Pacemaker battery status should be evaluated with each interrogation. At the beginning of life (BOL) the battery voltage is approximately 2.8 V (specific values vary from manufacturer to manufacturer), and pacemaker behavior is as programmed. Over the life of the pacemaker, the battery reaches elective replacement indicators (ERI). At ERI, the battery voltage is reduced, but still able to support most if not all of the pacemaker functions. At this point, generator replacement should be scheduled in weeks to months depending upon the degree of dependence upon the pacemaker. As voltage reduces further, battery end of life (EOL) is reached. At this junction, the voltage is unable to support basic pacer function, and immediate generator change is required. It usually takes 3–6 months for the pacemaker battery to reach EOL status after the battery reaches ERI. Another parameter used to determine the pacemaker’s battery status is the battery’s impedance. As the battery voltage declines, the battery impedance rises.

While different leads offer differ impedances, once a lead is implanted, the fluctuation of impedance is very narrow. The lead impedance of each implanted lead should also be measured during each interrogation. Lead impedance is the sum of all factors that retard current flow. Very high lead impedances suggest the existence of lead fractures or a loose connection in the device header (between the lead pin and the set screw). Very low lead impedances suggest insulation failure. The change in impedance from a previous recording is more important than the absolute value of the lead impedance. Changes greater than 300 Ω are abnormal and should prompt further evaluation.

Although many devices have automated evaluations of pacing and sensing thresholds, many require manual pacing and sensing threshold determinations. Sensing is the ability of the pacemaker to detect and respond to intrinsic atrial and ventricular activity. Sensing thresholds are unable to be assessed without the presence of native atrial and/or ventricular activity. Most current programmers will automatically check the amplitude of the underlying atrial or ventricular electrograms by transiently inhibiting pacing or lowering the pacing rate in the respective chambers. This would allow the emergence of the underlying rhythm and measurement of its amplitude as sensed by the pacemaker in its respective chamber. Two other techniques can be used used to evaluate sensing thresholds if the programmer lacks the automated mode. One technique involves recording telemetered electrograms and measuring peak-to-peak amplitudes of the resulting signal. The more common technique utilized in both automated and semi-automated fashions, is to progressively reduce the sensitivity setting of the pacemaker until an inappropriate spike is delivered indicating that the pacemaker no longer senses an intrinsic electrical activity in the chamber being tested. To use this method to assess ventricular sensing manually, the pacing rate needs to be programmed to a rate below the patient’s intrinsic heart rate. The patient’s dependency upon the pacemaker can also be assessed during this maneuver. By programming the ventricular chamber to a less sensitive mode (increasing the millivolt values) in the VVI mode the sensitivity value (in mV) at which an inappropriate pacer output is displayed corresponds to the sensing threshold of the ventricle. Atrial sensing thresholds can be manually determined in a similar fashion.