Appropriate or inappropriate ICD shock; what is the post-shock rhythm?

Excerpt

At first sight, this may seem an appropriate shock for ventricular fibrillation, followed by conversion to sinus rhythm. However, the abrupt change in morphology of the RV electrogram with extreme short fibrillation sense (FS) intervals below 200 ms is not suggestive of ventricular fibrillation. The intervals are also comparable with the atrial sense (AS) and atrial sensing in the blanking period (Ab) intervals in the atrial channel. These observations suggest that the sensed arrhythmia in the ventricular channel is not ventricular fibrillation, but sensing of atrial fibrillation. This observation can only be explained by a displacement of the ventricular lead towards the right atrium. Review of the X‑rays, which at implant showed a normal RV apical position of the shock lead (Fig. 1, left panel), showed migration of the lead into the right atrium in the post-shock X‑ray (Fig. 1, right panel). It is therefore clear that the shock therapy was inappropriate. …