To Örebro University

Background: Electroconvulsive therapy (ECT) is often considered for patients with treatment resistant depression (TRD), as recommended by guidelines from several countries. However, previous studies have shown inconsistent results regarding the response to ECT in patients with TRD.

Objectives: To assess and compare the response rate of ECT for patients with TRD to that of other patients with depression (i.e. non-TRD) in a large and clinically representative patient sample. We hypothesized that patients with TRD would have a lower ECTresponse rate than other patients with depression.

Methods: Patients ≥18 years old, treated for a unipolar, non-psychotic depressive episode with at least one ECT session as part of a first-time, index ECT series between Jan. 1 2011 and Dec. 31 2017 were identified from the Swedish National Quality Register for ECT, and individually linked with other population-based registers. Patients with any life timediagnosis of bipolar disorder, manicor hypomanic episode, psychotic disorder, or dementia as well as those lacking registration of the primary out-come measure were excluded. Using the Prescribed Drug Register, we classified patients as having TRD if they had initiated a third consecutive trial of antidepressants or add-on medications before starting ECT. Remaining patients were considered to have other depression. The main outcome measure was response to ECT according to the Clinical Global Impressions–Improvement scale (CGI-I) assessed within a week after the ECT series, defined as a CGI-I assessment of ‘much' or ‘very much improved'. Outcome measures were compared between patients with TRD and with other depression using logistic regression to calculate odds ratios of response and corresponding confidence intervals, adjusting for potential confounders including sociodemographic and clinical covariates.

Results: A total of 4244 patients were included. Of these, 1121 patients were classified as TRD (61.2% female, mean age 51.4 years) and 3123 (54.3 % female, mean age 50.4 years) patients had other depression. The CGI-I response rate after ECT among patients with TRD was 65.9% compared to 75.9% in other patients with depression (adjusted odds ratio 0.64 [95% CI 0.54–0.75]).

Conclusions: A clear majority of patients with TRD as well as patients with other depression responded to ECT, although the response rate was lower in TRD.