Incidence of magnet mode in patients with implantable cardioverter defibrillators

Purpose To determine the current incidence of antitachycardia therapy suspension due to magnet reversion in patients with implantable cardioverter defibrillators (ICDs). Methods From March 2012 to September 2018, all St. Jude Medical ICD interrogations performed at the Deutsches Herzzentrum München were screened for stored events of antitachycardia therapy suspension caused by static magnetic fields (flux densities ≥ 1 mT as defined in St. Jude Medical ICDs) affecting the giant magnetoresistance (GMR) sensor. Intentional ICD deactivation or inappropriate magnet application in the hospital was classified as non-environmental electromagnetic interference (EMI) whereas in the case of any other stored magnet reversion, the event was classified as presumably environmental EMI. Results Data from 201 St. Jude Medical ICD patients (mean age 62 ± 24 years, 165 males/36 females) were included in the analysis. ICD interrogations occurred at a mean follow-up of 25.1 months ± 15.6 months and summed up to a total of 464 patient-years of follow-up. A total number of 43 magnet reversion events were detected in 21 patients. Thirty-two events in 13 patients were presumably related to environmental EMI sources. Suspension of antitachycardia therapy only occurred in a temporary fashion. None of the patients experienced any ventricular tachyarrhythmia during ICD inhibition. The incidence of antitachycardia therapy suspension due to magnet reversion related to presumably environmental EMI sources was 6.9% per patient and year. Conclusion Although none of the patients experienced any harmful event, antitachycardia therapy suspension due to magnet reversion is a common issue. Patients should be well-educated about potential EMI sources as well as trained in handling them.