Method and apparatus for event processing in biological application

• US 5,788,645 A
• Filed: 06/03/1996
• Issued: 08/04/1998
• Est. Priority Date: 05/18/1992
• Status: Expired due to Term

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Swanson, David K., Beatty, Graydon, Lang, Douglas
• Primary Examiner(s): Hayes, Gail O.
• Assistant Examiner(s): Poinvil, Frantzy
• Application Number:
  US08/657,389
• Time in Patent Office: 792 Days
• Field of Search: 395/202, 395/203, 705/2, 705/3, 600/515, 600/516, 600/128, 600/702, 600/705, 600/710, 600/712
• US Class Current: 600/516
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/36507 controlled by gradient or slope of the heart potential

Abstract

A method and apparatus for processing biological signals on an event basis. An event low pass filter (LPF) is provided which passes variations in event features below an event cut-off value, which is analogous to the time-based cutoff frequency. An event high pass filter (HPF) is provided which passes variations in event features that are above an event-rate cutoff. An event variability detector is provided which determines the variation of a discrete variable from values at prior events. An event discriminator is provided for filtering out contributions of unrelated events that are superimposed on a discrete periodic measurement of interest. In all of these techniques, sampling of a biological signal is performed in coincidence with a biological event which does not occur at a constant frequency. In accordance with another aspect, an algorithm is provided using event-based techniques for discriminating abnormal rhythms from normal sinus rhythm on the basis of atrial rate, ventricular rate, and A-V intervals. An interval conditioning stage is provided for processing intervals of atrial beats, ventricular beats, and atrial to ventricular beats and classifying intervals for each according to an adaptive triple-bin technique. The three bins are defined as "current", "fast" and "slow" and each comprises memory space for storing the count of intervals stored into the particular bin and the average value of those intervals.

Claims

1. A method for sensing biological parameters to evaluate a cardiac rhythm comprising the steps of:

sensing a biological parameter at a non-constant frequency associated with a naturally occurring biological event;

converting said biological parameter to corresponding signals;

utilizing said signals to determine an abnormal condition in said naturally occurring biological event by;

determining atrial interval values, ventricular interval values and atrial-ventricular interval values; and

comparing said atrial interval values, said ventricular interval values and said atrial-ventricular interval values with stored data from a previous event, thereby evaluating the cardiac rhythm.

2. A method for sensing and processing biological parameters related to cardiac activity for determining cardiac abnormalities comprising the steps of:

sensing a biological parameter related to cardiac activity at a non-constant frequency coincident with a naturally occurring biological event;

converting said biological parameter to corresponding signals;

determining values of the biological parameter from said signals;

low pass filtering the values of the biological parameter by computing a running average of a value of said biological parameter at each biological event comprising the step of adding a fraction of a value of said biological parameter at a current event to an average of all prior values of said biological parameter calculated at an immediately preceding biological event;

transmitting said values to an arrhythmia detector; and

determining atrial interval values, ventricular interval values and atrial-ventricular interval values; and

determining cardiac abnornalities by comparing said atrial interval values, said ventricular interval values and said atrial-ventricular integral values with stored data from a previous event.

3. The method of claim 2, wherein said biological event is a ventricular beat.

4. The method of claim 3, wherein said biological parameter is the time interval between consecutive heart beats.

5. The method of claim 3, wherein said biological parameter is the time interval between consecutive atrial beats.

6. The method of claim 3, wherein said biological parameter is the time interval between an atrial beat and the next ventricular beat.

7. The method of claim 2, and further comprising the step of high pass filtering on an event basis the values of the biological parameters by subtracting from the current value of said biological parameter the low pass average computed at the immediately preceding event.

8. The method of claim 7, and further comprising the step of determining the variation of the value of said biological parameter at a current event from values at preceding biological events by determining the absolute value of the high pass filtered value of the biological parameter.

9. A method for sensing and processing values of a biological parameter for determining cardiac abnormalities comprising the steps of:

sensing a biological parameter related to cardiac activity at a non-constant frequency coincident with a naturally occurring biological event;

converting said biological parameter to corresponding signals;

low pass filtering values of said biological parameter by passing unaltered, variations in values of said biological parameter that are below an event-rate cutoff and attenuating variations in values of said biological parameter that are above the event-rate cutoff;

transmitting said values to an arrhythmia detector; and

determining atrial interval values, ventricular interval values and atrial-ventricular interval values; and

determining cardiac abnormalities by comparing said atrial interval values, said ventricular interval values and said atrial-ventricular interval values with stored data from a previous event.

