A cardiac-activity based prediction of a rapid drop in a patient's blood pressure during extracorporeal blood treatment is disclosed. A proposed alarm apparatus includes a primary beat morphology analysis unit bank of secondary analysis units and an alarm generating unit. The primary beat morphology analysis unit discriminates heart beats in a received basic electrocardiogram signal, classifies each beat into one out of at least two different beat categories, and associates each segment of the signal with relevant event-type data. The event-type data and the basic electrocardiogram signal together form an enhanced electrocardiogram signal, based upon which the primary beat morphology analysis unit determines whether one or more secondary signal analyses should be performed. Depending on the enhanced electrocardiogram signal's properties, the bank of secondary analysis units performs none, one or more of up to at least two different types of secondary analyses, and for each analysis performed produces a respective test signal. The alarm generating unit receives the test signals, and triggers an alarm signal indicative of an estimated rapid blood pressure decrease, if at least one alarm criterion is fulfilled.
