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Stratos LV/LV-T Technical Manual 99
2.16 Rate Fading
Rate Fading is intended to prevent a sudden drop in heart rate
when the Stratos CRT-Ps transition from tracking an intrinsic
rhythm to pacing due to an abrupt decrease in the intrinsic rate
or due to Mode Switching. This smooth drop in pacing rate is
designed to prevent symptoms such as dizziness, light
headedness, lack of energy and fainting spells. With Rate
Fading enabled, the Stratos CRT-Ps calculate a “Backup Rate”
that is always active in the background. As soon as the rate
decreases, the CRT-P begins pacing at the Backup Rate. The
Backup Rate corresponds to a delay of the intrinsic rate
corresponding to a programmable rate increase and
programmable rate decrease; these parameters determine the
sensitivity of the controlled rate smoothing. After four
consecutive intrinsic events (A
s
– A
s
), the CRT-P calculates the
Target Rate for the “Backup Rate”, which is a four beat average
of the intrinsic rate reduced by 10 ppm. The Target Rate cannot
exceed the Maximum Fading Rate (programmed as Max Activity
Rate) and cannot increase faster than the RF Rate Increase
(programmable in ppm/cycle).
When the intrinsic rate drops considerably (below the Target
Rate), the pacing rate drops to the Backup Rate and is then
decreased gradually by the programmable Decay Rate to the
Sensor Indicated Rate or Basic Rate. The Backup and Target
Rates are defined in Table 23
.
If an atrial tachycardia occurs suddenly, triggering a mode
switch, the target rate is set to the sensor rate or basic rate. The
current pacing rate in the ventricle results from the current value
of the Target rate before the mode switching event.
If the pacing rate reaches the intrinsic rate during rate decay, at
least four consecutive intrinsic cycles above the pacing rate are
required before the pacing rate is once again adapted to the last
intrinsic event. Controlled rate smoothing is thereby continued
during intermittent sensed events.
The Rate Fading feature is suspended while in magnet mode
and disabled at ERI and in backup mode.