Activity Vector Test Feature

The Micra™ Transcatheter Pacing System (TPS) Activity Vector Test is an in-office, programmer-based test performed to determine the vector that provides appropriate rate response. Together, the Activity Vector Test and Exercise Test provide data to help optimize the Rate Response settings for the patient. The Activity Vector Test is performed before the patient is discharged, or any time you are concerned about adequate Rate Response, to ensure the selected vector isn’t overly sensitive to cardiac motion.

This feature can be found in Medtronic Micra TPS. Please go to manuals.medtronic.com or consult with your local Medtronic representative regarding device models available in your geography.

The Activity Vector Test is an in-office only test. To access from the Quick Look™II screen, select Tests  -> Exercise

This test compares level of activity at various postures to make sure the Activity Vector is appropriate. If there is not a sufficient difference in activity counts between resting and walking, this test can be conducted in one of the other two orthogonal Activity Vectors to find a better performance for the patient. Each vector represents a different axis of the accelerometer, depending on the orientation of Micra TPS in the patient’s right ventricle. Prior to beginning the test, explain to the patient that they will be performing a variety of activities, as described in Figure 1 further below in this document.
 
To begin the Activity Vector Test, navigate to Tests -> Exercise
 
 
  1. Select the Test Vector, starting with Vector 1. Repeat the test using the remaining two vectors if necessary. 
  2. Set the Duration – 5 or 20 minutes. Five minutes is the recommended value as it provides the best resolution. 
  3. Select PROGRAM.
  4. Press Start, and then Continue, to begin the test. Remove the programmer head and have the patient perform the following activities in the order described in Figure 1 below. 

 

Figure 1: Vector Activity Test: Patient Positioning

Once the patient has completed all of the activities, press Stop and Retrieve to display the test data.

Activity Vector Test Results for Vector 1

Evaluating the Activity Vector Test Results

 

1 = Left Side     
2 = Back
3 = Right Side
4 = Sitting
5 = Walking
6 = Back

 

The example above shows a good differential between resting and walking counts using Vector 1. 

To analyze the data, look at the the peak activity counts observed while the patient was stationary in each posture, and compare to the peak counts while the patient was walking. There should be a difference of at least 8 counts. If this difference is not observed, then Rate Response may perform better for this patient using an alternate Activity Vector. If needed, run the test again for Vectors 2 and/or 3 and permanently program whichever of the 3 vectors has the largest differential between resting and walking counts and also shows a decrease in counts after activity is completed. Allow at least 3 minutes of rest between vectors.

Programming the ActivityVector and Setpoints

The Activity Vector and the Rate-Response Setpoints can only be programmed from the Exercise Test screen.

Considerations 
  1. Rate Profile Optimization (RPO) is nominally On and automatically adjusts the Setpoints once each day. In the unlikely occurrence that there is a need to turn RPO off, then run the Exercise Test on the new vector to manually establish and program new Setpoints.  
  2. If you wish to program Setpoints immediately, select the corresponding field and set a new value appropriate for the patient and then press [PROGRAM].
Note: Assuming the resting postures generate less activity than the hallway walk, the following programming is suggested:
  • LR Setpoint should be a value greater than the highest count while the patient is resting
  • ADL Setpoint should be set to the highest peaks while walking
  • UR Setpoint should be set 1.5 X (ADL Setpoint – LR Setpoint) + ADL Setpoint

The example below illustrates the Activity Vector Test results for Vectors 1, 2, and 3. The activities are labeled at the top of the chart (i.e., patient lies on back, on side, sitting, walking). Vector 3 is the vector that most closely represents the patient activity, as it has the largest differential between resting and walking counts and shows a clear decrease in counts after activity has completed.

References

Sources: Medtronic Micra™ Clinician Manual.

Last updated: 
30 Aug 2016