Patent ID: 8428718

Claim:
An implantable medical device, comprising: a plurality of electrodes; an output circuit outputting a plurality of output pulse signals along a vector formed by electrodes of the plurality of electrodes; a measurement circuit generating a corresponding plurality of measurement signals in response to the plurality of output pulse signals; and a microprocessor configured to determine a plurality of period average impedances in response to the plurality of output pulse signals and the plurality of measurement signals corresponding to a predetermined time period, determine an adaptive baseline trend of period average impedances of the plurality of period average impedances corresponding to a first time period, determine a short term trend of period average impedances of the plurality of period average impedances corresponding to a second time period different from the first time period, determine changes in relative position of the short term trend and the baseline trend, determine differences between the baseline trend and the calculated period average impedances, and accumulate, in response to the determined changes in relative position of the baseline trend and the short term trend, the determined differences between the baseline trend and the calculated period average impedances.