ACUTE ISCHEMIA DETECTION BASED ON PARAMETER VALUE RANGE ANALYSIS

• US 20120053479A1
• Filed: 08/25/2010
• Published: 03/01/2012
• Est. Priority Date: 08/25/2010
• Status: Active Grant

• Current Assignee: Angel Medical Systems, Inc.
• Original Assignee: Angel Medical Systems, Inc.
• Inventors: HOPENFELD, BRUCE
• Granted Patent: US 8,428,703 B2
• Time in Patent Office: Days
• US Class Current: 600/517
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61B 5/0022 Monitoring a patient using a global network, e.g. telephone networks, internet
• CPC Class Codes: A61B 5/02028 Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B
• CPC Class Codes: A61B 5/7465 Arrangements for interactive communication between patient and care services, e.g. by using a telephone network telemetry of measured physiological signal A61B5/0002

Abstract

A heart monitor is disclosed. The monitor computes ST segment deviations and stores the results in heart rate based histograms. Periodically, the monitor analyzes the histogram data to determine a normal range of ST deviation for a particular heart rate range. The monitor computes heart rate dependent ischemia detection thresholds based on the upper and lower boundaries of the normal range.

Claims

1. A cardiac monitor comprising:

(a) a sensor adapted to sense an analog signal from a heart;

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

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

(i) compute a plurality of ST deviations from the digitized waveform, the plurality of ST deviations being characterized by a statistical distribution characterized by an upper boundary, a lower boundary, and a measure of dispersion;

(ii) storing data pertaining to the plurality of ST deviations in a form that enables characteristics of the statistical distribution to be computed;

(iii) form an upper detection threshold based on the upper boundary and the dispersion;

(iv) compute a subsequent ST deviation from the digitized waveform;

(v) apply a test to detect a cardiac event, wherein the test is based on the subsequent ST deviation and the upper detection threshold.

2. The system of claim 1 wherein the measure of dispersion is based on the upper boundary.

3. The system of claim 2 wherein the statistical distribution is further characterized by a median, and wherein the measure of dispersion is the difference between the upper boundary and the median.

4. The system of claim 1 wherein the plurality of ST deviations are associated with a particular heart rate range.

5. The system of claim 4 wherein the processor is further configured to store data pertaining to the plurality of ST deviations according to heart rate, thereby generating a corresponding plurality of values correlated with heart rate, and thereby generating set of statistical distributions, and for each member of the set, to form an upper detection threshold based on the upper boundary and the dispersion associated with the set.

6. The system of claim 5 wherein both the plurality of ST deviations and the corresponding plurality of values correlated with heart rate each were generated at least in part with a corresponding one of two low pass filters.

7. The system of claim 6 wherein each of the low pass filters is an exponential average filter.

8. The system of claim 1 wherein the data pertaining to the plurality of ST deviations is stored in histogram format.

9. The system of claim 1 wherein the upper boundary is determined by searching for an ST deviation value above which there are less than a specified number of ST deviation values.

10. The system of claim 9 wherein the specified number of ST deviation values increases over time as the amount of stored data pertaining to the plurality of ST deviations increases.

11. The system of claim 1 wherein the processor is further configured to process digitized waveform data in the form of segments, and wherein each of the plurality of ST deviations corresponds to a measure of average ST deviation within each of a corresponding plurality of segments.

12. The system of claim 1 wherein the processor is further configured to form an form a lower detection threshold based on the upper boundary and the dispersion.

13. The system of claim 1 wherein the processor is further configured to compute a measure of average value of the statistical distribution, and wherein the upper detection threshold is based on the difference between the average value and the upper boundary.

14. The system of claim 1 wherein the threshold is equal to the value at the boundary plus a specified distance that is based on the dispersion.

15. The system of claim 13 wherein the measure of the average value is a median.

16. A cardiac monitor comprising:

(a) a sensor adapted to sense an analog signal from a heart;

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

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

(i) compute a plurality of ST deviations from the digitized waveform, the plurality of ST deviations being characterized by a statistical distribution characterized by an upper boundary and a lower boundary, the lower boundary being characterized by a boundary value;

(ii) storing data pertaining to the plurality of ST deviations in a form that enables characteristics of the statistical distribution to be computed;

(iii) form a lower detection threshold that depends on the difference between the boundary value and a preset value;

(iv) compute a subsequent ST deviation from the digitized waveform;

(v) apply a test to detect a cardiac event, wherein the test is based on the subsequent ST deviation and the lower detection threshold.

17. The system of claim 16 wherein the lower detection threshold is equal to a first function or a second function depending on whether the difference between the boundary value and the preset value exceeds a specified threshold.

18. The system of claim 17 wherein the second function is equal to the first function or a third function, whichever results in a lower detection threshold closer to the boundary value.

19. The system of claim 18 wherein the third function is equal to the sum of a preset value and the boundary value.

20. The system of claim 17 wherein the statistical distribution is characterized by a dispersion, and wherein the first function is equal to a specified distance from the boundary value, wherein the specified distance is based on the dispersion.

21. The system of claim 16 wherein the preset value corresponds to a change in polarity of ST deviation.