Accurate cardiac event detection in an implantable cardiac stimulus device

• US 8,565,878 B2
• Filed: 03/06/2009
• Issued: 10/22/2013
• Est. Priority Date: 03/07/2008
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Allavatam, Venugopal, Palreddy, Surekha, Sanghera, Rick, Warren, Jay A.
• Primary Examiner(s): Koharski, Christopher D
• Assistant Examiner(s): Bays, Pamela M
• Application Number:
  US12/399,901
• Publication Number:
  US 20090228057A1
• Time in Patent Office: 1,691 Days
• Field of Search: 607/9, 607/8, 607/27, 607/4, 607/28, 600/508, 600/509, 600/516, 600/512
• US Class Current: 607/28
• 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; and

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

wherein a plurality of electrodes are provided on the lead electrode assembly and/or canister, the plurality of electrodes being coupled to the operational circuitry;

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

capturing electrical signals from the electrodes;

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; and

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.

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 configured such that the values for CTA and DTA are defined as percentages of an estimated peak value for peaks identified in detected events.

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

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

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

wherein a plurality of electrodes are provided on the lead electrode assembly and/or canister, the plurality of electrodes being coupled to the operational circuitry;

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

capturing electrical signals from the electrodes;

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;

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.

7. 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 measure 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;

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; and

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.

8. The method of claim 7 wherein the first detection threshold profile is more sensitive than the second detection threshold profile.

9. The method of claim 7 wherein the first detection threshold profile is less sensitive than the second detection threshold profile.

10. The method of claim 7 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.

11. The method of claim 10 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 refractory period and CTD are shorter for the fast rate detection threshold profile than for the detection threshold profiles used in the sim/dissim method.

12. The method of claim 11 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.

13. The method of claim 12 wherein the sim/dissim method further comprises selecting from among first, second, third and fourth 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 fourth detection profiles using amplitude similarity/dissimilarity of detected events.

14. The method of claim 7 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.

15. 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 an estimated peak amplitude;

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.

16. The ICSD of claim 15 wherein the operational circuitry is configured such that the first detection threshold configuration has higher sensitivity than the second detection threshold configuration.