An implantable medical device and associated method to determine an optimal control parameter setting for controlling a cardiac therapy that includes a plurality of electrodes, a therapy module to deliver cardiac pacing signals between the plurality of electrodes at a plurality of pacing rates, an admittance measurement module to determine admittance signals associated with each of the plurality of pacing rates, and a control unit to determine, for each pacing rate of the plurality of pacing rates, intervals between admittance signals associated with the pacing rate, compare the determined intervals, and determine a pacing rate of the plurality of pacing rates as an optimal rate for delivering the cardiac therapy in response to the determined intervals.
