Method and apparatus for reducing the effect of evoked responses on polarization measurements in an automatic capture pacing system

• US 6,618,619 B1
• Filed: 09/26/2000
• Issued: 09/09/2003
• Est. Priority Date: 05/12/2000
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Florio, Joseph J., Bornzin, Gene A.
• Primary Examiner(s): Evanisko, George R.
• Assistant Examiner(s): BRADFORD, RODERICK D
• Application Number:
  US09/670,243
• Time in Patent Office: 1,078 Days
• Field of Search: 607/27, 607/28, 607/11, 607/7, 607/8, 607/9
• US Class Current: 607/27
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold
• CPC Class Codes: A61N 1/3716 with reduction of residual polarisation effects

Abstract

An initial polarization measurement is made by applying two electrical calibration pulses to the heart separated by a first time period. The first pulse is sufficient to generate an evoked response. The second pulse is applied during a refractory period associated with the first pulse. A polarization measurement is made following the second pulse and compared against a predetermined threshold. If the polarization does not exceed the threshold, the evoked response is adjusted using the measured polarization and an automatic capture function of the pacing system is programmed using the adjusted evoked response. However, if the polarization exceeds the threshold, a second pair of pulses are applied to the heart separated by a second time period, different from the first time period. A second polarization measurement is made after the second pulse and, if the second measured polarization does not exceed the predetermined threshold, the evoked response is adjusted using the newly measured polarization and the automatic capture function is programmed using the adjusted evoked response. If the polarization measurement again exceeds the predetermined threshold, the automatic capture function is disabled. Alternatively, a sequence of three pulses are applied to the heart and polarization is measured after the second and third pulses or calibration pulses may be applied after intrinsic depolarization events such as QRS complexes.

Claims

1. A method for determining an amount of polarization occurring following generation of electrical pulses in heart tissue from an implantable cardiac stimulation device, the method comprising the steps of:

delivering a first pair of electrical pulses separated by a first amount of time to measure a magnitude of electrical polarization occurring within the heart tissue; and

if the magnitude of electrical polarization exceeds a predetermined threshold, delivering a second pair of electrical pulses separated by a second amount of time, different than the first amount of time, to re-measure the magnitude of electrical polarization.

2. The method of claim 1 wherein the second amount of time is greater than the first amount of time.

3. The method of claim 2 wherein the first amount of time is between 60 and 90 milliseconds and wherein the second amount of time is between 40 and 200 milliseconds.

4. The method of claim 1 wherein the step of measuring the magnitude of electrical polarization occurring within the heart tissue using a first pair of electrical pulses comprises the steps of:

generating a first primary pulse sufficient to produce an evoked response within the heart tissue, wherein the first primary pulse causes the heart to become refractory for a first refractory period;

waiting the first amount of time, wherein the first amount of time is less than the first refractory period, and then generating a first calibration pulse; and

detecting the magnitude of electrical polarization occurring within the heart tissue following the first calibration pulse but still during the first refractory period.

5. The method of claim 4 wherein the step of re-measuring the magnitude of electrical polarization occurring within the heart tissue using a second pair of electrical pulses comprises the steps of:

waiting for the first refractory period to elapse;

generating a second primary pulse sufficient to produce another evoked response within the heart tissue, wherein the second primary pulse causes the heart to become refractory for a second refractory period;

waiting the second amount of time, wherein the second amount of time is less than the second refractory period, and then generating a second calibration pulse; and

detecting the magnitude of electrical polarization occurring within the heart tissue following the second calibration pulse but still during the second refractory period.

6. The method of claim 5 wherein the first and second primary pulses are substantially equal in magnitude to one another.

7. The method of claim 1 further including the steps of:

wherein the first;

pair of electrical pulses and the second pair of electrical pulses each generates an evoked response;

measuring the magnitude of the evoked response generated by each pair of pulses.

8. The method of claim 7 further including the steps of:

if the magnitude of electrical polarization measured using the first pair of pulses does not exceed the predetermined threshold, adjusting the magnitude of the evoked response generated by the first pair of pulses by the magnitude of corresponding electrical polarization and programming an automatic capture function with the adjusted evoked response;

, and

if the magnitude of electrical polarization measured using the first pair of pulses exceeds the predetermined threshold, adjusting the magnitude of the evoked response generated by the second pair of pulses by the magnitude of corresponding electrical polarization and programming an automatic capture function with the adjusted evoked response.

9. The method of claim 8 further including the step of disabling the automatic capture function if the electrical polarization magnitudes measured using the first and second pair of pulses both exceed the predetermined threshold.

10. A system for determining an amount of polarization occurring following generation of electrical pulses in heart, the system comprising:

an implantable cardiac stimulation device to stimulate the heart tissue;

a first pair of electrical pulses separated by a first amount of time, the first pair of electrical pulses delivered by the implantable cardiac stimulation device;

means for measuring a magnitude of electrical polarization occurring within the heart tissue resulting from the first pair of electrical pulses;

means for determining whether the magnitude of electrical polarization exceeds a predetermined threshold;

if the magnitude of electrical polarization exceeds the predetermined threshold, a second pair of electrical pulses separated by a second amount of time, different than the first amount of time, the second pair of electrical pulses delivered by the implantable cardiac stimulation device; and

means, responsive to a determination that the magnitude of electrical polarization exceeds a predetermined threshold, for re-measuring the magnitude electrical polarization delivered by the second pair of electrical.

