System and method of automatically adjusting sensitivity in an implantable cardiac stimulation device

• US 6,539,259 B1
• Filed: 07/15/1999
• Issued: 03/25/2003
• Est. Priority Date: 07/15/1999
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Weinberg, Lisa P., McClure, Kelly H., Bornzin, Gene A.
• Primary Examiner(s): Bockelman, Mark
• Application Number:
  US09/354,244
• Time in Patent Office: 1,349 Days
• Field of Search: 607/9, 607/28, 600/509
• US Class Current: 607/9
• CPC Class Codes: A61N 1/368 comprising more than one electrode co-operating with different heart regions A61N1/3622, A61N1/3627 take precedence
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control

Abstract

A system and method are disclosed for automatically adjusting the sense amplifier sensitivity based on the sensing threshold of the undesired signals (i.e., far-field signals or undesired near-field signals). Specifically, R-wave sensitivity is based on the peak amplitude of the T-waves. Since the relationship between R-waves and T-waves is so repeatable, high confidence is achieved in setting the sensitivity above the T-wave sensing threshold. For atrial sensing, P-wave sensitivity is based on the sensing threshold of R-waves and/or T-waves, whichever is larger. Several embodiments are disclosed for determining the threshold for sensing the undesired signals, such as, double sensing until single sensing occurs, or otherwise detecting the peak amplitude of two or more cardiac signals. Additional error checking may be employed, particularly for atrial sensitivity adjustment, to ensure proper detection of the sensing threshold for the undesired signals in patients with heart block: including analysis of the respective amplitude, cardiac signal duration, and time relationships to appropriately classify the cardiac signals.

Claims

1. In an implantable cardiac stimulation device, a system for Automatically adjusting sensitivity, comprising:

a sensing circuit configured to sense first and second cardiac signals, the sensing circuit having programmable sensitivity settings;

a pulse generator configured to generate stimulation pulses in the absence of the first cardiac signal;

a control system, coupled to the sensing circuit and the pulse generator, programmed to automatically determine an appropriate sensitivity setting for sensing the first cardiac signal based on the sensing of the second cardiac signal.

2. The system of claim 1, wherein the control system further comprises:

means for determining a sensing threshold for detecting the second cardiac signal; and

means for selectively adjusting the sensing circuit to a sensitivity setting greater than the sensing threshold of the second cardiac signal.

3. The system of claim 1, wherein:

the sensing circuit includes a comparator configured to simultaneously detect the first and second cardiac signals whenever the sensitivity is equal to or below a first value, the first value corresponding to the peak amplitude of the second signal, and further configured to single detect the first cardiac signal when the sensitivity is adjusted above the first value; and

the control system is programmed to determine an appropriate setting for the sensing circuit above the first value.

4. The system of claim 1, wherein:

the sensing circuit includes an A/D converter configured to measure a first and a second amplitude corresponding to the first and second cardiac signals, respectively; and

the control system is programmed to determine an appropriate sensitivity setting based on the measured amplitude of the second cardiac signal.

5. The system of claim 1, wherein the control system comprises:

control means for adjusting the sensitivity setting between a first and a second sensitivity setting, the first sensitivity setting corresponding to a peak amplitude of the first cardiac signal, and the second sensitivity setting corresponding to a peak amplitude of the second cardiac signal; and

sensitivity setting means for setting the sensitivity setting to a value between the first and second sensitivity setting so that the second cardiac signal will not be sensed.

6. The system of claim 1, wherein:

the sensing circuit comprises a ventricular sensing circuit;

the first and second cardiac signals include R-waves and T-waves, respectively; and

the control system is programmed to automatically determine an appropriate ventricular sensitivity setting for sensing R-waves based on the sensed T-wave.

7. The system of claim 6, wherein the control system further comprises:

control means for determining a first range of sensitivity settings that simultaneously detects the R-waves and the T-waves, and for determining a second range of sensitivity settings that detects the R-waves without detecting the T-waves; and

sensitivity setting means for adjusting the ventricular sensitivity setting to a value within the second range of sensitivity settings so that T-waves will not be sensed.

8. The system of claim 1, wherein:

the sensing circuit comprises an atrial sensing circuit;

the first and second cardiac signals include P-waves and R-waves; and

the control system is programmed to automatically determine an appropriate atrial sensitivity setting for sensing P-waves based on the sensed R-wave.

9. The system of claim 8, wherein the control system comprises:

control means for determining a first range of sensitivity settings that simultaneously detects P-waves and the R-waves, and for determining a second range of sensitivity settings that detects P-waves without detecting the R-waves; and

sensitivity setting means for adjusting the atrial sensitivity setting to a value within the second range of sensitivity settings so that R-waves will not be sensed.

10. The system of claim 8, wherein:

the sensing circuit is adapted to detect a third cardiac signal corresponding to T-waves; and

the control system is programmed to automatically determine an appropriate atrial sensitivity setting for sensing P-waves based on the amplitude of at least one of the sensed R-wave and the sensed T-wave.

11. The system of claim 1, wherein:

the sensing circuit includes means for measuring a first and a second amplitude corresponding to the first and second cardiac signals, respectively; and

the control system includes means for determining the time relationship between the first and second cardiac signals, and for determining an appropriate sensitivity setting based on the measured amplitude and timing of the second cardiac signal relative to the first cardiac signal.

12. The system of claim 11, wherein:

the sensing circuit comprises a ventricular sensing circuit;

the first and second cardiac signals include R-waves and T-waves;

the control system is programmed to automatically analyze both timing and amplitude relationships of the first and second waveforms to determine which waveform is an R-wave and which waveform is a T-wave, and to determine a sensitivity setting for the R-wave based on the amplitude of the T-wave.

