Implantable medical device for tracking patient cardiac status

• US 6,190,324 B1
• Filed: 04/28/1999
• Issued: 02/20/2001
• Est. Priority Date: 04/28/1999
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Kieval, Robert S., Riff, Kenneth M.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US09/301,206
• Time in Patent Office: 664 Days
• Field of Search: 600/483, 600/510, 600/513, 607/18, 607/19, 607/20, 607/27
• US Class Current: 600/483
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/222 combined with detection or measurement of physiological parameters, e.g. heart rate
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/36514 controlled by a physiological quantity other than heart potential, e.g. blood pressure controlled by two or more physical parameters A61N1/36585
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

An implantable medical device determines activity levels and Heart Rate and from a combination of these produces a value for a heart rate activity coefficient (HRAC). This value has significant diagnostic and patient tracking value. Methods and apparatus for determining this HRAC value are described. This enables physician review of patient cardiac status. Additional physiologic data can be recorded along with the HRAC data if desired, and this too, as well as the HRAC data alone, may be reported out from the implanted device to a medical communications system for alarm purposes, titrating drugs/therapies or other monitoring tasks. Further, substitutes for heart rate measurements and activity measurements are described which can be used to augment or substitute for heart rate measurements and activity measurements. These substitutes should represent cardiovascular or cardiac responsiveness to substitute for heart rate in the HRAC signal; and should represent cardiac demand to substitute for activity in the HRAC signal.

Claims

1. An implantable medical device for determining a Heart Rate Activity Coefficient (HRAC) comprising:

a sealed housing adapted for chronic implantation into a living body, said housing having located therewithin,

an activity sensor and activity level determining circuitry for producing an activity output signal having a value indicating a present level related to cardiac demand,

a heart rate (HR) determining circuit for producing a HR output signal having a value indicating a present HR level,

a timing circuit for use in relation of both said HR and activity output signal values to passing time which produces a timing signal,

a processing circuit for relating said activity output signal and said HR output signals to a current time available by reference to said timing signal from said timing circuit, and

a memory circuit for storing a time marked pair of values relating current HR output signals and activity output signals to a current time, in a series.

2. A system comprising the implantable medical device as set forth in claim 1 and further comprising an external processing unit having a processor circuit for reading said memory circuit and wherein said processing circuit comprises;

an analysis means for analyzing either said HR output signal values over time or said activity signal values over time and determining therefrom, based on a predetermined formula, which of said time related pairs of said HR signal values and said activity signal values provides appropriate basis for producing an HRAC signal value from their combination, and then selecting said determined pairs of HR and activity signal values for combining, and

a combination circuit means for combining said selected pairs of activity and HR signal value pairs to produce an HRAC signal value.

3. A system comprising the implantable medical device as set forth in claim 2 and further comprising an external processing unit having a processor circuit for reading said memory circuit and wherein said processing circuit comprises;

an analysis means for combining said HRAC signal values in said series for display as a long term trend, and

a display member for displaying long term trend.

4. A system as set forth in claim 2 wherein said external processor further comprises a display member for displaying HRAC values over time.

5. An implantable medical device as set forth in claim 1 wherein said heart rate (HR) determining circuit comprises:

electrode means for receiving an electrocardiogram signal from a patient, and

electrocardiogram signal analysis circuitry for determining heart rate from said electrocardiogram signal and for producing an output signal representing heart rate (HR).

6. The implantable medical device of claim 1 wherein said HR determining circuit further comprises means for measuring an alternative cardiac responsiveness signal comprising a combination of said HR signal and said which produces an augmented HR level signal and circuit means for producing said HR signal alternative cardiac responsiveness signal.

7. The implantable medical device of claim 1 wherein said HR determining circuit further comprises means for measuring an alternative cardiac responsiveness signal and employing said alternative cardiac responsiveness signal as said HR output signal.

8. The implantable medical device of claim 1 wherein the activity output signal is bolstered with a measure of cardiac demand.

9. The implantable medical device of claim 1 wherein measures of cardiac demand substitute for said activity output signal.

10. An implantable medical device as set forth in claim 1 wherein said processing circuit comprises;

an analysis means for analyzing either said HR output signal values over time or said activity signal values over time and determining therefrom, based on a predetermined formula, which of said time related pairs of said HR signal values and said activity signal values provides appropriate basis for producing an HRAC signal value from their combination, and then selecting said determined pairs of HR and activity signal values for combining, and

a combination circuit means for combining said selected pairs of activity and HR signal value pairs to produce an HRAC signal value.

