Method for discriminating between ventricular and supraventricular arrhythmias

• US 20040254613A1
• Filed: 05/27/2004
• Published: 12/16/2004
• Est. Priority Date: 11/21/2001
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Ostroff, Alan H., Bardy, Gust H., Warren, Jay A.
• Granted Patent: US 7,330,757 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock

Abstract

The present invention is directed toward a detection architecture for use in implantable cardiac rhythm devices. The detection architecture of the present invention provides methods and devices for discriminating between arrhythmias. Moreover, by exploiting the enhanced specificity in the origin of the identified arrhythmia, the detection architecture can better discriminate between rhythms appropriate for device therapy and those that are not.

Claims

1. A method for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the method comprising:

receiving a cardiac complex using implanted electrodes;

obtaining a cardiac rate from the cardiac signal;

determining whether the cardiac rate;

exceeds a first threshold but does not exceed a second threshold;

or;

exceeds the second threshold;

and;

if the cardiac rate exceeds the second threshold, directing therapy to the heart;

or

if the cardiac rate exceeds the first threshold but does not exceed the second threshold, directing further analysis of the cardiac complex to determine whether therapy is indicated.

2. The method of claim 1, wherein the further analysis includes comparison of the cardiac complex to a template.

3. The method of claim 2, wherein the comparison includes a correlation waveform analysis.

4. The method of claim 2, wherein the template is formed by averaging a number of recent cardiac complexes.

5. The method of claim 2, wherein the template is a static template.

6. The method of claim 1, wherein the further analysis includes determination of a correlation between the cardiac complex and a template and comparison of the correlation for the cardiac complex to correlations for a number of recent cardiac complexes.

7. The method of claim 1, wherein the further analysis includes a QRS complex width measurement.

8. The method of claim 1, wherein the further analysis includes a determination of whether the cardiac rate accelerated significantly.

9. The method of claim 1, wherein the further analysis includes a determination of the interval rate stability between cardiac complexes.

10. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein the lead electrode assembly is coupled to the canister and the operational circuitry is configured to perform the method of claim 1.

11. A method of cardiac signal analysis comprising:

receiving a cardiac complex from an implanted electrode pair;

analyzing the cardiac complex to determine whether a patient is likely experiencing an arrhythmia; and

comparing a portion of the cardiac complex to a template by performing a mathematical calculation between the cardiac complex and the template;

wherein the comparing step is performed only if it is determined that the patient is likely experiencing an arrhythmia.

12. The method of claim 11, wherein the step of analyzing the cardiac complex to determine whether an arrhythmia is likely includes estimating a cardiac rate and comparing the cardiac rate to a threshold value.

13. The method of claim 11, further comprising updating the template using data from the cardiac complex.

14. The method of claim 11, wherein the mathematical calculation is a correlation waveform analysis.

15. The method of claim 11, wherein the step of receiving a cardiac complex from an implanted electrode pair includes:

receiving a first electrical signal from a first combination of electrodes;

receiving a second electrical signal from a second combination of electrodes;

comparing the first electrical signal to the second electrical signal to determine which electrical signal is more amenable to data analysis; and

using the electrical signal that is more amenable to data analysis as the cardiac complex for comparison with the template.

16. The method of claim 11, further comprising selecting a template for use in the comparison step in response to an observed event occurring prior to the receipt of the cardiac complex.

17. The method of claim 11, wherein the arrhythmia is a monomorphic ventricular tachycardia, a polymorphic ventricular tachycardia, or ventricular fibrillation.

18. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein the lead electrode assembly is coupled to the canister and the operational circuitry is configured to perform the method of claim 11.

19. A method of discriminating between cardiac rhythms comprising:

receiving a first electric signal between a first electrode pair;

analyzing the first electric signal to calculate a cardiac rate for a patient;

comparing the cardiac rate to first and second thresholds; and

;

selecting one of the following options;

a) if the cardiac rate is below the first threshold, advancing to a next iteration of the method by receiving a second electric signal between the first electrode pair, the second electric signal coming temporally after the first electric signal;

or

b) if the cardiac rate is above the second threshold, determining that therapy should be delivered to the patient;

or

c) advancing into a subroutine for enhanced analysis;

wherein the subroutine for enhanced analysis includes comparing a portion of the first electric signal to a template.

