Rate warying pacemaker apparatus and method for deriving a preferred one of different patient activity control signals

This pacing system relates to a rate varying cardiac pacemaker (1) for electrically stimulating the heart of a pacemaker wearer. The electrical cardiogenic heart is detected on a multipolar single probe with the aid of individual electrodes (7 to 10). Bipolar electrodes in the atrium allows for detection of the intra-atrial actions (P-wave) as a first rate control signal for controlling the pacemaker in the atrially triggered ventricular pacing mode (VDD). A second rate control signal other than the P-wave correlating with patient activity is deter mined in parallel with the P-wave control signal. The two control signals are compared to decide if the intra atrial actions (P-waves) are appropriate control signals. Pace rate control is switched between the two signals in order to produce the most beneficial pacing mode to the patient, for example, VDD or VVI rate responsive modes. This control system can respond to unreliability or instabilities of the intrinsic atrial P-wave signal, for example, fibrillation and shift control to another appro priate rate responsive mode.