Oversensing of diaphragmatic myopotentials

Patient

This 69-year-old man received a Lumax 340 HF-T triple chamber defibrillator for ischemic cardiomyopathy with left bundle branch block. An event report (yellow color) was issued in the context of a classified VF.

Main programmed settings

VF zone (270 ms) and VT1 zone (330 ms)
12/16 cycles in the VF zone and 26 cycles in the VT1 zone were needed for the diagnosis
Maximum sensitivity programmed at 0.5 mV
VF zone: ATP one shot and 8 shocks of maximum strength (40 J); VT1 zone: 3 bursts of ATP, followed by 3 ramps of ATP, followed by 8 shocks of maximum strength;
Pacing mode: biventricular DDDR pacing at 50 bpm.

Trace

Remote tracing

atrial and biventricular paced rhythm;
oversensing of a high-frequency low-amplitude signal in the VF zone on the RV channel;
classification of VF episode after 12/16 cycles (3 VS and 1 VT2, 12 VF: VF counter full) classified in the VF zone;
no therapy delivered;
end of episode.

Programmer tracing (same episode)

onset of the charge of the capacitors (dark horizontal line);
end of oversensing and interruption of the charge after 3 ventricular paced cycles.

Comments

This patient presented with oversensing of diaphragmatic myopotentials, a phenomenon that might be reproduced with deep breathing. Oversensing of diaphragmatic myopotentials is suspected when low-amplitude signals are observed, preferentially visualized in the RV sensing channel, while often invisible on the shock channel. Oversensing is most likely to occur at the end of the cardiac cycle when gain and sensitivity are highest. This oversensing is most common in recipients of RV apical leads. In this patient, the sensitivity was reprogrammed to 0.8 mV, which eliminated this oversensing.

Pacing & Defibrillation

ECG

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