Method for adapting charge initiation for an implantable cardioverter-defibrillator

• US 8,249,702 B2
• Filed: 01/23/2009
• Issued: 08/21/2012
• Est. Priority Date: 01/25/2005
• Status: Active Grant

• Current Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Original Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Inventors: Warren, Jay A., Bardy, Gust H.
• Primary Examiner(s): Layno, Carl H
• Assistant Examiner(s): Oropeza, Frances
• Application Number:
  US12/359,072
• Publication Number:
  US 20090131998A1
• Time in Patent Office: 1,306 Days
• Field of Search: 607/5, 607/14, 607/28, 607/116, 607/119, 607/122
• US Class Current: 607/5
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/3943 for threshold determination
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

Adaptive methods for initiating charging of the high power capacitors of an implantable medical device for therapy delivery after the patient experiences a non-sustained arrhythmia. The adaptive methods adjust persistence criteria used to analyze an arrhythmia prior to initiating a charging sequence to deliver therapy.

Claims

1. A method of cardiac signal analysis in an implantable cardiac stimulus device comprising electrodes configured for implantation in a patient, the method comprising:

capturing a signal from the electrodes;

detecting, using analysis of the captured signal, a series of detected events; and

determining whether a malignant arrhythmia appears likely by;

a) using an X/Y counter having an indication of likely malignant events (X) out of a set of detected events (Y); and

b) comparing the X/Y counter to a predetermined counter ratio; and

wherein the method also comprises the implantable device selecting the predetermined counter ratio using the following rules;

c) if nonsustained high rate event conditions have not been previously detected, a first counter ratio is selected; and

d) if nonsustained high-rate event conditions have been previously identified, a second counter ratio is selected, wherein the selection of the second counter ratio remains in place for use in identifying future malignant arrhythmias and avoiding unnecessary treatment of future nonsustained high rate event conditions.

2. The method of claim 1 wherein the second counter ratio reduces a likelihood that the device, in response to a nonsustained high rate event condition, will determine that a malignant arrhythmia appears likely, relative to the first counter ratio.

3. The method of claim 2 further comprising, as a prerequisite to performing the step of determining whether a malignant arrhythmia appears likely, identifying a likelihood of present arrhythmia from the detected events such that, if no likelihood of present arrhythmia is identified, the step of determining whether a malignant arrhythmia appears likely is not performed following at least one detected event.

4. The method of claim 3 wherein the device further comprises a stimulus capacitor and associated charging circuitry and, if a malignant arrhythmia appears likely, the method further comprises the following:

preparing to deliver therapy by charging of the stimulus capacitor; and

continuing to observe cardiac function while preparing to deliver therapy and, if malignant arrhythmia continues to appear likely, delivering therapy to the patient once the device is prepared to deliver the therapy.

5. The method of claim 4 wherein the electrodes are all implanted subcutaneously in the patient, without any electrode disposed in or on the patient'"'"'s heart.

6. The method of claim 4 wherein at least one electrode is transvenously implanted.

7. The method of claim 3 wherein the step of identifying a likelihood of present arrhythmia includes calculating an event rate across a series of detected events and determining whether the event rate exceeds a threshold.

8. The method of claim 1 wherein the device further comprises a stimulus capacitor and associated charging circuitry and if a malignant arrhythmia appears likely, the method further comprises the following:

preparing to deliver therapy by charging of the stimulus capacitor; and

continuing to observe cardiac function while preparing to deliver therapy and, if malignant arrhythmia continues to appear likely, delivering therapy to the patient once the device is prepared to deliver the therapy.

9. A method of cardiac signal analysis in an implantable cardiac stimulus device, the device comprising electrodes configured for implantation in a patient and telemetry circuitry allowing an operator to program parameters used in the device to determine whether to deliver therapy, the method comprising:

capturing a signal from the electrodes;

detecting, by analysis of the signal, detected events in the signal; and

determining whether a malignant arrhythmia appears likely by;

a) using an X/Y counter having an indication of likely malignant events (X) out of a set of detected events (Y);

b) comparing the X/Y counter to a predetermined counter ratio; and

c) if the X/Y counter exceeds the predetermined ratio, determining whether the X/Y counter has exceeded the predetermined ratio at least N times and, if so, determining that a malignant arrhythmia appears likely;

wherein N is automatically predetermined by the implantable device such that N has an initial value and, following identification of nonsustained apparently malignant conditions, N is increased to a higher value than the initial value and remains at the higher value for use in subsequent event processing to identify future malignant arrhythmias and avoid treatment for future nonsustained high-rate condtiions.

10. The method of claim 9, further comprising identifying a likelihood of present tachyarrhythmia from the detected events using event rate.

11. The method of claim 10 wherein the device further comprises a stimulus capacitor and associated charging circuitry and, if a malignant arrhythmia appears likely, the method further comprises the following:

preparing to delivery therapy by charging the stimulus capacitor; and

continuing to observe cardiac function while preparing to deliver therapy and, if malignant arrhythmia continues to appear likely, delivering therapy to the patient once the device is prepared to deliver the therapy.

12. The method of claim 11 wherein the electrodes are all implanted subcutaneously in the patient, without any electrode disposed in or on the patient'"'"'s heart.

13. The method of claim 11 wherein at least one electrode is implanted transvenously.

14. The method of claim 10 wherein the step of identifying a likelihood of present arrhythmia includes calculating an event rate across a series of detected events and determining whether the event rate indicates a tachyarrhythmia.

