What should a nurse expect when an on-demand pacemaker is functioning effectively?

When an on-demand pacemaker is functioning effectively, it is expected that the heart rate will be at least at the demand rate set by the pacemaker. This means that the device is sensing the intrinsic cardiac activity and providing pacing when the heart's own impulses fall below the established threshold. The demand rate is the minimum heart rate the pacemaker is programmed to maintain, ensuring that the patient achieves adequate cardiac output and preventing bradycardia.

For the other options, if no pulse changes are observed, it might indicate that the pacemaker is either not functioning properly or is not needed at that moment, as the heart's own rhythm is adequate. A heart rate consistently below the demand rate would suggest that the pacemaker is not providing enough pacing, potentially leading to insufficient heart rate and inadequate blood flow. Frequent pacing spikes would indicate that the pacemaker is actively pacing, which could be a sign of inadequate intrinsic heart activity rather than effective functioning, where one would expect to see pacing spikes only when the heart's own rate drops below the demand setting. Thus, the presence of pacing spikes alone does not indicate effective functioning of the pacemaker.