Impedance should remain stable over what period?

Impedance, which refers to the opposition that the pacing system encounters during electrical stimulation, is an important measure in cardiac pacing. It should remain stable over the lifetime of the device. This stability is crucial because it indicates that the lead is functioning properly, the contacts are stable, and there are no significant changes that could affect pacing thresholds or lead integrity.

Fluctuations or increases in impedance might suggest issues such as lead dislodgement or fracture, or changes in tissue characteristics around the lead that could lead to complications. Therefore, monitoring impedance over the entire lifespan of the pacing device helps in ensuring the ongoing safety and efficacy of the pacing therapy provided to the patient.

In this context, the other options suggest more limited periods for stability, which do not encompass the entire operational life of the device as needed for effective monitoring and management of pacing systems.