An implantable
medical device (IMD) capable of monitoring physiologic data, distinguishing relatively noisy and
noise free physiologic data, and recording noisy and relatively
noise free segments of physiologic data in separate memory registers of a limited memory for retrieval and analysis at a later time. Preferably the physiologic data comprises the sampled EGM of the heart detected from sense
electrode pairs that are implanted in the patient at sites where extraneous electrical
noise, e.g., electromyographic signals, are also capable of being detected. The sense
electrode pairs can constitute one or both sense electrodes located on or adjacent to the atrial and / or ventricular
heart chambers and coupled to the IMD by a lead body or sense
electrode pairs that are located remotely from the heart, e.g. at a
subcutaneous implantation site of the IMD. A plurality of noisy EGM episode data registers store a corresponding plurality of noisy EGM episode data sets on a FIFO basis and another plurality of noise free EGM episode data registers to store a corresponding plurality of relatively noise free EGM episode data sets on a FIFO basis. Any form of discrimination of
noisy data from relatively noise free data can be employed at the time of recording, but because the stored EGM episode data sets are subsequently viewed and analyzed by a physician, discrimination with absolute certainty is not required, and the physician can alter the detection criteria to fine tune it.