Implantable cardiac stimulation device having a capture assurance system which minimizes battery current drain and method for operating the same

• US 6,738,668 B1
• Filed: 11/01/2001
• Issued: 05/18/2004
• Est. Priority Date: 11/01/2001
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Mouchawar, Gabriel A., Mouchawar, Nabil A.
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US10/000,058
• Time in Patent Office: 929 Days
• Field of Search: 607/5-28
• US Class Current: 607/28
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold

Abstract

An improved pacing system and related method for use in an implantable pacemaker or defibrillator are disclosed which operate using a predetermined subset of combinations of possible combinations for pacing stimulus pulse amplitude and pulse width, which subset of combinations are the most energy-efficient pairs, thereby ensuring reduced battery current drain. This is accomplished by ensuring that each combination has the lowest battery charge drain of any combination having at least the rheobase value of that particular combination as a function of cardiac chronaxie. The preferred embodiment of the pacing system of the present invention includes capture verification to enable a substantially reduced safety margin to further minimize the level of battery charge drain. The preferred embodiment of the pacing system of the present invention also includes the capability to produce a safety backup pulse, to ensure that the pacing system never misses a beat. The preferred embodiment of the pacing system of the present invention further includes the capability to initially and periodically determine the stimulation threshold and cardiac chronaxie.

Claims

1. An implantable cardiac stimulation device capable of providing pacing therapy, the implantable cardiac stimulation device comprising:

a first memory that is capable of storing a plurality of pulse amplitude/pulse width combinations each of which is associated with a rheobase value and a stimulation pulse energy content, wherein each of the pulse amplitude/pulse width combinations has the lowest battery charge drain of any possible pulse amplitude/pulse width combination having at least the rheobase value of that particular pulse amplitude/pulse width combination;

control circuitry, operatively connected to the first memory, that is operative to select a pulse amplitude/pulse width combination;

a stimulation pulse generator that is operative to generate stimulation pulses at the selected pulse amplitude/pulse width combination, at prescribed times upon demand, to stimulate cardiac tissue; and

an automatic capture detector which detects and provides an output indicative of whether the stimulation pulses obtain capture of cardiac tissue, the output of the automatic capture detector being supplied to the control circuitry, the control circuitry causing the stimulation pulse generator to generate stimulation pulses at the selected pulse amplitude/pulse width combination if the stimulation pulses obtain capture of cardiac tissue, the output of the automatic capture detector causing the stimulation pulse generator to generate stimulation pulses at another pulse amplitude/pulse width combination from the first memory which is associated with an incrementally higher rheobase value and stimulation pulse energy content to obtain capture with a safety margin.

2. An implantable cardiac stimulation device as defined in claim 1, wherein the plurality of pulse amplitude/pulse width combinations are permanently programmed into the first memory.

3. An implantable cardiac stimulation device as defined in claim 1, additionally comprising:

telemetry circuitry, coupled to the control circuitry, for establishing a telemetry link with an external programming unit, and for facilitating the transfer of the plurality of pulse amplitude/pulse width combinations into the first memory.

4. An implantable cardiac stimulation device as defined in claim 3, additionally comprising:

a second memory, the second memory containing at least two different pluralities of pulse amplitude/pulse width combinations, the external programmer being operable to cause one of the two different pluralities of pulse amplitude/pulse width combinations to be supplied from the second memory to the first memory for storage therein.

5. An implantable cardiac stimulation device as defined in claim 4, wherein the second memory is located in the implantable cardiac stimulation device.

6. An implantable cardiac stimulation device as defined in claim 4, wherein the second memory is located in the external programming unit.

7. An implantable cardiac stimulation device as defined in claim 4, wherein each of the different pluralities of pulse amplitude/pulse width combinations is associated with one of a corresponding different chronaxie values, a specific one of which may be selected by an operator of the external programming unit.

