A system comprises an implantable medical device (IMD) (100) coupled to a lead (124, 130) having electrodes (126, 132, 134, 136) configured to sense near field (NF) signals (314) and far field (FF) signals (316). A processor (160, 402) is configured to apply an arrhythmia detection algorithm to the NF signals (314) for identifying events within the NF signal and designating events marker based thereon. The processor (160, 402) monitors the event markers to detect, in the NF signals (314), a candidate arrhythmia condition comprising at least one of an under-detected arrhythmia or over-sensing. The processor (160, 402) analyzes, in response to detection of the candidate arrhythmia condition, the FF signals (316) for presence of an under-detected arrhythmia indicator and deliver an arrhythmia therapy based on the presence of the under-detected arrhythmia indicator in the FF signals (316) and the candidate arrhythmia condition in the NF signals (314).
