Specifications

Overview of Rate Adaptive AV Operation
In the normal heart, AV conduction times tend to shorten as the heart rate
increases and lengthen as the heart rate decreases. The Rate Adaptive AV
(RAAV) feature, available in the DDDR, DDD, DDIR, DVIR, DOOR, and
VDD modes, mimics this physiologic response. When RAAV is
programmed ON, the pacemaker shortens AV intervals at higher atrial
rates. This feature provides increased opportunity for atrial sensing, as
follows:
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Shortened SAV intervals increase the tracking range at fast atrial rates
by shortening the total atrial refractory period (TARP) and increasing
the 2:1 block rate (refer to “Total Atrial Refractory Period” and “High
Rate Atrial Tracking” later in this chapter).
■
Shortened PAV intervals lengthen the atrial sensing window of the VA
interval at higher sensor-driven rates.
RAAV Operations
For RAAV operation, the SAV and PAV are programmed (as applicable) to
the values desired for low rates. At higher rates, RAAV shortens AV
intervals as follows:
■
RAAV operation starts at 60 ppm and ends at 120 ppm.
■
As the rate increases above 60 ppm, the SAV and PAV intervals are
gradually shortened to the minimum values of 80 ms and 110 ms
(respectively) at 120 ppm. The minimum values also apply at all
higher rates above 120 ppm.
Adjustment of the SAV is pertinent to the DDDR, DDD, and VDD modes,
while PAV adjustment pertains to the DDDR, DDIR, DVIR, and DOOR
modes. The adjustment of AV interval(s) occurs as follows:
■
The mean atrial rate is used to determine SAV adjustments. Therefore,
the SAV is not adjusted for isolated events (PACs), and SAV
adjustment will lag during rapid increases or decreases in intrinsic
atrial rate.
■
The sensor-indicated rate is used to determine PAV adjustments.
Atrial refractory sensed events may affect the Rate Adaptive SAV because
they are included in the mean atrial rate if the next atrial event is not paced.
Pacemaker Timing 12-11
9879EN-12_9501043EN/CTC.qxd 5/10/99 11:27 Page 12-11
7 x 9 inches (178 mm x 229 mm)
Medtronic Confidential
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196407001 Rev A