Signal analysis in implantable cardiac treatment devices

• US 20080077030A1
• Filed: 09/26/2006
• Published: 03/27/2008
• Est. Priority Date: 09/26/2006
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Ostroff, Alan H., Allavatam, Venugopal, Phillips, James W.
• Granted Patent: US 8,014,851 B2
• Time in Patent Office: Days
• US Class Current: 600/512
• CPC Class Codes: A61B 5/30 Input circuits therefor
• 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 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61N 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: A61N 1/0563 specially adapted for defibrillation or cardioversion
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: A61N 1/3756 Casings with electrodes thereon, e.g. leadless stimulators
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting

Abstract

Methods and devices for cardiac signal analysis in implantable cardiac therapy systems. Several signal processing and/or conditioning methods are shown including R-wave detection embodiments including the use of thresholds related to previous peak amplitudes. Also, some embodiments include sample thresholding to remove extraneous data from sampled signals. Some embodiments include weighting certain samples more heavily than other samples within a sampled cardiac signal for analysis.

Claims

1. A method of cardiac signal analysis, the method comprising:

capturing a cardiac signal by the use of first and second electrodes disposed within a patient;

detecting a cardiac event;

conditioning a portion of the cardiac signal associated with the cardiac event; and

analyzing at least some parts of the portion of the cardiac signal to determine whether the patient is likely experiencing a malignant cardiac condition;

wherein the step of conditioning a portion of the cardiac signal associated with the cardiac event includes sampling the cardiac signal to generate a number of samples and comparing a selected sample to a sample threshold and, if the sample magnitude does not exceed the sample threshold, replacing the sample with a different value.

2. The method of claim 1, wherein the samples are at least temporarily stored in a form having a least amplitude and a greatest amplitude, wherein, if the sample magnitude does not exceed the sample threshold, the method includes replacing the selected sample with a value corresponding to the least amplitude.

3. The method of claim 1, wherein the samples are at least temporarily stored in a signed format, wherein, if the sample magnitude does not exceed the sample threshold, the method includes replacing the selected sample with a value corresponding to a zero in the signed format.

4. The method of claim 1, wherein, if the sample magnitude does not exceed the sample threshold, the method includes replacing the selected sample with a value corresponding to the sample threshold.

5. The method of claim 1, wherein the step of analyzing the portion of the cardiac signal includes comparing the portion of the cardiac signal to a stored template, wherein the stored template includes a number of template samples and, if one or more of the template samples do not exceed the threshold, those template samples are marked, and the selected sample of the portion of the cardiac signal is selected such that it corresponds to a marked sample of the template when the portion of the cardiac signal is compared to the stored template.

6. The method of claim 1, further comprising weighting the sample vector to give some signal samples greater analytical weight than others.

7. The method of claim 1, wherein the step of analyzing the portion of the cardiac signal includes a step of comparing the portion of the cardiac signal to a stored template and the comparing step includes weighting certain samples of the portion of the cardiac signal more than other samples.

8. A method of cardiac signal analysis, the method comprising:

capturing a cardiac signal by the use of first and second electrodes disposed within a patient;

detecting a cardiac event;

sampling the cardiac signal, treating the sampled signal as a sample vector, and multiplying the sample vector by a weighting vector to yield a weighted sample vector; and

analyzing the weighted sample vector to determine whether the patient is likely experiencing a malignant cardiac condition.

9. The method of claim 8, wherein the weighting vector has at least some components that are greater than at least some other components within the weighting vector.

10. The method of claim 8, wherein the sample vector includes a component identified as a fiducial point for the sample vector, and the weighting vector has a peak component corresponding to the fiducial point within the sampled vector, the peak component having a greater amplitude than other components of the weighting vector.

11. A method of determining whether a patient is undergoing a malignant cardiac condition, the method comprising:

capturing a cardiac signal having a cardiac event from a patient using implanted electrodes;

sampling the cardiac signal such that it is comprised of a number of signal samples; and

comparing the cardiac signal to a stored template to yield a score indicative of correlation between the cardiac signal and the stored template, wherein at least some of the signal samples are provided with greater weight during the comparison and others of the signal samples are provided with a lesser weight during the comparison.

12. The method of claim 11, wherein the cardiac signal includes a fiducial point, and greater weight is given to samples nearer the fiducial point than other samples.

13. The method of claim 11, wherein the cardiac signal includes one or more slopes, wherein lesser weight is given to samples taking along a sloped portion of the cardiac signal.

14. A method of cardiac signal analysis, the method comprising:

capturing a cardiac signal by the use of first and second electrodes disposed within a patient;

detecting a cardiac event;

conditioning a portion of the cardiac signal associated with the cardiac event; and

analyzing the portion of the cardiac signal to determine whether the patient is likely experiencing a malignant cardiac condition;

wherein;

the step of detecting a cardiac event includes observing whether a captured cardiac signal exceeds a threshold value in the following manner;

a) after a previous cardiac event, selecting a refractory period;

b) identifying peak signal amplitudes of one or more previous cardiac events and selecting first and second thresholds related to the peak signal amplitudes, the first threshold having a greater value than the second threshold; and

c) generating the threshold value with a continuously decreasing value over a time following the refractory period and before sensing of a next cardiac event, the threshold value having a first value equal to the first threshold and, at a later point in time, having a value approaching the second threshold; and

the step of analyzing includes comparing the cardiac signal to a stored template and providing greater weight to comparisons of first corresponding portions of the cardiac signal and the template, and lesser weight to comparisons of second corresponding portions of the cardiac signal and the template.

15. The method of claim 14, wherein the first threshold is at least fifty percent of an average of a number of previous peak signal amplitudes.

16. The method of claim 14, wherein the second threshold is less than ten percent of an average of a number of previous peak signal amplitudes.

17. The method of claim 14, wherein the first corresponding portions correspond to greatest amplitude portions of the cardiac signal.

18. The method of claim 14, wherein the second corresponding portions correspond to greatest slope regions of the cardiac signal.

19. The method of claim 14, wherein the step of analyzing includes observing whether certain portions of the cardiac signal have a magnitude that exceeds a sample threshold and, if not, replacing those portions of the cardiac signal with a preselected value.