LV-only pacing with oversensing on the LV and on the RV channel
Patient
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RESONATE CRT-D pacing the LV only (LV Only: only LV paces on the markers) at 70 bpm (855 ms); the atrial channel is flat
Two real-time EGMs sent remotely: 9 months after implant, and 5.5 months later. What does oversensing on each channel do to pacing?
Trace
- First real-time EGM (channels: atrial, RV, LV, shock EGM). The atrial channel is flat; every beat starts with an LV pace 855 ms after the previous one (LVP 855, 70 bpm), with no RV pace: LV-only pacing
- A small signal on the LV channel (noise) is sensed about 800 ms after the last pace (LVS, label half hidden), 50 ms before the next LV pace: the LV protection period withholds that pace (Inh-LVP) and an RV pace is delivered instead, on time (RVP 855). No pause, but an RV-paced beat: the shock EGM changes and the LV is activated later (large LV deflection)
- The same again, the LV sense coming 150 ms before the LV pace due (LVS about 700 ms): Inh-LVP and RVP 855. The LV sense did not restart the timing: the RV pace still comes 855 ms after the previous pace
- A spontaneous ventricular beat, sensed in the LV (LVS 615) and in the RV (RVS 625), with large signals on both channels and a different shock EGM: the RV sense restarts the timing, and the next LV pace comes 855 ms later
- 5.5 months later (second EGM): a small signal (noise), barely visible on the RV channel and clearer on the LV and shock channels, is sensed by the RV (RVS 828). An RV sense restarts all the ventricular timing: neither the LV nor the RV is paced
- The next LV pace comes 855 ms after that RV sense: no ventricular beat for 1.68 s (828 + 855 ms), a pause
- Same during sensor-driven pacing (LVP-Sr 845 ms): RVS 755 on a tiny signal (a notch on the LV and shock channels), no pace, and the next LVP-Sr 845 ms later: a 1.6-s pause
Comments
LV-only pacing with noise sensed on the LV channel, then, 5.5 months later, on the RV channel. An LV sense only withholds the LV pace, and an RV pace replaces it; an RV sense withholds all pacing and gives a pause
Points to remember
- A sensed event with no ventricular activation on the shock EGM is not a heartbeat: compare the channels to find which one oversenses, because the consequence differs
- Noise sensed on the LV channel costs only the LV pace: it is withheld (Inh-LVP) and the RV is paced instead, on time, as a backup. No pause, but that beat is paced from the RV
- Noise sensed on the RV channel stops all pacing: even when only the LV is paced, the RV channel runs the timing, so an RV sense withholds every pace and restarts the timing. Each one gives a pause, here 1.6-1.7 s
Take home message
Like in most CRT devices, in a Boston CRT the RV channel runs the timing, even when only the LV is paced: noise on the RV channel inhibits all pacing and causes pauses, whereas noise on the LV channel does not inhibit RV pacing
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