After the implant of an unipolar LV lead, 2 programming choices are available, since the pulse generator can be included in the stimulation vector.
The 2 electrodes are the distal and proximal LV. After the implant of a bipolar LV lead, 6 programming configurations are available.
The 4 electrodes are labeled dist LV1, prox LV2, prox LV3 and prox LV4, with dist LV1 as the most distal electrode, and 17 different programming configurations are available.
Automatic left ventricular threshold
The PaceSafe LV function is available for all unipolar and bipolar stimulation configurations, though is not available with the IS4 (quadripolar lead) defibrillators.
In the ambulatory setting, the threshold is automatically measured every 21 h with the following programmed settings: paced AV delay at 140 ms; sensed AV delay at 110 ms; rescue RV stimulation occurs throughout the LV test with an 80 ms LV preexcitation. The initial amplitude corresponds to the programmable maximum amplitude, decreasing in 0.5-V steps above 3.5 V, and in 0.1-V steps below 3.5 V.
The measurement of the threshold is based on an analysis of the evoked response. The evoked response channel is an unipolar sensing channel that utilizes the distal or proximal LV electrode, depending on the programmed stimulation configuration. Should the daily test fail, the LV PaceSafe function returns to the previously measured output, and up to 3 new attempts are then made, at hourly intervals. Should the daily test fail over 4 consecutive days, a lead alert is triggered and the PaceSafe LV function switches to “Failure” mode (delivered output = 5 V/0.4 ms).
If the automatic adaptation has been programmed, following the measurements made at 21 h intervals, the output is then adapted with a programmable safety margin between 0.5 and 2.5 V, without cycle-by-cycle verification of capture. Instead of being adapted relatively to the very last measurement, the LV stimulation output is set with a programmable safety margin added to the threshold measured at the time of the last 7 successful tests performed during ambulatory follow-up. This enables a rapid increase in stimulation amplitude, should the threshold increase suddenly. It is noteworthy, that a single low threshold measurement does not lower the stimulation amplitude.