A medical system includes an implantable cardiac monitoring device (ICMD) configured to monitor one or more physiological signals of a patient and in response to detecting a current or imminent arrhythmia in the patient, transmit first data to an external user device. The external user device is configured to: in response to receiving the first data from the ICMD, outputting a notification of the current or imminent arrythmia; confirm the presence of the current or imminent arrhythmia in the patient; and in response to confirming the current or imminent arrhythmia in the patient, cause an external defibrillator device to deliver a shock to the patient.