8. An implantable cardiac stimulation device as defined in claim 4, wherein each of the different pluralities of pulse amplitude/pulse width combinations is associated with one of a corresponding different chronaxie values, wherein the particular one of the plurality of sequences to be used is determined by threshold testing of the patient to determine pulse amplitude threshold at at least two different pulse widths.

9. An implantable cardiac stimulation device as defined in claim 3, additionally comprising:

means for calculating the plurality of pulse amplitude/pulse width combinations based upon a value of chronaxie.

10. An implantable cardiac stimulation device as defined in claim 9, wherein the value of chronaxie is entered by an operator of the external programming unit.

11. An implantable cardiac stimulation device as defined in claim 9, wherein the value of chronaxie is determined by threshold testing of the patient to determine pulse amplitude threshold at at least two different pulse widths.

12. An implantable cardiac stimulation device as defined in claim 9, wherein the calculation of the plurality of pulse amplitude/pulse width combinations based upon a value of chronaxie occurs in the external programming unit, following which the plurality of pulse amplitude/pulse width combinations based upon the value of chronaxie entered by an operator of the external programming unit are transferred into the implantable cardiac stimulation device and stored in the first memory.

13. An implantable cardiac stimulation device as defined in claim 9, wherein the value of chronaxie entered by an operator of the external programming unit is transferred into the implantable cardiac stimulation device, where the control circuitry performs pulse amplitude/pulse width combination the calculation of the plurality of pulse amplitude/pulse width combinations and stores them in the first memory.

14. An implantable cardiac stimulation device as defined in claim 1, wherein rheobase value is calculated according to the formula

15. An implantable cardiac stimulation device as defined in claim 1, wherein each pulse amplitude/pulse width combination is associated with a particular rheobase value which differs from the next lower rheobase value associated with a pulse amplitude/pulse width combination by at least a predetermined amount.

16. An implantable cardiac stimulation device as defined in claim 1, additionally comprising:

a threshold detector which detects and provides an output indicative of which of the plurality of pulse amplitude/pulse width combinations has the lowest battery charge drain while still obtaining capture of cardiac tissue.

17. An implantable cardiac stimulation device as defined in claim 16, wherein the output of the threshold detector is supplied to the control circuitry, the control circuitry causing the stimulation pulse generator to generate stimulation pulses at one of the plurality of pulse amplitude/pulse width combinations which has the same or an incrementally higher rheobase value and stimulation pulse energy content as the pulse amplitude/pulse width combination determined by the threshold detector to have the lowest battery charge drain while still obtaining capture of cardiac tissue.

18. An implantable cardiac stimulation device as defined in claim 1, additionally comprising:

a safety backup pulse generator which automatically causes the stimulation pulse generator to issue a high voltage safety backup stimulation pulse immediately following a detection by the capture detector of a failure of any stimulation pulse to obtain capture.

19. An implantable cardiac stimulation device as defined in claim 1, wherein the incrementally higher rheobase value and stimulation pulse energy content is the next highest rheobase value and stimulation pulse energy content from the first memory.

20. An implantable cardiac stimulation device capable of providing pacing therapy, the implantable cardiac stimulation device comprising:

a memory that stores a plurality of pulse amplitude/pulse width combinations each of which is associated with a rheobase value and a stimulation pulse energy content, each of which pulse amplitude/pulse width combinations has the lowest battery charge drain of any possible pulse amplitude/pulse width combination having at least the rheobase value of that particular pulse amplitude/pulse width combination;

control circuitry, operatively connected to the memory, that is operative to select one pulse amplitude/pulse width combination from the plurality of pulse amplitude/pulse width combinations;

a stimulation pulse generator that generates stimulation pulses at the selected pulse amplitude/pulse width combination, at prescribed times upon demand, to stimulate cardiac tissue; and

