The invention relates to cardiac-activity based prediction of a rapid drop in a patients blood pressure during hemodialysis. A proposed alarm apparatus includes an input interface, primary and secondary analysis units and an alarm-generating unit. An electrocardiogram signal (HECG) of the patient is received via the input interface by the primary analysis unit, which in response thereto produces a heart-rate-variability signal (PHRV). The secondary analysis unit determines an intensity of ectopic beats (PEBC) based on the electrocardiogram signal (HECG). The alarm-generating unit investigates whether the intensity of ectopic beats (PEBC) is relatively low or relatively high. In case of a relatively low intensity, the unit triggers an alarm signal (&alpha) indicative of an estimated rapid blood pressure decrease if the heart-rate-variability signal (PHRV) fulfills a first alarm criterion. In case of a relatively high intensity, however, the unit triggers the alarm signal (&alpha) if the intensity of the ectopic beats (PEBC) fulfills a second alarm criterion.
