Electrode placement

Figure 7 illustrates the sensitivity of the current distribution to electrode placement for two similar interdigitated designs. In the parallel row design, alternating rows of cylindrically shaped cathodes and... 

FIGURE 7.9 Three common electrode placements for an electrochemical detector. (A) The working electrode is integrated into the flow cell wall while the reference and auxiliary electrodes are placed downstream. (B) Both the working and auxiliary electrodes are integrated into the flow cell wall and the reference electrode is placed downstream. (C) The working electrode is integrated into the flow cell wall adjacent to the column effluent. As in example A, the reference and auxiliary electrodes are placed downstream. 

Electroconvulsive therapy may be administered using unilateral or bilateral electrode placement. Either mode requires consideration of seizure threshold. Several studies involving adults have shown that neither age nor other demographic variables are good predictors of seizure threshold (Coffey et ah, 1995 Enns and Kar-velas, 1995). Knowledge of seizure threshold may be... 

Finally, traditional electrode placements have also been reexamined. Letemendia et al. [1993] compared the efficacy of unilateral ECT, standard bilateral ECT [i.e., bifrontotemporal electrode placement], and bilateral ECT using a bifrontal placement. Both forms of bilateral ECT had superior antidepressant efficacy compared with that of unilateral ECT, and the bifrontal condition was somewhat superior to the standard bilateral placement. This finding further challenges the idea that the elicitation of a generalized seizure in and of itself is both necessary and sufficient for the antidepressant effect of ECT. Rather, the site or sites of seizure initiation, and perhaps propagation, may be critical determinants of therapeutic efficacy. 

Coffey et al. (1995b) assessed seizure threshold at the first and sixth treatments in 62 patients (50 patients received unilateral and 12 patients received bilateral ECT). Across the sample, seizure threshold increased by 47%. Only 56% of the patients demonstrated an increase in threshold, and electrode placement had no bearing on change in threshold. However, a fundamental limitation in this study was that the majority of patients had seizures at the first stimulation in the titration schedule. This overestimation of initial seizure threshold led to an underestimation of subsequent rise in threshold. 

Krystal and colleagues (1993, 1995) have similarly demonstrated differences in the EEG according to electrode placement and stimulus intensity. 

Neuroimaging techniques assessing cerebral blood flow (CBF] and cerebral metabolic rate provide powerful windows onto the effects of ECT. Nobler et al. [1994] assessed cortical CBE using the planar xenon-133 inhalation technique in 54 patients. The patients were studied just before and 50 minutes after the sixth ECT treatment. At this acute time point, unilateral ECT led to postictal reductions of CBF in the stimulated hemisphere, whereas bilateral ECT led to symmetric anterior frontal CBE reductions. Regardless of electrode placement and stimulus intensity, patients who went on to respond to a course of ECT manifested anterior frontal CBE reductions in this acute postictal period, whereas nonresponders failed to show CBF reductions. Such frontal CBF reductions may reflect functional neural inhibition and may index anticonvulsant properties of ECT. A predictive discriminant function analysis revealed that the CBF changes were sufficiently robust to correctly classify both responders (68% accuracy] and nonresponders (85% accuracy]. More powerful measures of CBF and/or cerebral metabolic rate, as can be obtained with positron-emission tomography, may provide even more sensitive markers of optimal ECT administration. 

Letemendia FJJ, Delva NJ, Rodenburg M, et al Therapeutic advantage of bifrontal electrode placement in ECT. Psychol Med 23 349-360, 1993 Letty S, Child R, Dumis A, et al 5-HT4 receptors improve social olfactory memory in the rat. Neuropharmacology 36 681-687, 1997 Levin E Nicotinic systems and cognitive function. Psychopharmacology 108 417-431, 1992... 

McEwen BS, Angulo J, Cameron H, et al Paradoxical effects of adrenal steroids on the brain protection vs. degeneration. Biol Psychiatry 31 177-199, 1992 McCarvey K, Zis AP, Brown EE, et al ECS-induced dopamine release effects of electrode placement, anticonvulsant treatment and stimulus intensity. Biol Psychiatry 34 152-157, 1993... 

