What is ventricular fibrillation undersensing?

Ventricular fibrillation (VF), uninterrupted, is fatal within minutes. Implantable cardioverter defibrillators (ICDs) sense ventricular electrograms (EGMs) during VF and detect the VF rhythm (a sequence of VF sensed events) to deliver a shock to terminate VF and save lives. VF sensing and detection in Medtronic ICDs has been reported to be highly sensitive. However, Castellano et al. reported that Medtronic ICDs have the potential for high levels of undersensing in VF, sufficient to underdetect VF and withhold life-saving therapy. This manuscript reviews the process of EGM sensing and VF detection in ICDs and compares the process of sensing in Medtronic ICDs with the process described in this recent publication.