电图在枕叶癫痫诊断及手术定位中的应用

目的：探讨长程视频脑电（V-EEG）在枕叶癫痫（OLE）手术诊断及定位中的应用。方法：27例难治性癫痫经过带蝶骨电极的长程V—EEG监测,结合磁共振成像（MRI）、发作间期正电子发射计算机断层扫描（PET）及视力视野检测结果确定癫痫起源位置为枕叶,对该27例长程V-EEG监测结果进行回顾分析,总结OLE的长程VEEG特点。结果：癫痫起源位置的EEG定位,4例位于颞枕区、4例顶枕区、1例颞顶枕区,18例单纯枕区。OLE具有较高视觉先兆出现率,本组为21例（78％）。发作间期EEG可以具有以下特征：①正常,②慢a节律或广泛θ节律,③一侧枕区脑波被抑制,④一侧或者双侧枕区存在异常电活动,⑤病灶周围脑区存在异常电活动,⑥病灶一侧半球各导联均分布有异常电活动,⑦异常电活动主要为尖波及尖慢波。OLE发作期初期（起始）EEG具有以下特征：①一侧枕区优先优势异常放电,②一侧颞枕区优先优势异常放电,③一侧顶枕区优先优势异常放电,④半球优势异常放电,⑤无侧别优势。结论：OLE具有相应的EEG及临床发作特征,蝶骨电极长程V-EEG结合影像学以及视力视野检查结果能有效诊断OLE,为准确定位提供一定可靠依据,有效指导手术治疗。     

Advances in Cardiac Pacing: Beyond the Transvenous Right Ventricular Apical Lead

While for decades right ventricular (RV) apical pacing has been the standard of care for patients requiring pacemaker or defibrillator lead placement, investigators have sought alternatives to achieve more physiologic electrical activation of the heart and reduce long‐term pathologic effects of nonphysiologic apical pacing. These investigations have included attempts at identifying superior pacing sites within the right atrium and RV and development of new leads to enhance specificity of sensing and capture. This review focuses on recent advances in alternative sites for pacing and developments in novel pacing technology ranging from intramyocardial electrodes to leadless pacemakers. First, there have been several studies demonstrating potential benefits of site‐specific pacing, including His bundle pacing and RV outflow tract pacing in potentially attenuating electromechanical dyssynchrony and long‐term functional decline seen with RV apical pacing. Available options for lead placement have been enhanced by development of intramyocardial electrodes that may significantly reduce far‐field oversensing and nonchamber specific capture. With development of intramyocardial electrodes, the potential for atrioventricular septal pacing has recently been described, making synchronous activation of both ventricles with a one‐lead system possible without crossing the tricuspid valve and offering an alternative to modern cardiac resynchronization therapy (CRT). Finally, recent advances in leadless pacemaker systems using ultrasound or magnetic fields are briefly discussed. The results of these studies suggest that there may be options to the RV apex, made possible by novel lead and pacemaker technology. These advances can potentially aid in reducing long‐term negative effects of chronic pacemaker therapy.     

自主研发电化学治疗同轴电极在动物模型中的初步应用

目的观察同轴电极和针式电极对肝脏毁损的情况,初步评价自主研发电化学治疗（EChT）同轴电极的应用价值。方法同轴电极和传统针式电极分别对5只犬肝脏进行EChT。在25 mA条件下,分别检测电量5、10、20、40、90 C时阴、阳极周围组织坏死量,并观察病变及相邻区域组织结构的变化。EChT前后检测血中肝脏酶ALT、AST、GGT和ALP的变化。结果两种电极的阴、阳极均随着电量的增大而组织毁损范围增大,其走向接近对数曲线。外周阴极的毁损体积较阳极为大,在相同电量作用下,同轴电极与传统针式电极效力相当。在阳极区呈凝固坏死,阴极水肿坏死。超微结构显示在阳极坏死程度与距电极的距离相关。阳极周围坏死边缘pH4.5~5.5,阴极周围坏死边缘pH9~10。EChT前后肝脏酶谱没有显著差异,但AST、ALT、GGT和ALP均有升高趋势。结论自主研发电化学治疗同轴电极与传统针式电极具有相近的肝脏毁损作用,毁损范围与电量呈正相关;并发症少,安全性高,是具有广泛临床治疗前景的电化学治疗电极。     

Preeminence of extrahippocampal structures in the generation of mesial temporal seizures: evidence from human depth electrode recordings

