Patent ID: 7120484

Claim:
A method for use by an Implantable Medical Device (IMD) of filtering an analog cardiac electrogram (EGM) signal having a predetermined frequency bandwidth, the method comprising: obtaining an analog cardiac electrogram (EGM) signal from an implantable sensor coupled to the IMD; filtering the EGM signal with a high pass filter (HPF) having a cut-of frequency within a predetermined frequency bandwidth, and wherein a low-frequency band portion of the predetermined frequency bandwidth is attenuated in the filtered EGM signal; sampling and digitizing the filtered EGM signal as a digital data set in a time order and optionally, generating a compressed digital data set having at least a 2:1 data compression factor; filtering one of said digital data set or said compressed data set in reverse time order employing a digital Infinite Impulse Response (IIR) filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF to substantially remove distortions of the filtered analog EGM signal introduced by the HPF; and analyzing a reconstituted EGM to determine whether cardiac ischemia is present.