10. A method for sensing and processing values of a biological parameter for detecting cardiac abnormalities comprising the steps of:

sensing a biological parameter related to cardiac activity at a non-constant frequency coincident with a naturally occurring biological event;

converting said biological parameter to corresponding signals;

determining values of the biological parameter from said signals;

high pass filtering values of said biological parameter by passing unaltered, variations in values of said biological parameter that are above an event-rate cutoff and attenuating variations in values of said biological parameter that are below the event-rate cutoff;

transmitting said values to an arrhythmia detector; and

determining atrial interval values, ventricular interval values and atrial-ventricular interval values; and

detecting cardiac abnormalities by comparing said atrial interval values, said ventricular interval values and said atrial-ventricular interval values with stored data from a previous event.

11. A method for detecting an abnormal cardiac rhythm comprising the steps of:

sensing atrial and ventricular activity of the heart;

converting said activity to signals corresponding to atrial (A) beats;

converting said activity to signals corresponding to ventricular (V) beats;

computing at the occurrence of each ventricular beat the time interval between consecutive atrial beats, consecutive ventricular beats and the A-V time interval;

continuously computing at the occurrence of each ventricular beat the average of the time interval between consecutive atrial beats, consecutive ventricular beats and the A-V time interval;

comparing the time interval between consecutive atrial beats, consecutive ventricular beats and the A-V time intervals, computed at the current ventricular beat with the average computed at the immediately preceding ventricular beat;

providing first, second and third memory locations for each of the time intervals of atrial beats and ventricular beats and A-V time intervals;

storing the average of the time intervals of the atrial beats, ventricular beats and A-V time intervals at the current ventricular beat in the respective first memory location dedicated to time intervals which are a predetermined amount of the average at the immediately preceding ventricular beat and incrementing a count of the number of time intervals stored to said first memory location;

storing the average of the time intervals of the atrial beats, ventricular beats and A-V time intervals at the current ventricular beat in the respective second memory location dedicated to time intervals stored to said first memory location and incrementing a count of the number of time intervals stored to said second memory location;

storing the average of the atrial beats, ventricular beats and A-V time intervals at the current ventricular beat in the respective third memory location dedicated to time intervals which differ from the average at the immediately preceding ventricular beat less than said predetermined amount and incrementing a count of the number of time intervals stored to said third memory location;

comparing the counts of the second and third memory locations of the respective atrial beats, ventricular beats, and A-V time intervals, with the count of the first memory location at each ventricular beat;

replacing the contents of the first memory location with the contents of the second memory location of the respective atrial beats, ventricular beats and A-V time intervals, if the count of time intervals stored to said second memory location exceeds the count of time intervals stored to said first memory location;

replacing the contents of the first memory location with the contents of the third memory location of the respective atrial beats, ventricular beats and A-V time intervals, if the count of time intervals stored to said third memory location exceeds the count of time intervals stored to said first memory location;

examining the contents of said first memory location of the respective atrial beats, ventricular beats and A-V time interval, at each ventricular beat; and

detecting an abnormal cardiac rhythm based on the average of the contents of the first memory location and by comparing atrial beats, ventricular beats and A-V time intervals with stored data from a previous event.

12. The method of claim 11, and further comprising the steps of:

decrementing the count of time intervals stored to said second and third memory locations each time the count of time intervals stored to said first memory location is incremented;

decrementing the count of time intervals stored to said first and third memory locations each time the count of time intervals stored to said second memory location is incremented; and

decrementing the count of time intervals stored to said first and second memory locations each time the count of time intervals stored to said third memory location is incremented.

13. The method of claim 11, wherein said step of determining the type of cardiac rhythm comprises the step of declaring that the cardiac rhythm is normal sinus rhythm if the content of the first memory location for ventricular beats is greater than a first predetermined threshold.

14. The method of claim 11, wherein said step of determining the type of cardiac rhythm comprises the step of declaring that the cardiac rhythm is ventricular tachycardia with hemodynamic compromise if the content of the first memory location for ventricular beats is less than a second predetermined threshold and not greater than a first predetermined threshold.

15. The method of claim 11, wherein said step of determining the type of cardiac rhythm comprises the step of declaring that the cardiac rhythm is ventricular tachycardia if the content of the first memory location for atrial time intervals is greater than the content of the first memory location of ventricular beats and the content of the first memory location for ventricular beats is not greater than a first predetermined threshold.

16. The method of claim 11, wherein said step of determining the type of cardiac rhythm comprises the step of declaring that the cardiac rhythm is supraventricular tachycardia or sinus tachycardia if the content of the first memory location for atrial time intervals is less than the content of the first memory location for ventricular beats and the content of the first memory location for ventricular beats is not greater than a first predetermined threshold and not less than a second predetermined threshold.

