Pacemaker "mode change"

I wear a pacemaker, implanted three years ago against bradycardia, and
have intermittent afib with 0 to 1 episodes monthly, lasting from a
few hours to a couple of days.

Reading the printouts released upon my periodical pacemaker controls,
I notice that the detected "mode changes" are a lot more than the
detected "atrial high frequency episodes" (frequency indicated as
"over 400").
Can you explain such apparent non-correlation between those two event
categories?

One more question: I hearsay that a pacemaker cannot detect
tachycardia events with frequency in the range of 100-110.
Is that correct?
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Uplbet
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