Syncope triggered by atrial flutter in a patient with a pace
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Syncope in a patient with a pacemaker is a serious event requiring urgent action to ascertain its cause. Around 5% of cases are due to a pacemaker system malfunction.

An 82-year-old man underwent dual-chamber permanent pacemaker implantation due to intermittent high-degree atrioventricular block (AVB) in sinus rhythm. Nine months later, the patient reported episodes of syncope. The chest X-ray showed both leads to be at their expected positions. The electrocardiography (ECG) showed common atrial flutter. Ventricular capture during pacing in atrial demand pacing (AAI) mode confirmed cross-stimulation due to the switching of the atrial and ventricular leads at the pacemaker header.

Cross-stimulation is a rare possibility in a differential diagnosis of causes of syncope. The diagnosis is frequently made during the procedure or a few hours later. The lack of symptoms during 9 months in this case was likely due to the patient having normal sinus rhythm with preserved AV conduction most of the time, as well as ventricular capture from the atrial lead related to non-sensed P waves.

When atrial arrhythmias occurred, the sensing of the F waves inhibited ventricular pacing. In order to avoid this complication, in patients with intermittent bradycardia, pacing at a slightly higher heart rate during implantation of the device should be recommended to see the chamber paced with the surface ECG connected to the device interrogator. The ECG and electrogram (EGM) should correlate during device interrogation in order to identify this complication.