17. The method of claim 11, wherein said step of determining the type of cardiac rhythm comprises the step of declaring that the cardiac rhythm is supraventricular tachycardia or sinus tachycardia if the atrial interval value is within a programmed percentage boundary above and below the ventricular interval value and if the content of the first memory location for A-V time intervals is within a programmed first percentage above and second percentage below a long-term exponential average of A-V intervals measured during normal sinus rhythm.

18. The method of claim 11, wherein said step of determining the type of cardiac rhythm comprises the step of declaring that the cardiac rhythm is ventricular tachycardia if the atrial interval value is within a programmed percentage boundary above and below the ventricular interval value and if the content of the first memory location for A-V time intervals is not within a programmed first percentage above and second percentage below a long-term exponential average of A-V intervals measured during normal sinus rhythm.

19. An apparatus for sensing biological parameters to evaluate a cardiac rhythm comprising:

sensing electrodes for sensing a biological parameter at a non-constant frequency associated with a naturally occurring biological event;

an amplifier connected to said sensing electrodes for amplifying and developing a signal corresponding with said biological parameter; and

a digital signal processor connected to said amplifier for analyzing and processing said signal to determine an abnormal condition in said naturally occurring biological event including means for determining atrial internal values and ventricular interval values; and

an arrhythmia detector included in said digital signal processor for determining an abnormal condition by comparing the atrial interval values and ventricular interval values, whereby the cardiac rhythm is evaluated.

20. An apparatus for sensing and processing biological parameters related to cardiac activity for determining cardiac abnormalities comprising:

sensing electrodes for sensing a biological parameter related to cardiac activity at a non-constant frequency coincident with a naturally occurring biological event and for converting said biological parameter to corresponding signals;

a digital signal processor including a low pass filter for determining values of the biological parameter from said signals;

said low pass filter for filtering the values of the biological parameter by computing a running average of a value of said biological parameter at each biological event comprising means for adding a fraction of a value of said biological parameter at a current event to an average of all prior values of said biological parameter calculated at an immediately preceding biological event; and

an arrhythmia detector connected to said digital signal processor for determining cardiac abnormalities by comparing obtained atrial interval values, ventricular interval values and atrial-ventricular interval values obtained from said processor with stored data from a previous event.

21. The apparatus of claim 20, wherein said biological event is a ventricular beat.

22. The apparatus of claim 21, wherein said biological parameter is the time interval between consecutive heart beats.

23. The apparatus of claim 21, wherein said biological parameter is the time interval between consecutive atrial beats.

24. The apparatus of claim 21, wherein said biological parameter is the time interval between an atrial beat and the next ventricular beat.

25. The apparatus of claim 20, and further comprising a high pass filter for filtering on an event basis the values of the biological parameter by subtracting from current values of said biological parameter a low pass average computed at the immediately preceding event.

26. The apparatus of claim 25, and further comprising means for determining the variation of the value of said biological parameter at a current event from values at preceding biological events by determining the absolute value of the high pass filtered value of the biological parameter.

27. An apparatus for sensing and processing values of a biological parameter for determining cardiac abnormalities comprising:

sensing electrodes for sensing a biological parameter related to cardiac activity at a non-constant frequency coincident with a naturally occurring biological event and for converting said biological parameter to corresponding signals;

a low pass filter for filtering values of said biological parameters by passing unaltered, variations in values of said biological parameter that are below an event-rate cutoff and attenuating variations in values of said biological parameter that are above the event-rate cutoff; and

an arrhythmia detector connected to said digital signal processor for determining cardiac abnormalities by comparing obtained atrial interval values, ventricular interval values and atrial-ventricular interval values obtained from said processor with stored data from a previous event.

28. An apparatus for sensing and processing values of a biological parameter for detecting cardiac abnormalities comprising:

sensing electrodes for sensing a biological parameter related to cardiac activity at a non-constant frequency coincident with a naturally occurring biological event and for converting said biological parameter to corresponding signals;

a digital signal processor including a high pass filter for determining values of the biological parameter from said signals;

said high pass filter for filtering values of said biological parameter by passing unaltered, variations in values of said biological parameter that are above an event-rate cutoff and attenuating variations in values of said biological parameter that are below the event-rate cutoff; and

an arrhythmia detector connected to said digital signal processor for determining cardiac abnormalities by comparing obtained atrial interval values, ventricular interval values and atrial-ventricular internal values obtained from said processor with store data from a previous event.

