The Comparative Effectiveness of Fixed and Stimulus Dosing Forms of Electroconvulsive Therapy for the Treatment of Unipolar Depression: A ‘Quality Assurance’ Study

Abstract

While the necessity for suprathreshold dosing has become widely accepted as the most effective means of administering ECT, there are differing schools of thought regarding the utilisation of this approach in day-to-day clinical practice. Abrams [1,2] and Fink [3] support fixed dosing whereby patients receive a fixed dose of about 2.5 times the average population seizure threshold (approximately 375–500 mC). On the other hand, Sackeim [4] developed the technique of stimulus dosing with which individual seizure thresholds and suprathreshold doses are determined. Both the American, and Australian and New Zealand Psychiatric Associations [5,6] view both fixed and stimulus dosing in ECT as appropriate and acceptable alternatives. This has also been endorsed in recent literature [7].

Common to both fixed and stimulus dosing procedures in ECT is the concept of the seizure threshold. Recent studies [8,9] suggest that this threshold varies with electrode placement (higher for bilateral), age (increases with increasing age), and gender (higher in males) [4]. Sackeim et al. [10] have demonstrated that it is the degree to which the stimulus intensity exceeds the seizure threshold that determines the efficacy of unilateral ECT and also the speed of response to unilateral and bilateral ECT.

Studies comparing low (seizure threshold) and high (2 to 3 times seizure threshold) dose ECT have tended to show favourable results for the latter form of treatment. Sackeim [12] studied patients in four randomly allocated groups and noted that patients receiving low dose unilateral therapy required a greater number of treatments and showed a poorer response than those treated with high dose therapy.

METHOD

This study was performed at the Prince Henry Hospital in Little Bay, New South Wales, Australia. The psychiatric unit included a tertiary referral Mood Disorders Unit.

Prior to July 1990, ECT was given with a Kabtronics machine using a 150 mC (milliCoulomb) fixed dose (as did many facilities throughout Australia at the time [14]). This will subsequently be referred to as ‘fixed low dose’ therapy. This was doubled using the same machine to a fixed dose of 300 mC (referred to as ‘fixed high dose’ therapy) in 1990. In October of 1993, stimulus dosing was introduced as described by Sackeim [4] initially using the Kabtronics, then later the Thymatron apparatus, thus providing the occasion to study three groups of patients treated with different doses and types of ECT each over a two-year period. A search using Medline failed to reveal any study comparing course lengths amongst these three groups.

ECT records were searched for the names of all patients treated with ECT. Three periods of two years were selected for each of the three forms of ECT (the last two years of ‘low dose’, the middle two years of ‘high dose’, and the first two years of stimulus dosing). Individual hospital records were reviewed and information obtained regarding patient's age and gender, the clinical psychiatric diagnosis, and the number and type of treatments given per course of ECT.

Results were analysed using SPSS [13], and means and standard deviations were calculated using ANOVA. This generated levels of significance using the pooled variance estimate. Analyses were limited to patients with unipolar Major Depression, as the numbers of those with other conditions were too small to be meaningful.

RESULTS

Table 1 details the numbers, genders and diagnoses of all patients with unipolar depression treated with ECT during the periods defined above. Note that individual patients may have had more than one course of ECT during the study period.

Table 1:

Clinical details of unipolar depressed patients treated with ECT

Comparisons of the length of courses of treatment for the three types of ECT were then performed. The results are detailed in Table 2.

Table 2:

Means of ECT course lengths for patients with Unipolar Depression

Table 3 details those patients who had unilateral ECT only, while Table 4 compares those who had bilateral ECT at some stage.

Table 3:

Means of ECT course lengths for patients with Unipolar Depression treated with unilateral ECT only

When all unipolar depressed patients treated with ECT were considered (Table 2) there was a trend towards shorter course lengths from the fixed low dose to fixed high dose to stimulus dosing. The difference in the mean number of treatments per courbetween the fixed low dose ECT group and the stimulus dosing group (14.6 v 11.7 treatments) was statistically significant (P < 0.01).

Data from patients with Unipolar Depression who only received unilateral ECT (Table 3) revealed significant differences (P < 0.001) in the mean numbers of treatments per course between those treated with fixed low dose ECT and those treated with other types of ECT.

Considering those patients with Unipolar Depression treated with bilateral ECT at some stage (Table 4), there was, once again, an overall reduction in the mean number of treatments per course for stimulus dosing compared to fixed low dose therapy (P < 0.05).

Table 4:

Means of ECT course lengths for patients with Unipolar Depression treated with bilateral ECT at some stage

DISCUSSION

This retrospective case note quality assurance study found that the mean number of ECT treatments per course for patients diagnosed with Unipolar Depression tended to be less in those treated with either fixed high dose or stimulus dose therapy than those who received fixed low dose ECT. However, with the exception of patients with Unipolar Depression who received unilateral ECT only, significant statistical differences in the mean number of treatments were only found between the low dose therapy and stimulus dosing groups. Assuming that shorter courses of ECT equate to shorter hospital admissions, this finding may represent a significant economic advantage in treating patients with stimulus dosing ECT for depressive disorders.

A number of possible explanations for the above findings have not been explored in this study. The study spanned a period from 1988 to 1995, and in this time a number of pharmacological, psychological and social advances in the treatment of depression were introduced to the field of psychiatry. It is possible that these, rather than the type of ECT given, may have led to shorter average courses. The possible effect of referral bias and changes in routine practice, while being acknowledged, were not examined in this study.

In conclusion, this quality assurance study of the practical impact – on treatment course length – of various forms of ECT, suggests a significant cost benefit of stimulus dosing over fixed low dose treatment. There was also some evidence of an advantage of fixed high dose treatment over fixed low dose therapy. No substantial differences between stimulus dosing and fixed high dose therapy were demonstrated.

Acknowledgements

The assistance of Dusan Hadzi-Pavlovic and Philip Ward with statistical analyses is acknowledged with thanks. We are also grateful to the assistance given by Caroline Newton, Kerrie Vandervegt and Deanne Vandervegt in locating patient files for this study.

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