Means and method for the detection of cardiac events

• US 20040215092A1
• Filed: 05/26/2004
• Published: 10/28/2004
• Est. Priority Date: 09/20/2002
• 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, Fischell, Tim A.
• Granted Patent: US 7,558,623 B2
• Time in Patent Office: Days
• US Class Current: 600/515
• CPC Class Codes: A61B 2560/0209 adapted for power saving
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• 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 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7465 Arrangements for interactive communication between patient and care services, e.g. by using a telephone network telemetry of measured physiological signal A61B5/0002
• 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 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

Disclosed is a system for the detection of cardiac events that includes an implanted device called a cardiosaver, a physician'"'"'s programmer and an external alarm system. The system is designed to provide early detection of cardiac events such as acute myocardial infarction or exercise induced myocardial ischemia caused by an increased heart rate or exertion. The system can also alert the patient with a less urgent alarm if a heart arrhythmia is detected. Using different algorithms, the cardiosaver can detect a change in the patient'"'"'s electrogram that is indicative of a cardiac event within five minutes after it occurs and then automatically warn the patient that the event is occurring. To provide this warning, the system includes an internal alarm sub-system (internal alarm means) within the cardiosaver and/or an external alarm system (external alarm means) which are activated after the ST segment of the electrogram exceeds a preset threshold.

Claims

1. A system for detecting a cardiac event in a human patient the system including:

at least two implanted electrodes for sensing electrical signals from the patient'"'"'s heart;

an implantable device for detecting a cardiac event, the device including;

means for periodically processing an electrogram segment of the electrical signals from the patient'"'"'s heart, the processing being designed to detect an abnormality in the electrogram segment, the abnormality being the electrogram segment being processed for a predetermined segment time period, the segment time period occurring after a sleep state time period during which sleep state time period the implantable device does not process the electrical signals from the patient'"'"'s heart; and

means to reduce the sleep state time period when an abnormality is detected and means to increase the sleep state time period when no abnormality is detected.

2. The system of claim 1 where the abnormality is a voltage of the ST segment whose magnitude exceeds a pre-set threshold.

3. The system of claim 2 where the abnormality is indicative of acute myocardial infarction.

4. The system of claim 2 where the abnormality is indicative of exercise induced ischemia.

5. The system of claim 1 where the abnormality is an excessive ST shift.

6. The system of claim 1 where the abnormality is indicative of an arrhythmia.

7. The system of claim 6 where the arrhythmia is selected from the group consisting of tachycardia, bradycardia, unsteady heart rate, bigeminal rhythm, premature ventricular contractions, premature atrial contractions and atrial fibrillation.

8. The system of claim 1 where at least one of the electrodes is located within the heart.

9. The system of claim 8 where the electrode located within the heart is located within the right ventricle.

10. The system of claim 1 where at least one electrode is located subcutaneously.

11. The system of claim 1 where the sleep state time period is increased to a maximum sleep state time period if no abnormality is detected.

12. The system of claim 1 where the sleep state time period is reduced to minimum sleep state time period if an abnormality is detected.

13. The system of claim 1 where the sleep state time period is reduced to less than 60 seconds when an abnormality is detected.

14. The system of claim 1 where the sleep state time period is increased to a maximum sleep time period if two or more successive electrogram segments have no detected abnormality.

15. The system of claim 1 where the criteria for detecting an abnormality in an electrogram segment differs from the criteria to detect a cardiac event.

16. A system for detecting a cardiac event in a human patient the system including:

at least two implanted electrodes for sensing the electrogram signal from the patient'"'"'s heart;

an implanted device designed to store the electrogram signal from the patient'"'"'s heart, the implanted device being further designed to detect an ischemic event when the magnitude of a voltage change of the ST segment of the electrogram signal exceeds a detection threshold; and

means to process the stored electrogram signal to calculate the detection threshold.

17. The system of claim 16 further including a programmer, the programmer providing the means to process the stored electrogram signal to calculate the detection threshold.

18. The system of claim 17 where the detection threshold is set to be the mean value of the ST segment voltage plus a multiple of the standard deviation of the ST segment voltage for all the stored electrograms beats.

