Accurate Cardiac Event Detection in an Implantable Cardiac Stimulus Device

• US 20090228057A1
• Filed: 03/06/2009
• Published: 09/10/2009
• Est. Priority Date: 03/07/2008
• Status: Active Grant

• Current Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Original Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Inventors: Warren, Jay A., Sanghera, Rick, Allavatam, Venugopal, Palreddy, Surekha
• Granted Patent: US 8,565,878 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/355 Detecting T-waves
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock

Abstract

Methods, systems, and devices for signal analysis in an implanted cardiac monitoring and treatment device such as an implantable cardioverter defibrillator. In some illustrative examples, detected events are analyzed to identify changes in detected event amplitudes. When detected event amplitudes are dissimilar from one another, a first set of detection parameters may be invoked, and, when detected event amplitudes are similar to one another, a second set of detection parameters may be invoked. Additional methods determine whether the calculated heart rate is “high” or “low,” and then may select a third set of detection parameters for use when the calculated heart rate is high.

Claims

1. An implantable cardiac stimulus device (ICSD) comprising:

a canister housing operational circuitry configured to perform cardiac signal analysis and configured to provide cardiac stimulus;

a lead electrode assembly coupled to the canister and operatively coupled to the operational circuitry;

wherein the operational circuitry is configured to perform a beat detection method comprising;

capturing electrical signals from the electrodes when implanted in a patient;

identifying events in the captured electrical signals using a detection profile, the detection profile providing a threshold having a threshold configuration for comparison to the captured signals such that, when the captured signals exceed the threshold, a detected event is declared;

comparing a peak amplitude of a first detected event to a peak amplitude of a second detected event to determine whether the first and second events are similar or dissimilar; and

if the first and second events are similar, using a first threshold configuration for detecting a subsequent event;

or

if the first and second events are dissimilar, using a second threshold configuration for detecting a subsequent event,

wherein a sensitivity of the second threshold configuration is different than that of the first threshold configuration.

2. The ICSD of claim 1 wherein the operational circuitry is further configured such that the first threshold configuration defines a more sensitive detection threshold than the second threshold configuration.

3. The ICSD of claim 1 wherein the operational circuitry is further configured such that the first threshold configuration defines a less sensitive detection threshold than the second threshold configuration.

4. The ICSD of claim 1 wherein the operational circuitry is also configured to perform a rhythm analysis method including the following steps:

identify and mark detected events as either shockable or non-shockable;

maintain an X/Y counter indicating how many detected events out of a set of detected events are marked as shockable;

determine whether the X/Y counter indicates a malignant rhythm is occurring and, if so, whether the malignant rhythm has persisted for a predetermined number, N, of consecutive events;

if the X/Y counter indicates a malignant rhythm, and the malignant rhythm has persisted for the predetermined number, N, of consecutive events, the operational circuitry is still further configured to begin charging a capacitor to a therapy voltage in preparation for stimulus delivery.

5. The ICSD of claim 1 wherein the operational circuitry is further configured such that the first and second threshold configurations define at least the following time periods:

a refractory period during which detected events are not declared;

a constant threshold time period having a duration, CTD and an amplitude CTA; and

a decay time period during which the threshold changes with time from a starting amplitude DTA;

and further wherein;

the first threshold configuration has a longer CTD and higher CTA and DTA than the second threshold configuration.

6. The ICSD of claim 5 wherein the operational circuitry is configured such that the values for CTA and DTA are defined as percentages of an estimated peak value for peaks identified in detected events.

7. The ICSD of claim 1 wherein the operational circuitry is further configured such that the first and second threshold configurations define at least the following time periods:

a refractory period during which detected events are not declared;

a constant threshold time period with duration CTD and amplitude CTA;

a time period during having start amplitude TSA, final amplitude TFA and a maximum duration MD; and

a second decay time period during which the threshold changes over time from a decay starting amplitude DSA to a noise floor for the device;

and further wherein;

the first threshold configuration has a longer CTD and higher CTA, and TSA and TFA than the second threshold configuration.

