Methods and apparatus for filtering EGM signals detected by an implantable medical device

• US 7,120,484 B2
• Filed: 01/14/2002
• Issued: 10/10/2006
• Est. Priority Date: 01/14/2002
• Status: Expired due to Fees

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Lu, Steven N., Stadler, Robert W.
• Primary Examiner(s): Bockelman, Mark
• Application Number:
  US10/045,722
• Publication Number:
  US 20030135125A1
• Time in Patent Office: 1,730 Days
• Field of Search: 600/513, 600/510, 600/515
• US Class Current: 600/515
• CPC Class Codes: A61B 5/0008 Temperature signals
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/308 for electrocardiography [ECG]
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control

Abstract

An analog physiologic signal, e.g., the cardiac EGM, sensed by an IMD is filtered with a high pass filter (HPF), the cut-off frequency of the HPF being within a predetermined frequency bandwidth, wherein a low-band portion of the predetermined frequency bandwidth is attenuated in the filtered physiologic signal. The filtered physiologic signal is digitized in real time order, and the digital data set is filtered in reverse time order employing a digital IIR filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF. When the system is implemented within an IMD, the filtered digital data set is compressed by lossy compression algorithm, and the compressed data set is filtered in reverse time order. In certain embodiments, the filtered digital data set is uplink telemetry transmitted to an external medical device, and the uplink telemetered data set is filtered in reverse time order employing a digital backward IIR filter resident in the external medical device.

Claims

1. 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.

2. The method of claim 1, wherein the method is implemented using programmed instructions.

3. The method of claim 2, wherein the programmed instructions are executed on a processing circuit included within the IMD.

4. The method of claim 2, wherein the programmed instructions are executed on a processing circuit located external to the IMD.

5. The method of claim 1, wherein the EGM signal is generated using at least one of:

an endocardial electrode, an epicardial electrode, a subcutaneously implanted electrode, an electrode mechanically coupled to a portion of a housing for the IMD.

6. The method of claim 1, further comprising the step of storing the reverse time order filtered digital data set in a memory structure of the IMD.

7. The method of claim 1, further comprising the steps of:

storing the digital data set in memory of the IMD; and

uplink telemetry transmitting the stored digital data set to an external medical device (EMD); and

wherein the reverse time order filtering step of filtering the digital data set in reverse time order employing a digital IIR filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF is conducted by the EMD.

8. Apparatus for use by an Implantable Medical Device (IMD) for filtering a physiological signal having a predetermined frequency bandwidth, the method comprising:

a sensor coupled to the IMD for sensing an analog cardiac electrogram (EGM) signal;

a high pass filter (HPF) for filtering the analog EGM signal, the HPF having a the cut-off frequency within the predetermined frequency bandwidth, wherein a low-band portion of the predetermined frequency bandwidth is attenuated in the filtered analog EGM signal;

means for sampling and digitizing the filtered analog EGM signal as a digital data set In a real time order;

means for compressing the digital data set via a lossy data compression technique wherein said lossy data compression technique comprises a peak preserving compression algorithm providing at least a 2;

1 data compression;

a digital Infinite Impulse Response (IIR) filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF for reverse time order filtering either said digital data set or said compressed digital data set to substantially remove distortions of the filtered analog physiologic signal introduced by the HPF; and

means for comparing an EGM reconstituted from said reverse filtered data to a template to detect ischemia.

9. The apparatus of claim 8, wherein the filtering of the stream of samples with the IIR filter is implemented using programmed instructions.

10. The apparatus of claim 9, wherein the programmed instructions are executed on a processing circuit included within the IMD.

11. The apparatus of claim 9, wherein the programmed instructions are executed on a processing circuit located external to the IMD.

12. The apparatus of claim 8, wherein the EGM signal is generated by at least one of:

an endocardial electrode, an epicardial electrode, a subcutaneously implanted electrode, an electrode mechanically coupled to a portion of a housing for the IMD.

13. The apparatus of claim 8, further comprising means for storing the reverse time order filtered digital data set in memory of the IMD.

14. The apparatus of claim 8, further comprising:

means for storing the compressed digital data set in memory of the IMD; and

means for uplink telemetry transmitting the stored compressed digital data set to an external medical device (EMD); and

wherein;

the digital IIR filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF is within the EMD; and

the EMD further comprises means for receiving the uplink telemetry transmitted compressed digital data set and applying the received compressed digital data set to the digital IIR filter in reverse time order.

15. Apparatus for use by an Implantable Medical Device (IMD) for filtering a physiological signal having a predetermined frequency bandwidth, the method comprising:

a sensor coupled to the IMD for sensing an analog cardiac electrogram (EGM) signal;

a high pass filter (HPF) for filtering the analog EGM signal, the HPF having a the cut-off frequency within the predetermined frequency bandwidth, wherein a low-band portion of the predetermined frequency bandwidth is attenuated in the filtered analog EGM signal;

means for sampling and digitizing the filtered EGM signal as a digital data set in a real time order;

optionally, means for compressing said digital data set;

a digital Infinite Impulse Response (IIR) filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF for reverse time order filtering the digital data set, or a compressed data set if said optional means for compressing is included, to substantially remove distortions of the filtered analog EGM signal introduced by the HPF; and

means for comparing an EGM reconstituted from said reverse filtered data to a template to detect ischemia.

16. The apparatus of claim 15, wherein the filtering of the stream of samples with the IIR filter is implemented using programmed instructions.

17. The apparatus of claim 16, wherein the programmed instructions are executed on a processing circuit included within the IMD.

18. The apparatus of claim 16, wherein the programmed instructions are executed on a processing circuit located external to the IMD.

19. The apparatus of claim 15, wherein the physiologic signal is generated by at least one of:

an endocardial electrode, an epicardial electrode, a subcutaneously implanted electrode, an electrode mechanically coupled to a portion of a housing for the IMD.

20. The apparatus of claim 15, further comprising means for storing the reverse time order filtered digital data set in memory of the IMD.

21. The apparatus of claim 15, further comprising:

means for storing the digital data set in memory of the IMD; and

means for uplink telemetry transmitting the stored digital data set to an external medical device (EMD); and

wherein;

the digital IIR filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF is within the EMD; and

the FMD further comprises means for receiving the uplink telemetry transmitted digital data set and applying the received digital data set to the digital IIR filter in reverse time order.