Capture detection method

A method of discriminating between captured and loss-of-captured heartbeats, comprising the steps of:

• (a) stimulating a patients heart with a pulse generator;
• (b) monitoring a plurality of segments of a cardiac impedance signal, each segment corresponding to one of a plurality of heartbeats occurring over a time interval corresponding to at least one of said patient's respiratory cycles;
• (c) measuring a peak-to-peak value for each monitored impedance signal segment;
• (d) computing a minimum peak-to-peak value for said plurality of impedance signal segments;
• (e) storing a threshold value corresponding to said minimum peak-to-peak value;
• (f) determining a direction value for each of said monitored impedance signal segments;
• (g) repeating steps (a) through (f) if all of said direction values determined in step (f) are not equal to a common direction;
• (h) monitoring a new plurality of segments of said cardiac impedance signal, each segment corresponding to a new plurality of heartbeats;
• (i) comparing a direction value for each of said new plurality of segments with said common direction;
• (j) for each one comparison performed in step (i), generating a loss-of-capture signal if said one comparison indicates that said direction for said one of said new plurality of segments is not said common direction;
• (k) for each of said new plurality of segments, comparing a peak-to-peak value therefor to said threshold value stored in step (e);
• (l) for each one comparison performed in step (k), generating a loss-of-capture signal if said one comparison indicates that said peak-to-peak value for said one of said plurality of segments is less than said threshold value;
• (m) for each one comparison performed in step (k), generating a capture signal if said one comparison indicates that said peak-to-peak value for said one of said plurality of segments is less than said threshold value.