19. The system of claim 16 where the detection threshold is calculated for each of at least two different heart rate ranges.

20. The system of claim 16 further including patient alerting means.

21. The system of claim 20 where the patient alerting means includes at least two types of alarm signals.

22. The system of claim 21 where the patient alerting means is provided by the implanted device.

23. The system of claim 22 where the patient alerting means is provided by an external alarm system.

24. The system of claim 16 where the ischemic event is an acute myocardial infarction.

25. The system of claim 24 where the ischemic event is ST elevation acute myocardial infarction.

26. The system of claim 24 where the ischemic event is non-ST elevation acute myocardial infarction.

27. The system of claim 16 where the ischemic event is an ST shift at an elevated heart rate.

28. The system of claim 16 where the ischemic event is ST depression at an elevated heart rate.

29. A method for setting the thresholds for detecting excessive shift in the voltage of the ST segment of a patient'"'"'s electrogram, the method including the steps:

(a) implanting a cardiosaver device having the capability to sense and store electrogram signals from the patient'"'"'s heart;

(b) causing the patient'"'"'s heart to have at least two different heart rates where a first heart rate is a lower rate compared to a second heart rate which is a higher heart rate;

(c) measuring the patient'"'"'s ST segment voltage at each of the at least two different heart rates;

(d) programming the detection thresholds for excessive shift in the voltage of the ST segment of the patient'"'"'s electrogram based on the electrogram data processed for the at least two different heart rate ranges.

30. The method of claim 29 where the means for causing the patient'"'"'s heart rate to increase to the second, higher heart rate is a stress test.

31. The method of claim 30 where the stress test is an exercise stress test.

32. The method of claim 30 where the stress test is a drug induced stress test where medications are used to increase the patient'"'"'s heart rate.

33. The method of claim 29 where the means for causing the patient'"'"'s heart rate to increase to the second, higher heart rate is to have the patient go about his normal daily activities and to record electrogram data during a period of increased physical activity which results in the second, higher heart rate.

34. A system for identifying an ischemic event in a human patient including:

at least two electrodes implanted in the patient for obtaining an electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram;

an implanted cardiosaver including;

(a) analog-to-digital converter circuitry for digitizing the electrogram to produce a multiplicity of electrogram segments, each having a time period of least 1 second duration;

(b) memory means designed to store a baseline electrogram segment at a first predetermined time;

(c) memory means designed to store a recently collected electrogram segment at a second time that is later than the first predetermined time;

(d) processor means coupled to said memory means for comparing the ST segment voltage of at least one beat of the recently collected electrogram segment at the second time with the average ST segment voltage of at least two beats of the baseline electrogram segment stored in the memory means at the first predetermined time; and

,

(e) means for identifying that the ischemic event has occurred when change in the ST segment voltage of the at least one beat of the recently collected electrogram segment as compared to the average ST segment voltage of the at least two beats of the baseline electrogram segment exceeds a detection threshold, the detection threshold being a preset percentage of the average signal amplitude of the at least two beats of the baseline electrogram segment.

35. The system of claim 34 where the average signal amplitude of the at least two beats of the baseline electrogram segment is the R wave peak voltage minus the average PQ segment voltage averaged over the at least two beats of the baseline electrogram.

36. The system of claim 34 where the average signal amplitude of the at least two beats of the baseline electrogram segment is the average peak-to-peak, R-to-S, signal amplitude of the at least two beats of the baseline electrogram.

37. The system of claim 34 where the average signal amplitude of the at least two beats of the baseline electrogram segment is the difference between the average PQ segment voltage and the peak S wave voltage averaged over the at least two beats of the baseline electrogram segment.

38. The system of claim 34 where the average signal amplitude of the at least two beats of the baseline electrogram segment is the larger of the R wave to PQ segment voltage difference or the PQ segment to S wave voltage difference.

