System and methods for sliding-scale cardiac event detection

• US 20080188763A1
• Filed: 02/12/2008
• Published: 08/07/2008
• Est. Priority Date: 03/01/2006
• Status: Active Grant

• Current Assignee: Angel Medical Systems, Inc.
• Original Assignee: Angel Medical Systems, Inc.
• Inventors: John, Michael Sasha, Hopenfeld, Bruce, Fischell, David R.
• Granted Patent: US 8,781,566 B2
• Time in Patent Office: Days
• US Class Current: 600/516
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period

Abstract

A system for the detection of cardiac events occurring in a human patient is provided. At least two electrodes are included in the system for obtaining an electrical signal from a patient'"'"'s heart. An electrical signal processor is electrically coupled to the electrodes for processing the electrical signal. The system determines the presence of a cardiovascular condition by applying a sliding scale rule to heart signal feature values. When the cardiovascular condition is ischemia, the ST segment may be analyzed. A sliding scale is applied to ST segment shifts such that when the magnitudes of ST segment shifts are relatively small, a larger number of beats is required to detect ischemia compared to the case when the magnitudes of ST shifts are large.

Claims

1. An implantable device for tracking the cardiovascular condition of a human patient, the device including:

an electrode adapted for placement inside a human patient to sense the electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram which consists of a multiplicity of beats;

a digital processor configured to acquire the electrogram and compute from the electrogram a plurality of values of a heart signal feature, the digital processor further configured to compute both first and second aspects pertaining to the first plurality of values, wherein the first and second aspects are at least partially independent of one another, and wherein the digital processor is further configured to detect a cardiovascular condition by applying a test to the plurality of values of the heart signal feature, wherein the test is at least partially based on a sliding scale such that the first and second aspects of the plurality of values vary in accordance with one another.

2. The implantable device of claim 1 wherein the first and second aspects pertain to magnitude and duration respectively, such that as the magnitude increases the duration required to detect the cardiovascular condition decreases.

3. The implantable device of claim 2 wherein the heart signal feature is ST segment shift.

4. The implantable device of claim 1 wherein the sliding scale is implemented by applying a threshold to the first aspect such that the value of the threshold depends on the value of the second aspect.

5. The implantable device of claim 1 wherein the sliding scale is implemented by forming a weighted sum of first and second cardiac state parameters, wherein each of the first and second cardiac state parameters is a function of the values of both the first and second aspects.

6. The implantable device of claim 5 wherein the first and second aspects pertain to magnitude and duration respectively, and the first state parameter is equal to the number of heart beats that a heart signal feature value exceeded a first threshold, and the second state parameter is equal to the number of heart beats that a heart signal feature value exceeded a second threshold.

7. The implantable device of claim 1 wherein the sliding scale is implemented by applying first and second thresholds to first and second cardiac state parameters, wherein each of the first and second cardiac state parameters is a function of the values of both the first and second aspects, and wherein the cardiac condition is detected if either of the first or second cardiac state parameter exceeds the corresponding first or second threshold.

8. The implantable device of claim 7 wherein the first and second aspects pertain to magnitude and duration respectively, and the first state parameter is equal to the number of heart beats that a heart signal feature value exceeded a first threshold, and the second state parameter is equal to the number of heart beats that a heart signal feature value exceeded a second threshold.

9. The implantable device of claim 7 wherein the sliding scale is implemented by applying third and fourth thresholds to first and second cardiac state parameters, wherein the third and fourth thresholds are smaller than the first and second thresholds, respectively, and wherein the cardiac condition is detected if both the first and second cardiac state parameters exceeded the third and fourth thresholds, respectively.

10. An implantable device for tracking the cardiovascular condition of a human patient, the device including:

an electrode adapted for placement inside a human patient to sense the electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram which consists of a multiplicity of beats,

a digital processor configured to acquire the electrogram and to compute from the electrogram both a first plurality of values of a first heart signal feature and a second plurality of values of a second heart signal feature, the digital processor further configured to apply a test to the first plurality of values and the second plurality of values, wherein the test is at least partially based on a sliding scale such that first plurality of values and the second plurality of values vary in accordance with one another.

11. The implantable device of claim 10 wherein the first heart signal feature pertains to cardiac repolarization.

12. The implantable device of claim 11 wherein the first heart signal feature pertains to the ST segment.

13. The implantable device of claim 11 wherein the second heart signal feature pertains to cardiac activation.

14. The implantable device of claim 11 wherein the second heart signal feature pertains to cardiac repolarization, and wherein the first and second heart signal features pertain to different aspects of cardiac repolarization.

15. The implantable device of claim 10 wherein the outcomes of the first and second tests are real numbers.

16. An implantable device for tracking the cardiovascular condition of a human patient, the device including:

an electrode adapted for placement inside a human patient to sense the electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram which consists of a multiplicity of beats,

a memory;

a digital processor configured to;

acquire the electrogram and to compute from the electrogram a plurality of values of a heart signal feature;

store the plurality of values in the memory;

evaluate the change in the value of the heart signal feature over time; and

detect a cardiovascular condition by applying a test that is adjusted according to the evaluation of the change in the value of the heart signal feature over time.

17. A device for tracking the cardiovascular condition of a human patient, the device including:

a sensor adapted to sense a cardiac signal from the patient'"'"'s heart, the cardiac signal being associated with a multiplicity of beats,

a memory;

a digital processor configured to;

provide signal conditioning to the cardiac signal to obtain a conditioned signal;

compute from the conditioned signal a plurality of values of a heart signal feature;

store the plurality of values in the memory;

evaluate the change in the value of the heart signal feature over time; and

detect a cardiovascular condition related to ischemia by applying a test that is adjusted according to the evaluation of the rate of change in the value of the heart signal feature over time.

18. A device of claim 17 wherein test that is adjusted according to the evaluation of the rate of change is adjusted by adjusting the coefficients used in the test to effect at least one sliding scale rule.

19. A device of claim 17 wherein the evaluation of the rate of change in the value of the heart signal feature over time occurs by comparing the rate of change to one of:

a recent self-normative value, a statistic computed upon at least two recent self-normative values (Bruce this is supported in the blue text of the app on page

     43).

20. A device of claim 17 wherein the sensor is implanted within the patient'"'"'s heart.

21. A device of claim 17 wherein the sensor is sub-dermal.

22. A device of claim 17 wherein the device evaluates the change in the value of the heart signal feature over time as reflected in trend data.

23. A device of claim 17 wherein the device evaluates the change in the value of the heart signal feature over time as reflected in histogram data.