13. The system of claim 12, wherein the control system further comprises:

means for classifying the second cardiac signal as a T-wave only when the timing between the first and the second cardiac signal is consistent within a prescribed amount.

14. The system of claim 13, wherein the control system further comprises:

means for classifying the second cardiac signal as a premature beat, and ignores such premature beats, when the timing between the first and the second cardiac signal is not consistent within a prescribed amount.

15. The system of claim 13, wherein the control system further comprises:

means for classifying the second cardiac signal as a high amplitude T-wave when the amplitude of the second waveform is greater than the first cardiac signal and the timing between the first and the second cardiac signal is consistent within a prescribed amount; and

means for blanking the sensing circuit from sensing the high amplitude T-wave.

16. The system of claim 11, wherein:

the sensing circuit comprises an atrial sensing circuit;

the first and second cardiac signals include P-waves and R-waves;

the control system is programmed to automatically analyze both timing and amplitude relationships of the first and second waveforms to determine which waveform is a P-wave and which waveform is an R-wave, and to determine a sensitivity setting for sensing the P-wave based on the amplitude of the R-wave.

17. The system of claim 16, wherein the control system further comprises:

means for classifying the second cardiac signal as an R-wave only when the timing between the first and the second cardiac signal is consistent within a prescribed amount, thereby indicating that conduction exists between the atrium and the ventricle.

18. The system of claim 16, wherein the control system further comprises:

means for detecting a first and a second amplitude pattern for a plurality of cardiac signals;

means for detecting a first timing pattern between the cardiac signals having the first amplitude pattern, and for detecting a second timing pattern between the cardiac signals having the second amplitude pattern;

means for determining which of the first and the second timing patterns is slower; and

means for classifying cardiac signals having the slower timing pattern as R-waves, and for classifying the cardiac signals having the faster timing pattern as P-waves.

19. The system of claim 18, wherein the control system further comprises:

means for determining if cardiac signals classified as R-waves are higher in amplitude than the amplitude of the cardiac signals classified as P-waves; and

means for blanking the sensing circuit from sensing the higher amplitude R-waves.

20. The system of claim 16, wherein:

the sensing circuit is adapted to detect a third cardiac signal corresponding to T-waves; and

the control system is programmed to automatically analyze both timing and amplitude relationships of the third waveform relative to the first and the second waveforms to determine which waveform is a P-wave, which waveform is an R-wave, and which waveform is a T-wave, and to determine a sensitivity setting for sensing the P-wave based on the amplitude of at least one of the sensed R-wave and the sensed T-wave.

21. The system of claim 20, wherein the control system further comprises:

means for determining the duration of each of the first, second and third cardiac signals;

means for automatically analyzing duration of the first, second and third waveforms before determining which waveform is a P-wave, which waveform is an R-wave, and which waveform is a T-wave; and

means for ignoring waveforms that have a duration greater than a prescribed amount.

22. In an implantable stimulation device having a sense amplifier configured to sense a first cardiac signal, a pulse generator configured to generate stimulation pulses in the absence of the first cardiac signal, and a control system capable of controlling the pulse generator and the sense amplifier, the sense amplifier having a plurality of programmable sensitivity settings, and a method for automatically adjusting sensitivity of the sense amplifier, comprising the steps of:

determining a sensing threshold for detecting a second cardiac signal; and

selectively programming the sense amplifier to a sensitivity setting greater than the sensing threshold of the second cardiac signal.

23. The method of claim 22, wherein the step of determining a sensing threshold for the second cardiac signal comprises the steps of:

adjusting the sensitivity setting of the sense amplifier until the threshold of double sensing occurs, corresponding to the simultaneous sensing of the first and the second cardiac signal.

24. The method of claim 22, wherein the step of determining a sensing threshold for the second cardiac signal comprises the steps of:

measuring a peak amplitude for the second cardiac signal and correlating the peak amplitude to a sensitivity threshold.

25. The method of claim 22, further comprising the steps of:

determining a sensing threshold for detecting the first cardiac signal; and

selectively programming the sense amplifier to a sensitivity setting between the sensing threshold of the first and second cardiac signals.

26. The method of claim 25, further comprising the steps of:

determining a safety margin below the sensitivity threshold for the first cardiac signal and above sensitivity threshold for the second cardiac signal to thereby define an allowable range of sensitivities that will detect the first cardiac signal; and

setting the sensitivity setting within the allowable range defined by the safety margin.

27. In an implantable stimulation device having a sense amplifier configured to sense a first and a second cardiac signal, a pulse generator configured to generate stimulation pulses in the absence of the first cardiac signal, a memory for storing measured data, and a control system capable of controlling the pulse generator and the sense amplifier, the sense amplifier having a plurality of programmable sensitivity settings, and a method for adjusting the sensitivity of the sense amplifier comprising the steps of:

sensing the first and second cardiac signals;

measuring amplitude, duration and a time relationship between the first and second cardiac signals;

storing statistical data for the amplitude, duration and the time relationship for the first and second cardiac signals;

comparing the current amplitude, duration and time relationship to the stored statistical data;

triggering the storage of the current amplitude, duration and time relationship only if such data is within a predetermined delta of the stored statistical data;

analyzing the stored statistical data to determine a first and a second amplitude pattern, and to determine a first timing pattern for cardiac signals having the first amplitude pattern, and to determine a second timing pattern for cardiac signals having the second amplitude pattern;

classifying the first cardiac signal as one of a P-wave or an R-wave based on the respective amplitude and time relationship patterns; and

adjusting the sensitivity setting for sensing the first cardiac signal based on the amplitude of the second cardiac signal so that the second cardiac signal is not detected.