Implantable stimulation device having means for optimizing current drain

• US 5,697,956 A
• Filed: 06/02/1995
• Issued: 12/16/1997
• Est. Priority Date: 06/02/1995
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Bornzin, Gene A.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US08/458,540
• Time in Patent Office: 928 Days
• Field of Search: 607/9, 607/11, 607/27, 607/28, 607/29
• US Class Current: 607/28
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold

Abstract

An implantable pacemaker maintains a prescribed relationship between stimulation pulse amplitude and pulse width so as to provide an adequate safety factor above a stimulation threshold, while minimizing the current drain on the pacemaker battery. A series of stimulation pulse energies, each realized with a prescribed pulse amplitude and pulse width pair, are determined that may be used by the pacemaker as operating points. These operating points are numbered in order of increasing energy, and all adjustments of the pacing energy are made by selecting one of these operating points.

Claims

1. An implantable pacemaker comprising:

a battery;

pulse generating means for selectively generating electrical stimulation pulses at appropriate times for the purpose of depolarizing cardiac tissue, the electrical stimulation pulses being formed from electrical energy derived from the battery;

means for detecting capture at a patient'"'"'s stimulation threshold; and

pulse setting means, wherein the pulse setting means comprises;

means for determining a plurality of stimulation thresholds at a plurality of pulse widths at which capture is detected corresponding to a strength-duration curve;

means for adding a desired safety factor to the strength-duration curve to produce a plurality of pulse amplitude/pulse width combinations that would ensure capture at the desired safety factor;

means for determining a pacing current drain for each of the plurality of pulse amplitude/pulse width combinations that would ensure capture at the desired safety factor; and

means for selecting an optimal pulse amplitude/pulse width combination corresponding to a pulse amplitude/pulse width combination which ensures capture at the desired safety factor with the lowest pacing current drain.

2. The implantable pacemaker, as set forth in claim 1, wherein the pulse setting means further comprises:

means, responsive to the capture detecting means, for determining a new stimulation threshold and for triggering a new optimal pulse amplitude/pulse width combination to be selected whenever capture is lost.

3. The implantable pacemaker, as set forth in claim 1, wherein the pulse setting means further comprises:

means for determining an optimal pulse amplitude/pulse width combination for each of a series of increasing strength-duration curves; and

means for determining a sequence of optimal pulse amplitude/pulse width combinations based on the series of increasing strength-duration curves and having increased efficacy; and

means for storing the sequence of optimal pulse amplitude/pulse width combinations so that if the stimulation threshold increases, then the next highest pulse in the sequence will be used as the optimal pulse amplitude/pulse width combination.

4. The implantable pacemaker, as set forth in claim 3, wherein the storing means comprises:

means for storing the sequence of optimal pulse amplitude/pulse width combinations as a plurality of energy data words, each energy data word including a pulse amplitude portion and a pulse width portion that define in combination an electrical stimulation pulse having a different stimulation efficacy, each energy word defining one of the plurality of pulse amplitude/pulse width combinations having increasing stimulation energy with the lowest overall pacing current drain.

5. The implantable pacemaker, as set forth in claim 4, further comprising:

a telemetry means, coupled to the pulse setting means, for establishing a telemetry link with an external programming unit, and for communicating the plurality of energy data words from the external programmer unit through the telemetry link to the memory means.

6. An implantable pacemaker comprising:

a battery;

automatic capture detection means, powered by the battery, for detecting capture and for measuring stimulation threshold whenever capture is lost;

stimulation means, powered by the battery, for generating electrical stimulation pulses of a prescribed pulse amplitude and width to cardiac tissue, the stimulation pulses being generated from electrical energy stored in the battery; and

control means, powered by the battery, for defining a series of optimal pulse amplitude/pulse width combinations corresponding to a plurality of stimulation thresholds, wherein each of the pulse amplitude/pulse width combinations is calculated to minimize current drain on the battery as a function of a prescribed safety factor above a respective stimulation threshold; and

selecting means, powered by the battery, for automatically selecting one of the series of optimal pulse amplitude/pulse combinations based on the measured stimulation threshold.

7. The implantable pacemaker, as set forth in claim 6, wherein:

the automatic capture detection means includes means for periodically measuring stimulation threshold; and

the selecting means includes means for automatically selecting a new one of the series of optimal pulse amplitude/pulse width combinations whenever the measured stimulation threshold changes.

