الکتروشوک درمانی یک طرفه پالس کوتاه و شناخت؛ اثرات قرار دادن الکترود، دوز محرک و زمان

To clarify advantages of unilateral electrode placement as an optimisation technique for electroconvulsive therapy (ECT) for depression, aims were to meta-analyse unilateral ECT effects on cognitive performance relative to: (1) bitemporal electrode placement, (2) electrical dosage, and (3) time interval between final treatment and cognitive reassessment. Relevant electronic databases were systematically searched through May 2009, using the terms: "electroconvulsive therapy" and ["cogniti∗", "neuropsycholog∗", "memory", "attention", "executive", "spatial", or "intellectual"]. Inclusion criteria were: independent study of depressed patients receiving unilateral or bitemporal brief-pulse ECT; within-subjects design; use of objective cognitive assessments; available mean electrical dosage for unilateral samples. Standardized pre-post ECT weighted effect sizes were computed and pooled within 16 cognitive domains by a mixed-effects model. Thirty-nine studies (1415 patients) were meta-analysed. Up to three days after final treatment, unilateral ECT was associated with significantly smaller decreases in global cognition, delayed verbal memory retrieval, and autobiographical memory, compared to bitemporal ECT. Significant publication bias was found for autobiographical memory, favouring reporting of larger percentage loss. Higher unilateral ECT electrical dosage predicted larger decreases in verbal learning, delayed verbal memory retrieval, visual recognition, and semantic memory retrieval. When retested more than three days after completing ECT, no significant differences remained between the two electrode placements; for unilateral ECT, electrical dosage no longer predicted cognitive performance whereas increasing interval between final treatment and retesting predicted growing improvement in some variables. This interval is a more useful long-term predictor of cognitive function than electrode placement or electrical dosage following unilateral ECT.

Electroconvulsive therapy (ECT) is a well-established and highly effective treatment for severe depression (American Psychiatric Association, 2001). However, its use remains limited mainly because of concerns about cognitive side-effects, especially effects upon both short- and long-term memory function. Several modifications of ECT technique have been introduced to minimise these side-effects. These include: using unilateral, instead of bilateral, electrode placement; moving from sine wave electrical stimulus to more efficient brief-pulse stimuli; and adjustment of stimulus intensity to the individual patient’s seizure threshold (ST, the minimum charge required to induce a generalised seizure that is needed for therapeutic effect). While moderately suprathreshold stimulation (e.g. 1.5 x ST) is effective for bitemporal ECT (Eranti et al., 2007), substantially higher charges are required for right unilateral ECT to approach the antidepressant effectiveness of bitemporal ECT (Little et al., 2003 and Sackeim et al., 2000). Although unilateral ECT is associated with less cognitive side-effects than bitemporal ECT, higher charges of unilateral ECT may result in more deficits than lower charges (UK ECT Review group, 2003). A major focus of recent research has therefore been to determine if, at higher dosage, unilateral ECT keeps its potential advantage over bitemporal ECT with regards to cognitive side-effects. Reports on this possible optimisation technique are inconsistent – some studies do not find significant differences between high-dose unilateral ECT and standard bitemporal ECT with regards to cognitive side-effects (McCall et al., 2002 and Schweitzer et al., 2004) while others demonstrate less severe effects following high-dose unilateral ECT (Sackeim et al., 2000 and Sackeim et al., 1993). The UK ECT review group (2003) systematically reviewed randomised controlled trials that assessed effect of electrical stimulus dose on cognitive functioning. Data at end of treatment from only five studies were described, but not meta-analysed. Conclusions were that there was no difference between high-dose and low-dose unilateral ECT on personal memory, with some indication that anterograde memory might be more impaired in the high-dose group. Findings on the Mini-mental State Examination (MMSE) described from two studies were inconsistent. No short- or long-term follow-up data were included in this systematic review. A recent meta-analysis of cognitive outcomes following ECT confirmed that electrode placement is a significant moderator of performance, with unilateral ECT being associated with less cognitive side-effects than bitemporal or mixed treatments (e.g. unilateral followed by bitemporal) in some cognitive domains (Semkovska and McLoughlin, 2010). However, because of methodology restrictions, the effect of electrode placement was not systematically meta-analysed and its contribution was not examined independently from stimulus waveform, which also was found to be a significant moderator of cognitive performance. In addition, that meta-analysis included only studies that assessed cognition using standardised and validated neuropsychological tests. This stringent inclusion criterion precluded the meta-analysis of retrograde amnesia. In fact, the accompanying systematic review of the ECT literature revealed that there was a significant paucity of standardised instruments used in assessment of retrograde amnesia and thus could not provide an estimate of its importance and resolution over time. As retrograde memory deficits are a major concern to patients (Rose et al., 2003), possible impairment of this cognitive function following ECT still needs to be quantified despite the limitations of available instruments. Therefore a less stringent inclusion criterion with regards to potentially suitable objective cognitive tests needed to be adopted in order to be able to include retrograde amnesia assessments. To clarify the effects of unilateral ECT for depression upon cognitive function, the aims of the present meta-analysis are: (1) to compare the pattern, extent and post-treatment resolution of cognitive side-effects following right-sided brief-pulse unilateral ECT with those observed following brief-pulse bitemporal ECT and (2) to examine the effects of both electrical stimulus dosage and reassessment time interval on cognitive outcomes following right unilateral brief-pulse ECT.

Our study provides evidence that differences in electrode placement and stimulus dosage on cognitive outcomes following unilateral ECT for depression are limited to the first three days after end of treatment. During this period, for some but not all variables, smaller cognitive disturbances are observed following unilateral ECT compared to bitemporal ECT, and higher electrical dosage in unilateral samples predicts greater decreases in performance. After this subacute period, no significant differences exist between unilateral and bitemporal samples, while no significant relationship remains between electrical stimulus dosage and change in cognitive performance following unilateral ECT. Time interval after final treatment predicts continuous improvement in anterograde episodic memory (both verbal and visual), autobiographical memory and executive functioning.