Methods and devices for determining optimal Atrial to Ventricular (AV)
pacing intervals and Ventricular to Ventricular (VV) delay intervals in
order to optimize cardiac output. Impedance, preferably sub-threshold
impedance, is measured across the heart at selected cardiac cycle times
as a measure of chamber expansion or contraction. One embodiment measures
impedance over a long AV interval to obtain the minimum impedance,
indicative of maximum ventricular expansion, in order to set the AV
interval. Another embodiment measures impedance change over a cycle and
varies the AV pace interval in a binary search to converge on the AV
interval causing maximum impedance change indicative of maximum
ventricular output. Another method varies the right ventricle to left
ventricle (VV) interval to converge on an impedance maximum indicative of
minimum cardiac volume at end systole. Another embodiment varies the VV
interval to maximize impedance change.