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Transmission

The patient had a single episode in the VT/VF zone, an episode with the VF label and treated by a shoch which was delivered with success according to the ICD. When we look at the episode, we do not see the occurrence of a typical ventricular arrhythmia, 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. Note 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 majority which is met (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 persistence 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-counting of ventricular rate (spike + R-wave) and the VF counter is filled again. There is no persistence counter for redetection, so the second charge begins. During the second charge, the oversensing decreases (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 stopped.

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 prevent it from expelling 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 responsible 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 performing TAVI procedures to remember to always disable therapies in ICD patients.