User Manual Part 1

PACING T HERAPIES
SENSORS AND TRENDING
5-13
NOTE: Activ ity involving minim a l upper body motion, such as bicycling, m a y
result in only a moderate pacing response.
NOTE: Adaptive-rate pacing has been shown to be potentially proarrhythmic.
Use caution when programming adaptive-rate features.
Accelerometer
The accelerometer detects motion that is associated with a patient’s physical
activity and generates an electronic signal that is proportional to the amount
of body motion. Based on accelerometer input, the pulse generator estimates
the patient’s energy expenditure as a result of exercise, then translates it into
a rate increase.
The pulse generator senses body motion by means of an integrated circuit
accelerometer located on the hybrid circuit. The accelerometer sensor
responds to activity in the frequency range of typical physiologic activity (1–10
Hz). The accelerom et er evaluates both the frequency and the amplitud e of
the sensor signal.
• Frequency reflects how often an activity occurs, such as the number of
steps taken per minute during a brisk walk
• Amplitude reflects the force of motion (e.g., the more deliberate steps
taken while walkin g)
Once detected, an algorithm translates the measured acceleration into a rate
increase above the LRL.
Because the accelerometer is not in contact with the pulse generator case, it
does not respond to s imple static pressure on the device case.
There are three Accelerometer settings: Off, On, and ATR Only. When you
program the respective rate-responsive modes for Normal Settings and ATR
Fallback, that action automatically updates the Accelerometer setting. If the
pulse generator is permanently programmed to a nonadaptive-rate mode, it is
possible to program the ATR Fallback mode to an adaptive-rate mode using
the accelerometer sensor. In this case, the Accelerometer field will dis play
ATR Only.
The following programmable parameters control the pulse generator ’s response
to the sensor values generated by the Accelerometer:
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