Method and device for optimally altering stimulation energy to maintain capture of cardiac tissue

• US 6,456,879 B1
• Filed: 10/05/2000
• Issued: 09/24/2002
• Est. Priority Date: 05/15/2000
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Weinberg, Lisa P.
• Primary Examiner(s): CHAMBERS, A MICHAEL
• Application Number:
  US09/685,332
• Time in Patent Office: 719 Days
• Field of Search: 607/14, 607/28, 607/11, 607/29, 607/30, 607/34
• US Class Current: 607/11
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold

Abstract

An improved system and method for performing automatic capture/threshold detection in an implantable cardiac stimulation device or any device capable of stimulating some body organ or tissue. Prior art systems determine the cardiac tissue'"'"'s stimulation threshold by detecting an evoked response to a fixed duration stimulation pulse and then increasing the stimulation pulse'"'"'s amplitude by a predetermined safety margin value. Such systems are inherently based upon a belief that the chronaxie of a particular patient'"'"'s strength-duration curve is essentially fixed and that the rheobase is variable. While this may be true at some times during the patient'"'"'s life, e.g., during the acute phase after lead implantation absent drug effects, it is reported that drugs alone may alter the chronaxie and it is believed that other factors may also affect the chronaxie either alone or in combination with the rheobase. Accordingly, the present invention compares the present stimulation pulse to at least two pulse duration regions and, if a loss-of capture criteria is met, alters the amplitude aid/or the duration of the stimulation pulse accordingly in order to take into account a rheobase and/or chronaxie shift. The decision of whether to increase amplitude and/or duration is dependent on the current operating point. For example, in an embodiment having two pulse duration regions, the amplitude and duration of the stimulation pulse may be increased in the first duration region below the chronaxie while, in the second duration region above the chronaxie, only the amplitude may be increased.

Claims

1. A method for stimulating a patient'"'"'s body tissue, the method comprising the steps of:

periodically delivering a stimulation pulse to the patient'"'"'s body tissue, the stimulation pulse having a selectable pulse shape, wherein the selectable pulse shape is defined by a set of characteristics including an amplitude component and a duration component;

detecting the presence or absence of an evoked response generated by the patient'"'"'s body tissue in response to the stimulation pulse during a detection window;

determining whether a loss-of-capture criteria is satisfied in response to the absence of an evoked response to at least one delivered stimulation pulse;

determining whether the stimulation pulse is within one of the at least two stimulation pulse duration regions; and

altering the selectable pulse shape from a first pulse shape having a first amplitude component and a first duration component to a second pulse shape having a second amplitude component and a second duration component as a function of the at least two stimulation pulse duration regions in response to the loss-of-capture criteria until a capture criteria is met.

2. The method of claim 1 wherein the altering the selectable pulse shape step is performed as a function of first, second and third stimulation pulse duration regions defined by first and second duration thresholds and wherein the altering step comprises:

in the first duration region less than the first duration threshold, setting the second amplitude component to be essentially the same as the first amplitude component and setting the second duration component to exceed the first duration component;

in the second duration region between the first duration threshold and the second duration threshold, setting the second amplitude component to exceed the first amplitude component and setting the second duration component to exceed the first duration component; and

in the third duration region greater than the second duration threshold, setting the second amplitude component to exceed the first amplitude component and setting the second duration component to be essentially the same as the first duration component.

3. The method of claim 2 wherein the ability to stimulate the cardiac tissue is defined by a strength-duration curve characterized by a chronaxie and a rheobase and wherein the second duration region includes the chronaxie, additionally comprising the step of remotely programming values corresponding to the chronaxie and rheobase.

4. The method of claim 3 additionally comprising the steps of:

determining a starting pulse shape having an amplitude component and a duration component in response to the strength-duration curve; and

altering the pulse shape from the starting pulse shape to an initial pulse shape to achieve a safety margin from the strength-duration curve.

5. The method of claim 2 wherein the ability to stimulate the cardiac tissue is defined by a strength-duration curve characterized by a chronaxie and a rheobase and wherein the second duration region includes the chronaxie, additionally comprising the step of periodically determining values corresponding to the chronaxie and rheobase.

6. The method of claim 1 wherein the altering the selectable pulse shape step is performed as a function of first, second and third stimulation pulse duration regions defined by an amplitude and a duration threshold and wherein the altering step comprises:

in the first operating region where the amplitude component is greater than the amplitude threshold, setting the second amplitude component to be essentially the same as the first amplitude component and setting the second duration component to exceed the first duration component;

in the second operating region where the amplitude component is less than the first amplitude threshold and the duration component is less than the duration threshold, setting the second amplitude component to exceed the first amplitude component and setting the second duration component to exceed the first duration component; and

in the third operating region where the duration component is greater than the duration threshold, setting the second amplitude component to exceed the first amplitude component and setting the second duration component to be essentially the same as the first duration component.

7. The method of claim 1 wherein the altering the selectable pulse shape step is performed as a function of first and second stimulation pulse duration regions defined by a first duration threshold and wherein the altering step comprises:

in the first duration region less than the first duration threshold, setting the second amplitude component to exceed the first amplitude component and setting the second duration component to exceed the first duration component; and

in the second duration region greater than the first duration threshold, setting the second amplitude component to exceed the first amplitude component and setting the second duration component to be essentially the same as the first duration component.

