SYSTEM AND METHOD FOR MONITORING CARDIAC SIGNAL ACTIVITY IN PATIENTS WITH NERVOUS SYSTEM DISORDERS

• US 20070260147A1
• Filed: 06/22/2007
• Published: 11/08/2007
• Est. Priority Date: 12/17/2004
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Carlson, David, Giftakis, Jonathon, Graves, Nina, Panken, Eric, Rise, Mark, Stanford, Chark, Bright, Kevin
• Granted Patent: US 8,112,148 B2
• Time in Patent Office: Days
• US Class Current: 600/483
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/02 Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: A61B 5/4094 Diagnosing or monitoring seizure diseases, e.g. epilepsy
• CPC Class Codes: A61N 1/36064 Epilepsy
• CPC Class Codes: A61N 1/36082 Cognitive or psychiatric applications, e.g. dementia or Alzheimer's disease
• CPC Class Codes: A61N 1/3611 Respiration control stimulating respiratory organs A61N1/3601
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/36585 controlled by two or more physical parameters
• CPC Class Codes: A61N 1/36592 controlled by the heart rate variability
• CPC Class Codes: A61N 1/37288 Communication to several implantable medical devices within one patient
• CPC Class Codes: A61N 1/3962 : in combination with another heart therapy
• CPC Class Codes: A61N 1/39622 : Pacing therapy

Abstract

A medical device system and method for monitoring cardiac signal activity in patients with nervous system disorders. In some embodiments, a brain signal and a cardiac signal are received by a processor, brain events are identified in the brain signal, and the brain events are used to identify portions of the cardiac signal. In some embodiments, Event portions of the cardiac signal are identified corresponding to brain event time periods, and Inter-event portions are identified corresponding to time periods between brain events. An Inter-event heart-rate variability (HRV) calculation is performed using Inter-event portions of the cardiac signal, and an output of the medical device system is modified based upon the calculated Inter-event HRV according to certain embodiments of the invention. An Event HRV may also be calculated according to certain embodiments, and an output modified based on comparisons of the Event HRV to the Inter-event HRV, for example.

Claims

1. A medical device system comprising:

a brain monitoring element for sensing activity of a brain of a patient and outputting a brain signal;

a cardiac monitoring element for sensing activity of a heart of the patient and outputting a cardiac signal; and

one or more processors adapted to communicate with the brain monitoring element and the cardiac monitoring element, the one or more processors configured to;

receive the brain signal;

identify brain events in the brain signal, each of the brain events having a start time and an end time defining a brain event time period;

receive the cardiac signal and store cardiac signal information in one or more data buffers;

identify one or more Inter-event portions of the cardiac signal, each of the one or more Inter-event portions corresponding in time to a period that is not a brain event time period;

calculate an Inter-event heart-rate variability (HRV) based on the cardiac signal information stored for the one or more Inter-event portions of the cardiac signal; and

modify an output of the medical device system based upon the Inter-event HRV.

2. The medical device system of claim 1 wherein the cardiac monitoring element is a leadless ECG electrode.

3. The medical device system of claim 1 wherein the cardiac monitoring element is an implantable cardiac lead.

4. The medical device system of claim 1 wherein the cardiac signal information includes R-R intervals and the Inter-event HRV is a periodic value representative of variability of the R-R intervals in the inter-event portions of the cardiac signal over a defined period.

5. The medical device system of claim 4 wherein the periodic value is representative of variability of the R-R intervals over a one day period.

6. The medical device system of claim 4 wherein the one or more processors are further configured to record a series of the periodic value of the Inter-event HRV to identify a trend.

7. The medical device system of claim 4 wherein the one or more processors are adapted to modify the output when the periodic value of the Inter-event HRV meets a threshold criterion.

8. The medical device system of claim 4 wherein the one or more processors are further adapted to calculate an unadjusted HRV based on cardiac signal information stored for both Inter-event and Event portions of the cardiac signal, and wherein the output of the medical device system is modified based upon both the Inter-event HRV and the unadjusted HRV.

9. The medical device system of claim 6 wherein the output is modified when the trend meets a threshold criterion.

10. The medical device system of claim 9 wherein the trend meets the threshold criterion when the periodic value changes by more than a certain amount.

11. The medical device system of claim 9 wherein the trend meets the threshold criterion when the periodic value changes by more than a certain percentage.

12. The medical device system of claim 11 wherein the threshold criterion is met when the periodic value changes by more than a certain percentage within a specified period of time.

13. The medical device system of claim 7 wherein the output is modified when the periodic value of the Inter-event HRV decreases below a threshold value.

14. The medical device system of claim 7 wherein the output is modified when the periodic value of the Inter-event HRV decreases by more than a threshold percentage.