29. An apparatus for detecting an abnormal cardiac rhythm comprising:

means for sensing atrial and ventricular activity of the heart;

means for converting said activity to signals corresponding to atrial (A) beats;

means for converting said activity to signals corresponding to ventricular (V) beats;

means for computing at the occurrence of each ventricular beat an atrial interval value between consecutive atrial beats, a ventricular interval value between consecutive ventricular beats and an A-V time interval;

means for continuously computing at the occurrence of each ventricular beat the average of the time interval between consecutive atrial beats, consecutive ventricular beats and the A-V time interval;

means for comparing the time interval between consecutive atrial beats, consecutive ventricular beats and the A-V time interval, computed at the current ventricular beat with the average computed at the immediately preceding ventricular beat;

means for providing first, second and third memory locations for each of the time intervals of atrial beats and ventricular beats and A-V time intervals;

means for storing the average of the time intervals of the atrial beats, ventricular beats and A-V time intervals at the current ventricular beat in the respective first memory location dedicated to time intervals which are a predetermined amount of the average at the immediately preceding ventricular beat and incrementing a count of the number of time intervals stored to said first memory location;

means for storing the average of the time intervals of the atrial beats, ventricular beats and A-V time intervals at the current ventricular beat in the respective second memory location dedicated to time intervals stored to said first memory location and incrementing a count of the number of time intervals stored to said second memory location;

means for storing the average of the atrial beats, ventricular beats and A-V time intervals at the current ventricular beat in the respective third memory location dedicated to time intervals which differ from the average at the immediately preceding ventricular beat less than said predetermined amount and incrementing a count of the number of time intervals stored to said third memory location;

means for comparing the counts of the second and third memory locations of the respective atrial beats, ventricular beats, and A-V time intervals with the count of the first memory location at each ventricular beat;

means for replacing the contents of the first memory location with the contents of the second memory location of the respective atrial beats, ventricular beats and A-V time intervals, if the count of time intervals stored to said second memory location exceeds the count of time intervals stored to said first memory location;

means for replacing the contents of the first memory location with the contents of the third memory location of the respective atrial beats, ventricular beats and A-V time intervals, if the count of time intervals stored to said third memory location exceeds the count of time intervals stored to said first memory location;

means for examining the contents of said first memory location of the respective atrial beats, ventricular beats and A-V time interval, at each ventricular beat; and

means for detecting abnormal cardiac conditions based on the average of the contents of the first memory location.

30. The apparatus of claim 29, and further comprising:

means for decrementing the count of time intervals stored to said second and third memory locations each time the count of time intervals stored to said first memory location is incremented;

means for decrementing the count of time intervals stored to said first and third memory locations each time the count of time intervals stored to said second memory location is incremented; and

means for decrementing the count of time intervals stored to said first and second memory locations each time the count of time intervals stored to said third memory location is incremented.

31. The apparatus of claim 29, wherein said means for determining the type of cardiac rhythm comprises means for declaring that the cardiac rhythm is normal sinus rhythm if the content of the first memory location for ventricular beats is greater than a first predetermined threshold.

32. The method of claim 29, wherein said means for determining the type of cardiac rhythm comprises means for declaring that the cardiac rhythm is ventricular tachycardia with hemodynamic compromise if the content of the first memory location for ventricular beats is less than a second predetermined threshold and not greater than a first predetermined threshold.

33. The apparatus of claim 29, wherein said means for determining the type of cardiac rhythm comprises means for declaring that the cardiac rhythm is ventricular tachycardia if the content of the first memory location for atrial time intervals is greater than the content of the first memory location of ventricular beats and the content of the first memory location for ventricular beats is not greater than a first predetermined threshold.

34. The apparatus of claim 29, wherein said means for determining the type of cardiac rhythm comprises means for declaring that the cardiac rhythm is supraventricular tachycardia or sinus tachycardia if the content of the first memory location for atrial time intervals is less than the content of the first memory location for ventricular beats and the content of the first memory location for ventricular beats is not greater than a first predetermined threshold and not less than a second predetermined threshold.

35. The apparatus of claim 29, wherein said means for determining the type of cardiac rhythm comprises means for declaring that the cardiac rhythm is supraventricular tachycardia or sinus tachycardia if the atrial interval value is within a programmed percentage boundary above and below the ventricular interval value and if the content of the first memory location for A-V time intervals is within a programmed first percentage above and second percentage below a long-term exponential average of A-V intervals measured during normal sinus rhythm.

36. The apparatus of claim 29, wherein said means for determining the type of cardiac rhythm comprises means for declaring that the cardiac rhythm is ventricular tachycardia if the atrial interval value is within a programmed percentage boundary above and below the ventricular interval value and if the content of the first memory location for A-V time intervals is not within a programmed first percentage above and second percentage below a long-term exponential average of A-V intervals measured during normal sinus rhythm.