 Compared to patients who are not medication resistant, who generally retain the highest likelihood of response to ECT alone, patients with TRD have a lower response rate to ECT with average estimates of response to ECT alone between 50-60 APA 2001 ECT Task Force. Additionally, while ECT for most patients may provide acute remission, those patients with TRD remain at high risk for rapid relapse Sackeim 2001, Petrides 2001, Sackeim 1990, Aronson 1987. Consequently, ECT alone may be insufficient to achieve remission or to prevent relapse. Interestingly, resistance to some types of medication was found also to predict resistance to ECT alone, i.e., resistance to tricyclic antidepressants correlated with a less likely response to ECT, though the same prediction did not hold for serotonin reuptake inhibitors Prudic 1996, Prudic 1990. 