11. The system of claim 10 wherein the second amount of time is greater than the first amount of time.

12. The system of claim 11 wherein the first amount of time is between 60 and 90 milliseconds and wherein the second amount of time is between 40 and 200 milliseconds.

13. The system of claim 10 wherein the means for measuring the magnitude of electrical polarization occurring within the heart tissue using a first pair of electrical pulses comprises:

means for generating a first primary pulse sufficient to produce an evoked response within the heart tissue, wherein the first primary pulse causes the heart to become refractory for a first refractory period;

means for waiting the first amount of time, wherein the first amount of time is less than the first refractory period, and then for generating a first calibration pulse; and

means for detecting the magnitude of electrical polarization occurring within the heart tissue following the first calibration pulse but still during the first refractory period.

14. The system of claim 13 wherein the means for re-measuring the magnitude of electrical polarization occurring within the heart tissue using a second pair of electrical pulses comprises:

means for waiting for the first refractory period to elapse;

means for generating a second primary pulse sufficient to produce another evoked response within the heart tissue, wherein the second primary pulse causes the heart to become refractory for a second refractory period;

means for waiting the second amount of time, wherein the second amount of time is less than the second refractory period, and then for generating a second calibration pulse; and

means for detecting the magnitude of electrical polarization occurring within the heart tissue following the second calibration pulse but still during the second refractory period.

15. The system of claim 14 wherein the first and second primary pulses are substantially equal in magnitude to one another.

16. The system of claim 10 further including means for measuring the magnitude of the evoked response generated by each pair of pulses.

17. The system of claim 16 further including:

means, responsive to a determination that the magnitude of electrical polarization measured using the first pair of pulses does not exceed the predetermined threshold, for adjusting the magnitude of evoked response generated by the first pair of pulses by the magnitude of corresponding electrical polarization and programming an automatic capture function with the adjusted evoked response; and

means, responsive to a determination that the magnitude of electrical polarization measured using the first pair of pulses exceeds the predetermined threshold, for adjusting the magnitude of evoked response generated by the second pair of pulses by the magnitude of corresponding electrical polarization and programming an automatic capture function with the adjusted evoked response.

18. The system of claim 17 further including means, responsive to a determination that the magnitudes of electrical polarization measured using the first pair and the second pair of pulses both exceed the predetermined threshold, for disabling the automatic capture function.

19. A system for determining an amount of polarization occurring following generation of electrical pulses in heart tissue, the system comprising:

an implantable cardiac stimulation device to stimulate the heart tissue;

a first pair of electrical pulses separated by a first amount of time, the first pair of electrical pulses delivered by the implantable cardiac stimulation device;

an electrical polarization measurement unit for measuring a magnitude of electrical polarization occurring within the heart tissue by delivering the first pair of electrical pulses;

a threshold comparison unit for determining whether the magnitude of electrical polarization exceeds a predetermined threshold,

if the magnitude of electrical polarization exceeds the predetermined threshold, a second pair of electrical pulses separated by a second amount time, different than the first amount of time, the second pair of electrical pulses delivered by the implantable cardiac stimulation device;

a control unit, responsive to a determination that the magnitude of electrical polarization exceeds a predetermined threshold, for controlling the electrical polarization unit to re-measure the magnitude electrical polarization resulting from the second pair of electrical pulses.

20. A method comprising:

delivering a first pair of electrical pulses to heart tissue, the first pair of electrical pulses separated by a first amount of time;

measuring a magnitude of electrical polarization resulting from the first pair of electrical pulses;

if the magnitude of electrical polarization exceeds a predetermined threshold, delivering a second pair of electrical pulses to the heart tissue, the second pair of electrical pulses separated by a second amount of time, the second amount of time being different from the first amount of time;

re-measuring the magnitude of electrical polarization resulting from the second pair of electrical pulses; and

if the magnitude of electrical polarization resulting from the second pair of electrical pulses is within the predetermined threshold, adjusting an evoked response in accordance with the magnitude of electrical polarization resulting from the second pair of electrical pulses.

21. The method of claim 20 further comprising:

if the magnitude of electrical polarization resulting from the second pair of electrical pulses exceeds the predetermined threshold, disabling an automatic capture function.

22. The method of claim 20 wherein the second amount of time is greater than the first amount of time.

23. The method of claim 20 wherein the first amount of time is between 60 and 90 milliseconds and wherein the second amount of time is between 40 and 200 milliseconds.

24. The method of claim 20 wherein the measuring the magnitude of electrical polarization resulting from the first pair of electrical pulses further comprises:

generating a first primary pulse sufficient to produce an evoked response within the heart tissue, wherein the first primary pulse causes the heart tissue to become refractory for a first refractory period;

waiting the first amount of time, wherein the first amount of time is less than the first refractory period, and then generating a first calibration pulse; and

detecting the magnitude of electrical polarization occurring within the heart tissue following the first calibration pulse but still during the first refractory period.

25. The method of claim 24 wherein the re-measuring the magnitude of electrical polarization resulting from the second pair of electrical pulses further comprises:

waiting for the first refractory period to elapse;

generating a second primary pulse sufficient to produce another evoked response within the heart tissue, wherein the second primary pulse causes the heart tissue to become refractory for a second refractory period;

waiting the second amount of time, wherein the second amount of time is less than the second refractory period, and then generating a second calibration pulse; and

detecting the magnitude of electrical polarization occurring within the heart tissue following the second calibration pulse but still during the second refractory period.

26. The method of claim 25 wherein the first and second primary pulses are substantially equal in magnitude to one another.