Adaptive real time ECG triggering and uses thereof

Abstract

The present invention provides methods and apparatus for generating a trigger from the R wave of an electrocardiogram (ECG) waveform using a threshold that adapts to the slope of the R wave while still within the leading edge of the R wave.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. R wave triggering during different ECG morphologies. Top panels in FIGS. 1-5 show, from top to bottom, simulated ECG, slope of ECG over 4 ms periods, and length filter or adaptive threshold for the R wave trigger. Bottom panels show, from top to bottom, occurrence of trigger, and ECG height over periods of 32 ms, 24 ms and 16 ms. The figure illustrates that the adaptive threshold can adjust the threshold for the R wave trigger during changes in R wave shape or morphology. The time scale on the X-axis of FIGS. 1-5 is in seconds.

FIG. 2. R wave triggering during changes in noise level. The figure illustrates how the threshold for R wave triggering quickly adapts to changes in the noise level on the ECG signal. The time period over which the ECG height is checked (bottom panel) prevents signal frequencies higher than expected for the R wave from meeting the trigger criteria.

FIG. 3. R wave triggering during introduction of 60 cycle noise on ECG. The threshold actively adapts to the 60 cycle noise by increasing the threshold level during real time. The time period over which the ECG height is checked prevents frequencies outside of the range of the R wave from generating a trigger.

FIG. 4. R wave triggering during modulated 60 cycle noise on ECG. The threshold rapidly adapts to changes in the amplitude of the 60 cycle noise.

FIG. 5. R wave triggering during skeletal muscle noise on the ECG. The threshold actively adapts to electromyographic (EMG) noise from skeletal muscles by increasing the threshold level to prevent the occurrence of a false trigger.

Claims

1. A method of generating a trigger from an R wave of an electrocardiogram (ECG) waveform using a threshold that adapts to the slope of the R wave while still within the leading edge of the R wave, the method comprising: a) setting a minimum threshold for the trigger, where the minimum threshold is a percentage of the amplitude of the expected R wave;b) measuring slopes of the R wave over successive small time periods during the leading edge of the R wave; where slopes corresponding to waveforms that consist of frequencies greater than the expected R wave prevent generation of a trigger;c) adjusting the threshold for the trigger for the R wave during the leading edge of the R wave, where the minimum threshold is increased if the slopes measured in b) are greater than expected for the R wave;d) applying a scalar value to the slopes measured in b) to set a frequency above which signal frequencies are not considered valid for recognition as an R wave; ande) generating a trigger within the leading edge of the R wave when the amplitude of the R wave reaches the threshold.

2. The method of claim 1, wherein the amplitude of the expected R wave is normalized based on preceding R waves recorded from the same subject.

3. The method of claim 2, wherein more recently occurring R waves are weighted more heavily in determining the amplitude of the expected R wave than less recently occurring R waves.

4. The method of claim 1, wherein the minimum threshold in step a) is set at ⅓rd of the amplitude of the expected R wave.

5. The method of claim 1, wherein the minimum threshold in step a) is set at ½ of the amplitude of the expected R wave.

6. The method of claim 1, wherein individual time periods in step b) are 1 msec to 5 msec in duration.

7. The method of claim 1, wherein individual time periods in step b) are at least 4 msec in duration.

8. The method of claim 1, wherein the successive time periods in step b) have a total duration of 16-40 msec.

9. The method of claim 1, wherein slopes corresponding to waveforms that predominately have frequencies greater than or equal to 40 Hz are excluded from generating a trigger.

10. The method of claim 1, wherein slopes corresponding to waveforms that predominately have frequencies greater than or equal to 30 Hz are excluded from generating a trigger.

11. The method of claim 1, wherein the adjusted threshold is not allowed to exceed a maximum percentage of the amplitude of the expected R wave.

12. The method of claim 1, wherein the adjusted threshold is not allowed to exceed ⅔rd of the amplitude of the expected R wave.

13. The method of claim 1, which further comprises excluding slopes corresponding to waveforms that predominately have frequencies less than or equal to 5 Hz from generating a trigger.

14. The method of claim 1, which further comprises excluding slopes corresponding to waveforms that predominately have frequencies less than or equal to 10 Hz from generating a trigger.

15. The method of claim 1, which further comprises requiring that a minimum number of changes in amplitude of the R wave measured over successive time periods in step b) are in the same direction of change in order to generate a trigger.

16. The method of claim 1, which further comprises requiring that a change in amplitude of the R wave measured over a time period in step b) has a minimum change with respect to the change in amplitude measured over the preceding time period in order to generate a trigger.

