Pacing output optimization to improve device longevity

A system including or for use with an implantable medical device (IMD) configured to deliver pacing pulses to cardiac tissue of a patient's heart, the system comprising one or more processors configured to:

• determine a pacing impedance of the cardiac tissue that is to be paced by the IMD;
• determine a first capture threshold of the cardiac tissue that is to be paced by the IMD when the cardiac tissue is paced using one or more pacing pulses having a first pulse width;
• determine an estimate of a maximum membrane response for the cardiac tissue of the patient's heart, based on the pacing impedance, the first pulse width, and the first capture threshold with or without a specified safety margin applied;
• wherein the first pulse width and the capture threshold with the specified safety margin applied collectively comprise a first pacing parameter set;
• determine an iso-safety factor strength duration curve by determining, based on the first pacing parameter set and the estimate of the maximum membrane response, a plurality of further pacing parameter sets that each includes a respective different pulse width and a respective pacing amplitude having the specified safety margin applied;
• determine a current or charge drain curve by determining, based on the pacing impedance, a respective current or charge drain value for each of the first pacing parameter set and the plurality of further pacing parameter sets;
• and
• determine, based on the iso-safety factor strength duration curve and the current or charge drain curve, a preferred pacing parameter set that includes a preferred pulse width and a preferred pacing amplitude, which provides the specified safety margin at a lower current or charge drain than the first pacing parameter set.