Specifications

Possible Atrial Competition at High Rates
At high sensor-driven rates in the DDDR and DDIR modes, sensor-driven
pacing may approximate the intrinsic atrial rate, with some intrinsic atrial
events falling into the PVARP. This could result in asynchronous pacing
with the potential for competitive atrial pacing. The potential for
asynchronous pacing at high rates should be considered before selecting an
Upper Activity Rate, especially for patients known to be susceptible to
induction of atrial tachyarrhythmias. The clinician may wish to weigh the
benefits of high rate sensor-driven pacing against the potential for
competitive pacing.
NOTE: Use of the Rate Adaptive AV feature and Non-Competitive Atrial
Pacing (DDDR mode only) can reduce the likelihood of the type of
asynchronous pacing described above.
Mean Atrial Rate
The mean atrial rate (MAR) is a running average of the atrial rate that is
continuously calculated by the pacemaker for use by the Mode Switch and
Rate Adaptive AV features. The average uses all A-A intervals except
those beginning with an atrial sense or atrial refractory sense and ending
with an atrial pace. The illustration below shows how the MAR tracks the
actual intrinsic atrial rate.
Mean Atrial Rate
Pacemaker Timing 12-7
Atrial Rate Increasing by 2 bpm/beat
Time (Seconds)
Rate (bpm)
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30 35
MAR
Intrinsic Rate
9879EN-12_9501043EN/CTC.qxd 5/10/99 11:27 Page 12-7
7 x 9 inches (178 mm x 229 mm)
Medtronic Confidential
Refer to the “Reference man.” category in doc#163256 for Printing
Instructions.
196407001 Rev A