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BackgroundsStudies to date detailing trajectories of depressive symptom dimensions in patients undergoing index electroconvulsive therapy (ECT) have been small in number; many studies have focused on the total score of the rating scale. This Study aimed to investigate the trajectories of depressive symptom dimensions and the time point when the difference in improvement of depressive symptom dimensions between the remitters and non-remitters appeared.MethodsA retrospective analysis was performed on 80 patients with major depressive disorder who underwent index ECT. The Hamilton Depression Rating Scale-17 was used, and each item was clustered into four dimensions (depression, anxiety, insomnia, and somatic symptoms). Dimensions were standardized to a T-score and assessed at five time points (pre-ECT, and after the third, sixth, ninth, and twelfth ECT session). The data were analyzed using the generalized estimating equations method.ResultsIn the total sample, the T-scores of all dimensions continued to reduce significantly until the sixth session. The reduction of the depression dimension T-score was prolonged until the ninth session. Significant differences in the amount of improvement between remitters and non-remitters appeared after the sixth session. The depression dimension showed a greater reduction in T-score than the other dimensions throughout the entire index ECT course.ConclusionsThe depression dimension improved more than other dimensions in patients undergoing ECT. It may be beneficial to administer at least six treatments to avoid early termination of ECT and relapse. Managing other depressive symptoms, such as insomnia, could play a significant role in improving therapeutic effect. Further studies examining depression symptoms using more accurate scales and specifying the neuronal circuits associated with each dimension are necessary.