Shock timing technology

• US 20080033494A1
• Filed: 05/18/2007
• Published: 02/07/2008
• Est. Priority Date: 04/15/2002
• Status: Active Grant

• Current Assignee: Imperception, Inc.
• Original Assignee: Imperception, Inc.
• Inventors: Swerdlow, Charles
• Granted Patent: US 8,150,510 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• 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 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61N 1/3943 for threshold determination
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock

Abstract

A method for accurately determining timing points for T-wave shocks is particularly useful in a system for determining a cardiac shock strength in an implantable cardioverter defibrillator (ICD. The method involves acquiring at least one first signal, acquiring at least a second signal, comparing the signals, and selecting a timing point with the T-wave of the signal. The first and second signals may be two different aspects of a single electrogram, first and second electrograms, or a combination thereof. Comparison preferably involves signal alignment and qualitative analysis.

Claims

1. A method for accurately determining timing points for T-wave shocks, comprising the steps of:

(a) deriving a first signal from a cardiac electrical signal, wherein the first derived signal relates to a change with respect to time of the cardiac electrical signal (b) deriving at least a second signal from a cardiac electrical signal, wherein the at least second derived signal relates to a change with respect to time of its respective cardiac electrical signal, and (c) selecting one or more timing points within a T wave of at least one of the derived signals.

2. The method of claim 1, further comprising the step, implemented after the steps of deriving the first and at least one second derived signals and before the selecting step, of comparing the first derived signal and at least one second derived signal.

3. The method of claim 2 in which the comparing step is applied to determine how to select the timing point within the T-wave.

4. The method of claim 2 wherein the comparing step includes quantitative analysis.

5. The method of claim 2 in which a timing point is selected within the T wave of each of the at least two derived signals and an analytical step is applied to determine a final, composite timing point based on the individual timing points determined from the at least two derived signals.

6. The method of claim 2, wherein the first and at least one second derived signals are different changes with respect to time from a single cardiac electrical signal.

7. The method of claim 2, wherein the first and at least one second derived signals are the same change with respect to time of a first cardiac electrical signal and at least one second, different, cardiac electrical signal.

8. The method of claim 2, wherein the first and at least one second derived signals are different changes with respect to time of a first cardiac electrical signal and at least one second, different, cardiac electrical signal.

9. The method of claim 2, wherein comparison includes signal alignment.

10. The method of claim 1 in which the one or more timing points are computed utilizing one, some, or all points in time in the T wave of the derived signal.

11. The method according to claim 10, wherein the one or more timing points are computed via a weighted (arithmetic, geometric, or harmonic) average using the parameter values relating to the timing points.

12. The method according to claim 10 wherein the one or more timing points are computed via a weighted ratio or weighted log-ratio using parameter values relating to the timing points.

13. The method of claim 10 in which a single parameter value is selected relating to a set of one or more timing points based on methods to analyze the set of timing points

14. The method according to claim 13, wherein the single parameter value is selected by sorting the one or more timing point values and then selecting one of the timing points.

15. The method according to claim 14, wherein the single parameter value relates to the minimum, mean, median, mode, or maximum of the values of the timing points.

16. The method of claim 1, which is used in a system for determining a cardiac shock strength for an implantable cardioverter defibrillator (ICD).

17. The method of claim 1, wherein at least one timing point is an extreme absolute value of the change with respect to time, selected from the group consisting of a minimum absolute value (such as a zero point), a minimum value, and a maximum value.

18. The method of claim 1, wherein at least one change with respect to time is determined by a calculation selected from the group of calculations consisting of a finite difference, an ordinary derivative, a directional derivative, a gradient and a partial derivative, an implicit differential, a variance calculation, a bounded variation calculation, a radial displacement vector, and a tangent vector approximation.

19. The method of claim 17, wherein the extreme absolute value is calculated by a method selected from the group of calculation methods consisting of a finite difference, an ordinary derivative, a directional derivative, a gradient and a partial derivative, an implicit differential, a variance calculation, a bounded variation calculation, a radial displacement vector, and a tangent vector approximation.

20. The method of claim 1, wherein a change with respect to time is the first derivative of T wave amplitude with respect to time.

21. The method of claim 1, wherein a change with respect to time is the second derivative of T wave amplitude with respect to time.

22. The method of claim 1, wherein at least one of the changes with respect to time is the first derivative of T wave amplitude with respect to time and another of the changes with respect to time is the second derivative of T wave amplitude with respect to time.

23. The method of claim 1 in which T-wave shock times are selected in relation to the minimum of the absolute value (zero point) of the second derivative of the T wave with respect to time.

24. The method of claim 1, in which a level of signal quality is calculated for the first derived signal and at least one second derived signal, and the one or more timing points are selected in relation to the calculated values of signal quality.

25. The method of claim 24, in which the level of signal quality is calculated using a pre-determined period of time and using a time-domain-based signal method selected from the group consisting of a minimum, a mean, a median, mode, and a maximum.

26. The method of claim 24, in which the level of signal quality is calculated using a pre-determined range of frequency and using a frequency-domain-based signal method selected from the group consisting of a minimum, a mean, a median, and a maximum signal value.

27. The method of claim 24, in which the level of signal quality is calculated using a method selected from the group consisting of an average signal difference, a sum of an absolute value of a difference from a signal mean and a power of a signal subtracted from a signal mean, a signal to noise ratio, a coefficient of signal variation, a signal histogram, a signal frequency spectrum, a signal power spectrum, a time-domain convolution technique, and a time-domain correlation technique.

