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.