17. The method of claim 1, which further comprises increasing the threshold for the trigger in the presence of ECG signals having a frequency component in the higher range expected for the R wave.

18. The method of claim 1, which further comprises triggering an intra-aortic balloon pump (IABP) by the trigger generated in step e).

19. The method of claim 1, which further comprises triggering deflation of an intra-aortic balloon (IAB) by an intra-aortic balloon pump (IABP) by the trigger generated in step e).

20. The method of claim 1, which further comprises triggering a cardiac device by the trigger generated in step e).

21. The method of claim 20, wherein the cardiac device is a cardiac stimulator, a defibrillator, or an ECG monitor.

22. An apparatus for generating a trigger from an R wave of an electrocardiogram (ECG) waveform using a threshold that adapts to the slope of the R wave while still within the leading edge of the R wave, the apparatus comprising a processing unit for: a) setting a minimum threshold for the trigger, where the minimum threshold is a percentage of the amplitude of the expected R wave;b) measuring slopes of the R wave over successive small time periods during the leading edge of the R wave, where slopes corresponding to waveforms that consist of frequencies greater than the expected R wave prevent generation of a trigger;c) adjusting the threshold for the trigger for the R wave during the leading edge of the R wave, where the minimum threshold is increased if the slopes measured in b) are greater than expected for the R wave;d) applying a scalar value to the slopes measured in b) to set a frequency above which signal frequencies are not considered valid for recognition as an R wave; ande) generating a trigger within the leading edge of the R wave when the amplitude of the R wave reaches the threshold.

23. The apparatus of claim 22, wherein the apparatus comprises an input from the electrocardiogram (ECG) of a subject.

24. The apparatus of claim 23, wherein the apparatus comprises an input from the subject's arterial pressure.

25. The apparatus of claim 22, wherein the apparatus comprises a processing unit for detecting cardiac arrhythmia from a subject's electrocardiogram (ECG) and/or from a subject's arterial pressure.

26. The apparatus of claim 22, wherein the amplitude of the expected R wave is normalized based on preceding R waves in the ECG.

27. The apparatus of claim 26, wherein more recently occurring R waves are weighted more heavily in determining the amplitude of the expected R wave than less recently occurring R waves.

28. The apparatus of claim 22, wherein the minimum threshold in a) is set at ⅓rd of the amplitude of the expected R wave.

29. The apparatus of claim 22, wherein the minimum threshold in a) is set at ½ of the amplitude of the expected R wave.

30. The apparatus of claim 22, wherein individual time periods in b) are 1 msec to 5 msec in duration.

31. The apparatus of claim 22, wherein individual time periods in b) are at least 4 msec in duration.

32. The apparatus of claim 22, wherein the successive time periods in b) have a total duration of 16-40 msec.

33. The apparatus of claim 22, wherein slopes corresponding to waveforms that predominately have frequencies greater than or equal to 40 Hz are excluded from generating a trigger.

34. The apparatus of claim 22, wherein slopes corresponding to waveforms that predominately have frequencies greater than or equal to 30 Hz are excluded from generating a trigger.

35. The apparatus of claim 22, wherein the adjusted threshold is not allowed to exceed a maximum percentage of the amplitude of the expected R wave.

36. The apparatus of claim 22, wherein the adjusted threshold is not allowed to exceed ⅔rd of the amplitude of the expected R wave.

37. The apparatus of claim 22, wherein the processing unit excludes slopes corresponding to waveforms that predominately have frequencies less than or equal to 5 Hz from generating a trigger.

38. The apparatus of claim 22, wherein the processing unit excludes slopes corresponding to waveforms that predominately have frequencies less than or equal to 10 Hz from generating a trigger.

39. The apparatus of claim 22, wherein the processing unit requires that a minimum number of changes in amplitude of the R wave measured over successive time periods in step b) are in the same direction of change in order to generate a trigger.

40. The apparatus of claim 22, wherein the processing unit requires that a change in amplitude of the R wave measured over a time period in step b) has a minimum change with respect to the change in amplitude measured over the preceding time period in order to generate a trigger.

41. The apparatus of claim 22, wherein the processing unit increases the threshold for the trigger in the presence of ECG signals having a frequency component in the higher range expected for the R wave.

42. The apparatus of claim 22, wherein the apparatus comprises an output that triggers an intra-aortic balloon pump (LABP).

43. The apparatus of claim 22, wherein the apparatus comprises an output that triggers deflation of an intra-aortic balloon (LAB) by an intra-aortic balloon pump (IABP).

44. The apparatus of claim 22, wherein the apparatus is incorporated in an intra-aortic balloon pump console system.