Waveform feature value averaging system and methods for the detection of cardiac events

• US 20090076403A1
• Filed: 09/14/2007
• Published: 03/19/2009
• Est. Priority Date: 09/14/2007
• Status: Active Grant

• Current Assignee: Angel Medical Systems, Inc.
• Original Assignee: Angel Medical Systems, Inc.
• Inventors: Hopenfeld, Bruce
• Granted Patent: US 9,943,244 B2
• Time in Patent Office: Days
• US Class Current: 600/516
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

Disclosed is a system for detecting pathophysiological cardiac conditions. The system comprises a diagnostic device that contains electronic circuitry that can detect a cardiac event such as an acute ischemia. The cardiac diagnostic device receives electrical signals from subcutaneous or body surface sensors. The cardiac diagnostic device includes a processor that computes QRS onset and offset points and fiducial points associated with T and U waves. The processor than baseline corrects the original signal/waveform by fitting a polynomial function to QRS offset points, and subtracting this function from the original waveform. Based on the baseline adjusted signal and/or the above mentioned fiducial points, the processor then computes averages of various waveform feature values, including a QRS measure sensitive to QRS curvature, T wave timing measures, ST segment deviation (difference between signal amplitudes at QRS offset and onset and/or minimum amplitude between QRS offset and peak T wave); and T/U wave amplitudes. These averages are computed by exponential averaging. From the exponential averages, the processor computes an average of the change in the averages over time. Based on the averages and the change in the averages, the processor applies an ischemia test to determine a likelihood of ischemia.

Claims

1. A device for assessing the condition of a mammalian heart, comprising:

a lead comprising two sensors,

a processor coupled to the lead, the processor configured to;

(i) obtain a first signal from the lead, and compute a first waveform corresponding to the first signal, the first waveform being characterized by a plurality of QRS complexes and T waves;

(ii) compute a plurality of first fiducial points associated with corresponding QRS complexes;

(iii) compute a plurality of second fiducial points associated with corresponding T waves;

(iv) compute a plurality of values of a T wave timing measure based on the differences in time between corresponding members of the first and second pluralities of fiducial points;

(v) derive an average of the T wave timing measure based on the plurality of values of the T wave timing measure;

(vi) apply a test to detect a pathological heart condition, wherein the test is based on the average of the T wave timing measure.

2. The device of claim 1 wherein each of the plurality of first fiducial points is a QRS onset point, and wherein each of the plurality of second fiducial points is a T wave peak.

3. The device of claim 1 wherein the sensors are adapted to be disposed less than 15 cm apart.

4. The device of claim 1 wherein the processor is adapted for implantation in a mammal.

5. The device of claim 1 wherein the sensors are adapted to be disposed outside of the heart.

6. The device of claim 1 wherein the sensors are adapted to sense an electrical signal, such that the first waveform corresponds to an electrical potential difference.

7. The device of claim 6 wherein the sensors comprise electrodes.

8. The device of claim 7 wherein the lead is bipolar, such that the first waveform corresponds to the electrical potential difference between the two electrodes.

9. A device for assessing the condition of a mammalian heart, comprising:

a lead comprising two sensors,

a processor coupled to the lead, the processor configured to;

(i) obtain a first signal from the lead, and compute a first waveform corresponding to the first signal, the first waveform being characterized by a plurality of QRS complexes;

(ii) compute a plurality of values of a first waveform feature indicative of the curvature of at least some portion of a corresponding one of the plurality of QRS complexes;

(iii) derive an average of the first waveform feature based on the plurality of values of the first waveform feature;

(iv) apply a test to detect a pathological heart condition, wherein the test is based on the average of the first waveform feature value.

10. A device for assessing the condition of a mammalian heart, comprising:

a lead comprising two sensors,

a processor coupled to the lead, the processor configured to;

(i) obtain a signal from the lead, and compute a waveform corresponding to the signal, the waveform being characterized by a plurality of QRS complexes;

(ii) compute a plurality of values of the waveform feature from the waveform representing the values of the waveform feature over time;

(iii) compute, based on the plurality of values of the waveform feature, a measure of the average change in the waveform feature over time, thereby deriving an average change metric;

(iv) apply a test to detect a pathological heart condition, wherein the test is based on the average change metric.

11. The device of claim 10 wherein the average change is a measure of the change in the waveform feature value over clock time.

12. The device of claim 10 wherein the average change is a measure of the change in the waveform feature value over a number of heart beats.

13. The device of claim 10 wherein the average change is an exponential average.

14. The device of claim 10 wherein the processor is further configured to compute a plurality of averages of the value of the waveform feature based on the plurality of values of the waveform feature;

and wherein the measure of the average change in the waveform feature is based on the plurality of averages of the value of the first waveform feature.

15. The device of claim 14 wherein each of the plurality of averages of the value of the waveform feature is an exponential average.

16. A device for assessing the condition of a mammalian heart, comprising:

a lead comprising two sensors,

a processor coupled to the lead, the processor configured to;

(i) obtain a signal from the lead, and compute a waveform corresponding to the signal, the waveform being characterized by a plurality of QRS complexes;

(ii) compute a plurality of values of the waveform feature from the waveform representing the values of the waveform feature over time;

(iii) apply a first filter the plurality of values of the waveform feature, thereby deriving a filtered waveform;

(iv) compute, based on the filtered waveform, a measure of the change in the waveform feature over time, thereby deriving a change metric;

(iv) apply a test to detect a pathological heart condition, wherein the test is based on the change metric.

17. The device of claim 16 wherein the measure of change in the waveform feature value over time is computed by differencing the filtered waveform, thereby deriving a differenced waveform.

18. The device of claim 17 wherein the measure of change in the waveform feature value over time is computed by applying a second filter the differenced waveform.

19. The device of claim 18 wherein both the first and second filters comprise an exponential average filter.

20. The device of claim 16 wherein the first filter is an exponential average filter