Implantable cardioversion device with automatic filter control

• US 6,208,899 B1
• Filed: 09/15/1999
• Issued: 03/27/2001
• Est. Priority Date: 09/15/1999
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Kroll, Mark W.
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US09/396,568
• Time in Patent Office: 559 Days
• Field of Search: 600/515, 600/516, 600/517, 600/518, 600/510, 607/9
• US Class Current: 607/9
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

An implantable cardioversion device includes a sensor for sensing intrinsic cardiac activity in a cardiac chamber, for example, the ventricle, and filtering the same using a bandpass filter having an adjustable center frequency. During normal sinus rhythm, the filter center frequency is set to correspond to the center frequency of normal R waves. If a sinus rhythm is not sensed, the filter center frequency is adjusted toward the frequency characteristic of an abnormal cardiac condition, such as ventricular fibrillation. The adjustable filter may be incorporated into an automatic threshold control system so that both the filter center frequency and the threshold are varied in synchrony. The adjustable filter may also be incorporated with an automatic gain control system wherein the filter center frequency and the gain are adjusted simultaneously.

Claims

1. An implantable cardiac stimulator configured to detect the presence of a normal sinus rhythm or an abnormal cardiac condition of a patient'"'"'s heart in response to a signal from a lead coupled to the patients heart, the stimulator comprising:

an amplifier for receiving and amplifying a signal from the lead in the patient'"'"'s heart;

a variable bandpass filter for receiving the amplified signal, the filter having a filter center frequency dynamically configurable to facilitate passing a filtered signal corresponding to a normal sinus rhythm or an abnormal cardiac condition;

a signal processor for processing the filtered signal to generate a detected output signal corresponding to the presence of a normal sinus rhythm or an abnormal cardiac condition; and

a control circuit for adjusting the center frequency of the variable bandpass filter in response to the detected output signal of the signal processor to facilitate detection of an abnormal cardiac condition.

2. The stimulator of claim 1, wherein at least one abnormal cardiac condition of the patient'"'"'s heart corresponds to fibrillation.

3. The stimulator of claim 1, wherein a normal sinus rhythm is comprised of periodic R waves and has a first center frequency and a signal corresponding to an abnormal cardiac condition has a second center frequency and whereby the control circuit causes the filter center frequency to adjust between the first center frequency and the second center frequency to facilitate detection of an abnormal cardiac condition.

4. The stimulator of claim 3, wherein the control circuit causes the filter center frequency to continuously adjust between the first center frequency and the second center frequency following each R wave to facilitate detection of an abnormal cardiac condition.

5. The stimulator of claim 3, wherein the filter center frequency adjusts linearly between the first center frequency and the second center frequency following each R wave to facilitate detection of an abnormal cardiac condition.

6. The stimulator of claim 3, wherein the center frequency adjusts linearly between the first and second center frequencies over a time period of approximately one second following each R wave.

7. The stimulator of claim 1, wherein the amplifier can amplify the signal from the lead by a gain factor and the gain factor is controllable by the control circuit.

8. The stimulator of claim 7, wherein the gain factor is continuously controllable between a first gain factor corresponding to a normal sinus rhythm and a second gain factor corresponding to an abnormal cardiac condition.

9. The stimulator of claim 7, wherein the control circuit causes the gain factor to increase in coordination with a decrease in the center frequency of the variable bandpass filter.

10. The stimulator of claim 1, wherein the signal processor is sensitive to signals above a threshold level and the threshold level is controllable by the control circuit.

11. The simulator of claim 10, wherein the threshold level is continuously adjustable between a first threshold level corresponding to a normal sinus rhythm and a second threshold level corresponding to an abnormal cardiac condition.

12. The stimulator of claim 11, wherein the control circuit causes the threshold level to decrease in coordination with a decrease in the center frequency of the variable band pass filter.

13. The stimulator of claim 1, wherein the stimulator includes cardioverter circuitry for generating therapy to revert the patient'"'"'s heart to a normal sinus rhythm when an abnormal cardiac condition is detected.

14. An implantable cardioversion device for detecting and reverting ventricular fibrillation in a patient'"'"'s heart, the device comprising:

a ventricular sensor for sensing intrinsic ventricular activity and generating a corresponding sense signal;

the ventricular sensor including;

a filter for filtering the sense signal to generate a filtered signal, wherein the filter has an adjustable center frequency;

a detector for detecting ventricular fibrillation or normal sinus rhythm based on the filtered signal; and

a controller for adjusting the center frequency to a value corresponding to the most recently detected normal sinus rhythm; and

a therapy generator for generating a prescribed therapy in response to the detector detecting ventricular fibrillation in the patient'"'"'s heart.

15. The device of claim 14, wherein the detector further includes a comparator for comparing the filtered signal to a threshold level.

