Evoke
®
SCS System Clinical Manual
CLIN-UMAN-005175
Revision: 9.00
Page 29 of 101
3. ECAP Minimum
The minimum ECAP amplitude recorded by the stimulator. The default setting is -20 µV.
Consider changing this to a value less than the ECAP amplitudes measured during
collection of the activation plot and posture testing (see Section 12.5) to ensure that
ECAP amplitude is recorded over the full range of activation
4. ECAP Target Minimum
The minimum ECAP target that can be set with the CPA or EPC when closed-loop is
enabled. The default setting is to always link this value to the ECAP Minimum, with a
default value of -20 µV. Consider de-linking this setting and changing to a value just
below the ECAP amplitude at the ECAP threshold to ensure the target cannot be set to a
low value that results in no therapy.
6.11
Set up closed-loop stimulation
The settings for closed-loop stimulation vary between patients and for different electrode
configurations. Settings can be optimized in the measurement and feedback settings menu
(Figure 6.14E). These settings depend on the sensitivity of the ECAP to changes in current.
The CPA can measure ECAP sensitivity as the current is varied (see Figure 6.14F), following
these steps:
1. Optimize the ECAP measurement (refer to Section 6.10).
2. Increase current from near paresthesia threshold to a strong level (e.g. the maximum
that the patient could tolerate for one minute), refer to Section 7.6 for information on
collecting the activation plot. From the activation plot, calculate the therapeutic
window, which is the difference between the ECAP amplitudes at threshold and
maximum.
3. The activation plot will display the ECAP amplitude as a function of current, and the
measured sensitivity is displayed on the plot (see Figure 6.19).
4. Ensure that the displayed activation plot meets the following criteria:
a. The activation plot should show an obvious inflection in the ECAP amplitude
close to the patient’s paraesthesia threshold. Above this inflection the ECAP
amplitude should increase linearly with the stimulation current (see Figure 6.19).
b. The therapeutic window should be >10 µV.
c. The measured sensitivity should be >10 µV/mA.
Note
: If a Measured Sensitivity value does not appear then decrease the current
increment (see Section 8.1) and repeat steps 2-4 above.
Caution:
Closed-loop may not operate as intended if the activation plot does not
meet these criteria. Do not enable closed-loop operation until the above criteria are
satisfied.
5. If the activation plot does not meet the above criteria you will need to improve the