39. A system for detecting a cardiac event in a human patient, the system including:

at least two electrodes implanted in the patient for obtaining the electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram;

an implanted cardiosaver having patient alerting means, the cardiosaver designed to detect a cardiac event by processing the electrical signal from the patient'"'"'s heart, the cardiosaver designed to categorize detected cardiac events into at least two different levels of severity;

40. The system of claim 39 further including:

a remote diagnostic center designed to receive data messages and to send and receive voice telephone calls, the remote diagnostic center also designed to prioritize calls based on the level of severity of the detected cardiac event; and

an external alarm transceiver having two-way data communications with the cardiosaver, the two-way data communications including the ability of the external alarm transceiver to receive notification of a cardiac event detected by the cardiosaver, the notification including the level of severity of the cardiac event, the external alarm transceiver also having the capability for data communication with the remote diagnostic center, the data communication including data messages indicating the level of severity of the detected cardiac event.

41. The system of claim 39 where there are exactly two levels of severity for detected cardiac events.

42. The system of claim 39 where one level of severity is an EMERGENCY ALARM indicating that the patient should seek immediate medical attention.

43. The system of claim 39 where one level of severity is a SEE DOCTOR ALERT indicating that the patient should schedule an appointment with a medical practitioner as soon as convenient.

44. A system for detecting a cardiac event in a human patient, the system including:

at least two skin surface electrodes for obtaining the electrical signal from the patient'"'"'s heart, the electrical signal being an electrocardiogram;

an externally located cardiosaver having patient alerting means, the cardiosaver designed to detect a cardiac event by processing the electrical signal from the patient'"'"'s heart, the cardiosaver designed to categorize detected cardiac events into at least two levels of severity.

45. The system of claim 44 further including:

a remote diagnostic center designed to receive data messages and to send and receive voice telephone calls, the remote diagnostic center also designed to prioritize calls based on the level of severity of the detected cardiac event; and

an external alarm transceiver having two-way data communications with the cardiosaver, the two-way data communications including the ability of the external alarm transceiver to receive notification of a cardiac event detected by the cardiosaver, the notification including the level of severity of the cardiac event, the external alarm transceiver also having the capability for data communication with the remote diagnostic center, the data communication including data messages indicating the level of severity of the detected cardiac event.

46. The system of claim 45 where the external alarm transceiver is incorporated into the external cardiosaver.

47. The system of claim 44 where there are exactly two levels of severity for detected cardiac events.

48. The system of claim 44 where one level of severity is an EMERGENCY ALARM indicating that the patient should seek immediate medical attention.

49. The system of claim 44 where one level of severity is a SEE DOCTOR ALERT indicating that the patient should schedule an appointment with a medical practitioner as soon as convenient.

50. An implantable system for detecting cardiac events in a human patient, the system including:

at least two electrodes implanted in the patient for obtaining the electrical signal from the patient'"'"'s heart, the electrical signal being an electrogram;

patient alerting means; and

a primary battery and a secondary battery where the primary battery has a larger capacity than the secondary battery.

51. The system of claim 50 where the secondary battery operates at a higher voltage than the primary battery.

52. The system of claim 50 where the secondary battery can provide a higher maximum current than the primary battery.

53. The system of claim 50 where the secondary battery is rechargeable.

54. The system of claim 53 where the secondary battery is recharged by the primary battery through a charging circuit.

55. The system of claim 50 where the secondary battery provides power to the patient alerting means.

56. The system of claim 50 further including a telemetry sub-system where the secondary battery provides power to the telemetry sub-system.

57. The system of claim 50 where the primary battery has a lower self discharge rate than the secondary battery.

58. The system of claim 50 further including pacemaker circuitry.

59. The system of claim 50 further including cardiac defibrillator circuitry.

60. The system of claim 50 where the cardiac events detected by the system include acute myocardial infarction.

61. The system of claim 50 where the cardiac events detected by the system include ischemia at an elevated heart rate.

62. The system of claim 50 where the cardiac events detected by the system include low heart rate.

63. The system of claim 50 where the cardiac events detected by the system include excessively high heart rate.

64. The system of claim 50 where the cardiac events detected by the system include arrhythmias.

65. A system for detecting cardiac events in a human patient, the system including:

at least two electrodes for obtaining an electrical signal from the patient'"'"'s heart;

processor means designed to detect at least one type of cardiac event by processing the electrical signal from the patient'"'"'s heart;

patient alerting means that are activated following the detection of a cardiac event by the processor means, the patient alerting means providing an alarm signal to the patient for a first period of time which is an initial alarm on-period, the initial alarm on-period being followed by an alarm off-period of time during which time the alarm signal is turned off, the patient alerting means also providing a reminder alarm signal to the patient for a reminder alarm on-period of time following the alarm off-period of time.

