Apparatus and Method of Arrhythmia Detection in a Subcutaneous Implantable Cardioverter/Defibrillator

• US 20080221632A1
• Filed: 05/16/2008
• Published: 09/11/2008
• Est. Priority Date: 11/21/2001
• Status: Active Grant

• Current Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Original Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Inventors: Ostroff, Alan H., Bardy, Gust H., Allavatam, Venugopal, Erlinger, Paul J., Rissmann, William J.
• Granted Patent: US 8,027,720 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/3931 Protecting, e.g. back-up systems
• CPC Class Codes: A61N 1/395 for treating atrial fibrillation
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock

Abstract

In a subcutaneous implantable cardioverter/defibrillator, cardiac arrhythmias are detected to determine necessary therapeutic action. Cardiac signal information is sensed from far field electrodes implanted in a patient. The sensed cardiac signal information is then amplified and filtered. Parameters such as rate, QRS pulse width, cardiac QRS slew rate, amplitude and stability measures of these parameters from the filtered cardiac signal information are measured, processed and integrated to determine if the cardioverter/defibrillator needs to initiate therapeutic action.

Claims

1. A method of cardiac signal analysis comprising:

capturing an electrical signal from electrodes implanted in a patient;

amplifying the captured electrical signal to generate an amplifier output;

using the amplifier output as follows;

in a first channel;

narrow-band filtering the amplifier output;

detecting cardiac events using the narrow-band filtered amplifier output; and

identifying whether and when cardiac events occur;

in a second channel separate from the first channel;

wide-band filtering the amplifier output; and

performing morphological analysis using the wide-band filtered amplifier output;

using the detected cardiac events and morphological analysis to determine whether the patient is in need of cardiac stimulus; and

if the patient is in need of cardiac stimulus, delivering cardiac stimulus to the patient.

2. The method of claim 1 wherein the wide-band filtering is wide relative to the narrow band filtering.

3. The method of claim 1 wherein the narrow-band filtering sets corners at 10 Hz and 30 Hz, and the wide-band filtering sets corners at 1 Hz and 50 Hz.

4. The method of claim 1 further comprising

measuring a first characteristic of the captured electrical signal;

and

observing stability of the first characteristic within a set of cardiac beats of the patient.

5. The method of claim 4 wherein the first characteristic includes the R-R intervals of the cardiac signal.

6. The method of claim 4 wherein the first characteristic includes the QRS width of cardiac beats.

7. The method of claim 4 wherein the first characteristic includes the peak amplitude of cardiac beats.

8. The method of claim 4 wherein the first characteristic includes slew rate.

9. The method of claim 1 wherein the electrodes are implanted in the patient at only subcutaneous locations outside the ribcage of the patient.

10. An implantable cardioverter defibrillator (ICD) comprising a housing containing operational circuitry that is coupled to a plurality of electrodes for implantation in a patient, wherein the operational circuitry is configured to perform the following method of cardiac signal analysis when implanted in a patient:

capturing an electrical signal from the plurality of electrodes;

amplifying the captured electrical signal to generate an amplifier output;

using the amplifier output as follows;

in a first channel;

narrow-band filtering the amplifier output;

detecting cardiac events using the narrow-band filtered amplifier output; and

identifying whether and when cardiac events occur;

in a second channel separate from the first channel;

wide-band filtering the amplifier output; and

performing morphological analysis using the wide-band filtered signal;

using the detected cardiac events and morphological analysis to determine whether the patient is in need of cardiac stimulus; and

if the patient is in need of cardiac stimulus, delivering cardiac stimulus to the patient.

11. The ICD of claim 10 wherein the operational circuitry is further configured such that the narrow-band filtering sets corners at 10 Hz and 30 Hz, and the wide-band filtering sets corners at 1 Hz and 50 Hz.

12. The ICD of claim 10 wherein the operational circuitry is further configured to perform the following steps as part of the method of cardiac signal analysis:

measuring a first characteristic of the captured electrical signal related to a single cardiac beat of the patient; and

observing stability of the first characteristic within a set of cardiac beats of the patient.

