Epidemiological studies of electroconvulsive therapy for depression

Major depressive disorder is a condition that causes great suffering and substantial disability world-wide. Severe forms of major depressive disorder (MDD) are also associated with a high risk of suicide. For severe forms of MDD, ECT is the most effective treatment. ECT is generally well tolerable but there are side-effects. Memory disturbances are the most common complaint. During the procedure the patient is sedated but there is no consensus on optimal anaesthetic regime. Even though ECT often relieves the symptoms greatly, MDD is often a recurring condition and relapse the first six months is common. As of now there is no consensus on optimal pharmacological treatment strategy post ECT.

In study I we investigated the effect of electrical charge on subjective memory worsening. The study was a register-based cohort-study. Data was gathered from the Q-ECT. The study included 154 patients. 57 patients had received a higher electrical charge, and 97 patients received a lower electrical charge. Subjective memory worsening (SMW) was measured with a global memory rating scale (CPRS-M). There was a significant difference in SMW among the two groups, patients with a higher electrical charge had a higher occurrence of SMW compared to patients with a lower electrical charge (44% vs 25%, p=0.014). There was no significant difference in terms of relief of depressive symptoms between the two groups. The study concluded that there are limited benefits of a high electrical charge compared to a moderate.

In study II we wanted to explore prescription patterns and compare the effect of different pharmacological strategies on risk of relapse following ECT for MDD among patients who responded distinctively to the initial treatment. The study included a total of 2858 patients, and the risk of relapse was investigated during the first year after ECT. Relapse in MDD was defined as; suicide, attempted suicide, psychiatric rehospitalisation or renewed ECT. During the first year of follow-up 52.2% of patients relapsed, according to our definition. We used a Cox proportional hazards model to calculated adjusted hazard ratios (HR). The model was adjusted for several factors including age, sex, psychiatric comorbidity and previous pharmacological treatment attempts. We found a non-significant association between dispensation of lithium and a lower risk of relapse (HR 0.86, 95% CI 0.69-1.07, p=0.17). Dispensation of antipsychotics were associated with an increased risk of relapse (HR 1.17, 95% CI 1.05-1.31, p=0.006).

In study III we examined the effect of anaesthetic dosage intervals on the antidepressant effect of ECT. The study was a register-based cohort study and included 7197 patients. We compared high, medium, and low dosage intervals associations with response to treatment. The primary outcome was measured with the Clinical Global Impressions - Improvement Scale (CGI-I). Secondary outcomes were remission from depressive symptoms, measured with the Montgomery-Åsberg Depression Self-rating scale (MADRS-S). We used a logistic regression model and calculated adjusted odds ratios. The model was adjusted for several factors including age, sex, psychiatric comorbidity and number of treatments. We found that a lower dosage, compared to high, was associated with a greater chance of response (OR 1.22, 95% CI 1.07-1.40, P = 0.004). There was an increase of reported SMW among the patients who received a lower dosage interval, most likely attributed to the increased seizure duration and activity. In conclusion, lower dosage intervals of anaesthetics improve treatment outcome but could potentially increase reports of SMW.

In study IV we investigated patient attitudes towards renewed ECT treatment after receiving ECT for MDD. Patients who received ECT for MDD participated in a six-month follow-up. During this follow-up, patients were asked if they would accept renewed ECT under similar circumstances. A total of 1917 patients were included in the study. Among these, 51.1% of patients were positive, 27.6% undecided and 21.3% negative towards receiving ECT under similar circumstances at the time of the six-month follow up. We examined which factors were associated a negative attitude towards renewed ECT. Adjusted odds ratios were calculated using a logistic regression model. Patients who responded to treatment were less likely to have a negative attitude towards renewed ECT (odds ratio 0.32, 95% CI 0.25-0.41, P < 0.001). In addition, patients with previous experience of ECT were less likely to have a negative attitude towards renewed ECT (odds ratio 0.44, 95% CI 0.34-0.58-1.02, P < 0.001). In conclusion, response is an important factor in terms of predicting future attitudes towards renewed ECT.

List of scientific papers

I. Kronsell A, Nordenskjöld A, Tiger M. Less memory complaints with reduced stimulus dose during electroconvulsive therapy for depression. J Affect Disord. 20 augusti 2019;259:296-301. https://doi.org/10.1016/j.jad.2019.08.064

Il. Kronsell A, Nordenskjold A, Boden R, Mittendorfer-Rutz E, Reutfors J, Rossides M, Tiger M. Real-world analysis of pharmacological treatments to prevent relapse after electroconvulsive therapy for major depressive disorder: A nation-wide cohort study. [Manuscript]

III. Kronsell A, Nordenskjold A, Bell M, Amin R, Mittendorfer-Rutz E, Tiger M. The effect of anaesthetic dose on response and remission in electroconvulsive therapy for major depressive disorder: nationwide register-based cohort study. BJPsych Open. 23 mars 2021;7(2):e71. https://doi.org/10.1192/bjo.2021.31

IV. Kronsell A, Nordenskjöld A, Mittendorfer-Rutz E, Tiger M. Long-term follow-up on patient attitudes towards renewed ECT: A register-based cohort study. J Psychiatr Res. 25 juni 2024;177:24-30. https://doi.org/10.1016/j.jpsychires.2024.06.040