A system comprising: an implantable medical device configured to be coupled to a lead (124, 130), the lead (124, 130) having electrodes (126, 132, 134, 136) to sense near field signals and far field signals between first and second combinations of electrodes (126, 132, 134, 136); memory (194, 404, 406) configured to store the NF signals and the FF signals and to store program instructions; and a processor (160, 402) that, when executing the program instructions, is configured to: apply an arrhythmia detection algorithm to the NF signals for identifying events within the NF signal and designating event markers based thereon; monitor the event markers to detect a candidate arrhythmia condition in the NF signals, characterized in that the candidate arrhythmia condition comprises an under-detected arrhythmia and optionally over-sensing, and the processor (160, 402) is, when executing the program instructions, configured to: in response to detection of the candidate arrhythmia condition, analyze the FF signals for a 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 and the candidate arrhythmia condition in the NF signals. an implantable medical device configured to be coupled to a lead (124, 130), the lead (124, 130) having electrodes (126, 132, 134, 136) to sense near field signals and far field signals between first and second combinations of electrodes (126, 132, 134, 136); memory (194, 404, 406) configured to store the NF signals and the FF signals and to store program instructions; and a processor (160, 402) that, when executing the program instructions, is configured to: apply an arrhythmia detection algorithm to the NF signals for identifying events within the NF signal and designating event markers based thereon; monitor the event markers to detect a candidate arrhythmia condition in the NF signals, characterized in that the candidate arrhythmia condition comprises an under-detected arrhythmia and optionally over-sensing, and the processor (160, 402) is, when executing the program instructions, configured to: in response to detection of the candidate arrhythmia condition, analyze the FF signals for a 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 and the candidate arrhythmia condition in the NF signals. apply an arrhythmia detection algorithm to the NF signals for identifying events within the NF signal and designating event markers based thereon; monitor the event markers to detect a candidate arrhythmia condition in the NF signals, characterized in that the candidate arrhythmia condition comprises an under-detected arrhythmia and optionally over-sensing, and the processor (160, 402) is, when executing the program instructions, configured to: in response to detection of the candidate arrhythmia condition, analyze the FF signals for a 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 and the candidate arrhythmia condition in the NF signals.