20. A method of discriminating between cardiac rhythms comprising:

receiving a cardiac complex;

determining that an arrhythmia is likely;

analyzing the cardiac complex using a first metric to determine whether a malignant arrhythmia is occurring and, if so, determining that therapy is indicated;

if not, then analyzing the cardiac complex using a second metric to determine whether a malignant arrhythmia is occurring and, if so, determining that therapy is indicated.

21. The method of claim 20, wherein both the first metric and the second metric are calculated using the cardiac complex, wherein the cardiac complex is captured using two electrodes.

22. A method of signal analysis comprising:

receiving a first cardiac complex from a first implanted electrode pair disposed to capture electrical information related to ventricular activity along a first sensing vector;

receiving a second cardiac complex from a second implanted electrode pair disposed to capture electrical information related to ventricular activity along a second sensing vector;

generating a first metric related to the first cardiac complex;

generating a second metric related to the second cardiac complex; and

comparing the first metric to the second metric to determine whether a ventricular originating arrhythmia is occurring.

23. The method of claim 22, wherein the first cardiac complex and the second cardiac complex are substantially temporally related.

24. The method of claim 22, wherein the first sensing vector and the second sensing vector are placed at an angle of greater than 45 degrees with respect to one another.

25. The method of claim 22, wherein the first electrode pair includes first and second electrodes, and the second electrode pair includes the second electrode and a third electrode.

26. The method of claim 22, wherein the first electrode pair and the second electrode pair are disposed to capture far-field signals for atrial and ventricular events.

27. A method of monitoring cardiac function as part of operation of an implantable cardiac treatment device comprising:

receiving a cardiac complex from first and second implanted electrodes;

comparing the cardiac complex to a template to determine whether therapy is indicated;

wherein the template is a dynamically changing template formed using a number of recently sensed cardiac complexes.

28. The method of claim 27, wherein the step of comparing the cardiac signal to a template includes performing a correlation waveform analysis to generate a correlation coefficient, and comparing the correlation coefficient to a threshold.

29. A method of discriminating between cardiac rhythms comprising:

receiving a cardiac complex from implanted electrodes;

obtaining a beat rate and determining whether an arrhythmia is likely; and

, if so;

(a) analyzing the cardiac complex using a first mathematical determination to yield a first result, and comparing the first result to a first threshold to yield a first Boolean value;

(b) analyzing the cardiac complex using a second mathematical determination to yield a second result, and comparing the second result to a second threshold to yield a second Boolean value;

(c) performing a first Boolean logic function using at least one of the first Boolean value and the second Boolean value to determine whether therapy is needed.

30. The method of claim 29, wherein:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is a variability of correlations of several recent cardiac complexes compared to a dynamic template;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

31. The method of claim 29, wherein:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is a variability of correlations of several recent cardiac complexes compared to a static template;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

32. The method of claim 29, wherein:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is an analysis of an interval rate stability for a number of recent cardiac complexes;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

33. The method of claim 29, wherein:

the first mathematical determination is a variability of correlations of several recent cardiac complexes compared to a dynamic template;

the second mathematical determination is an analysis of the width of the cardiac complex;

the Boolean logic function observes whether the first Boolean value is one and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

34. The method of claim 29, wherein:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is a variability of correlations of several recent cardiac complexes compared to a static template;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is zero; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

35. The method of claim 29, further comprising:

analyzing the cardiac complex using a third mathematical determination to yield a third result, and comparing the third result to a third threshold to yield a third Boolean value;

performing a second Boolean logic function using at least one of the first, second, and/or third Boolean values to determine whether therapy is needed.

36. A method of discriminating between cardiac rhythms comprising:

receiving a cardiac complex from implanted electrodes;

obtaining a cardiac rate and determining whether an arrhythmia is likely; and

, if so;

(a) analyzing the cardiac complex using a first metric to determine whether a malignant arrhythmia is occurring and, if so, determining that therapy is indicated;

(b) if not, then analyzing the cardiac complex using a second metric to determine whether a malignant arrhythmia is occurring and, if so, determining that treatment is indicated.

37. The method of claim 36, wherein the first metric is a comparison of the cardiac complex width to a threshold wherein, if the width is greater than the threshold value it is determined that a malignant arrhythmia is occurring.

