Apparatus and method of arrhythmia detection in a subcutaneous implantable cardioverter/defibrillator

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; and

wherein the first operation comprises narrow-band filtering the captured signal and using R-wave detection to detect events, and the second operation comprises wide-band filtering the signal and performing morphology analysis of detected events.

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. The method of claim 17 wherein the narrow-band filtering is narrow relative to the wide-band filtering.

21. The method of claim 17 wherein the narrow band is defined at frequencies of 10 Hz and 30 Hz, and the wide band is defined at frequencies of 1 Hz and 50 Hz.