15. The method of claim 10 wherein the step of identifying a likelihood of present arrhythmia includes calculating an event rate across a series of detected events and determining whether the event rate exceeds a threshold.

16. The method of claim 9 wherein the device further comprises a stimulus capacitor and associated charging circuitry and, if a malignant arrhythmia appears likely, the method further comprises the following:

preparing to deliver therapy by charging the stimulus capacitor; and

continuing to observe cardiac function while preparing to deliver therapy and, if malignant arrhythmia continues to appear likely, delivering therapy to the patient once the device is prepared to deliver the therapy.

17. An implantable cardiac stimulus device comprising:

a canister containing a battery, charging circuitry, energy storage circuitry, control circuitry, and coupling circuitry, in which the control circuitry controls operation and use of the charger, energy storage and coupling circuitry to provide cardiac signal monitoring and, when indicated, cardiac therapy; and

a plurality of electrodes connected to the coupling circuitry which, in turn, couples the control circuitry to the plurality of electrodes to allow cardiac signal monitoring and, when indicated, cardiac therapy;

wherein the control circuitry is configured to perform the following method;

capturing cardiac signals from the electrodes via the coupling circuitry when implanted in a patient to detect the patient'"'"'s cardiac condition;

determining from captured signals whether a likely arrhythmia is occurring; and

,

if a likely arrhythmia is occurring;

determining whether the device has previously identified indication(s) of nonsustained tachyarrhythmia(s);

selecting between a first X/Y counter ratio and a second X/Y counter ratio for use in determining whether cardiac stimulus is indicated by using at least a step of determining whether previous nonsustained tachyarrhythmia(s) have occurred;

applying the selected X/Y counter ratio to determine whether cardiac stimulus is indicated;

further wherein, if previous nonsustained tachyarrhythmia(s) have been detected, the selection between the first and second X/Y counter ratios reduces the likelihood that a new nonsustained tachyarrythmia could lead to therapy delivery by the device.

18. The implantable cardiac stimulus device of claim 17 wherein the control circuitry is further configured such that:

if previous nonsustained tachyarrhythmia(s) have been detected, the second X/Y counter ratio is selected, else the first X/Y counter ratio is selected; and

the second X/Y counter ratio uses a larger X and larger Y than the first X/Y counter ratio.

19. The implantable cardiac stimulus device of claim 17 wherein the control circuitry is further configured such that:

if previous nonsustained tachyarrhythmia(s) have been detected, the second X/Y counter ratio is selected, else the first X/Y counter ratio is selected; and

the second X/Y counter ratio requires consideration of a larger sampling of cardiac signals than the first X/Y counter ratio.

20. The implantable cardiac stimulus device of claim 17 wherein the control circuitry is configured such that, if cardiac stimulus is indicated, the method further comprises the following:

preparing to deliver therapy by charging the energy storage circuitry; and

continuing to observe cardiac function while charging the energy storage circuitry and, if cardiac stimulus continues to be indicated, delivering therapy to the patient once the device is prepared to deliver the therapy.

21. The implantable cardiac stimulus device of claim 17 wherein the first counter ratio is 18/24 and the second counter ratio is 21/27.

22. An implantable cardiac stimulus device configured for implantation into a patient'"'"'s body comprising a housing, operational circuitry contained in the housing, and a number of electrodes coupled to the operational circuitry and disposed either on the housing, as part of the housing, or on one or more leads coupled to the housing, wherein the operational circuitry is configured to perform a method of cardiac signal analysis comprising:

capturing signals from the electrodes when implanted in a patient;

identifying detected events in the captured signals with the intent that detected events represent cardiac events;

determining whether a high-rate arrhythmia appears likely;

if so, analyzing detected events to identify those which likely indicate a malignant cardiac rhythm; and

determining whether an X/Y counter in which X represents the number of detected events identified as likely indicating a malignant cardiac rhythm out of a set of Y detected events indicates therapy for the patient;

wherein the operational circuitry is configured to identify nonsustained tachycardia and, if nonsustained tachycardia is identified, to determine whether to modify the X/Y counter to use a larger sample size and the larger sample size is used for future cardiac signal analysis to avoid therapy on future nonsustained tachycardia.

23. An implantable cardiac stimulus device comprising an implantable canister and a plurality of electrodes, the canister containing operational circuitry configured to perform cardiac signal captured and analysis, as well as defibrillation circuitry configured to provide defibrillation therapy if indicated by analysis of cardiac signal, the operational circuitry further configured to perform a method of cardiac signal analysis comprising:

capturing a signal from the electrodes when implanted in a patient;

detecting, using analysis of the captured signal, a series of detected events; and

determining whether a malignant arrhythmia appears likely by;

a) using an X/Y counter having an indication of likely malignant events (X) out of a set of detected events (Y);

b) comparing the X/Y counter to a predetermined counter ratio; and

c) if the X/Y counter exceeds the predetermined counter ratio, determining whether the predetermined counter ratio is exceeded by the X/Y counter for at least N iterations and, if so, determining that a malignant arrhythmia appears likely; and

wherein the method also comprises the implantable device selecting N as follows;

if nonsustained high rate event conditions have not been previously detected, a first number is selected; and

if nonsustained high-rate event conditions have been previously identified, a second number larger than the first number is selected;

wherein the selection of the second number remains in place for use in identifying future malignant rhythms.

24. The implantable cardiac stimulus device of claim 23 wherein the operational circuitry is further configured such that reliance upon the second number reduces a likelihood that the device, in response to a nonsustained high rate event condition, will determine that a malignant arrhythmia appears likely, relative to the first number.