12. The implantable medical device of any of claims 1-4 or 11 wherein said implantable medical device further comprises a device of the following set of devices:

a pacemaker, an ICD, a drug pump, a neurostimulator, an implantable electrocardiogram monitor, and an implantable physiologic sensor monitor.

13. The implantable medical device of any of claims 1-4 or 11 wherein said implantable medical device compasses a therapy delivery control circuit responsive to adjust therapy delivery based on said HRAC signal.

14. The implantable medical device of any of claims 1-4 or 11 wherein said implantable medical device further comprises Alarm circuit means for monitoring said HRAC signal level to determine if said HRAC signal level matches an alarm level, and for generating an alarm signal if said HRAC signal level does match said alarm level.

15. The implantable medical device of any of claims 1-4 or 11 wherein said implantable medical device further comprises Alarm circuit means for monitoring said HRAC signal level to determine if said HRAC signal level matches an alarm pattern, and for generating an alarm signal if said HRAC signal pattern does match said alarm pattern.

16. The implantable medical device of any of claims 1-4 or 11 wherein said implantable medical device further comprises telemetry circuit for communication of HRAC signal levels from said memory to an external device.

17. The implantable medical device of any of claims 1-4 or 11 wherein said implantable medical device further comprises telemetry circuit for communication of HRAC signal levels from said memory to an external device, and wherein said external medical device has communications means for communicating said HRAC signal levels across a Medical network wherein said medical network includes a display for displaying said HRAC signal levels for review by a physician.

11. An implantable medical device for determining a Heart Rate Activity Coefficient (HRAC) comprising:

a sealed housing adapted for chronic implantation into a living body, said housing having located therewithin,

an activity sensor and activity level determining circuitry for producing an activity output signal having a value indicating a present level related to cardiac demand,

a heart rate (HR) determining circuit for producing a HR output signal having a value indicating a present HR level,

a timing circuit for use in relation of both said HR and activity output signal values to passing time which produces a timing signal,

a processing circuit for producing a HRAC signal by combining said HR output signal and said activity signal, and for relating said HRAC signal to a time determined by reference to said timing circuit output to produce a time coded HRAC signal output, iteratively, and

a memory circuit for storing said iteratively produced time coded HRAC signal in a series.

18. A method of obtaining an HRAC measurement from an implantable medical device comprising:

determining that an HRAC measurement is needed by monitoring a physiologic signal for a predetermined indicator in said physiologic signal,

when it is determined that an HRAC measurement is needed, simultaneously maintaining a time record and measuring a HR signal level and an activity signal level and relating said measurements to said time record,

combining said HR signal level and activity signals for a related time period as indicated by said time record and from said combination producing a signal representing an HRAC measurement, and

storing said HRAC signal measurement.

19. The method of claim 18 further comprising:

determining if said HRAC signal measurement that was stored matches a predetermined trigger pattern and if so,

triggering the delivery of HRAC related therapy.

20. The method of claim 18 further comprising:

evaluating said HRAC signal measurement and modifying a therapy delivery based on said evaluation.

21. The method of claim 18 further comprising:

determining if said HRAC signal measurement that was stored matches a predetermined trigger pattern and if so,

triggering an alarm signal and,

transmitting said alarm externally to said implantable medical device.

22. The method of claim 18 further comprising:

producing a memory record of a set of HRAC measurements over a long time period.

23. The method of any of claims 18-22 further comprising the step of transferring said HRAC measurements from said implantable medical device to an external medical device, and compiling said HRAC measurements over a predetermined period of time, and displaying said HRAC measurements with respect to said predetermined period of time.

24. A method of obtaining an HRAC measurement from an implantable medical device comprising:

Setting a program for determining when to take HRAC measurements when it is determined that an HRAC measurement is needed, simultaneously maintaining a time record a HR signal level and an activity signal level and relating said measurements to said time record,

Combining said HR signal level and activity signals for related time period as indicated by said time record and from said combination producing a signal representing an HRAC measurement, and

storing said HRAC signal measurement.

25. The method of claim 24 wherein said setting step is automatic and based on the results of a step of making physiologic measurements.

26. The method of claim 25 wherein said physiologic measurements include HRAC.

27. The method of claim 24 wherein said settingstep is accomplished by programming intervention by a medical worker.

28. A method of obtaining an HRAC measurement from an implantable medical device comprising:

determining that an HRAC measurement is needed by monitoring a patient activation device for a signal indicating that the patient wants an HRAC measurement, and when it is determined that an HRAC measurement is needed, simultaneously maintaining a time record and measuring a HR signal level and an activity signal level and relating said measurements to said time record, combining said HR signal level and activity signals for a related time period as indicated by said time record and from said combination producing a signal representing an HRAC measurement, and

storing said HRAC signal measurement.