A cardiac rhythm management apparatus may include a monitored energy source, a reference energy source, and a measurement module. The monitored source provides an initial pacing amplitude voltage and a pacing droop voltage, while the reference source provides a substantially fixed reference voltage. The measurement module, coupled to the monitored source and the reference source, provides a measurement related to the lead impedance associated with the rhythm management apparatus that is substantially independent of the reference voltage. Thus, a system may include the apparatus coupled to a lead wire. An article may cause a machine to implement a method which operates to determine a ratio of the actual initial pacing amplitude voltage to the actual pacing droop voltage.