RESONATE CRT-D, DDD 50-145 bpm, with a Medtronic 3830 conduction-system pacing lead on the LV port, paced LV Only (LVtip>>RV); LV output Auto (PaceSafe LV)
LATITUDE remote transmission, nearly 9 months after implant: no alert
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Trace
Left Ventricular = the 3830 lead: pace threshold 1.0 V at implant, Auto 0.9 V at the office check 5 weeks earlier, 4.0 V on the last daily measurement; pace impedance 850 → 413 → 320 Ω. The atrial and RV values are stable, and the report shows no alert
Pacing Output, Left Ventricular (right column): Auto 5.0 V @ 0.4 ms. PaceSafe LV has followed the threshold up: highest threshold of the last 7 tests plus the safety margin, never above the programmed maximum amplitude (nominal 5.0 V)
Ventricular Pacing Chamber: LV Only; LV configuration LVtip>>RV (right column): only the 3830 lead paces; the RV lead senses, runs the timing cycles and defibrillates
LV pace impedance over 6 months (vertical lines: the 1st of each month): a slow fall from about 520 to 370 Ω over 5 months, then about 300 Ω a week before the transmission and unstable values since (300-450 Ω); 320 Ω on the last day
LV automatic threshold (PaceSafe LV): about 0.5 V at first, creeping up to 1.0-1.1 V over 5 months, then a jump to 4.5 V a week before the transmission, the day of the impedance drop, and 4.0 V since
Another recording: atrial pacing at the lower rate limit (AP 1200 ms = 50 bpm)
Less than 100 ms after each AP, before any ventricular activation, a sharp signal on the LV channel is sensed (LV marker, half hidden under the RVP label): the 3830 lead is recording atrial activity
The LV pace due at the end of the paced AV delay (180 ms) falls in the LV protection period (LVPP) started by that LV sense: it is inhibited (Inh-LVP) and, in LV Only, replaced by an RV pace (RVP 1200): RV pacing instead of conduction-system pacing
Comments
Dislodgement of a conduction-system lead on the LV port: a jump in the LV threshold with a fall in LV impedance, without any alert
Points to remember
A conduction-system lead on the LV port of a CRT-D is followed like an LV lead: the device tests its threshold about once a day, and the LV threshold and impedance trends show how it is doing
Here the LV threshold jumped within a day from about 1 V to 4.5 V while the impedance fell: the picture of a dislodged lead. The device sent no alert: it simply raised the LV output to 5.0 V, so the jump shows only in the lead table and the LV trends
With a threshold of 4.0-4.5 V, the 5.0 V output leaves a margin of only 0.5-1.0 V, and capture is not checked beat by beat, so it can be lost unnoticed
In LV Only, an LV pace withheld after an LV sense is replaced by an RV pace: when the LV-port lead senses the atrium, the patient silently gets RV pacing instead of conduction-system pacing
Chest X-ray shown with the case (frontal view): the CRT-D and its three leads, atrial, RV defibrillation and the 3830 on the LV port; the 3830 is the middle, thin one
Take home message
No alert does not mean no problem: the automatic LV output simply follows a rising threshold. Read the LV trends in every report: a sudden threshold jump with a fall in impedance means lead dislodgement until proven otherwise
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