METHOD AND APPARATUS FOR PACING SAFETY MARGIN

• US 20110245890A1
• Filed: 03/25/2011
• Published: 10/06/2011
• Est. Priority Date: 03/30/2010
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Shome, Shibaji, Hayes, Kenneth N., Meyer, Scott A., McCabe, Aaron R., Dong, Yanting, Stalsberg, Kevin John, Brisben, Amy Jean
• Granted Patent: US 8,565,879 B2
• Time in Patent Office: Days
• US Class Current: 607/28
• CPC Class Codes: A61N 1/36585 controlled by two or more physical parameters
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold

Abstract

An apparatus comprises a cardiac signal sensing circuit, a pacing therapy circuit, and a controller circuit. The controller circuit includes a safety margin calculation circuit. The controller circuit initiates delivery of pacing stimulation energy to the heart using a first energy level, changes the energy level by at least one of: a) increasing the energy from the first energy level until detecting that the pacing stimulation energy induces stable capture, or b) reducing the energy from the first energy level until detecting that the stimulation energy fails to induce capture, and continues changing the stimulation energy level until confirming stable capture or the failure of capture. The safety margin calculation circuit calculates a safety margin of pacing stimulation energy using at least one of a determined stability of a parameter associated with evoked response and a determined range of energy levels corresponding to stable capture or intermittent failure of capture.

Claims

1. An apparatus comprising:

a cardiac signal sensing circuit configured to provide an electrical cardiac signal representative of cardiac activity of a subject;

a therapy circuit configured to deliver electrical pacing stimulation energy to a heart of a subject; and

a controller circuit communicatively coupled to the cardiac signal sensing circuit and the therapy circuit, and including a capture detection circuit configured to detect cardiac capture, wherein the controller circuit is configured to;

initiate delivery of pacing stimulation energy to the heart using a first energy level;

change the stimulation energy level by at least one of;

a) increasing the stimulation energy from the first energy level until detecting that the pacing stimulation energy induces stable capture, or b) reducing the stimulation energy from the first energy level until detecting that the stimulation energy fails to induce cardiac capture; and

continue the changing of the stimulation energy level until confirming the stable capture or the failure to induce capture;

wherein the controller circuit includes a safety margin calculation circuit configured to calculate a safety margin of pacing stimulation energy using at least one of;

a determined stability of a parameter associated with evoked response; and

a determined range of energy levels corresponding to intermittent failure to induce capture.

2. The apparatus of claim 1,

wherein the controller circuit is configured to measure the evoked response parameter during the delivery of the stimulation energy and induced capture, and

wherein the safety margin calculation circuit is configured to:

categorize parameter measurements into specified ranges of parameter values;

determine stability of the evoked response parameter by identifying the range of values that includes the largest number of parameter measurements;

identify the smallest pacing stimulation energy that induced capture resulting in a measured parameter in the identified range; and

calculate the safety margin using the identified smallest stimulation energy.

3. The apparatus of claim 1,

wherein the controller circuit is configured to measure the parameter during delivery of the stimulation energy and induced capture, and

wherein the safety margin calculation circuit is configured to:

determine stability of the evoked response parameter by specifying a range of values of the evoked response parameter;

identify a largest stimulation energy resulting in a measured parameter value outside the specified range of parameter values; and

calculate the safety margin using the identified largest stimulation energy.

4. The apparatus of claim 1, wherein the evoked response parameter includes at least one of:

a peak amplitude of the evoked response;

a time between delivery of pacing stimulation energy and occurrence of the peak amplitude of the evoked response;

a time between delivery of pacing stimulation energy and occurrence of a zero-crossing of the amplitude of the evoked response;

a polarity of a detected T-wave associated with the evoked response;

a positive slope of a sensed cardiac signal that includes the evoked response; and

a negative slope of a sensed cardiac signal that includes the evoked response.

5. The apparatus of claim 1, including a cardiac impedance sensing circuit communicatively coupled to the controller circuit and configured to provide a signal representative of cardiac impedance, and wherein the evoked response parameter includes at least one of:

a near-DC value of the cardiac impedance signal;

a peak-to-peak amplitude of the cardiac impedance signal; and

a zero-to-peak amplitude of the cardiac impedance signal.

6. The apparatus of claim 1, including at least one of:

a heart sound sensor configured to provide a signal representative of mechanical activity of the heart; and

a pulmonary pressure sensor configured to provide a signal representative of pulmonary pressure, and

wherein the evoked response parameter includes at least one of;

a measured amplitude of a heart sound associated with evoked response;

a time of occurrence of a heart sound associated with evoked response;

a power of a heart sound associated with the evoked response; and

pulmonary pressure.

7. The apparatus of claim 1, wherein the safety margin circuit is configured to:

calculate the safety margin using the range of energy levels corresponding to intermittent failure to induce capture; and

when stimulation energy corresponding to the stable capture is different from the stimulation energy corresponding to confirmed capture, then calculate the safety margin as the energy level of the stimulation energy corresponding to stable capture plus a specified stimulation energy increment value minus the energy level corresponding to confirmed capture,

otherwise use a specified minimum increment of stimulation energy as the safety margin.

8. The apparatus of claim 1, wherein the safety margin circuit is configured to:

calculate the safety margin using the range of energy levels corresponding to intermittent failure to induce capture; and

when a stimulation energy level corresponding to the confirmed loss of capture is different from the stimulation energy corresponding to the first detected loss of capture, then calculate the safety margin as the difference between the energy level immediately prior to first detecting loss of capture and the energy level immediately prior to confirming loss of capture,

otherwise use a specified minimum increment of stimulation energy as the safety margin.

