Implantable system for monitoring the condition of the heart

• US 7,512,438 B2
• Filed: 09/28/2004
• Issued: 03/31/2009
• Est. Priority Date: 11/26/2003
• Status: Active Grant

• Current Assignee: Angel Medical Systems, Inc.
• Original Assignee: Angel Medical Systems, Inc.
• Inventors: Fischell, David R., Fischell, Robert E., Johnson, Steven R., Harwood, Jonathan
• Primary Examiner(s): Layno; Carl H
• Assistant Examiner(s): PATEL, NATASHA
• Application Number:
  US10/950,401
• Publication Number:
  US 20050113705A1
• Time in Patent Office: 1,645 Days
• Field of Search: 600/509, 600/515, 600/519, 600/521, 607/9, 607/5, 128/898
• US Class Current: 600/509
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/355 Detecting T-waves
• CPC Class Codes: A61B 5/358 Detecting ST segments
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/413 Monitoring transplanted tissue or organ, e.g. for possible rejection reactions after a transplant
• CPC Class Codes: A61N 1/025 Digital circuitry features of electrotherapy devices, e.g. memory, clocks, processors
• CPC Class Codes: A61N 1/37235 Aspects of the external programmer
• CPC Class Codes: A61N 1/37247 User interfaces, e.g. input or presentation means

Abstract

A “tracker system” that includes electrical leads which are part of an implanted cardiotracker plus external equipment that includes external alarm and a physician'"'"'s programmer. The tracker system is designed to monitor the degradation of a patient'"'"'s cardiovascular condition from one or more causes, These causes include the rejection of a transplanted heart and/or the progression of a stenosis in a coronary artery. As one or more stenoses in a coronary artery become progressively more narrow thereby causing reduced blood flow to the heart muscle coronary circulation, the tracker system can alert the patient by either or both internal and/or external alarm to take the appropriate medical action. The physician'"'"'s programmer can be used to display histograms of key heart signal parameters that are indicative of the patient'"'"'s cardiovascular condition.

Claims

1. An implantable device for tracking the cardiovascular condition of a human patient, the device including:

at least two implanted electrodes that are positioned within the human patient to sense the electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram which consists of a multiplicity of beats;

a processor to compute the value of at least one heart signal parameter for every beat of at least a portion of the multiplicity of beats of the electrogram; and

digital memory designed to store the computed values of the at least one heart signal parameter during each of at least two time periods that are each at least one hour long, where said at least one heart signal parameter stored in said digital memory is the value of a QRS voltage, and the QRS voltage is indicative of the amplitude of the QRS complex;

circuitry entirely contained within the implantable device indicating rejection of a heart transplanted into the human patient, the circuitry being configured for determining a pre-determined decrease in the median or mean value of a plurality of QRS voltages over a pre-determined time interval.

2. The implanted device of claim 1 where the at least one heart signal parameter that is stored in memory is the value of the ST segment voltage.

3. The implanted device of claim 1 where the at least one heart signal parameter that is stored in memory is the value of the ST segment voltage minus the PQ segment voltage which is the ST deviation.

4. The implanted device of claim 1 where the at least one heart signal parameter that is stored in memory is the value of the ST shift which is defined as the ST deviation for a specific beat in a recent time period minus a baseline ST deviation recorded at some prior time.

5. The implanted device of claim 1 where the QRS voltage is the difference between the maximum and minimum QRS complex voltage for a specific beat.

6. The implanted device of claim 1 where the at least one heart signal parameter that is stored in memory is the QRS shift which is the difference between the average QRS voltage in a recent data collection time period minus a baseline QRS voltage taken at some prior data collection time period, the baseline QRS voltage being the average QRS voltage during the prior time period.

7. The implanted device of claim 6 where the prior time period when the baseline QRS voltage was measured is at a time when a heart transplant patient was not rejecting the heart that was surgically placed into his body.

8. The implanted device of claim 1 where the at least one heart signal parameter that is stored in memory is the value of the R-R interval.

9. The implanted device of claim 1 where the at least one heart signal parameter that is stored in memory is the QRS complex width.

10. The implanted device of claim 9 further including a counter which stores the number of times that the width of the QRS complex exceeded a preset value during the time periods.

11. The implanted device of claim 10 where the preset value of the width of the QRS complex is at least 150 milliseconds.

12. The implanted device of claim 1 where the number of the premature atrial contractions (PACs) that have occurred in the electrogram within the time period is stored in memory.

13. The implanted device of claim 1 where the number of the premature ventricular contractions (PVCs) that have occurred in the electrogram within the time periods is stored in memory.

14. The implanted device of claim 1 where the at least one heart signal parameter that is stored in memory is the peak value of the T wave voltage.

