Sensing failure in a tiered therapy implantable cardioverter defibrillator: role of auto adjustable gain

Implantable cardioverter defibrillators have an established role in the management of life-threatening tachyarrhythmias. These devices use sophisticated sensing circuitry to detect and promptly treat a vast majority of these arrhythmias. However, they are not foolproof. We report one case where the device failed to sense every other QRS complex during induced ventricular fibrillation due to marked electrical alterans. Thus, undersensing can be a potentially fatal problem despite the use of auto adjustable gain.