User's Manual

42
Timing Functions
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AV Repetitive Hysteresis
In AV repetitive hysteresis, the AV delay is also extended by the defined
hysteresis value after the sensing of an intrinsic ventricular event. In
contrast to normal AV hysteresis, once the ventricular pace event
occurs, the long AV delay remains intact for a programmed number of
cycles. If intrinsic activity occurs during one of these repetitive cycles,
the long AV delay remains intact. Only once the repetitive cycles have
elapsed without any instances of spontaneous AV conduction does the
pacemaker switch back to the short AV delay. The AV repetitive
hysteresis hence reduces pacing when existing intrinsic activity is
suppressed by occasional pace events within the extended AV delay.
AV Scan Hysteresis
In AV scan hysteresis, 180 consecutive cycles are observed and if there
were only paced events and no spontaneous ventricular activity, the AV
delay is extended by the additional AV hysteresis interval. The long AV
delay remains intact for a pre-defined number of cycles. If spontaneous
AV conduction occurs within the defined number of cycles, the AV
hysteresis remains intact. The short AV delay interval resumes only
when no ventricular event has been detected within the defined number
of cycles and instead every one of these cycles ends with a pace. The
cycle counter once again begins counting the consecutive cycles in
which there was pacing. Intrinsic ventricular events (excluding VES)
reset the counter to zero. AV scan hysteresis hence reduces pacing in
situations in which intrinsic conduction exists but does not fall within
the defined AV delay.