A 65-year-old male with persistent atrial fibrillation underwent implantation of a dual chamber implantable cardioverter defibrillator (ICD) for primary prevention after previous myocardial infarction with an ejection fraction of 32%. A Boston Scientific 4471 screw-in lead was implanted in the right atrial appendage, and a Medtronic Sprint Quattro Secure 6935 shock lead in the right ventricular (RV) apex. Both leads were subsequently connected to a Medtronic Protecta DR ICD. The intrinsic rhythm at the time of implant was atrial fibrillation with a varying ventricular response below 100 bpm (Fig. 1). Shortly after implant, the patient experienced an ICD shock. Review of the ICD diagnostics showed a sudden onset of a fast rhythm which was diagnosed by the device as ventricular fibrillation according to the fibrillation sense (FS) annotation (Fig. 1), followed by a direct current (DC) shock that terminated the arrhythmia in both the RA electrogram and the RV electrogram (Fig. 2).

Fig. 1
figure 1

Initial part of the recording shows atrial fibrillation in the atrial electrogram (RA egm) with a varying ventricular response below 100 bpm in the ventricular electrogram (RV egm). There is a sudden change in the RV egm, diagnosed as ventricular fibrillation according to the fibrillation sense (FS) annotation

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Fig. 2
figure 2

Recording of the ICD shock (CD charge delivered) that terminates the arrhythmia in the right atrial (RA) egm and right ventricular (RV) egm

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Was this shock appropriate and can you explain the rhythm after the DC shock?

Answer

You will find the answer elsewhere in this issue.