You are quite right that informed consent with severely ill persons is a major issue. The medical community and the legal system agree, which is why the laws on this are very clear. If a person is unable to appropriately weigh the risks and benefits of a medical decision, they are considered to lack decisional capacity, and having them sign an informed consent is illegal. In that case, care can be given only on an emergency basis (ECT doesn’t qualify) or with the informed consent of their legal decision maker, often whoever is their medical power of attorney. Even with the consent of the POA, at least in my state, ECT cannot be given against the wishes of the patient without going through a separate and very extensive legal process regarding guardianship. Usually a patient will agree to treatment because they trust their loved one to make the right decision. It is absolutely appropriate to question the ethics of this whole situation. However, in practical terms, what is the alternative? Severe depression is life-threatening, and medications will take several weeks, at best, to take effect. It is basically impossible to do meaningful psychotherapy with most severely depressed individuals. In many cases ECT is the only treatment that will take effect quickly enough.