DISCUSSION
MDD, depression, HAMD, depressive symptoms
The present study identified 3 distinct and clinically relevant classes of MDD patients undergoing ECT treatment. Class 1 was a non-remit group with 12.5% of patients remitted after 3 weeks, Class 2 was a rapid-response group with 100% of patients remitted after 3 weeks, and Class 3 was a slow-response group with 90.73% of patients remitted after 3 weeks. The 3 groups observed significant differences in demographic variables and clinical symptoms. The more severe depression scores were putative predictors contributing to a more rapid response to ECT treatment. In comparison, older MDD patients with severe symptoms were associated with less response to ECT treatment.In line with previous latent class growth analysis (LCGA) analysis in ECT treatment (Based on the trajectory analysis, we identified 2 characteristics associated with the response trajectory: age and baseline HAMD score. These findings suggest that patients at an older age with severe HAMD scores are less likely to respond to the ECT treatment, but patients with more severe depressive symptoms are more likely to respond rapidly. Previous studies indicated the influence of age in the ECT outcomes (A recent meta-analysis has demonstrated that medication failure could predict a lower response rate to ECT (This study has several limitations. Firstly, the present study included 3 treatment protocols, which may affect the impact of predictors, especially the unilateral protocol, which shows significant differences between the 3 groups. Though the treatment types did not contribute to the classification of the 2 groups, the underlying influence has not been entirely ruled out. Besides, we only included demographic and clinical characteristics in the model. Adding neurobiological and neurophysiological markers might improve its accuracy. For example, previous studies suggested that baseline cingulate theta cordance and fronto-temporal connectivity can predict response to ECT (In conclusion, the present study identified 3 subgroups and established a predictive model for MDD patients undergoing ECT treatment. Age and baseline HAMD score showed vital clinical utility in predicting ECT treatment response. Further studies with larger samples are required to improve the generalization of the model for clinical application.