🫀 Mirza's Cardiology Notes

Cardiac Resynchronization Therapy (CRT)

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  • Cardiac resynchronization therapy (CRT) response is dependent on >90% biventricular pacing.

    • The mortality benefit associated with CRT has been shown to be steeply dependent on a ventricular pacing percentage that is near 100%.

![[Cardiac Resynchronization Therapy CRT-1747237188375.webp]]

ECG in CRT

  • For optimal CRT pacing of the LV, 1 recommend 3 step review of ECG to identify LV positioning
    • V1: LV free wall position → upright V1
    • aVF: determine LV lead position in circumferential direction (inferior/superior axis)
    • precordial leads: assess transition for apico-basal direction

Optimizing AV delay

Via stepwise increase of the AV delay during simultaneous BiV pacing starting with a short AV delay, the onset can be identified as the AV delay where the QRS morphology changes as illustrated in the figure below. To ensure 100% capture of LV pacing, the AV delay in CRT should preferably be programmed to a value shorter than the onset of intrinsic ventricular activation, since exercise fastens intrinsic AV conduction time. Figure source: 1. Caption: The AV delay before the change in QRS morphology (asterix), while stepwise increasing the AV delay with simultaneous BiV pacing, indicates the time of onset of intrinsic ventricular activation.

CRT Non-response

  • Preimplantation causes of CRT nonresponse include non–LBBB native conduction or a relatively narrow native QRS.
  • Loss of LV lead capture
    • When the LV threshold has changed from implantation, LV noncapture may be correctible by ↑ the LV stimulation output or selecting an alternate stimulation vector.
  • Poor LV lead position
  • Diminished pacing
    • AFib with rapid conduction,
    • inappropriate device programming, and
    • frequent ventricular ectopy, e.g. PVCs
      • In a prospective database of CRT implantation, 10% of the patients with a lack of CRT response had frequent PVCs. PVC ablation in this group restored CRT response in two-thirds of the patients who underwent a successful PVC ablation.
    • excessive LV scar burden

Footnotes

  1. van Deursen CJ, Blaauw Y, Witjens MI, Debie L, Wecke L, Crijns HJ, Prinzen FW, Vernooy K. The value of the 12-lead ECG for evaluation and optimization of cardiac resynchronization therapy in daily clinical practice. J Electrocardiol. 2014 Mar-Apr;47(2):202-11. doi: 10.1016/j.jelectrocard.2014.01.007. Epub 2014 Jan 6. PMID: 24444866. ↩ ↩2

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