8. An implantable cardiac stimulation device comprising:

pulse generator means for providing stimulation pulses to cardiac tissue, such stimulation pulses having selectable pulse shapes, each pulse being defined by a pulse amplitude and pulse width;

detection means for detecting the presence or absence of an evoked response corresponding to each stimulation pulse and indicative thereof of the presence or absence of capture;

control means for controlling the stimulation pulse amplitude and pulse width as a function of at least two stimulation pulse duration regions in response to a loss of capture criteria; and

wherein

the control means alters the stimulation pulse shape from a first pulse shape having a first amplitude component and a first duration component to a second pulse shape having a second amplitude component and a second duration component.

9. The cardiac stimulation device of claim 8 having first, second and third stimulation pulse duration regions defined by first and second duration thresholds and wherein:

in the first duration region less than the first duration threshold, the second amplitude component is essentially the same as the first amplitude component and the second duration component exceeds the first duration component;

in the second duration region between the first duration threshold and the second duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component exceeds the first duration component; and

in the third duration region greater than the second duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component is essentially the same as the first duration component.

10. The implantable cardiac stimulation device of claim 8 wherein the ability to stimulate the cardiac tissue is defined by a strength-duration curve characterized by a chronaxie and a rheobase, wherein the second duration region includes the chronaxie.

11. The implantable cardiac stimulation device of claim 10 wherein values corresponding to the chronaxie and rheobase are remotely programmable.

12. The implantable cardiac stimulation device of claim 10 wherein the control means periodically determines the chronaxie and rheobase.

13. The implantable cardiac stimulation device of claim 10 wherein:

a starting pulse shape having an amplitude component and a duration component is determined in response to the strength-duration curve; and

the control means is configured to alter the pulse shape from the starting pulse shape to an initial pulse shape to achieve a safety margin from the strength-duration curve.

14. The cardiac stimulation device of claim 8 having first, second and third operating regions wherein the operating regions are defined by an amplitude and a duration threshold and wherein:

in the first operating region where the amplitude component is greater than the amplitude threshold, the second amplitude component is essentially the same as the first amplitude component and the second duration component exceeds the first duration component;

in the second operating region where the amplitude component is less than the first amplitude threshold and the duration component is less than the duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component exceeds the first duration component; and

in the third operating region where the duration component is greater than the duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component is essentially the same as the first duration component.

15. The cardiac stimulation device of claim 8 having first and second stimulation pulse duration regions defined by a first duration threshold and wherein:

in the first duration region less than the first duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component exceeds the first duration component; and

in the second duration region greater than the first duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component is essentially the same as the first duration component.

16. An implantable cardiac stimulation device configured for stimulating a patient'"'"'s heart through at least one electrode implanted in electrical contact with selected cardiac tissue wherein the ability to stimulate the selected cardiac tissue is dependent upon the amplitude and duration of a stimulation pulse delivered to the cardiac tissue, the stimulation device comprising:

a pulse generator configured for electrical coupling to the electrode and configured to generate stimulation pulses at a controlled energy level to thereby stimulate the patient'"'"'s heart, wherein the controlled energy level is defined by a set of characteristics including an amplitude component and a duration component;

a detection circuit configured for electrical coupling to the electrode and configured to receive cardiac signals for determining the presence or absence of an evoked response to each of the stimulation pulses;

a controller, coupled to the pulse generator and the detection circuit, for increasing the controlled energy level in response to a loss-of-capture criteria related to the absence of at least one evoked response; and

wherein

the controlled energy level is increased from a first energy level having a first amplitude component and a first duration component to a second energy level having a second amplitude component and a second duration component, wherein the change in amplitude and duration components is a function of at least two stimulation pulse duration regions determined by the controller.

17. The cardiac stimulation device of claim 16 having first, second and third stimulation pulse duration regions determined by the controller according to first and second duration thresholds, wherein:

in the first duration region less than the first duration threshold, the second amplitude component is essentially the same as the first amplitude component and the second duration component exceeds the first duration component;

in the second duration region between the first duration threshold and the second duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component exceeds the first duration component; and

in the third duration region greater than the second duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component is essentially the same as the first duration component.

18. The implantable cardiac stimulation device of claim 17 wherein the ability to stimulate the cardiac tissue is defined by a strength-duration curve characterized by a chronaxie and a rheobase, wherein the second duration region includes the chronaxie.

19. The implantable cardiac stimulation device of claim 18 wherein values corresponding to the chronaxie and rheobase are remotely programmable.

20. The implantable cardiac stimulation device of claim 18 wherein the controller periodically determines the chronaxie and rheobase.

21. The implantable cardiac stimulation device of claim 18 wherein:

a starting controlled energy level having an amplitude component and a duration component is determined in response to the strength-duration curve; and

the controller is configured to increase the controlled energy level from the starting controlled energy level to an initial controlled energy level to achieve a safety margin from the strength-duration curve.

22. The implantable cardiac stimulation device of claim 21 wherein the initial controlled energy level is greater than the starting controlled energy level by a variable safety margin.

23. The cardiac stimulation device of claim 16 having first, second and third operating regions determined by the controller according to an amplitude and a duration threshold, wherein:

in the first operating region where the amplitude component is greater than the amplitude threshold, the second amplitude component is essentially the same as the first amplitude component and the second duration component exceeds the first duration component;

in the second operating region where the amplitude component is less than the first amplitude threshold and the duration component is less than the duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component exceeds the first duration component; and

in the third operating region where the duration component is greater than the duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component is essentially the same as the first duration component.

24. The cardiac stimulation device of claim 16 having first and second stimulation pulse duration regions determined by the controller according to first duration threshold, wherein:

in the first duration region less than the first duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component exceeds the first duration component; and

in the second duration region greater than the first duration threshold, the second amplitude component exceeds the first amplitude component and the second duration component is essentially the same as the first duration component.