A method for delivering electrotherapy from a defibrillator includes the steps of providing a source of patient ECG signals received during a CPR period, estimating from the patient ECG signals the likelihood of a shockable rhythm existent during the CPR period, and determining whether CPR should be interrupted prior to the end of the CPR period to deliver electrotherapy based on the estimating step. Based on the determining step, the defibrillator may then provide an output instruction to stop CPR. The AED (10) thus enables an improved rescue protocol.