PURPOSE: To examine the intralimbic localization and morphology of mesial temporal seizure onsets and to correlate the findings with patterns of initial seizure spread and the presence or absence of clinical manifestations. METHODS: Eighteen patients with temporal lobe epilepsy were investigated with intracranial depth electrodes implanted in the amygdala (AM), anterior hippocampus (HP), and parahippocampal gyrus (PH). Focal and regional ictal-onset morphologies were classified as rhythmic limbic spiking <2 Hz (RLS), spike-and-wave activity >2 Hz (S/W), rhythmic polyspike activity >13 Hz (RPS), and rhythmic sharp activity <13 Hz (RS). RESULTS: Onset morphologies in 389 total seizures (260 regional + 129 focal) were 50% RPS, 35% RS, 11% RLS, and 4% S/W. Focal AM or HP onsets (30% and 58% of focal onsets, respectively) were more likely to show RLS, whereas RPS was more common in regional onsets. Most patients showed two or more different morphologies and focal onsets at more than one ipsilateral limbic site. Seizure propagation and clinical manifestations were significantly more common with AM or PH onsets (both 67% clinical seizures): only 23% of focal HP onsets resulted in clinical seizures. CONCLUSIONS: (a) There is substantial inter- and intrapatient variability in the morphology and localization of mesial temporal seizure onsets, which suggests that the epileptogenic temporolimbic system may be conceptualized as a dynamic network containing a multiplicity of potential ictal generators; (b) Seizures beginning in the AM or PH are more likely to propagate and give rise to clinical manifestations than are focal-onset HP seizures, which suggests that inhibitory circuits within the HP may function to prevent seizure spread.     

Sonographic imaging of foramen ovale electrodes.

OBJECTIVE: In patients with medically intractable partial epilepsy of mesiotemporal origin, video electroencephalographic monitoring with foramen ovale electrodes is necessary to plan neurosurgical interventions. Imaging of these electrodes after implantation hitherto required conventional radiography, magnetic resonance imaging, or computed tomography of the skull. These methods are expensive. Therefore, the aim of our work was to show the capability of more cost-effective transcranial B-mode sonography for visualization of the electrodes. METHODS: In this pilot study, a 42-year-old female patient with implanted foramen ovale electrodes was examined transtemporally with a 2-MHz sector transducer to visualize the intracranially implanted electroencephalographic recording device. RESULTS: Foramen ovale electrodes could be detected easily in the patient, and bedside monitoring of explantation was possible. CONCLUSIONS: We were able to show the applicability of transcranial B-mode sonography for visualization of foramen ovale electrodes in preoperative electroencephalographic monitoring of patients with epilepsy. Further evaluation of this method in additional patients will follow.     

Numerical analysis of a theoretical one-dimensional amperometric enzyme sensor

The switch-on transient in a miniaturised amperometric sensor with an enzyme layer covered by a diffusion retardation layer is analysed theoretically. The time-dependent mass transfer equations with enzyme catalysed reactions are solved numerically in a one-dimensional geometry with a stationary liquid sample of the same size as the active sensor volume. No steady-state operation is normally achieved and the sensor structure and material parameters have a complicated effect on the oxygen flow behaviour. The theoretical model is used to calculate the measuring range, sensitivity and response time of the sensor. Their dependence on sensor structure is presented in a dimensionless form suitable for sensor design and for analysis of measurement data.     

Corrosion of Pacemaker Electrodes

As improvements in pacemaker components and design increase pacemaker life, problems with other components may emerge such as corrosion of the electrodes. Explanted electrodes were examined under a scanning electron microscope and the degree of corrosion was graded and correlated with the reasons for expiantation, the status of the explanted pacemaker, and the duration of the implant. Fifty-six explanted electrodes were removed for loss of capture or sensing, pacemaker extrusion, broken wires, or after death. A numerical grading system was used to qualitate the degree of corrosion. The pacemaker itself was retrieved in 50 cases, permitting evaluation of the entire pacing system. The dc component of the pacemaker output was measured. Without She aid of magnification most electrodes appeared shiny and smooth. With one exception all corrosion was microscopic. Significant corrosion was seen on all pacemaker electrodes that had been connected to pacemakers with dc offset currents greater than 5 microamperes. All except the "youngest" explanted electrode showed some degree of corrosion. The data suggest that corrosion was directly related to the duration of implantation. With the possible exception of one case, no consistent adverse clinical effects were observed, even when electrodes were heavily corroded. Whether or not corrosion eventually will progress to the point that clinical problems become manifest cannot be predicted at this time.     

Apparatus for the rapid measurement of electrocardiographic body surface potentials

A method for the rapid and reproducible recording of 24 chest electrode potentials is described. Rigid electrodes are equally spaced around the thorax in three rows of eight. The electrodes move radially and are spring loaded so as to maintain contact with the skin regardless of the shape of the subject's torso. The inclusion of an impedance convertor in the electrode assembly removes the necessity for using electrode cream. Although equal spacing of the electrodes around the thorax is inefficient in terms of information content per electrode the attention to detail required for electrode placement using the described system is minimised as compared with other multiple lead systems. Furthermore, the principles adopted in the design and construction of the apparatus do not limit the number of chest electrodes to 24.