Clinical introduction A 69-year-old man with a left-sided, dual-chamber implantable cardioverter defibrillator (ICD) (Atlas+V-243, Tendril 1688T atrial lead and Riata 7040 ventricular lead, St Jude Medical) implanted 7 years before he underwent a routine ICD follow-up visit in May 2014.

He reported one external direct-current electrical cardioversion (ECV) 1 month before for persistent symptomatic atrial fibrillation: one 360 J biphasic shock was delivered through a parasternal and a precordial paddle. Postprocedure ICD interrogation was not performed.

Previous device and lead parameters were unremarkable.

Figure 1A shows ICD battery status, pacing and antitachycardia parameters at the time of device interrogation.

Pacing and sensing thresholds and lead impedance were normal.

Several episodes of non-sustained ventricular arrhythmias were retrieved (figure 1B).

The ICD parameters were reset, but 1 week later the same malfunction was observed.

Question Which is the most likely diagnosis?

1. ICD battery depletion

2. Riata lead failure

3. ICD circuitry damage

4. External electromagnetic field interference (eg, walk-through surveillance system)