15. The implanted device of claim 1 where the number of T wave alternans occurring in the electrogram within the time periods is stored in memory.

16. The implanted device of claim 1 where each of the time periods is approximately one day.

17. The implanted device of claim 1 where each of the time periods is less than one day.

18. The implanted device of claim 1 where each of the time periods is selected from the group consisting of one segment of the electrogram. approximately one minute, approximately one hour approximately one day, approximately two days, approximately one week, approximately on month and approximately one year.

19. The implanted device of claim 1 where the aggregate form is a measure of a central tendency of the values of the at least one heart signal parameter over a corresponding time period.

20. The implanted device of claim 19 where the central tendency is the mean value.

21. The implanted device of claim 19 where the central tendency is the median value.

22. The implanted device of claim 1 where one of the at least two time periods is designated as a baseline time period and the average value of the heart signal parameter for the baseline time period is the average baseline value of that heart signal parameter during that baseline time period.

23. The implanted device of claim 22 further including an alarm signal generator designed to generate an internal alarm signal when the average value of a heart signal parameter for a recent time period exceeds the average baseline value of that heart signal parameter by an amount that is greater than a preset threshold value.

24. The implanted device of claim 23 where the device has the capability to generate at least two different types of internal alarm signals.

25. The implanted device of claim 23 where the internal alarm signal that is generated by the device is a SEE DOCTOR ALERT that indicates to the human patient that he or she should seek medical attention on a non-emergency basis.

26. The implanted device of claim 23 where the internal alarm signal that is generated by the device is an EMERGENCY ALARM that indicates to the human patient that he or she should seek immediate medical attention.

27. The implanted device of claim 23 where the internal alarm signal is selected from the group consisting of a vibratory alarm signal, an electrical stimulation alarm signal or an audio alarm signal.

28. The implanted device of claim 1 further including external equipment designed to provide two-way wireless communication with the implanted device.

29. The implanted device of claim 28 where the external equipment includes an external alarm system that is designed to provide an alarm signal that is an external alarm signal.

30. The implanted device of claim 29 where the external alarm system includes means to manually turn off the external alarm signal.

31. The implanted device of claim 29 where the external alarm system includes means to manually turn off the internal alarm signal generated by the device.

32. The implanted device of claim 29 where the external alarm system includes means to manually turn off both the internal alarm signal generated by the device and the external alarm signal generated by the external alarm system.

33. The implanted device of claim 1 further including external equipment having the capability to display data stored within the digital memory of the implanted device.

34. The implanted device of claim 33 where the external equipment includes a physician'"'"'s programmer designed to program specific operating parameters of the implanted device.

35. The implanted device of claim 33 where the data displayed includes the values of the at least one heart signal parameter stored during the time periods.

36. The implanted device of claim 33 where the data displayed is extracted data including the average value of the at least one heart signal parameter computed for at least one of the time periods.

37. The implanted device of claim 36 where the external equipment has the capability to display the average values of the at least one heart signal parameter over an extracted data retention time period.

38. The implanted device of claim 37 where extracted data retention time period is at least one month.

39. The implanted device of claim 37 where extracted data retention time period is at least six months.

40. The implanted device of claim 36 where the extracted data is selected from the group consisting of the average ST segment voltage, the average ST deviation, the average ST shift, the average QRS voltage and the average QRS shift

41. The implanted device of claim 1 where the digital memory includes sufficient capacity to retain the values of the at least one heart signal for a multiplicity of time periods, the multiplicity of time periods being a collected data retention time period.

42. The implanted device of claim 41 where the collected data retention time period is at least one week.

43. The implanted device of claim 1 where the computed values of the at least one heart signal parameter are stored in at least one histogram, the at least one histogram having a multiplicity of bins, each bin corresponding to a different range of the at least one heart signal parameter.

44. The implanted device of claim 43 where the processor computes the values of two heart signal parameters which are a first heart signal parameter and a second heart signal parameter.

45. The implanted device of claim 44 further including a set of histograms where each histogram in the set corresponds to a different range of the first heart signal parameter and the bins in each histogram correspond to a range of the second heart signal parameter.

46. The implanted device of claim 43 where the processor computes and places into the digital memory the average value of the at least heart signal parameter stored in the histogram format for each of the time periods.

47. The implanted device of claim 46 where the average value of the at least one heart signal parameter is computed from histogram data which is retained in the digital memory for an extracted data retention time period.

48. A method for detecting a significant change in the cardiovascular condition of a human subject, the method comprising the steps of:

a. implanting into the human subject a device having an alarm, said device designed to calculate and retain in memory the average value of a heart signal parameter for each of at least three time periods that collectively span a period of at least two days, where the heart signal parameter that is retained in memory is a value of a QRS voltage based on the at least three average values;

b. determining if a significant change in the human subject'"'"'s cardiovascular condition has occurred by operation of the device; and

c. alerting the patient via the device'"'"'s alarm that a significant change in cardiovascular condition has been detected, and where the QRS voltage is indicative of the amplitude of the QRS complex.

