Failure to treat ventricular tachycardia or ventricular fibrillation by implantable cardioverter-defibrillators

BACKGROUND Normally functioning implantable cardioverter-defibrillators (ICDs) with intact lead systems occasionally fail to deliver therapy for ventricular tachycardia/fibrillation (VT/VF) or deliver it only after clinically significant delays (failure-to-treat). OBJECTIVE We aimed to investigate ICD failure-to-treat VT/VF in a large patient cohort. METHODS We searched the US Food and Drug Administration's online Manufacturer and User Facility Device Experience (MAUDE) database from 2019 to 2023 for manufacturer-verified reports in which normally functioning ICDs failed to treat VT/VF. RESULTS We identified 854 reports classified as deaths (n = 96 [11.2%]), injuries (n = 585 [68.5%]), or malfunctions (n = 173 [20.3%]) for normally functioning ICDs. The most common causes were misclassification as supraventricular tachycardia (SVT) or atrial fibrillation (AF; 54.8%), undersensing (21.1%), and failure to satisfy programmed rate/duration criteria (8.7%). Most events caused by misclassification as SVT/AF (89.5%) and failure to satisfy rate/duration criteria (70.3%) were VT; most caused by undersensing were either VF (54.4%) or not specified as VT or VF (19.4%). Undersensing caused 65.6% of deaths, although it represented only 21.1% of reports. In the United States, the number of reports increased faster than that of ICD patients. CONCLUSION In the largest reported series of failure-to-treat VT/VF by normally functioning ICDs, the most common cause was misclassification of VT as SVT/AF; the most common cause of death was undersensing of VF. Although relatively few patients with normally functioning ICDs experience failure-to-treat VT/VF, the absolute number of verified MAUDE reports suggests that more work is needed to quantify the magnitude of the problem, to identify root causes, and to develop solutions.