User Manual Part 2

PACING THERAPIES
ATRIAL TACHY RESPONSE
5-21
ATR Duration
ATR Duration determines the number of cardiac cycles during which the
atrial events continue to be evaluated after initial detection. This feature is
intended to avoid mode switching due to short, nonsustained episodes of atrial
tachycardia. If the ATR counter reaches zero during ATR Duration, the ATR
algorithm w ill be reset, and no mode switch will occur.
If the atrial tachycardia persists for the programmed ATR Duration, then
mode switching occurs and the ventricular rate begins decreasing to the
sensor-indic ated rate, VRR rate or the ATR/VTR Fallback LRL, depending
on the programmed Fallback Mode.
Entry C ount
The Entry Count determines how quickly an atrial arrhythmia is initially detected.
The lower the programmable value, the fewer the fast atrial events required to
fulfill initial detection. Once the number of fast atrial events detected equals
the programmable Entry Count, ATR Duration begins, and the Exit Count is
enabled.
CAUTION: Exercise care when programming the Entry Count to low values
in conjunction with a sh ort ATR Duration. This combination allows mode
switching with very few fast atrial beats. For example, if the Entry Count was
programmed to 2 and the ATR Duration to 0, ATR mode switching could occur
on 2 fast atrial intervals. In these instan ce s, a short series of prematu re at ria l
events could cause the device to mode switch.
Exit Count
The Exit Count determines how quickly the ATR algorithm is terminated once
the atrial arrhythmia is no longer detected.
The lower the programmed value, the more quickly the pulse generator will
return to an atrial tracking mode. Once the number of slow atrial events
detected equals the programmable Exit Count, ATR Duration and/or Fallback
will be terminated, and the ATR algorithm will be reset.
CAUTION: Exercise care when programming the Exit Count to low values.
Forexample,iftheExitCountwasprogrammedto2,afewcyclesofatrial
undersensing could cause termination of mode switching.
- DRAFT -