A pacemaker having a motion sensor delivers atrial-synchronized ventricular pacing by detecting events from a signal produced by the motion sensor and delivering ventricular pacing pulses at a rate that tracks the rate of the detected events. The pacemaker is configured to confirm atrial tracking of the ventricular pacing pulses by determining if detected events from the motion sensor signal are atrial events. The pacemaker is configured to adjust a control parameter used for detecting events from the motion sensor signal if atrial tracking is not confirmed.