A case report of undetected cardiac arrest in a patient with an insertable cardiac monitor

Insertable cardiac monitors (ICMs) are small electrocardiographs implanted subcutaneously to automatically record electrocardiograms when arrhythmia is detected in patients with syncope. If the ICM misses a significant arrhythmia, it may delay the diagnosis of arrhythmogenic syncope and put the patient at risk. Herein, we describe a case of undetected cardiac arrest in a patient with ICM. An 87-year-old man with syncope was admitted to the hospital. After 8 days of monitoring, the cause could not be determined, and an ICM was implanted. Nine hours after implantation, the patient experienced cardiopulmonary arrest. Despite a body surface electrocardiogram showing ventricular flatline and fibrillation, the ICM failed to record. The cause of failure to record was considered to be the fluctuation in the R-wave amplitude of the ICM and noise oversensing. In conclusion, albeit infrequently, ICMs might overlook life-threatening arrhythmias. Even in cases where the ICM fails to detect an arrhythmia matching the symptoms, it may not be feasible to entirely rule out the presence of arrhythmias.