The invention relates to cardiac-activity based prediction of a rapid drop in a patients blood pressure during hemodialysis. A proposed alarm apparatus (100) includes an input interface (110), primary and secondary analysis units (130 140) and an alarm-generating unit (150). An electrocardiogram signal (HECG) of the patient is received via the input interface (110) by the primary analysis unit (130), which in response thereto produces a heart-rate-variability signal (PHRV)- The secondary analysis unit (140) determines an intensity of ectopic beats (PEBC) based on the electrocardiogram signal (HECG)- The alarm-generating unit (150) investigates whether the intensity of ectopic beats (PEBC) is relatively low or relatively high. In case of a relatively low intensity, the unit (150) triggers an alarm signal (a) 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 (150) triggers the alarm signal (a) if the intensity of the ectopic beats (PEBC) fulfills a second alarm criterion.