a threshold detector which detects and provides an output indicative of which of the plurality of pulse amplitude/pulse width combinations has the lowest battery charge drain while still obtaining capture of cardiac tissue, the output of the threshold detector being supplied to the control circuitry, the control circuitry causing the stimulation pulse generator to generate stimulation pulses at one of the plurality of pulse amplitude/pulse width combinations which has the same or higher rheobase value and stimulation/pulse energy content as the pulse amplitude/pulse width combination determined by the threshold detector to have the lowest battery charge drain while still obtaining capture of cardiac tissue;

wherein the stimulation pulse generator generates stimulation pulses at another pulse amplitude/pulse width combination from the memory which is associated with an incrementally higher rheobase value and stimulation pulse energy content to obtain capture with a safety margin.

21. An implantable cardiac stimulation device as defined in claim 20, wherein the incrementally higher rheobase value and stimulation pulse energy content is the next highest rheobase value and stimulation pulse energy content from the memory.

22. An implantable cardiac stimulation device comprising:

a memory that stores a plurality of pulse amplitude/pulse width combinations which are associated with different rheobase values, each of the combinations having the lowest battery charge drain of any pulse amplitude/pulse width combination having at least the rheobase value of that particular combination;

a stimulation pulse generator that generates stimulation pulses at a selected pulse amplitude/pulse width combination to stimulate cardiac tissue; and

a capture detector which detects whether the stimulation pulses obtain capture of cardiac tissue, the capture detector causing the stimulation pulse generator to generate stimulation pulses at the selected pulse amplitude/pulse width combination if the stimulation pulses capture cardiac tissue, the output of the automatic capture detector causing the stimulation pulse generator to generate stimulation pulses at another pulse amplitude/pulse width combination which is associated with an incrementally higher rheobase value from the memory to obtain capture with a safety margin.

23. An implantable cardiac stimulation device comprising:

means for providing power to the stimulation device;

means for providing stimulation pulses to cardiac tissue, such stimulation pulses have selectable pulse shapes;

means for selecting a pulse shape from a plurality of selectable pulse shapes, each pulse being defined by a pulse amplitude and pulse width, forming a unique pair thereby, each pair having associated therewith a specific rheobase value, a pulse shape being selected to provide the lowest battery drain relative to other pairs having the same specific rheobase value; and

means for detecting whether capture of the cardiac tissue has occurred and for triggering the selection means to select a pair with an incrementally higher rheobase value to obtain capture with a safety margin.

24. An implantable cardiac stimulation device as defined in claim 23, further comprising:

means for storing the plurality of selectable pulse shapes and their associated specific rheobase value, such plurality including only those pairs that provide the lowest battery drain relative to the other pairs having the same specific rheobase value.

25. An implantable cardiac stimulation device as defined in claim 24, further comprising:

means for sequentially selecting during periods of sustained detected capture, a pair with an incrementally lower rheobase value until capture is lost and selecting immediately thereafter the last pair wherein capture was obtained.

26. An implantable cardiac stimulation device as defined in claim 25, wherein the selecting means maintains cardiac stimulation using the selected last pair only if capture is obtained for at least two consecutive cardiac timing cycles.

27. An implantable cardiac stimulation device as defined in claim 24, wherein the incrementally higher rheobase value is the next highest rheobase value from the means for storing the plurality of selectable pulse shapes.

28. In an implantable cardiac stimulation device, a method of selecting a stimulation energy level for the device, the method comprising:

a) selecting an initial rheobase value to use to stimulate the heart;

b) determining a corresponding pulse amplitude/pulse width combination for the selected rheobase value, where the combination provides relatively low battery charge drain for the rheobase value;

c) determining whether applied pulses at the combination level capture the heart;

d) selecting another rheobase value if the applied pulses fail to capture the heart;

e) repeating actions b) through d) to determine at least one rheobase value that results in capture of the heart; and

f) generating stimulation pulses at a value that is incrementally higher than the rheobase value that results in capture of the heart to obtain capture with a safety margin.