66. The system of claim 65 where reminder alarm signal which lasts for the reminder alarm on-period is repeated periodically, the time between the periodic reminder alarm signals being an additional alarm off-period.

67. The system of claim 66 where the periodic reminder alarm on-period is greater than 15 minutes.

68. The system of claim 66 where the periodic reminder alarm on-period is less than 5 hours.

69. The system of claim 66 where the alarm off-period after the initial alarm on-period has a different time duration as compared to the time duration of the alarm off-period after a periodic reminder alarm on-period.

70. The system of claim 65 where the alarm off-period of time is at least twice as long as the alarm on-period.

71. The system of claim 65 further including an external alarm system having an alarm disable button.

72. The system of claim 65 where the alarm on-period is less than 10 minutes.

73. The system of claim 65 where at least a portion of the system is implanted in the human patient.

74. The system of claim 65 where the cardiac events detected by the system include acute myocardial infarction.

75. The system of claim 65 where the cardiac events detected by the system include ischemia at an elevated heart rate.

76. The system of claim 65 where the cardiac events detected by the system include low heart rate.

77. The system of claim 65 where the cardiac events detected by the system include excessively high heart rate.

78. The system of claim 65 where the cardiac events detected by the system include arrhythmias.

79. A system for detecting cardiac events in a human patient, the system including:

at least two electrodes for obtaining the electrical signal from the patient'"'"'s heart;

patient activity monitoring means including an accelerometer designed to identify when the patient is active; and

processor means designed to process the electrical signal from the patient'"'"'s heart to detect at least one type of cardiac event that occurs when the patient activity monitoring means indicates that the patient is active.

80. The system of claim 79 where the entire system is implanted into the patient.

81. The system of claim 79 further including patient alerting means that are activated following the detection of a cardiac event by the processor means.

82. The system of claim 79 where the cardiac event detected is exercise induced ischemia.

83. The system of claim 79 where the cardiac event is an arrhythmia.

84. The system of claim 79 further including means to record the electrical signal from the patient'"'"'s heart.

85. A system for displaying segments of an electrogram of a patient in whom a cardiac event has previously been detected, the system including at least two electrodes implanted in the patient for obtaining the electrical signal from the patient'"'"'s heart which electrical signal is the electrogram, the system also including an implanted cardiosaver and an external alarm system;

the implanted cardiosaver including;

(a) analog-to-digital converter circuitry for digitizing the electrogram to produce a baseline electrogram segment at a first predetermined time and a recently collected electrogram segment at a second predetermined time that is later than the first predetermined time;

each electrogram segment having a time duration that is at least 1 second;

(b) memory means designed to store the baseline electrogram segment and the recently collected electrogram segment

(c) processor means coupled to said memory means to detect a cardiac event by comparing the recently collected electrogram segment with the baseline electrogram segment, and

the external alarm system having two-way wireless communication to and from the implanted cardiosaver, the external alarm system also having an external alarm signal that is actuated when the implanted device detects the cardiac event, the external alarm system also having means to display the baseline and recently collected electrogram segments whose comparison resulted in the detection of the cardiac event.

86. A system for detecting ischemia in a human patient, the system including

at least two electrodes implanted in the patient for obtaining the electrical signal from the patient'"'"'s heart;

and

an implanted cardiosaver designed to process the electrical signal to measure the ST segment voltage and to identify R waves, the processing of the electrical signal designed to identify the R waves including a separate high pass filter having greater low frequency attenuation as compared with the high pass filter of the electrical signal used for measurement the ST segment voltage.

87. The system of claim 86 further including implantable cardiac defibrillator circuitry.

88. The system of claim 86 further including pacemaker circuitry.