A system and method for use in an implanted cardiac pacing device, whereby
an optimal AV delay is determined at or near lower rate (pacing) limit
(LRL) by determining measuring the variance, or instability, of the QT
interval for a set of intervals. In one embodiment, asynchronous "LRL
pacing" with a first programmed AV delay determines a measure of QT
variance. The difference between the maximum QT and the minimum QT is
expressed as QT difference (QTD). For each programmed AV delay the QT
variance is again measured and the optimal AV delay produces minimum QTD.
In another embodiment, AV delay is modulated around base values for a
time. The difference between QT for the modulated AV and for the base AV
(dQT) is measured at each base value, and the optimal AV delay
corresponds to the smallest dQT.