Nobler MS, Sackeim HA Augmentation strategies in electroconvulsive therapy a synthesis. Convulsive Therapy 9 331-351, 1993 Nobler MS, Sackeim HA Electroconvulsive therapy clinical and biological aspects, in Prediction of Treatment Response in Mood Disorders. Edited by Goodnick P. Washington, DC, American Psychiatric Press, 1996, pp 177-198 Nobler MS, Sackeim HA, Solomou M, et al EEG manifestations during ECT effects of electrode placement and stimulus intensity. Biol Psychiatry 34 321-330, 1993 Nobler MS, Sackeim HA, Prohovnik 1, et al Regional cerebral blood flow in mood disorders. III treatment and clinical response. Arch Gen Psychiatry 51 884-897, 1994... 

Sackeim HA, Decina P, Kanzler M, et al Effects of electrode placement on the efficacy of titrated, low-dose ECT. Am J Psychiatry 144 1449-1455, 1987a Sackeim HA, Decina P, Prohovnik 1, et al Seizure threshold in electroconvulsive therapy. Effects of sex, age, electrode placement, and number of treatments. Arch Gen Psychiatry 44 355-360, 1987b... 

When the results from several studies are converted into similar units, a simple inspection of a graph or table readily reveals which studies have different outcomes from the majority. Such discrepancies can also be examined by a variety of statistical indices. For example, one can calculate a statistical index of homogeneity, remove the most discrepant study, and recalculate, revealing that all but one study is homogenous. If two studies are discrepant, one could remove both and again reexamine the indices of homogeneity, and so on. For an example, we summarize the relative efficacy of unilateral nondominant versus bilateral electrode placement for the administration of electroconvulsive therapy (ECT). Here, 10 studies had one result, and two others a different outcome (see Table 8-10 and Table 8-11, in Chapter 8). 

Use of caffeine has also been recommended to lower the threshold in patients who do not experience an adequate seizure (104,105 and 106). One report, however, found that caffeine appeared to produce neuronal damage in rats receiving ECS (107). Because adenosine may have neuroprotective effects, one postulated mechanism is the ability of methyixanthines (e.g., caffeine, theophylline) to block adenosine receptors. On a positive note, studies have not found a difference in cognitive disruption between patients receiving ECT with or without caffeine (108). Although the implications of the animal data for humans are not clear, and because shorter seizures may be effective in some patients, a conservative approach would be to augment with caffeine only when seizure duration is less than 20 seconds and response is inadequate ( 38). Alternatively, it may be appropriate to switch to BILAT electrode placement or from methohexital to etomidate when UND electrode stimulation produces inadequate seizure duration (even at maximal stimulus intensity) and response is insufficient ( 97, 98). 

Electrode Placement, Energy Levels, and Treatment Frequency... 

Attempts to attenuate the memory dysfunction seen with BILAT ECT have led to studies of alternate bilateral electrode placements. For example, asymmetric left frontal-right frontal temporal bilateral (ABL) electrode placement has been reported to produce the same degree of efficacy while inducing fewer cognitive side effects... 

Short-term adverse cognitive effects, which may be more severe with bilateral electrode placement, could delay or preclude an adequate trial with ECT. Strategies to circumvent this problem include the following ... 

Sackeim HA, Decina P, Kanzier M, et al. Effects of electrode placement on the efficacy of titrated, low-dose ECT. Am J Psychiatry 1987 144 1449-1455. 

Sackeim HA, Pmdic J, Devanand DP, et al. Effects of stimulus intensity and electrode placement on efficacy and cognitive effects of electroconvulsive therapy. N Engl J Med 1993 328 839-846. 

Swartz CM. Asymmetric bilateral right frontotemporal left frontal stimulus electrode placement. Neuropsychobiology 1994 29 174-178. 

Given an inadequate drug response, or in patients with manic delirium who pose an immediate risk to themselves or others, we would consider ECT. Although BILAT stimulus electrode placement may be more effective than unilateral (UND) placement, this conclusion is currently only tentative, given the small number of patients studied. Finally, the combined use of ECT plus an antipsychotic may benefit the most treatment-resistant patient and has not been reported to induce serious adverse events (303, 304, 305 and 306). 

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