15. The medical device system of claim 1 wherein the brain events are identified by a seizure detection algorithm.

16. The medical device system of claim 1 wherein the brain events are identified by an algorithm that detects changes in EEG signals indicative of a psychiatric condition.

17. The medical device system of claim 16 wherein the psychiatric condition is a depressive state, and wherein the changes in EEG signals include EEG asymmetry and/or reduced EEG amplitudes.

18. The medical device system of claim 16 wherein the psychiatric condition is an anxiety or panic state, and wherein the changes in EEG signals include increased EEG amplitudes and/or frequency.

19. The medical device system of claim 1 wherein the brain events are identified by the patient indicating an occurrence of symptoms.

20. The medical device system of claim 7 wherein the one or more processors are adapted to modify the output when the periodic value of the Inter-event HRV increases a predetermined amount.

21. The medical device system of claim 1 wherein the output being modified is a warning of a patient condition.

22. The medical device system of claim 1 wherein the one or more processors are further adapted to

calculate an Event HRV based on the cardiac signal information corresponding in time to each of the one or more brain event time periods, and

modify the output of the medical device system based upon a comparison between the Inter-event HRV and the Event HRV.

23. The medical device system of claim 22 wherein the Inter-event HRV is based on a long-term value, and wherein the output of the medical device system is modified when the Event HRV differs from the Inter-event HRV by more than a specified amount.

24. The medical device system of claim 23 wherein the output of the medical device system is modified when the Event HRV is more than a specified percentage less than the Inter-event HRV.

25. The medical device system of claim 22 wherein the one or more processors are further adapted to

assign a weighting measure to the comparison between the Inter-event HRV and the Event HRV based upon an Inter-event interval.

26. The medical device system of claim 25 wherein the inter-event interval is the duration of all of the inter-event portions of the cardiac signal on which the Inter-event HRV is based.

27. The medical device system of claim 25 wherein the inter-event interval is the time elapsed between two successive brain event time periods.

28. The medical device system of claim 1 further comprising a therapy module, wherein the output of the medical device system is a therapy delivered by the therapy module to the brain of the patient.

29. The medical device system of claim 28 wherein the one or more processors are adapted to modify the output of the therapy module by changing a programmable setting that determines when the therapy module delivers therapy.

30. The medical device system of claim 28 wherein the one or more processors are adapted to modify the output of the therapy module by changing a programmable setting that determines a type of therapy to be delivered by the therapy module.

31. The medical device system of claim 1 further comprising a therapy module, wherein the output of the medical device system is a therapy delivered by the therapy module to the heart of the patient.

32. The medical device system of claim 31 wherein the one or more processors are adapted to modify the output of the therapy module by changing a programmable setting that determines when the therapy module delivers therapy.

33. The medical device system of claim 31 wherein the one or more processors are adapted to modify the output of the therapy module by changing a programmable setting that determines a type of therapy to be delivered by the therapy module.

34. The medical device system of claim 1 wherein the one or more brain events are epileptic seizures, and wherein the brain event time periods corresponding to the seizures define ictal portions of the cardiac signal during the seizures, and inter-ictal portions of the cardiac signal between the seizures.

35. The medical device system of claim 1 wherein the Inter-event HRV is calculated based on Inter-event portions of the cardiac signal corresponding to sleep periods of the patient.

36. The medical device system of claim 35 wherein a sleep sensor is employed to determine the sleep periods of the patient.

37. The medical device system of claim 36 wherein the sleep sensor determines sleep periods based on body position.

38. The medical device system of claim 36 wherein the sleep sensor determines sleep periods based on respiration rate.

39. The medical device system of claim 1 wherein the Inter-event HRV is a night-time value calculated based on Inter-event portions of the cardiac signal corresponding to defined night-time periods.

40. The medical device system of claim 1 wherein the Inter-event HRV is a day-time value calculated based on Inter-event portions of the cardiac signal corresponding to defined day-time periods.

41. The medical device system of claim 1 wherein the Inter-event HRV is calculated and recorded once every 24 hours.

42. The medical device system of claim 41 wherein both a day-time and a night-time Inter-event HRV are calculated and recorded once every 24 hours.

43. The medical device system of claim 41 wherein the one or more processors are further configured to calculate a Therapy HRV based on cardiac signal information corresponding in time to periods of therapy delivery to the patient.

44. The medical device system of claim 43 wherein the therapy delivered to the patient includes electrical stimulation therapy to the brain of the patient.

45. The medical device system of claim 43 wherein the therapy delivered to the patient includes electrical stimulation therapy to the heart of the patient.

46. The medical device system of claim 43 wherein the therapy delivered to the patient includes drug delivery to the patient.

