Unipolar pacer artifacts induced failure of an automatic implantable cardioverter/defibrillator to detect ventricular fibrillation

The automatic implantable cardioverter-defibrillator (AICD®)1–5 has been implanted in over 500 patients with life-threatening ventricular arrhythmias. For detection of ventricular tachycardia or fibrillation (VF), the sensing system of the standard AICD uses a combination of the rate of electric signals received by sensing leads, and a probability density function.1–3 Because of the nature of sensing system of the AICD, several kinds of interactions with temporary or permanent pacemakers have been described.4,6 We have observed another phenomenon: failure of an AICD to detect VF due to large electrical signals from a unipolar pacemaker.