16. The device of claim 14, wherein the threshold level is time varying.

17. The device of claim 14, wherein the threshold level has a first threshold value corresponding to a normal sinus rhythm and a second value corresponding to a ventricular fibrillation.

18. The device of claim 14, wherein the filter center frequency has a first filter frequency value corresponding to a normal sinus rhythm and a second filter frequency value corresponding to a ventricular fibrillation.

19. The device of claim 18, wherein the controller is configured to set the filter center frequency to the first filter frequency value in the presence of a normal sinus rhythm and to adjust the filter center frequency toward the second filter frequency value in the absence of a normal sinus rhythm.

20. The device of claim 19, wherein the controller changes the filter center frequency gradually from the first to the second center frequency value.

21. The device of claim 19, wherein the controller changes the filter center frequency linearly from the first to the second frequency value.

22. The device of claim 19, wherein the controller changes the filter center frequency from the first to the second frequency value over a time period of about one second.

23. The device of claim 18, wherein the detector further includes a comparator for comparing the filtered signal to a threshold level.

24. The device of claim 23, wherein the threshold level is time varying.

25. The device of claim 23, wherein the threshold level has a first threshold value corresponding to a normal sinus rhythm and a second threshold value corresponding to a ventricular fibrillation.

26. The device of claim 25, wherein the controller is configured to set the filter frequency in a range between the first and the second frequency values and for setting the threshold in a range between the first and second threshold values.

27. The device of claim 26, wherein the controller gradually and cooperatively changes the center frequency and the threshold level.

28. A method of applying cardioversion therapy to a patient with an implantable cardioversion device coupled to the patient'"'"'s heart, the method comprising the steps of:

sensing an intrinsic signal in a cardiac chamber of the patient'"'"'s heart to obtain a sensed signal;

bandpass filtering the sensed signal to generate a filtered signal using a filter having a center frequency adjustable between a first frequency value corresponding to a normal sinus rhythm and a second frequency value corresponding to an abnormal cardiac condition;

analyzing the filtered signal to detect a normal sinus rhythm condition;

adjusting the center frequency toward the second value if a normal sinus rhythm is not detected to facilitate detecting the presence of an abnormal cardiac condition; and

applying therapy in the presence of a detected abnormal cardiac condition.

29. The method of claim 28, wherein the second frequency value is selected to correspond to a ventricular fibrillation.

30. The method of claim 28, wherein the step of analyzing includes comparing the bandpassed signal to a sensing threshold value.

31. The method of claim 30, further comprising adjusting the threshold value dependent on the absence of a normal sinus rhythm.

32. The method of claim 30, wherein the sensing threshold is adjusted gradually from a first threshold value corresponding to a normal sinus rhythm toward a second threshold value corresponding to an abnormal cardiac condition in the absence of a normal sinus rhythm.

33. The method of claim 32, further comprising adjusting the gain value from a first gain level corresponding to a normal sinus rhythm toward a second gain level corresponding to an abnormal cardiac condition.

34. The method of claim 28, further comprising amplifying the sensed signal by a gain value.

35. A method of applying cardioversion therapy to a patient'"'"'s heart with an implantable cardioversion device having an input bandpass filter with a center frequency adjustable between first and second frequency values, the method comprising the steps of:

sensing an intrinsic signal in a chamber of the patient'"'"'s heart to obtain a sensed signal;

filtering the sensed signal with the input bandpass filter set at a first center frequency value corresponding to a normal sinus rhythm to generate a filtered signal;

determining the presence of a normal sinus rhythm based on the filtered signal;

adjusting the center frequency toward the second center frequency value corresponding to an abnormal cardiac condition if a normal sinus rhythm is not detected at the first center frequency value;

determining the presence of an abnormal cardiac condition or a normal sinus rhythm; and

changing the center frequency back to the first center frequency when a normal sinus rhythm is detected.

36. The method of claim 35, further comprising comparing the filtered signal to a threshold, the threshold being settable to a first threshold value corresponding to a normal sinus rhythm and a second threshold value corresponding to an abnormal cardiac condition.

37. The method of claim 36, wherein the threshold value adjusts from the first threshold value toward the second threshold value when a normal sinus rhythm is not detected.

38. The method of claim 37, further comprising adjusting the threshold from the second to the first threshold value when a normal sinus rhythm is detected.

39. The method of claim 36, further comprising amplifying the sensed signal by a gain setting settable between a first gain value corresponding to a normal sinus rhythm and a second gain value corresponding to an abnormal cardiac condition.

40. The method of claim 39, further comprising adjusting the gain setting from the first gain value toward the second gain value when a normal sinus rhythm condition is not detected.

41. The method of claim 40, further comprising changing the gain setting to the first gain value when a normal sinus rhythm is detected.