Parameter value rejection for a cardiac monitor

• US 8,396,542 B2
• Filed: 10/28/2010
• Issued: 03/12/2013
• Est. Priority Date: 08/25/2010
• Status: Active Grant

• Current Assignee: Angel Medical Systems, Inc.
• Original Assignee: Angel Medical Systems, Inc.
• Inventors: Johnson, Steven R., Hopenfeld, Bruce
• Primary Examiner(s): Holmes, Rex R
• Application Number:
  US12/914,548
• Publication Number:
  US 20120053473A1
• Time in Patent Office: 866 Days
• Field of Search: 600508-509, 600515-519, 607 25- 26
• US Class Current: 600/515
• 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 median value of ST deviation. Subsequently, beats are excluded from the computation of the time series if their ST deviations both varies too far from the long term median value and varies too far from the then current time series value.

Claims

1. A cardiac monitor for estimating the value of a heart signal parameter, the monitor comprising:

(a) a sensor for sensing an analog signal from a human 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; and

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

(i) analyze the waveform to detect a plurality of beats;

(ii) analyze the plurality of beats to generate a corresponding plurality of values of a heart signal parameter;

(iii) compute a parameter value time series which is a running estimate of the value of the heart signal parameter by low pass filtering at least a portion of the plurality of values of the heart signal parameter;

(iv) compute a long term average value of the heart signal parameter from the time series over a time period that is at least ten minutes long;

(v) measure the value of the heart signal parameter for a current beat that is one of the plurality of beats, thereby generating a current beat value;

(vi) compare the current beat value with the long term average value of the heart signal parameter, thereby generating a first comparison result indicative of the distance between the current beat value and the long term average value; and

,

(vii) based on the first comparison result, selectively update the low pass filtered time series based on the value of the heart signal parameter for the current beat, thereby generating a new estimate of the value of the heart signal parameter responsive to the addition of the value of the heart signal parameter for the current beat to the low pass filtered time series.

2. The cardiac monitor of claim 1 wherein the processor is further configured to:

compare the current beat value with a measure of a current value of the time series, thereby generating a second comparison result indicative of the distance between the current beat value and the measure of the current value of the time series, and

based on the first and second comparison results, selectively updating the time series based on the value of the heart signal parameter for the current beat.

3. The cardiac monitor of claim 2 wherein the device is configured to process the analog signal in a plurality of non-overlapping segments, and wherein the low pass filtering involves averaging values of the heart signal parameter within segments, thereby generating segment averages.

4. The cardiac monitor of claim 1 wherein the low pass filtering further involves updating a recursive filter based on the segment averages.

5. The cardiac monitor of claim 4 wherein the recursive filter is an exponential average filter.

6. The cardiac monitor of claim 1 wherein the time series is stored in the form of at least one histogram, and the long term average is computed from the at least one histogram.

7. The cardiac monitor of claim 6 wherein the time series is stored in the form of a plurality of histograms, and the long term average is computed from one of the plurality of histograms.

8. The cardiac monitor of claim 2 wherein a number of elements in the time series is less than the number of the plurality of beats.

9. The cardiac monitor of claim 8 wherein each element of the time series is an output of a recursive filter.

10. The cardiac monitor of claim 2 wherein the current beat is excluded from updating the time series if both the first comparison result indicates the distance between the current beat value and the measure of the current value of the time series is too large, and the second comparison result indicates the distance between the current beat value and the long term average value of the time series is too large.

11. The cardiac monitor of claim 1 wherein the heart signal parameter is ST segment deviation.

14. The cardiac monitor of claim 1 wherein the selective updating of the low pass filtered time series includes excluding the value of the heart signal parameter for the current beat responsive to a determination that the value includes noise greater than a threshold value.

15. The cardiac monitor of claim 1 wherein the selective updating of the low pass filtered time series includes updating the low pass filtered time series based on a weighted function of the value of the heart signal parameter for the current beat responsive to a determination that the value includes noise greater than a threshold value.

12. A cardiac monitor for estimating the value of a heart signal parameter, the monitor comprising:

(a) a sensor for sensing an analog signal from a human 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; and

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

(i) analyze the waveform to detect a plurality of beats;

(ii) analyze the plurality of beats to generate a corresponding plurality of values of a heart signal parameter;

(iii) compute a parameter value time series which is a running estimate of the value of the heart signal parameter by low pass filtering the plurality of values of the heart signal parameter;

(iv) measure the value of the heart signal parameter for a current beat that is one of the plurality of beats, thereby generating a current beat value;

(v) compare the current beat value with a measure of a current value of the low pass filtered time series, thereby generating a first comparison result indicative of the distance between the current beat value and the measure of the current value of the low pass filtered time series; and

,

(vi) based on the first comparison result, selectively update the low pass filtered time series based on the value of the heart signal parameter for the current beat.

13. The cardiac monitor of claim 12 wherein the selective updating of the low pass filtered time series includes excluding the value of the heart signal parameter for the current beat responsive to a determination that the value includes noise greater than a threshold value.

16. A cardiac monitor for estimating the value of a heart signal parameter, the monitor comprising:

(a) a sensor for sensing an analog signal from a human 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; and

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

(i) analyze the waveform to detect a plurality of beats;

(ii) analyze the plurality of beats to generate a corresponding plurality of values of a heart signal parameter;

(iii) compute a parameter value time series by low pass filtering the plurality of values of the heart signal parameter;

(iv) compute a long term average value of the heart signal parameter from the plurality of values over a time period that is at least ten minutes long;

(v) measure the value of the heart signal parameter for a current beat that is one of the plurality of beats, thereby generating a current beat value;

(vi) compare the current beat value with the long term average value of the heart signal parameter, thereby generating a first comparison result indicative of the distance between the current beat value and the long term average value;

(vii) based on the first comparison result, selectively updating the time series based on the value of the heart signal parameter for the current beat;

(viii) compare the current beat value with a measure of a current value of the time series, thereby generating a second comparison result indicative of the distance between the current beat value and the measure of the current value of the time series, and

(ix) based on the first and second comparison results, selectively updating the time series based on the value of the heart signal parameter for the current beat.

17. The cardiac monitor of claim 16 wherein the device is configured to process the analog signal in a plurality of non-overlapping segments, and wherein the low pass filtering involves averaging values of the heart signal parameter within segments, thereby generating segment averages.

18. The cardiac monitor of claim 16 wherein a number of elements in the time series is less than the number of the plurality of beats.

19. The cardiac monitor of claim 16 wherein the current beat is excluded from updating the time series if both the first comparison result indicates the distance between the current beat value and the measure of the current value of the time series is too large, and the second comparison result indicates the distance between the current beat value and the long term average value of the time series is too large.