Sensing and Detection Functions in Implantable Cardioverter Defibrillators: The Good, the Bad and the Ugly.

Implantable cardioverter defibrillators are small devices that have been proven to be beneficial by preventing sudden cardiac death, whether in primary or secondary prevention. Appropriate functioning of implantable cardioverter defibrillators is mainly dependent on the "good" sensing of ventricular electrogram waves, allowing for the adequate detection of ventricular arrhythmias in order to deliver appropriate therapy of either antitachycardia pacing or by delivering a shock according to the detected rhythm. Basic sensing function in defibrillators is based on detection rate and detection duration; additional parameters that are involved in the process of adequate detection include ventricular electrogram sensing, auto-adjusting sensitivity, supraventricular arrhythmia discrimination criteria, noise detection, and various dedicated algorithms. Defective sensing may result in the delivery of inappropriate therapy (oversensing) or inappropriate withholding of therapy (undersensing); the latter of which may lead to sudden cardiac death. This paper describes different clinical scenarios and programming tips to avoid abnormal or critical clinical situations.