13. The ICD of claim 10 wherein the first characteristic includes the R-R intervals of the cardiac signal.

14. The ICD of claim 10 wherein the first characteristic includes the QRS width of cardiac beats.

15. The ICD of claim 10 wherein the first characteristic includes the peak amplitude of cardiac beats.

16. The method of claim 10 wherein the first characteristic includes slew rate.

17. A method of cardiac signal analysis comprising:

capturing an electrical signal from electrodes implanted in a patient, the electrodes being coupled to an implantable cardiac stimulus device;

using the captured electrical signal in separate operations within the device, a first operation including identifying whether and when cardiac events occur, and a second operation including performing morphological analysis of the captured electrical signal;

combining data resulting from the first operation and the second operation;

using the combined data to characterize the patient'"'"'s cardiac condition as requiring treatment or not requiring treatment; and

if the patient'"'"'s cardiac condition requires treatment, providing electrical stimulus to the patient to treat the cardiac condition;

wherein the implantable device and all electrodes coupled thereto are disposed subcutaneously in the patient outside of the patient'"'"'s ribcage, such that all electrodes are far-field electrodes relative to the patient'"'"'s heart.

18. The method of claim 17 wherein the first operation includes filtering at least some frequencies that are not filtered while performing the second operation, and detecting R-waves in the filtered captured signal.

19. The method of claim 18 wherein the first operation includes filtering out frequencies below 10 Hertz that are not filtered in the second operation.

20. A method of treating a patient comprising:

implanting a cardioverter-defibrillator in the patient;

capturing far-field cardiac signals from electrodes disposed beneath the skin and outside of a patient'"'"'s ribcage;

identifying the patient'"'"'s P-wave in the far-field cardiac signals;

monitoring the patient'"'"'s P-wave; and

if the patient'"'"'s P-wave abruptly disappears, determining that the patient is experiencing atrial fibrillation and withholding cardiac stimulus that would otherwise be delivered to the patient.

21. The method of claim 20 wherein the cardioverter-defibrillator comprises a lead assembly coupled to a canister that houses operational circuitry for the cardioverter-defibrillator, and the step of implanting comprises placing the canister and the lead assembly in the patient beneath the skin and outside of the patient'"'"'s ribcage without accessing the vasculature or heart of the patient.

22. The method of claim 20 further comprising withholding cardiac stimulus that would otherwise be delivered to the patient if it is determined that the patient is experiencing atrial fibrillation.

23. An implantable cardioverter defibrillator (ICD) comprising a housing containing operational circuitry that is coupled to a plurality of electrodes for implantation in a patient, wherein the operational circuitry is configured to perform the following method of cardiac signal analysis while implanted in a patient:

capturing far-field cardiac signals from electrodes disposed beneath the skin and outside of a patient'"'"'s ribcage;

identifying the patient'"'"'s P-wave in the far-field cardiac signals;

monitoring the patient'"'"'s P-wave; and

if the patient'"'"'s P-wave abruptly disappears, determining that the patient is experiencing atrial fibrillation.

24. The ICD of claim 23 wherein the operational circuitry is further configured to withhold cardiac stimulus that would otherwise be delivered to the patient if it is determined that the patient is experiencing atrial fibrillation.

25. A method of identifying atrial fibrillation in an implantable cardiac stimulus device comprising:

capturing cardiac signals from electrodes disposed beneath the skin and outside of a patient'"'"'s ribcage;

identifying R-waves in the cardiac signals and observing whether intervals between R-waves are stable or irregular;

if the R-wave intervals are irregular, observing whether QRS morphology is similar on a beat-to-beat basis; and

if R-wave intervals are irregular and QRS morphology is similar on a beat-to-beat basis, determining that the patient is experiencing atrial fibrillation.

26. The method of claim 25 wherein the cardioverter-defibrillator comprises a lead assembly coupled to a canister that houses operational circuitry for the cardioverter-defibrillator, and the step of implanting comprises placing the canister and the lead assembly in the patient beneath the skin and outside of the patient'"'"'s ribcage without accessing the vasculature or heart of the patient.

27. The method of claim 25 further comprising withholding cardiac stimulus that would otherwise be delivered to the patient if it is determined that the patient is experiencing atrial fibrillation.

28. An implantable cardioverter defibrillator (ICD) comprising a housing containing operational circuitry that is coupled to a plurality of electrodes for implantation in a patient, wherein the operational circuitry is configured to perform the following method of cardiac signal analysis while implanted in a patient:

capturing cardiac signals from the electrodes;

identifying R-waves in the cardiac signals and observing whether intervals between R-waves are stable or irregular;

if the R-wave intervals are irregular, observing whether QRS morphology is similar on a beat-to-beat basis; and

if R-wave intervals are irregular and QRS morphology is similar on a beat-to-beat basis, determining that the patient is experiencing atrial fibrillation.

29. The ICD of claim 28 wherein the operational circuitry is further configured to withhold cardiac stimulus that would otherwise be delivered to the patient if it is determined that the patient is experiencing atrial fibrillation.