47. A method of treating a patient, the method comprising:

receiving a brain signal from the patient;

identifying one or more brain events in the brain signal, each of the one or more brain events having a start time and an end time defining a brain event time period for each of the one or more brain events;

receiving a cardiac signal from the patient and storing cardiac signal information in one or more data buffers;

identifying one or more Inter-event portions of the cardiac signal, each of the one or more Inter-event portions corresponding in time to a period between two of the one or more brain event time periods;

calculating an Inter-event heart-rate variability (HRV) based on the cardiac signal information stored for the one or more Inter-event portions of the cardiac signal; and

modifying a therapy delivered to the patient based upon the calculated Inter-event HRV.

48. A medical device system comprising:

a brain monitoring element for sensing activity of a brain of a patient and outputting a brain signal;

a cardiac monitoring element for sensing activity of a heart of the patient and outputting a cardiac signal; and

one or more processors adapted to communicate with the brain monitoring element and the cardiac monitoring element, the one or more processors configured to;

receive the brain signal;

identify one or more brain events in the brain signal, each of the one or more brain events having a start time and an end time defining a brain event time period for each of the one or more brain events;

determine at least one reference point for a current brain event time period by evaluation of the brain signal, the current brain event time period following a preceding brain event time period by an inter-event interval;

receive the cardiac signal and store cardiac signal information in one or more data buffers;

identify a first portion and a second portion of the cardiac signal based on the at least one reference point of the current brain event time period;

calculate a first cardiac metric from the first portion of the cardiac signal and a second cardiac metric from the second portion of the cardiac signal;

compare the first cardiac metric to the second cardiac metric;

assign a weighting measure to the comparison of the first and second cardiac metrics based upon the inter-event interval; and

modify an output of the medical device system based on the weighting measure and on the comparison of the first cardiac metric to the second cardiac metric.

49. The medical device system of claim 48 wherein the weighting measure is zero if the inter-event interval is less than a predetermined amount.

50. The medical device system of claim 48 wherein the weighting measure is 1 if the inter-event interval is greater than a predetermined amount.

51. The medical device system of claim 48 wherein the weighting measure is a fraction between zero and one if the inter-event interval is between two predetermined amounts.

52. The medical device system of claim 48 wherein the inter-event interval is determined by counting the data buffers between the preceding brain event time period and the current brain event time period.

53. The medical device system of claim 48 wherein each data buffer corresponds to approximately 30 seconds of cardiac signal information.

54. The medical device system of claim 48 wherein the cardiac signal information stored in the data buffers includes data related to R-R intervals of the patient.

55. The medical device of claim 48 wherein each of the first cardiac metric and the second cardiac metric is a statistical measure of the patient'"'"'s heart rate.

56. The medical device of claim 55 wherein the first cardiac metric is a mean heart rate over the first portion of the cardiac signal, and the second cardiac metric is a mean heart rate over the second portion of the cardiac signal.

57. The medical device of claim 56 wherein the mean heart rate over the first portion of the cardiac signal is based upon one or more representative heart rates determined for each data buffer during the first portion, and wherein the mean heart rate over the second portion of the cardiac signal is based upon one or more representative heart rates determined for each data buffer during the second portion.

58. The medical device of claim 55 wherein the first cardiac metric is a heart rate variability over the first portion of the cardiac signal, and the second cardiac metric is a heart rate variability over the second portion of the cardiac signal.

59. The medical device system of claim 48 wherein the one or more processors are configured to compare the first cardiac metric to the second cardiac metric by computing the percentage change from the first cardiac metric to the second cardiac metric.

60. The medical device system of claim 48 wherein the at least one reference point is the start time of the current brain event time period, and wherein the second portion of the cardiac signal occurs generally during the current brain event time period.

61. The medical device system of claim 48 wherein the one or more processors are adapted to compare the second cardiac metric to a baseline metric if the inter-event interval is less than the predetermined amount.

62. The medical device system of claim 61 wherein the baseline metric is a long-term statistical measure of the patient'"'"'s heart rate.

63. The medical device system of claim 62 wherein the baseline metric is determined based on at least 2 hours of cardiac signal information obtained during periods other than brain event time periods.

64. The medical device system of claim 48 wherein the at least one reference point for the current brain event time period is determined by analyzing the brain signal with a seizure detection algorithm.

65. The medical device system of claim 48 wherein the inter-event interval is from the end time of the preceding brain event time period to the start time of the current brain event time period.

66. The medical device system of claim 48 further comprising a therapy delivery subsystem adapted to communicate with the one or more processors, wherein the therapy delivery subsystem is adapted to deliver a therapy based on the comparison of the first cardiac metric to the second cardiac metric.