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Transmission

The patient has had a single episode in the VT/VF zones, an episode with the VF label and treated by a choc wich was with success according to the ICD. When we look at the episode, we do not see the occurrence of a typical ventricular arrythmia, but rather the alternance of very narrow noise artifacts (on both RV and atrial channels) followed by what looks like true ventricular events. They are in fact pacing artifacts (not generated by the ICD but by an external source) followed by ventricular capture. Not that some of the pacing spikes are not followed by ventricular events due to intermittent loss of capture. In case of intermittent loss of capture, only the pacing spikes are oversensed. This triggers the VT counter which is filled (6 out of 8 ventricular intervals are in the VT zone) but as it is considered unstable, the label is SVT/ST. When all pacing spikes are followed by R waves, the double counting is persistent which fills the VF counter (6 out of 8) and we observe the VF label. After this VF label, the VF persistance is filled (20 events in the VF zone) and the charge begins (blue C). Throughout the charge, the oversensing (double counting) continues and the shock is delivered. As expected, it does not stop the oversensing as it is caused by something external. After a post-shock blanking of one second, the oversensing begins again with double-coutning of ventricular rate (spike + R-wave) and the VF counter is filled again. There is no persistance counter for redetection so the second charge begins. During the second charge, the oversensing diminishes (due to loss of capture) and stops (due to termination of pacing by external source). The VF majority is lost and the charge is therefore lost.

Next steps

When receiving an episode which shows pacing spikes not caused by the implanted device, medical records need to be examined to discover the source of the noise. In this case, the external pacing spikes were caused by rapid ventricular pacing during a transcatheter aortic valve implantation (TAVI/TAVR procedure). The ventricle is rapidly paced for a few seconds to refrain it from expulsing the freshly implanted valve. As the TAVI procedure is becoming more and more common, these types of episodes are becoming quite frequent. Other sources of external pacing may be due to pacing maneuvres during ablation procedures or co-implants (like a leadless pacemaker). Most often these episodes are received only a few days later as most patients do not have the remote monitoring transmitters in their room during hospitalisation. Also in this case, the VF episode was received 4 days after the event.

The device is functioning properly with correct sensing and pacing. No changes are needed in programming after receiving the alert. However, the medical team responsable for the intervention which caused the inappropriate shock should have disabled the therapies in this patient implanted with an ICD. The remote monitoring alert offers an opportunity to educate the colleagues who perform TAVI procedures to remember to always disable therapies in ICD patients.