38. The method of claim 37, wherein the second metric is a correlation between the cardiac complex and a template, wherein if the correlation is low then it is determined that a malignant arrhythmia is occurring.

39. The method of claim 38, wherein the template is static.

40. The method of claim 38, wherein the template is dynamic.

41. The method of claim 37, wherein the second metric is a comparison of the correlation of the cardiac complex and a template to the correlation of a number of recent cardiac complexes to the template to yield a variability, wherein if the variability is high then it is determined that a malignant arrhythmia is occurring.

42. The method of claim 41, wherein the template is static.

43. The method of claim 41, wherein the template is dynamic.

44. The method of claim 36, wherein the first metric is a comparison of a threshold to a correlation between the cardiac complex and a template wherein, if the correlation is low, then it is determined that a malignant arrhythmia is occurring.

45. The method of claim 44, wherein the template is static.

46. The method of claim 45, wherein the second metric is a comparison of a threshold to a correlation between the cardiac complex and a dynamic template wherein, if the correlation is low, then it is determined that a malignant arrhythmia is occurring.

47. The method of claim 44, wherein the template is dynamic.

48. The method of claim 44, wherein the second metric is a determination of the variability of the correlation between the cardiac complex and the template to correlations between recent cardiac complexes and the template wherein, if the variability is high, then it is determined that a malignant arrhythmia is occurring.

49. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a cardiac complex using the lead electrode assembly;

obtaining a cardiac rate from the cardiac signal;

determining whether the cardiac rate;

exceeds a first threshold but does not exceed a second threshold;

or;

exceeds the second threshold; and

;

if the cardiac rate exceeds the second threshold, directing therapy to the heart;

or

if the cardiac rate exceeds the first threshold but does not exceed the second threshold, directing further analysis of the cardiac complex to determine whether therapy is indicated.

50. The implantable cardioverter/defibrillator claim 49, wherein the operational circuitry is configured such that the further analysis includes comparison of the cardiac complex to a template.

51. The implantable cardioverter/defibrillator of claim 50, wherein the operational circuitry is configured such that the comparison includes a correlation waveform analysis.

52. The implantable cardioverter/defibrillator of claim 50, wherein the operational circuitry is configured such that the template is formed by averaging a number of recent cardiac complexes.

53. The implantable cardioverter/defibrillator of claim 50, wherein the operational circuitry is configured such that the template is a static template.

54. The implantable cardioverter/defibrillator of claim 49, wherein the operational circuitry is configured such that the further analysis includes:

determination of a correlation between the cardiac complex and a template; and

comparison of the correlation for the cardiac complex and the template to correlations between a number of recent cardiac complexes and the template.

55. The implantable cardioverter/defibrillator of claim 49, wherein the operational circuitry is configured such that the further analysis includes a QRS complex width measurement.

56. The implantable cardioverter/defibrillator of claim 49, wherein the operational circuitry is configured such that the further analysis includes a determination of whether the cardiac rate accelerated significantly.

57. The implantable cardioverter/defibrillator of claim 49, wherein the operational circuitry is configured such that the further analysis includes a determination of the interval rate stability between cardiac complexes.

58. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a cardiac complex using at least one electrode on the lead electrode assembly;

analyzing the cardiac complex to determine whether a patient is likely experiencing an arrhythmia; and

comparing a portion of the cardiac complex to a template by performing a mathematical calculation between the cardiac complex and the template;

wherein the comparing step is performed only if it is determined that the patient is likely experiencing an arrhythmia.

59. The implantable cardioverter/defibrillator of claim 58, wherein the operational circuitry is configured such that the step of analyzing the cardiac complex to determine whether an arrhythmia is likely includes estimating a cardiac rate and comparing the cardiac rate to a threshold value.

60. The implantable cardioverter/defibrillator of claim 58, wherein the operational circuitry is configured to further perform the step of updating the template using data from the cardiac complex.

61. The implantable cardioverter/defibrillator of claim 58, wherein the operational circuitry is configured such that the mathematical calculation is a correlation waveform analysis.