9. The apparatus of claim 1, including a memory circuit integral to or communicatively coupled to the controller circuit, and wherein the safety margin calculation circuit is configured to:

trend pacing stimulation energy thresholds that induce an evoked response;

trend calculated safety margins, and

wherein the controller circuit is configured to determine a pacing stimulation energy using a trended pacing stimulation energy threshold and a trended calculated safety margin.

10. The apparatus of claim 1,

wherein the therapy circuit is configured to deliver pacing stimulation energy to the heart using a plurality of pacing vectors,

wherein the safety margin calculation circuit is configured to calculate a safety margin for at least a portion of the plurality of the pacing vectors, and

wherein the controller circuit is configured to select a pacing vector for delivering pacing stimulation energy using the calculated safety margins.

11. The apparatus of claim 10, wherein the controller circuit is configured to:

identify candidate pacing vectors for delivering pacing stimulation energy to a heart chamber;

receive a parameter measurement from a hemodynamic function circuit, wherein the parameter measurement indicates hemodynamic function of pacing for at least a portion of the identified candidate vectors;

determine a pacing stimulation energy threshold that induces an evoked response for the portion of the identified candidate vectors;

determine a phrenic nerve stimulation threshold for the portion of the identified candidate vectors;

calculate a pacing stimulation energy for a candidate vector using its calculated safety margin; and

select a pacing vector from among the candidate vectors according to its measured hemodynamic function parameter and a difference between its measured phrenic nerve stimulation threshold and its calculated pacing stimulation energy.

12. A method comprising:

delivering pacing stimulation energy to a heart of a subject using a medical device, wherein the stimulation energy includes a first energy level;

changing the stimulation energy level by at least one of;

a) increasing the stimulation energy from the first energy level until detecting that the pacing stimulation energy induces cardiac capture, or b) reducing the stimulation energy from the first energy level until detecting that the stimulation energy fails to induce cardiac capture;

continuing the changing of the stimulation energy level until confirming the inducement of stable capture or the failure to induce capture; and

calculating, with the medical device, a safety margin of pacing stimulation energy using at least one of;

a determined stability of a parameter associated with evoked response; and

a range of energy levels corresponding to intermittent failure to induce capture.

13. The method of claim 12,

wherein stability of the evoked response parameter is determined by:

measuring the parameter during the delivery of the stimulation energy and induced capture;

grouping parameter measurements into specified ranges of values;

identifying the range of values that includes the largest number of parameter measurements; and

identifying the smallest stimulation energy that induced evoked response resulting in a measured parameter in the identified range, and

wherein calculating a safety margin includes calculating the safety margin using the identified smallest stimulation energy.

14. The method of claim 12,

wherein stability of the evoked response parameter is determined by:

specifying a range of parameter values;

measuring the parameter during delivery of the stimulation energy and induced capture; and

identifying a largest stimulation energy resulting in a measured parameter value outside the specified range of parameter values, and

wherein calculating a safety margin includes calculating the safety margin using the identified largest stimulation energy.

15. The method of claim 12, wherein the evoked response parameter includes at least one of:

a time between delivery of pacing stimulation energy and occurrence of the peak amplitude of the evoked response;

a peak amplitude of the evoked response;

a time between delivery of pacing stimulation energy and occurrence of a zero-crossing of the amplitude of the evoked response;

a polarity of a detected T-wave associated with the evoked response;

a positive slope of a sensed cardiac signal that includes the evoked response;

a negative slope of a sensed cardiac signal that includes the evoked response;

a near-DC cardiac impedance value;

amplitude of cardiac impedance;

amplitude of a heart sound associated with evoked response;

a time of occurrence of a heart sound associated with evoked response;

a power of a heart sound associated with evoked response; and

pulmonary pressure.

16. The method of claim 12, including:

calculating the safety margin using a range of energy levels corresponding to intermittent failure to induce capture; and

when stimulation energy corresponding to the stable capture is different from the stimulation energy corresponding to confirmed capture, then calculating a safety margin as the energy level of the stimulation energy corresponding to the stable capture plus a specified stimulation energy increment value minus the energy level corresponding to the confirmed capture,

otherwise using a specified minimum increment of stimulation energy as the safety margin.

17. The method of claim 12, including:

calculating the safety margin using a range of energy levels corresponding to intermittent failure to induce capture; and

when a stimulation energy level corresponding to the confirmed loss of capture is different from the stimulation energy corresponding to the first loss of capture, then calculating a safety margin of pacing stimulation energy as the difference between the energy level immediately prior to detecting loss of capture and the energy level immediately prior to confirming loss of capture,

otherwise using a specified minimum increment of stimulation energy as the safety margin.

18. The method of claim 12, including:

trending a pacing stimulation energy threshold that induces capture;

trending the calculated safety margin; and

determining a pacing stimulation energy using the trended pacing stimulation energy and the trended calculated safety margin.

19. The method of claim 12, including using the calculated safety margin to determine a pacing vector for delivering pacing stimulation energy to the heart.

20. The method of claim 19, wherein determining a pacing vector for delivering pacing stimulation energy to the heart includes:

identifying candidate vectors for delivering the pacing stimulation energy;

measuring a parameter indicating hemodynamic function of pacing for at least a portion of the identified candidate vectors;

measuring a pacing stimulation energy threshold that induces capture for the portion of the identified candidate vectors;

measuring a phrenic nerve stimulation threshold for the portion of the identified candidate vectors;

calculating a pacing stimulation energy for a candidate vector using its calculated safety margin; and

identifying a preferred vector from among the candidate vectors according to its measured hemodynamic function parameter and a difference between its measured phrenic nerve stimulation threshold and its calculated pacing stimulation energy.