8. The implantable pacemaker, as set forth in claim 6, wherein the control means comprises:

memory means for storing a plurality of data words, a first data word defining a first pulse amplitude/width combination that maintains the prescribed safety factor at a first pacing energy and minimal current drain, a second data word defining a second pulse amplitude/width combination that maintains the prescribed safety factor at a second pacing energy and minimal current drain, the second pacing energy being greater than the first pacing energy; and

so on, with an nth data word defining an nth pulse amplitude/width combination that maintains the prescribed safety factor at an nth pacing energy and minimal drain current, the nth pacing energy being greater than an (n-1)th pacing energy;

whereby an ordered set of n data words is stored in the memory means that defines a series of n stimulation pulses of increasing stimulation efficacy, each stimulation pulse having an amplitude and width combination that maintains the prescribed safety factor, yet minimizes current drain on the pacemaker battery.

9. The implantable pacemaker, as set forth in claim 8, further comprising:

a telemetry means, coupled to the control means, for establishing a communication link with an external programmer unit, the n data words being communicable through the telemetry link for storage within the memory circuit from the external programmer unit.

10. The implantable pacemaker, as set forth in claim 8, wherein the control means comprises:

means for adaptively and automatically adjusting which one of the n data words is selected to define the prescribed pulse amplitude and width of the electrical stimulation pulse generated by the stimulation means as a function of stimulation threshold.

11. An implantable pacemaker comprising:

a battery;

sensing means, powered by the battery, for sensing a cardiac rhythm;

control means, powered by the battery, for analyzing the sensed cardiac rhythm to determine if it is an acceptable rhythm as defined by a set of pre-defined parameters;

stimulation means, powered by the battery and controlled by the control means, for generating electrical stimulation pulses of a prescribed pulse amplitude and width that are generated and delivered to cardiac tissue at appropriate times so as to maintain the acceptable rhythm defined by the set of pre-defined parameters, the stimulation pulses being generated from electrical energy stored in the battery; and

pulse forming means for defining an optimal pulse amplitude/pulse width combination as a pulse amplitude/pulse width combination that maintains a minimal current drain on the battery, as a function of a first prescribed safety factor when the rhythm is acceptable and as a function of a second prescribed safety factor when the rhythm is not acceptable.

12. The implantable pacemaker, as set forth in claim 11, wherein the pulse forming means comprises:

memory means for storing a plurality of data words, the plurality of data words defining a plurality of pulse amplitude/pulse width combinations, corresponding to a plurality of stimulation thresholds, that maintains the first and second prescribed safety factors with minimal current drain;

whereby a first and a second sequence of data words is stored in the memory means that defines a series of optimal pulse amplitude/pulse width combinations of increasing stimulation efficacy with the first and second prescribed safety factors, respectively, yet minimizes current drain on the pacemaker battery.

13. An implantable pacemaker that includes:

a battery;

means for detecting stimulation threshold;

pulse generating means, powered by the battery, for selectively generating electrical stimulation pulses, the electrical stimulation pulses having a pulse amplitude and pulse width that is defined by one of a plurality of operating points, each operating point being defined by a specific stimulation pulse amplitude and a specific stimulation pulse width, which pulse amplitude and pulse width have been calculated to provide a minimal pacing current drain on the battery as a function of a desired safety factor above the stimulation threshold.

14. The implantable pacemaker, as set forth in claim 13, further comprising:

control means for controlling the pulse generating means;

a telemetry means, coupled to the control means, for establishing a telemetry link with an external programmer, a set of command signals being transferable through the telemetry link from the external programmer to the control means, a single command signal within the set of command signals specifying an operating point at which the electrical stimulation pulses are to be generated

whereby both a stimulation pulse width and stimulation pulse amplitude are programmed by transferring the single command signal through the telemetry link, and further whereby the stimulation pulse width and stimulation pulse amplitude thus programmed achieve a desired safety factor while maintaining a minimal drain current.

15. A pacing system for stimulating cardiac tissue with electrical stimulation pulses, the stimulation pulses having a pulse amplitude and width that assures that a given stimulation pulse, when delivered to the cardiac tissue, is above a stimulation threshold by a prescribed safety factor, the system comprising:

(1) an implantable pacemaker including;

(a) a battery,

(b) control means, powered by the battery, for determining capture threshold, and

(c) stimulation means, controlled by the control means, for generating electrical stimulation pulses of a prescribed pulse width and amplitude, and for delivering the electrical stimulation pulses to the cardiac tissue at appropriate times, the stimulation pulses being generated from electrical energy stored in the battery; and

(2) an external programmer including;

(a) means for selectively establishing a communication link with the implantable pacemaker,

(b) means for defining, through the communication link, the prescribed pulse amplitude and width of the stimulation pulses to be generated by the stimulation means of the implantable pacemaker, the prescribed pulse amplitude and pulse width being calculated, as a function of a prescribed safety factor, to draw minimal energy from the battery of the implantable pacemaker.

16. The pacing system, as set forth in claim 15, wherein the means for defining the prescribed pulse amplitude and width comprises:

a memory circuit wherein a series of stimulation pulse operating points of increasing stimulation efficacy are defined, each operating point defining a stimulation pulse of increasing stimulation energy that is realized by a specific stimulation pulse amplitude in combination with a specific stimulation pulse width that maintains the prescribed safety factor, and that draws minimal energy from the battery.