8. A method of operation in an implantable cardiac stimulus system configured to detect cardiac events from an implanted location, the method incorporating a first detection threshold profile and a second detection threshold profile, both for use in detecting cardiac events, the method comprising a sim/dissim method of event detection comprising:

detecting a first detected event using one of the detection threshold profiles;

determining whether the first detected event is similar to or dissimilar from an amplitude of previous detected events; and

;

if the first detected event is similar to the amplitude measure of previous detected events, using the first detection threshold profile to detect at least one subsequent event;

or

if the first detected event is dissimilar from the amplitude measure of previous detected events, using the second detection threshold profile to detect at least one subsequent event;

wherein the first and second detection threshold profiles differ in sensitivity.

9. The method of claim 8 wherein the first detection threshold profile is more sensitive than the second detection threshold profile.

10. The method of claim 8 wherein the first detection threshold profile is less sensitive than the second detection threshold profile.

11. The method of claim 8 wherein the detection threshold profiles used in the sim/dissim method of event detection comprise:

a refractory period during which no events are declared;

a constant threshold period having an amplitude CTA and a duration CTD;

a decay period having a starting amplitude DPSA and an ending amplitude at a sensing floor for the system;

wherein the second detection threshold profile has higher CTA and DPSA and a longer CTD than the first detection threshold profile.

12. The method of claim 11 wherein the detection threshold profiles used in the sim/dissim method each include an intermediate period that follows the constant threshold period and precedes the decay period and having a starting amplitude IPSA and an ending amplitude IPEA such that IPSA and IPEA for the first detection threshold profile are less than IPSA and IPEA for the second detection threshold profile.

13. The method of claim 12 wherein:

a fast rate detection threshold profile is also available for use in the system when an event rate above a rate threshold is identified;

the fast rate detection threshold profile includes a refractory period, a constant threshold period and a decay period, but no intermediate period; and

CTA and DPSA are lower and RPD and CTD are shorter for the fast rate detection threshold profile than for the detection threshold profiles used in the sim/dissim method.

14. The method of claim 13 further comprising:

estimating the cardiac rate of an implantee;

determining whether to use the fast rate detection threshold profile and, if so, using the fast rate detection threshold profile for detecting cardiac events and activating a method of identifying overdetected cardiac events;

or else

using the sim/dissim method for detecting cardiac events.

15. The method of claim 14 wherein the sim/dissim method further comprises selecting from among four detection profiles, the first and second detection profiles for use in a first rate zone, and third and fourth detection profiles for use in a second rate zone, both the first and second rate zones being below the fast rate causing use of the fast rate detection threshold profile, wherein the sim/dissim method selects between the third and four detection profiles using amplitude similarity/dissimilarity of detected events.

16. The method of claim 8 further comprising:

determining whether a high-rate malignant cardiac condition is occurring and, if so,

delivering electrical stimulus to the patient to convert the high-rate malignant cardiac condition to a non-malignant condition.

17. An implantable cardiac stimulus device (ICSD) comprising a canister housing operational circuitry coupled to a plurality of electrodes, the canister being coupled to a lead electrode assembly having at least some of the plurality of electrodes disposed thereon, the operational circuitry being configured to perform a method comprising:

detecting cardiac events while implanted in a patient by capturing electrical signals and comparing captured electrical signals to a detection threshold;

determining whether a first detected event is similar in amplitude to a second detected event;

selecting a detection threshold configuration for use in subsequent event detection based on whether the first detected event is similar in amplitude to the second detected event wherein;

if the first and second detected events are similar in amplitude, a first detection threshold configuration is selected;

if the first and second detected events are not similar in amplitude, a second detection threshold configuration is selected; and

detecting a subsequent event using a detection threshold defined by the selected detection threshold configuration and the estimated peak amplitude.

18. The ICSD of claim 17 wherein the operational circuitry is configured such that the first detection threshold configuration has higher sensitivity than the second detection threshold configuration.

