Lead alert: shock impedance out of range
Tracing
Manufacturer Biotronik
Device Remote monitoring
Field Messages and events
N° 7
Patient
This 73-year-old woman received a Lumax VR-T DX single chamber defibrillator for primary prevention in the context of ischemic cardiomyopathy with a 28% left ventricular ejection fraction. She was monitored by telecardiology and, 6 months after device implantation, an alert was delivered.
Graph and trace
Telemedicine report
Alert (red status) for <30 or >100 Ohms defibrillation shock impedance.
The shock impedance was 105 ohms. The curve shows an initially stable impedance, near 80 ohms, which is slightly elevated, though acceptable for a single-coil lead, before increasing relatively rapidly above the 100-Ohms threshold, prompting an alert message. The right ventricular pacing lead impedance remained within normal limits, with a slight increase within the last days. The quality of sensing by the right ventricular pacing lead remained normal and without any recent variations.
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This example illustrates one of the challenges of the follow-up of recipients of defibrillators. Telemedicine enables the detection of shock impedance values that are judged abnormal. It also enables the tracking of the dynamic changes in these measurements. In this patient, the value exceeded the programmed limit, prompting an alert message. Several choices were available: 1) consider that this high impedance was a manifestation of lead dysfunction; since the lead had been recently implanted, it could easily be extracted and replaced by a new one, a choice, however, that seemed overly invasive and probably premature; 2) induce ventricular fibrillation, to verify the efficacy of defibrillation and measure the impedance of a shock that has been effectively delivered; 3) continue the surveillance and measure daily the shock and pacing impedance, verify the efficacy of sensing and stimulation and, scrutinise the changes in the evolution of the measurements. This last choice was favoured for this patient and the shock impedance gradually stabilized near 120 ohms.