17. The pacing system, as set forth in claim 16, wherein the control means of the implantable pacemaker further comprises:

means for measuring a stimulation threshold as a function of a prescribed stimulation pulse width;

means for communicating the measured stimulation thresholds to the external programmer through the communication link; and

wherein the external programmer includes processing means for processing the measured stimulation thresholds so as to generate the series of stimulation pulse operating points.

18. The pacing system, as set forth in claim 16, wherein the series of stimulation pulse operating points includes at least 20 points.

19. A method of operating an implantable pacemaker to use optimal stimulation pulse widths and stimulation pulse amplitudes as it performs its stimulation function, the optimal selection being made to minimize the pacemaker current drain while maximizing a safety factor of the pacemaker, the method comprising the steps of:

(a) determining a stimulation threshold for a particular patient as a function of stimulation pulse width;

(b) determining a stimulation pulse amplitude as a function of stimulation pulse width so as to achieve a given safety factor above the stimulation threshold;

(c) computing a pacing current drain as a function of the stimulation pulse widths and amplitudes determined in step (b);

(d) selecting a stimulation pulse amplitude and pulse width combination that provides a minimal pacing current drain as a function of pacing energy; and

(e) programming the pacemaker to use the stimulation pulse amplitude and pulse width combination determined in step (d).

20. The method, as set forth in claim 19, wherein steps (c) and (d) include:

defining a relationship between pacing current drain, stimulation threshold, pulse amplitude, pulse width and safety factor;

selecting a desired safety factor;

generating a plurality of data sets for the pacing current drain, pulse amplitude, pulse width and safety factor for a plurality of stimulation thresholds;

evaluating the plurality of data sets to determine optimal pulse width and pulse amplitude pairs that may be used as operating points for the pacemaker at each stimulation threshold, the optimal pulse width and pulse amplitude pairs being defined as the pair which achieves the desired safety factor with the lowest current drain;

determining a sequence for the optimal pulse width and pulse amplitude pairs in order of increasing stimulation efficacy;

measuring a given patient'"'"'s stimulation threshold; and

selecting operating points for the pacemaker from the sequence of pulse width and pulse amplitude pairs so as to provide a selected safety factor above the patient'"'"'s stimulation threshold with the lowest current drain.

21. The method, as set forth in claim 20, wherein the pacemaker includes an output capacitor that stores the energy of the stimulation pulse, which stimulation pulse is delivered to a known pacing resistance, and wherein:

the step of defining the relationship between pacing current drain (I_d), stimulation threshold (V_TH), pulse amplitude (V_out), pulse width (PW), and safety factor (SF) comprises defining;

I_d =V_out ×

C×

1-e^-(PW/RC) !×

(HR/60)×

CPF; and

V_TH =a×

PW^-B

V_out =SF×

a×

PW^-B

where V_out is the pulse amplitude in volts, PW is the pulse width in milliseconds, R is the pacing resistance, C is the capacitance value of the output capacitor in microfarads, HR is the stimulation rate provided by the pacemaker in stimulations/minute, and CPF is a charge-pump-factor that defines how many times the battery voltage of the pacemaker is stepped-up or multiplied in order to place a sufficient voltage on the output capacitor to achieve a specified pulse amplitude, "a" and "B" are constants for a given stimulation threshold.

22. The method, as set forth in claim 21, wherein the constant "a" can be estimated by measuring the stimulation threshold of a patient at approximately 1 msec.

23. The method, as set forth in claim 22, wherein the constant "B" is approximately 0.60.

24. The method, as set forth in claim 22, wherein the step of generating a plurality of data sets comprises the step of:

determining the plurality of stimulation thresholds by varying the constant "a" to produce a plurality of strength-duration curves.

25. A method of operating an implantable pacemaker to use optimal stimulation pulse widths and stimulation pulse amplitudes as it performs its stimulation function, the optimal selection being made to minimize the pacemaker current drain while maximizing a safety factor of the pacemaker, the method comprising the steps of:

(a) determining a strength-duration curve for a particular patient;

(b) determining an Iso-Safety Factor curve corresponding to a plurality of stimulation pulse amplitude/pulse width combinations which achieve a given safety factor above the strength-duration curve;

(c) computing a pacing current drain as a function of the stimulation pulse widths and amplitudes determined in step (b);

(d) selecting an optimal stimulation pulse amplitude and pulse width combination that provides a minimal pacing current drain as a function of pacing energy; and

(e) programming the pacemaker to use the stimulation pulse amplitude and pulse width combination determined in step (d).

