Chapter 3 · Oversensing · Case 8
An unexpected cause of syncope
Patient and episode
Patient
- Patient implanted with a dual-chamber defibrillator (Evera MRI XT DR) for episodes of VT due to ischaemic cardiomyopathy; patient in third degree AV block with episodes of syncope.
The recording
Tap a number on the trace, or an entry in the list below
Rate / interval plot
EGM
- What is your diagnosis? The EGM shows a characteristic feature of oversensing of electromagnetic interference with saturated signals on both channels.
- What causes fainting? Electromagnetic interference leads to saturation of the baseline with oversensing of very rapid ventricular cycles that fall within the VF zone; the oversensing inhibits ventricular pacing resulting in a ventricular pause and loss of consciousness in this dependent patient; the ventricular pause terminates with the occurrence of a spontaneous ventricular beat.
Points to remember
- Ventricular oversensing of small amplitude signals (myopotentials, 50 Hz, etc.) in a dependent patient is doubly problematic in that 1. oversensing may be prolonged because the sensitivity level does not readjust following the detection of spontaneous ventricular activity 2. the oversensing inhibits pacing, which may lead to syncope.
- The main preventive measure is to identify the source of radiation and avoid using certain poorly insulated instruments; as the patient was being monitored remotely, an alert was received the next day linking the episode to the use of a poorly insulated household appliance.
Practice out loud
Just describe the tracing. What do you think is going on? Describing the numbers can help.
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From Medtronic ICD — clinical cases by P. Bordachar, A. Thiyagarajah, L. Fontagne, M. Strik, S. Ploux. Published by Cardiocases. Every numbered marker on a recording is explained in the list beneath it; tap a marker on the trace or an entry in the list.
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