19. The ICSD of claim 17 wherein the operational circuitry is further configured to include the following steps in the method:

detecting a plurality of detected events by repeatedly selecting detection threshold configurations based upon whether individual detected events are similar or dissimilar to one another in amplitude;

determining whether the plurality of detected events indicates a high-rate condition for the patient, and, if so, declaring a high-rate condition and selecting a third detection threshold configuration for use in detecting events while in the high-rate condition;

continuing to detect events if in the high-rate condition using the third detection threshold configuration until either;

the high-rate condition is found to be terminated;

or

the patient'"'"'s cardiac condition is found to be malignant, upon which the ICSD prepares for and delivers a cardiac therapy to terminate the malignant condition.

20. An implantable cardiac stimulus device (ICSD) comprising a canister housing operational circuitry coupled to a plurality of electrodes, the canister being coupled to a lead electrode assembly having at least some of the plurality of electrodes disposed thereon, the operational circuitry being configured to perform a method comprising:

capturing cardiac signals using at least some of the plurality of electrodes while implanted in a patient;

detecting, from the captured cardiac signals, detected events by the use of comparison of the captured signal to detection threshold criteria, wherein the detection threshold criteria are generated for a given detected event by reference to whether a preceding detected event is similar or dissimilar to stored data;

declaring a Tachy-on condition if the detected events indicate a cardiac rate for the patient that exceeds a predetermined threshold;

while the Tachy-on condition is declared, determining whether the patient'"'"'s cardiac rhythm is malignant and, if so, delivering cardiac stimulus to the patient.

21. The ICSD of claim 20 wherein the operational circuitry is further configured such that the detection threshold criteria are generated by:

if an immediately preceding detected event is similar to the stored data, a first detection threshold configuration is used to generate the detection threshold criteria; and

if an immediately preceding detected event is dissimilar from the stored data, a second detection threshold configuration is used to generate the detection threshold criteria;

wherein the first detection threshold configuration is more sensitive than the second detection threshold configuration.

22. The ICSD of claim 20 wherein the operational circuitry is further configured such that the detection threshold criteria are generated by:

if an immediately preceding detected event is similar to the stored data, a first detection threshold configuration is used to generate the detection threshold criteria; and

if an immediately preceding detected event is dissimilar from the stored data, a second detection threshold configuration is used to generate the detection threshold criteria;

wherein the first detection threshold configuration is less sensitive than the second detection threshold configuration.

23. The ICSD of claim 20 wherein operational circuitry is further configured such that the first and second detection threshold configurations include:

a refractory period having a duration;

a first relatively high threshold time period having an amplitude and a duration;

a first decay period having a starting amplitude, an ending amplitude, and a duration; and

a second decay period having a starting amplitude;

wherein the second decay period follows the first decay period, which follows the first relatively high threshold time period, which follows the refractory period; and

wherein the combined duration of the refractory period and the first relatively high threshold time period for the first detection threshold configuration is shorter than the combined duration of the refractory period and the first relatively high threshold time period for the second detection threshold configuration.

24. A method of event detection in an implantable cardiac stimulus device having a plurality of electrodes adapted for implantation in a patient, the method comprising:

capturing electrical signals from the electrodes;

comparing captured electrical signals to a detection threshold that varies with time following a detection profile;

when the captured electrical signals cross the detection threshold, declaring a detected event;

determining whether either of these conditions is met;

a) the detected event is similar to a prior detected event, or

b) whether the detected event is separated from an immediately prior detected event by an interval exceeding an interval threshold;

selecting from between first and second variants of a selected detection profile for use in subsequent event detection as follows;

if b) is met, then selecting the first variant;

if b) is not met and a) is met, then selecting the first variant; and

else selecting the second variant; and

detecting a subsequent cardiac event using the selected variant of the selected detection profile.

25. The method of claim 24 wherein the selected detection profile is selected by selecting from among a plurality of detection profiles each corresponding to one of:

a calculated beat rate range for a patient; and

a post-shock state of the device.