26. A method of operating an implantable pacemaker, having a discharge circuit, to use optimal stimulation pulse widths and stimulation pulse amplitudes as it performs its stimulation function, the optimal selection being made to minimize the pacemaker current drain while maximizing a safety factor of the pacemaker, the method comprising the steps of:

(a) determining a strength-duration curve for a particular patient;

(b) determining an Iso-Safety Factor curve corresponding to a plurality of stimulation pulse amplitude/pulse width combinations which achieve a given safety factor above the strength-duration curve;

(c) computing a pacing current drain as a function of the discharge circuit and stimulation pulse widths and amplitudes determined in step (b);

(d) selecting an optimal stimulation pulse amplitude and pulse width combination that provides a minimal pacing current drain; and

(e) programming the pacemaker to use the stimulation pulse amplitude and pulse width combination determined in step (d).

27. The implantable pacemaker of claim 26, wherein the discharge circuit comprises a charge pump, output capacitor and pacing load and wherein computing the pacing current drain as a function of the discharge circuit considers the charge pump factor;

capacitance of the output capacitor; and

pacing load.

28. An implantable pacemaker comprising:

a battery;

a discharge circuit, comprising a charge pump, output capacitor and pacing load;

pulse generating means for selectively generating electrical stimulation pulses at appropriate times for the purpose of depolarizing cardiac tissue, the electrical stimulation pulses being formed from electrical energy derived from the battery;

means for detecting capture at a patient'"'"'s stimulation threshold; and

pulse setting means, wherein the pulse setting means comprises;

means for determining a plurality of stimulation thresholds at a plurality of pulse widths at which capture is detected corresponding to a strength-duration curve;

means for adding a desired safety factor to the strength-duration curve to produce a plurality of pulse amplitude/pulse width combinations that would ensure capture at the desired safety factor;

means for determining a pacing current drain, as a function of the discharge circuit, for each of the plurality of pulse amplitude/pulse width combinations that would ensure capture at the desired safety factor, wherein said means includes consideration of the charge pump factor, capacitance of the output capacitor and pacing load; and

means for selecting an optimal pulse amplitude/pulse width combination corresponding to a pulse amplitude/pulse width combination which ensures capture at the desired safety factor with the lowest pacing current drain.

29. An implantable pacemaker that includes:

a battery;

means for detecting stimulation threshold;

means for determining a stimulation efficacy as a function of the stimulation threshold and a desired safety factor; and

pulse generating means, powered by the battery, for selectively generating electrical stimulation pulses, the electrical stimulation pulses having a pulse amplitude and pulse width that is defined by one of a plurality of operating points, each operating point providing a different stimulation efficacy and being defined by a specific stimulation pulse amplitude and pulse width combination that minimizes current drain for that stimulation efficacy.

30. The implantable pacemaker, as set forth in claim 29, further comprising:

control means for controlling the pulse generating means;

a telemetry means, coupled to the control means, for establishing a telemetry link with an external programmer, a set of command signals being transferable through the telemetry link from the external programmer to the control means, a single command signal within the set of command signals specifying an operating point at which the electrical stimulation pulses are to be generated,

whereby both a stimulation pulse width and stimulation pulse amplitude are programmed by transferring the single command signal through the telemetry link, and further whereby the stimulation pulse width and stimulation pulse amplitude thus programmed achieve a desired safety factor while maintaining a minimal drain current.

31. A pacing system for stimulating cardiac tissue with electrical stimulation pulses, the stimulation pulses having a pulse amplitude and width that assures that a given stimulation pulse, when delivered to the cardiac tissue, is above a stimulation threshold by a prescribed safety factor, the system comprising:

(1) an implantable pacemaker including;

(a) a battery,

(b) control means, powered by the battery, for determining capture threshold, and

(c) stimulation means, controlled by the control means, for generating electrical stimulation pulses of a prescribed pulse width and amplitude, and for delivering the electrical stimulation pulses to the cardiac tissue at appropriate times, the stimulation pulses being generated from electrical energy stored in the battery; and

(2) an external programmer including;

(a) means for selectively establishing a communication link with the implantable pacemaker,

(b) means for defining, through the communication link, a series of stimulation pulse operating points of increasing stimulation efficacy, each operating point defining a stimulation pulse of increasing stimulation energy that is realized by a specific stimulation pulse amplitude in combination with a specific stimulation pulse width that draws minimal energy from the battery as a function of the prescribed safety factor.

32. The pacing system, as set forth in claim 31, wherein the control means of the implantable pacemaker further comprises:

means for measuring a stimulation threshold as a function of a prescribed stimulation pulse width;

means for communicating the measured stimulation thresholds to the external programmer through the communication link; and

wherein the external programmer includes processing means for processing the measured stimulation thresholds so as to generate the series of stimulation pulse operating points.

33. The pacing system, as set forth in claim 31, wherein the series of stimulation pulse operating points includes at least 20 points.