62. The implantable cardioverter/defibrillator of claim 58, wherein the operational circuitry is configured such that the step of receiving a cardiac complex from an implanted electrode pair includes:

receiving a first electrical signal from a first combination of electrodes;

receiving a second electrical signal from a second combination of electrodes;

comparing the first electrical signal to the second electrical signal to determine which electrical signal is more amenable to data analysis; and

using the electrical signal that is more amenable to data analysis as the cardiac complex for comparison with the template.

63. The implantable cardioverter/defibrillator of claim 58, wherein the operational circuitry is configured to further perform the step of selecting a template for use in the comparison step in response to an observed event occurring prior to the receipt of the cardiac complex.

64. The implantable cardioverter/defibrillator of claim 58, wherein the operational circuitry is configured to determine whether the arrhythmia is one of the group of a monomorphic ventricular tachycardia, a polymorphic ventricular tachycardia, or ventricular fibrillation.

65. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a first electric signal between a first electrode pair including an electrode on the lead electrode assembly;

analyzing the first electric signal to calculate a cardiac rate for a patient;

comparing the cardiac rate to first and second thresholds; and

;

selecting one of the following options;

a) if the cardiac rate is below the first threshold, advancing to a next iteration of the method by receiving a second electric signal between the first electrode pair, the second electric signal coming temporally after the first electric signal;

or

b) if the cardiac rate is above the second threshold, determining that therapy should be delivered to the patient;

or

c) advancing into a subroutine for enhanced analysis;

wherein the subroutine for enhanced analysis includes comparing a portion of the first electric signal to a template.

66. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a cardiac complex;

determining that an arrhythmia is likely;

analyzing the cardiac complex using a first metric to determine whether a malignant arrhythmia is occurring and, if so, determining that therapy is indicated;

if not, then analyzing the cardiac complex using a second metric to determine whether a malignant arrhythmia is occurring and, if so, determining that therapy is indicated.

67. The implantable cardioverter/defibrillator of claim 66, wherein the operational circuitry is configured such that both the first metric and the second metric are calculated using the cardiac complex, wherein the cardiac complex is captured using the same two electrodes.

68. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a first cardiac complex from a first implanted electrode pair disposed to capture electrical information related to ventricular activity along a first sensing vector;

receiving a second cardiac complex from a second implanted electrode pair disposed to capture electrical information related to ventricular activity along a second sensing vector;

generating a first metric related to the first cardiac complex;

generating a second metric related to the second cardiac complex; and

comparing the first metric to the second metric to determine whether a ventricular originating arrhythmia is occurring.

69. The implantable cardioverter/defibrillator of claim 68, wherein the operational circuitry is configured to receive the first and second cardiac complexes such that the first cardiac complex and the second cardiac complex are substantially temporally related.

70. The implantable cardioverter/defibrillator of claim 68, wherein the lead electrode assembly is configured to enable the first sensing vector and the second sensing vector to be placed at an angle of greater than 45 degrees with respect to one another.

71. The implantable cardioverter/defibrillator of claim 68, wherein the operational circuitry is configured to define the first electrode pair as including first and second electrodes, and the second electrode pair as including the second electrode and a third electrode.

72. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a cardiac complex from first and second implanted electrodes;

comparing the cardiac complex to a template to determine whether therapy is indicated;

wherein the template is a dynamically changing template formed using a number of recently sensed cardiac complexes.

73. The implantable cardioverter/defibrillator of claim 72, wherein operational circuitry is configured such that the step of comparing the cardiac complex to a template includes performing a correlation waveform analysis to generate a correlation coefficient, and comparing the correlation coefficient to a threshold.

74. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a cardiac complex from implanted electrodes;

obtaining a beat rate and determining whether an arrhythmia is likely; and

, if so;

(a) analyzing the cardiac complex using a first mathematical determination to yield a first result, and comparing the first result to a first threshold to yield a first Boolean value;

(b) analyzing the cardiac complex using a second mathematical determination to yield a second result, and comparing the second result to a second threshold to yield a second Boolean value;

(c) performing a first Boolean logic function using at least one of the first Boolean value and the second Boolean value to determine whether therapy is needed.

