Removing polarization artifacts from electrical activity signals to detect cardiac evoked response

• US 7,089,049 B2
• Filed: 04/25/2003
• Issued: 08/08/2006
• Est. Priority Date: 04/25/2003
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Oosterhoff, Peter, Kerver, Harry Bernardus Antonius
• Primary Examiner(s): Pezzuto, Robert E.
• Assistant Examiner(s): Heller, Tammie K.
• Application Number:
  US10/424,928
• Publication Number:
  US 20040215274A1
• Time in Patent Office: 1,201 Days
• Field of Search: 607/14, 607/25, 600/515
• US Class Current: 600/515
• CPC Class Codes: A61N 1/371 Capture, i.e. successful stimulation
• CPC Class Codes: A61N 1/3716 with reduction of residual polarisation effects

Abstract

A medical device is directed to techniques for removing polarization artifacts from electrical activity signals in order to detect presence of an evoked response. More specifically, a medical device receives a signal that represents electrical activity within a heart of a patient following delivery of a stimulation pulse to the heart and reconfigures a filter state of a filter from an initial filter state to remove the polarization artifact from the electrical activity signal in order to determine whether a cardiac event, such as an evoked response has occurred. The medical device may, for example, when the filter of the medical device is a digital filter, recalculate the values of digital filter components using the present input value of the electrical activity signal as a direct current (DC) input value of the digital filter.

Claims

1. A method comprising:

receiving a signal that represents electrical activity within a heart following delivery of a stimulation pulse to the heart;

reconfiguring a filter state of a filter from an initial filter state to remove an artifact from the electrical activity signal, wherein the filter comprises a digital filter and reconfigiuring the filter state of the filter comprises recalculating values of digitaI filter components of the digital filter by measuring a present input value of the electrical activity signal and recalculating the values of the digital filter components using the present input value of the electrical activity signal as a direct current (DC) input value of the digital filter; and

determining presence of a cardiac event based on the filtered electrical activity signal.

2. The method of claim 1, wherein the artifact comprises a polarization artifact.

3. The method of claim 1, wherein reconfiguring the filter state of the filter comprises reconfiguring the filter state of the filter at a peak amplitude of the electrical activity signal.

4. The method of claim 1, wherein reconfiguring the filter state of the filter comprises reconfiguring the filter state of the filter at a defined time interval after turning on the filter.

5. The method of claim 1, wherein measuring the present input value of the electrical activity signal comprises measuring the present input value of the electrical activity signal upon stabilization of a filter output.

6. The method of claim 1, wherein the filter comprises an analog filter and reconfiguring the filter state of the filter state of the filter comprises closing a switch of the analog filter to load a capacitor with a present input value of the electrical activity signal.

7. The method of claim 6, further comprising opening the switch to output an electrical activity signal with the artifact removed.

8. The method of claim 6, wherein the analog filter comprises a first order analog filter.

9. The method of claim 1, wherein the filter comprises a high pass filter.

10. The method of claim 1, wherein determining whether a cardiac event occurs comprises determining whether the filtered electrical activity signal exceeds a detection level.

11. The method of claim 1, wherein determining presence of a cardiac event based on the filtered electrical activity signal comprises determining presence of an evoked response based on the filtered electrical activity signal.

12. The method of claim 1, wherein determining presence of a cardiac event based on the filtered electrical activity signal comprises determining presence of T-wave based on the filtered electrical activity signal.

13. A medical device comprising:

at least one electrode to receive a signal that represents electrical activity within a heart following delivery of a stimulation pulse to the heart;

a filter to filter the received electrical activity signal;

a filter controller to reconfigure a filter state of the filter from an initial filter state to remove an artifact from the electrical activity signal, wherein the filter comprises a digital filter, and the filter controfler recalculates values of digital filter components of the digital filter and the filter controller measures a present input value of the electrical activity signal and recalculates the values of the digital filter components using the present input value of the electrical activity signal as a direct current (DC) input value of the digital filter; and

a processor to determine presence of a cardiac event based on the filtered electrical activity signal.

14. The device of claim 13, wherein the artifact comprises a polarization artifact.

15. The device of claim 13, wherein the filter controller reconfigures the filter state of the filter at a peak amplitude of the electrical activity signal.

16. The device of claim 13, wherein the filter controller reconfigures the filter state of the filter at a defined time interval after turning on the filter.

17. The device of claim 13, wherein the filter controller measures the present input value of the electrical activity signal upon stabilization of a filter output.

18. The device of claim 13, wherein an order of the digital filter is greater than or equal to one.

19. The device of claim 13, wherein the filter comprises an analog filter, and the filter controller closes a switch of the analog filter to load a capacitor with a present input value of the electrical activity signal.

20. The device of claim 19, wherein the filter controller opens the switch to output an electrical activity signal with the artifact removed.

21. The device of claim 19, wherein the analog filter comprises a first order analog filter.

22. The device of claim 13, wherein the filter comprises a high pass filter.

23. The device of claim 13, wherein the processor compares the filtered electrical activity signal to a defined detection level and determines presence of a cardiac event when the filtered signal exceeds the detection level.

24. The device of claim 13, wherein the cardiac event includes one of an evoked response of the heart or a T-wave contraction of the heart.

25. The device of claim 13, wherein the electrode delivers the stimulation pulse and receives the electrical activity signal.

26. The device of claim 13, wherein the medical device comprises an implanted medical device.

27. A computer-readable medium comprising instructions that cause a processor to:

receive a signal that represents electrical activity within a heart following delivery of a stimulation pulse to the heart;

reconfigure a filter state of a filter from an initial filter state to remove an artifact from the electrical activity signal, wherein instructions that cause a processor to reconfigure the filter state of the filter indudes instructions that cause a processor to recalculate values of digital filter components of the digital filter wherein instructions that cause a processor to recalculate the values of the digital filter components includes instructions that cause a processor to measure a present input value of the electrical activity signal and recalculate the values of the digital filter components using the present input value of the electrical activity signal as a direct current (DC) input value of the digital filter; and

determine presence of a cardiac event based on the filtered electrical activity signal.

28. The computer-readable medium of claim 27, wherein instructions that cause a processor to measure the present input value of the electrical activity signal comprises instructions that cause a processor to measure the present input value of the electrical activity signal upon stabilization of a filter output.

29. The computer-readable medium of claim 27, wherein instructions that cause a processor to determine whether a cardiac event occurs comprises instructions that cause a processor to determine whether the filtered electrical activity signal exceeds a detection level.

30. A medical device comprising:

means for receiving a signal that represents electrical activity within a heart following delivery of a stimulation pulse to the heart;

means for reconfiguring a filter state of a filter from an initial filter state to remove an artifact from the electrical activity signal; and

means for determining presence of a cardiac event based on the filtered electrical activity signal, wherein the filter comprises a digital filter, and the wherein the means for reconfiguring recalculates values of digital filter components of the dgital filter and the means for reconfiguring measures a present input value of the electrical activity signal and recalculates the values of the digital filter components using the present input value of the electrical activity signal as a direct current (DC) input value of the digital fitter.

31. The device of claim 30, wherein the artifact comprises a polarization artifact.

32. The device of claim 30, wherein the means for reconfiguring reconfigures the filter state of the filter at a peak amplitude of the electrical activity signal.

33. The device of claim 30, wherein the means for reconfiguring reconfigures the filter state of the filter at a defined time interval after turning on the filter.

34. The device of claim 30, wherein the filter comprises an analog filter, and the means for reconfiguring closes a switch of the analog filter to load a capacitor with a present input value of the electrical activity signal and opens the switch to output an electrical activity signal with the artifact removed.