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

• US 20030135125A1
• Filed: 01/14/2002
• Published: 07/17/2003
• Est. Priority Date: 01/14/2002
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Lu, Steven N., Stadler, Robert W.
• Granted Patent: US 7,120,484 B2
• Time in Patent Office: Days
• US Class Current: 600/510
• 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 a physiological signal having a predetermined frequency bandwidth, the method comprising:

obtaining an analog physiological signal from a sensor coupled to the IMD;

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

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

compressing the data set by lossy data compression; and

reverse time order filtering the compressed 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 to substantially remove distortions of the filtered analog physiologic signal introduced by the HPF.

2. The method of claim 1, wherein the filtering of the stream of samples with the IIR filter 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 physiologic signal is the cardiac EGM.

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

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

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

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

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

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

obtaining an analog physiological signal from a sensor coupled to the IMD;

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

sampling and digitizing the filtered physiologic signal as a digital data set in a time order; and

filtering the compressed 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 to substantially remove distortions of the filtered analog physiologic signal introduced by the HPF.

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

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

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

12. The method of claim 8, wherein the physiologic signal is the cardiac EGM.

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

14. The method of claim 8, 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.

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 physiological signal;

a high pass filter (HPF) for filtering the analog physiologic 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 physiologic signal;

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

means for compressing the data set by lossy data compression; and

a digital IIR filter having characteristics substantially matching the cut-off frequency and filter characteristics of the HPF for reverse time order filtering the compressed digital data set to substantially remove distortions of the filtered analog physiologic signal introduced by the HPF.

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 the cardiac EGM.

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 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.

22. 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 physiological signal;

a high pass filter (HPF) for filtering the analog physiologic 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 physiologic signal;

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

a digital IIR filter having characteristics substantially matching the cutoff frequency and filter characteristics of the HPF for reverse time order filtering the digital data set to substantially remove distortions of the filtered analog physiologic signal introduced by the HPF.

23. The apparatus of claim 22, wherein the filtering of the stream of samples with the IIR filter is implemented using programmed instructions.

24. The apparatus of claim 23, wherein the programmed instructions are executed on a processing circuit included within the IMD.

25. The apparatus of claim 23, wherein the programmed instructions are executed on a processing circuit located external to the IMD.

26. The apparatus of claim 22, wherein the physiologic signal is the cardiac EGM.

27. The apparatus of claim 22, further comprising means for storing the reverse time order filtered digital data set in memory of the IMD.

28. The apparatus of claim 22, 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 EMD 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.