49. A system for tracking the cardiovascular condition of a human patient the system including:

at least two implanted electrodes that are positioned within the human patient to sense the electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram which consists of a multiplicity of beats;

a histogram memory that stores the amplitude of at least one heart signal parameter into a specific bin of a specific histogram, each of the histograms associated with a different heart rate range, the histogram memory including memory capacity for at least one histogram, the histogram including at least two bins, each bin being a counter; and

a processor to compute the value of the at least one heart signal parameter for at least a portion of the multiplicity of beats of the electrogram data each beat of the portion of the multiplicity of beats that is processed being a processed beat, the processor also being designed to increment one of the at least two bins of the at least one histogram where the choice of bin to be incremented is dependent on the amplitude of the at least one heart signal parameter whose amplitude is computed by the processor.

50. The system of claim 49 where the histogram memory includes at least two sections, each section including at least one histogram.

51. The system of claim 50 where one of the at least two sections is the current section, the current section having at least one histogram that is incremented for a defined period of time which is a data collection time period.

52. The system of claim 50 where at least one of the at least two sections was the current section during a prior data collection time period.

53. The system of claim 50 where the histogram memory has at least seven sections.

54. The system of claim 49 where the histogram memory includes at least two histograms each histogram including at least two bins and the processor computes the values of at least two heart signal parameters which are a first heart signal parameter and a second heart signal parameter, the processor also being designed to select one of the at least two histograms based on the value of the first heart signal parameter, that histogram being the selected histogram the choice of bin to be incremented within the selected histogram being dependent on the value of the second heart signal parameter.

55. The system of claim 54 where the first heart signal parameter is R-R interval and the second heart signal parameter is ST deviation.

56. The system of claim 54 where the first heart signal parameter is heart rate and the second heart signal parameter is ST deviation.

57. The system of claim 49 where the electrodes are implanted under the skin of the human patient.

58. The system of claim 57 where one of the electrodes is placed under the skin of the human patient in the vicinity of the upper chest.

59. The system of claim 49 where the electrodes are placed within the heart of the human patient.

60. The system of claim 59 where at least one of the electrodes is placed within the right ventricle of the patient'"'"'s heart.

61. The system of claim 49 where at least one of the heart signal parameter is the average amplitude of a sub-segment of each processed beat of the electrogram data.

62. The system of claim 61 where the sub-segment is the ST segment.

63. The system of claim 49 where at least one of the heart signal parameters is the ST deviation.

64. The system of claim 49 where at least one of the heart signal parameters is the QRS voltage.

65. The system of claim 64 where the QRS voltage is the peak-to-peak voltage of the QRS complex.

66. The system of claim 49 where at least one of the heart signal parameters is the width of at least one sub-segment of the processed beats of the electrogram data.

67. The system of claim 66 where the sub-segment is the QRS complex.

68. The system of claim 49 where at least one of the heart signal parameters is the R-R interval of the processed beats of the electrogram data.

69. The system of claim 49 where at least one of the heart signal parameters is the R-R interval variability of the processed beats of the electrogram data.

70. The system of claim 49 where the processed beats comprise less than half of all beats during any data collection time period.

71. The system of claim 49 where the processed beats comprise less than 10% of all beats during any data collection time period.

72. The system of claim 49 where each histogram is incremented by the processor for a preset data collection time period.

73. The system of claim 72 where the data collection time period is approximately one day.

74. The system of claim 72 where the data stored in each histogram is retained in memory for a data retention time period which follows the data collection time period during which data collection time period the bins of the histogram are incremented.

75. The system of claim 74 where the data retention time period is at least one week.

76. The system of claim 49 further including an extracted histogram data memory containing extracted histogram data resulting from computations periodically performed by the processor on the values stored in the at least one histogram.

77. The system of claim 76 where the extracted histogram data includes the median value of at least one of the heart signal parameters stored in the at least one histogram.

78. The system of claim 76 where the extracted histogram data includes the mean value of the values of the at least one heart signal parameter stored in the at least one histogram.

79. The system of claim 76 where the system further includes the means to compute a moving average of two or more values of extracted histogram data.

80. The system of claim 49 where the system further includes means to compare the extracted histogram data with a preset threshold.

81. The system of claim 80 where the system further includes alarm means to alert the patient where the preset threshold is exceeded.

82. The system of claim 76 where the extracted histogram data is retained in the extracted histogram data memory for a preset extracted data retention time period.

83. The system of claim 82 where the extracted data retention time period is greater than 30 days.

84. The system of claim 82 where the extracted data retention time period is at least six months.