Heart rate correction system and methods for the detection of cardiac events

• US 20110040199A1
• Filed: 08/12/2009
• Published: 02/17/2011
• Est. Priority Date: 08/12/2009
• Status: Active Grant

• Current Assignee: Angel Medical Systems, Inc.
• Original Assignee: Angel Medical Systems, Inc.
• Inventors: Hopenfeld, Bruce
• Granted Patent: US 9,042,969 B2
• Time in Patent Office: Days
• US Class Current: 600/515
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening

Abstract

A device for detecting a cardiac event is disclosed. Detection of an event is based on a test applied to a parameter whose value varies according to heart rate. Both the parameter value and heart rate (RR interval) are filtered with an exponential average filter. From these filtered values, the average change in the parameter and the RR interval are also computed with an exponential average filter. Before computing the average change in the parameter, large changes in the parameter over short times, which may be caused by body position shifts, are attenuated are removed, so that the average change represents an average of small/smooth changes in the parameter'"'"'s value that are characteristic of acute ischemia, one of the cardiac events that may be detected. The test to detect the cardiac event depends on the heart rate, the difference between the parameter'"'"'s value and its upper and lower normal values, and its average change over time, adjusted for heart rate changes. The upper and lower normal parameter values as a function of heart rate are determined from long term stored data of the filtered RR values and parameter values. Hysteeresis related data and transitory deviations from normal (e.g. vasospasm related data) are excluded from the computation of normal upper and lower parameter bounds.

Claims

1. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured to;

(i) compute from the digitized waveform heart rate data;

(ii) low pass filter the heart rate data, thereby producing a filtered heart rate signal;

(iii) perform a test to detect the cardiac event, wherein the test is based on the filtered heart rate signal.

2. The system of claim 1 wherein the test involves comparing a parameter value with a heart rate dependent threshold, and wherein the threshold is selected according to the filtered heart rate signal.

3. The system of claim 1 wherein the heart rate data is filtered with a recursive filter.

4. The system of claim 3 wherein the recursive filter is an exponential average filter.

5. The system of claim 1 wherein the filter involves the computation of a moving average.

6. The system of claim 1 wherein the processor and the device are disposed in a housing suitable for implantation into an animal.

7. The system of claim 1 wherein the processor is further configured to compute a change in heart rate value from the filtered heart rate signal, and wherein the test to detect the cardiac event is based on the change in heart rate value.

8. The system of claim 1 wherein the cardiac event is acute ischemia.

9. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured to;

(i) compute from the digitized waveform both heart rate data and parameter value data;

(ii) low pass filter the heart rate data and the parameter value data, thereby producing filtered heart rate data and filtered parameter value data;

(iii) based on the filtered heart rate data and filtered parameter value data, generate upper and lower normal bounds of the value of the parameter as a function of heart rate;

(iv) perform a cardiac event detection test that involves comparing a value of the parameter with its associated heart rate dependent upper and lower normal bounds.

10. The system of claim 9 wherein the cardiac event detection test involves comparing the difference between the parameter value and its associated upper bound with a threshold.

11. The system of claim 9 wherein the heart rate data and the parameter value data are filtered with the same filter.

12. The system of claim 11 wherein the heart rate data and the parameter value data are filtered by computing a moving average.

13. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured to;

(i) compute from the digitized waveform both heart rate data and parameter value data, thereby generating a plurality of raw trajectories of parameter values as a function of heart rate;

(ii) process the plurality of raw trajectories to generate a plurality of processed trajectories of parameter values as a function of heart rate, wherein each processed trajectory has reduced high frequency components compared to its corresponding raw trajectory;

(ii) based on the plurality of processed trajectories, generate upper and lower normal bounds of the value of the parameter as a function of heart rate;

(iv) perform a cardiac event detection test that involves comparing a value of the parameter with its associated heart rate dependent upper and lower normal bounds.

14. The system of claim 13 wherein the processed trajectories are computed by filtering the raw trajectories.

15. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured to;

(i) compute from the digitized waveform both heart rate data and parameter value data;

(ii) low pass filter the heart rate data and the parameter value data, thereby producing filtered heart rate data and filtered parameter value data;

(iii) perform a cardiac event detection test that involves comparing the filtered parameter value data with upper and lower bound values that are determined from upper and lower normal bounds according to the filtered heart rate data.

16. The system of claim 15 wherein the processor is further configured to compute the upper and lower normal bounds.

17. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured to;

(i) compute from the digitized waveform both heart rate data and parameter value data;

(ii) select certain parameter value data associated with normal sinus rhythm beats to be excluded from a determination of upper and lower normal bounds of the value of the parameter as a function of heart rate;

(iii) based on the heart rate data and parameter value data other than the parameter value data selected for exclusion, generate upper and lower normal bounds of the value of the parameter as a function of heart rate;

(iv) perform a cardiac event detection test that involves comparing a value of the parameter with its associated heart rate dependent upper and lower normal bounds.

18. The system of claim 17 wherein the parameter value data selected for exclusion is associated with a rapid change in heart rate.

19. The system of claim 17 wherein the parameter value data selected for exclusion is associated with a cardiac event that does not persist for longer than a predetermined threshold.

20. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured to;

(i) compute from the digitized waveform heart rate data;

(ii) low pass filter the heart rate data, thereby producing filtered heart rate data;

(iii) compute a change in the heart rate from the filtered heart rate data;

(iv) based on the computed change in heart rate, perform a cardiac event detection test.

21. The system of claim 20 wherein the processor is configured to perform a cardiac event detection test only if the change in heart rate is less than a predetermined threshold.

22. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured to;

(i) compute from the digitized waveform both heart rate data and parameter value data;

(ii) compute the value of a function of changes in the value of the parameter;

(iii) correcting the value of the function according to a change in heart rate, thereby generating a corrected function value

(iii) perform a cardiac event detection test based on the corrected function value.

23. The system of claim 22 wherein the function is an estimate of the average value of the change in parameter over time.