An implantable medical stimulation device (1) for performing an anti-
bradycardia pacing in an atrium (RA) of a patient's heart (H) comprises a generator device (12) comprising
processing circuitry (120) for
processing cardiac sense signals and generating
cardiac stimulation signals and a housing (121), and an
electrode arrangement for sensing cardiac signals and outputting
cardiac stimulation signals. The
electrode arrangement comprises at least one atrial
electrode pole (102, 103). The
processing circuitry (120) is configured to perform a rate-adaptive
cardiac stimulation in which a paced
heart rate is adjusted based on a load state of the patient, wherein the processing circuitry (120) is configured to obtain a momentary impedance curve (ΔZ1), to compare said momentary impedance curve (ΔZ1) to a stored reference curve (ΔZrefRest) and to perform an adaption of the paced
heart rate based on the comparison of the momentary impedance curve (ΔZ1) to the stored reference curve (ΔZrefRest). The processing circuitry (120) is configured to obtain said momentary impedance curve (ΔZ1) by conducting a unipolar impedance measurement between the at least one atrial electrode pole (102) and the housing (121).