75. The implantable cardioverter/defibrillator of claim 74, wherein the operational circuitry is configured such that:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is a variability of correlations of several recent cardiac complexes compared to a dynamic template;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

76. The implantable cardioverter/defibrillator of claim 74, wherein the operation circuitry is configured such that:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is a variability of correlations of several recent cardiac complexes compared to a static template;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

77. The implantable cardioverter/defibrillator of claim 74, wherein the operational circuitry is configured such that:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is an analysis of an interval rate stability for a number of recent cardiac complexes;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

78. The implantable cardioverter/defibrillator of claim 74, wherein the operational circuitry is configured such that:

the first mathematical determination is a variability of correlations of several recent cardiac complexes compared to a dynamic template;

the second mathematical determination is an analysis of the width of the cardiac complex;

the Boolean logic function observes whether the first Boolean value is one and the second Boolean value is one; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

79. The implantable cardioverter/defibrillator of claim 74, wherein the operational circuitry is configured such that:

the first mathematical determination is a correlation between a static template and the cardiac complex;

the second mathematical determination is a variability of correlations of several recent cardiac complexes compared to a static template;

the Boolean logic function observes whether the first Boolean value is zero and the second Boolean value is zero; and

if the Boolean logic function yields a one, it is determined that therapy is needed.

80. The implantable cardioverter/defibrillator of claim 74, wherein the operational circuitry is configured to perform the further steps of:

analyzing the cardiac complex using a third mathematical determination to yield a third result, and comparing the third result to a third threshold to yield a third Boolean value;

performing a second Boolean logic function using at least one of the first, second, and/or third Boolean values to determine whether therapy is needed.

81. An implantable cardioverter/defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister; and

the operational circuitry is configured to perform steps for discriminating between cardiac rhythms of a patient'"'"'s heart which are appropriate for therapy, the steps including;

receiving a cardiac complex from implanted electrodes;

obtaining a beat rate and determining whether an arrhythmia is likely; and

, if so, analyzing the cardiac complex using a first metric to determine whether a malignant arrhythmia is occurring and;

if so, determining that therapy is indicated;

if not, analyzing the cardiac complex using a second metric to determine whether a malignant arrhythmia is occurring and, if so, determining that treatment is indicated.

82. The implantable cardioverter/defibrillator of claim 81, wherein the operational circuitry is configured such that the first metric is a comparison of the cardiac complex width to a threshold wherein, if the width is greater than the threshold value it is determined that a malignant arrhythmia is occurring.

83. The implantable cardioverter/defibrillator of claim 82, wherein the operational circuitry is configured such that the second metric is a correlation between the cardiac complex and a template, wherein if the correlation is low then it is determined that a malignant arrhythmia is occurring.

84. The implantable cardioverter/defibrillator of claim 83, wherein the operational circuitry is configured such that the template is static.

85. The implantable cardioverter/defibrillator of claim 83, wherein the operational circuitry is configured such that the template is dynamic.

86. The implantable cardioverter/defibrillator of claim 82, wherein the operational circuitry is configured such that the second metric is a comparison of the correlation of the cardiac complex and a template to the correlation of a number of recent cardiac complexes to the template to yield a variability, wherein if the variability is high then it is determined that a malignant arrhythmia is occurring.

87. The implantable cardioverter/defibrillator of claim 86, wherein the operational circuitry is configured such that the template is static.

88. The implantable cardioverter/defibrillator of claim 86, wherein the operational circuitry is configured such that the template is dynamic.

89. The implantable cardioverter/defibrillator of claim 81, wherein the operational circuitry is configured such that the first metric is a comparison of a threshold to a correlation between the cardiac complex and a template wherein, if the correlation is low, then it is determined that a malignant arrhythmia is occurring.

90. The implantable cardioverter/defibrillator of claim 89, wherein the operational circuitry is configured such that the template is static.

91. The implantable cardioverter/defibrillator of claim 90, wherein the operational circuitry is configured such that the second metric is a comparison of a threshold to a correlation between the cardiac complex and a dynamic template wherein, if the correlation is low, then it is determined that a malignant arrhythmia is occurring.

92. The implantable cardioverter/defibrillator of claim 89, wherein the operational circuitry is configured such that the template is dynamic.

93. The implantable cardioverter/defibrillator of claim 89, wherein the operational circuitry is configured such that the second metric is a determination of the variability of the correlation between the cardiac complex and the template to correlations between recent cardiac complexes and the template wherein, if the variability is high, then it is determined that a malignant arrhythmia is occurring.