28. The method of claim 24 in which the timing point is selected based on the derived signal with the highest quality.

29. The method of claim 24, in which, if more than one derived signal has sufficient quality, the priority in which such signals are used to select the timing point within the T-wave is specified in advance by predetermined instructions.

30. The method of claim 24, in which, if more than one derived signal has sufficient quality, the timing point for the T-wave shock is selected from a mathematical combination of the intervals from a predetermined base timing point (prior to the T wave) to each of the timing points within the T-wave that can be determined with sufficient quality.

31. The method of claim 30, in which the mathematical combination is selected from the group consisting of an average, a weighted average, a median, and a mode.

32. The method of claim 30, in which two changes with respect to time of a cardiac electrical signal are sensed, the first change with respect to time being the first derivative of one cardiac electrical signal and the second change with respect to time being the second derivative of a different cardiac electrical signal.

33. The method of claim 24 in which the signal with the highest quality is determined from the set consisting of the base cardiac electrical signal and the one or more signals derived therefrom.

34. The method of claim 1, in which a first timing point during the T wave for the T-wave shock is selected in relation to the maximum of the first derivative of the T wave with respect to time of one cardiac electrical signal and the at least one second timing point during the T wave is selected in relation to the to the minimum of the absolute value of the second derivative of the T wave with respect to time of a second, different, cardiac electrical signal.

35. The method of claim 34 in which, if the extreme absolute value of the change with respect to time of one cardiac electrical signal occurs at more than one point in time, the timing point selected from one sensed cardiac electrical signal depends on the value of one or more other, different cardiac electrical signals, or of a change with respect to time of the one or more other cardiac electrical signals.

36. The method of claim 35, in which the first timing point during the T wave for the test-shock is selected in relation to the maximum of the first derivative of the T wave with respect to time of one cardiac electrical signal and the at least one second timing point during the T wave is selected in relation to the to the minimum of the absolute value of the second derivative of the T wave with respect to time of the same cardiac electrical signal.

37. The method of claim 36, in which the minimum of the absolute value of the second derivative of the T wave with respect to time is a zero point.

38. The method of claims 37, and in which the zero point of the second derivative of the T wave with respect to time of the second cardiac electrical signal occurs when the first derivative of the same second cardiac electrical signal is not zero.

39. The method according to claims 37 or 38 in which:

(A) the maximum of the first derivative with respect to time of one cardiac electrical signal is used to select the timing point within the T wave only if the second derivative of the same cardiac electrical signal at the same point is a local minimum value, and

(B) otherwise, the minimum absolute value of the second derivative with respect to time of a different cardiac electrical signal is used to select the timing point within the T wave.

40. The method of claim 1, in which the cardiac electrical signals are recorded from a fully implantable device.

41. The method of claims 1 in which the cardiac electrical signals are selected from a subset of cardiac electrical signals recorded from permanently implantable and non-implantable electrodes.

42. The method of claim 1 in which the cardiac electrical signals are selected from a subset of non-implantable electrodes and transmitted wirelessly to an ICD programmer.

43. The method of claim 1 in which the cardiac electrical signals are selected from a subset of non-implantable electrodes and transmitted wirelessly to an ICD generator.

44. The method of claim 1 in which the cardiac electrical signals are selected from a subset of cardiac electrical signals including but not limited to pacing, sensing, recording, and defibrillation electrodes.

45. The method of claims 1 in which the cardiac electrical signals are selected from a subset of cardiac electrical signals including but not limited to subcutaneous electrodes, epicardial electrodes, transvenous endocardial electrodes, and transvenous endovascular electrodes.

46. The method of claims 1 in which the cardiac electrical signals are selected from a subset of cardiac electrical signals including but not limited to a right ventricular pace-sense tip electrode, a right ventricular pace-sense ring electrode, a left ventricular pace-sense tip electrode, a left ventricular pace-sense ring electrode, a left atrial pace-sense tip electrode, a left atrial pace-sense ring electrode, a tip electrode placed in the coronary venous system, a ring electrode placed in the coronary venous system, a defibrillation electrode in the right ventricle, a defibrillation electrode in the left ventricle, a defibrillation electrode in the right atrium, a defibrillation electrode in the left atrium, an epicardial pace-sense electrode, an epicardial defibrillation electrode, a subcutaneous sensing electrode, a subcutaneous defibrillation electrode, a submuscular sensing electrode, a submuscular defibrillation electrode, a localized “

button”

electrode on the housing (“

can”

) of an ICD pulse generator, an electrode consisting of the entire housing (“

can”

) of the ICD pulse generator.

47. The method of claim 1 in which a number of T-wave shocks is determined by the quality of the cardiac electrical signal signals.

48. A method for determining an optimal programmed first-shock strength of a first therapeutic shock of an implanted cardioverter defibrillator relative to the upper limit of vulnerability, the implanted cardioverter defibrillator having at least one sensing electrode and at least one shocking electrode, comprising the steps of:

(a) setting an initial test-shock strength, four offset times, and a shock strength decrement;

(b) delivering a set of up to four test shocks with the implantable cardioverter defibrillator to the patient, each test shock member of the set of test shocks comprising the sub steps of;

(i) sensing a cardiac electrical signal from the patient;

(ii) detecting at least one predetermined base timing point prior to the T wave of the cardiac electrical signal;

(iii) differentiating the cardiac electrical signal with respect to time;

(iv) detecting at least one minimum of the absolute value (zero point) of the second derivative of the T wave with respect to time that occurs when the first derivative of T wave with respect to time is not zero.

(v) measuring at least one base time interval from the at least one base timing point to the at least one minimum of the absolute value (zero point) of the second derivative of the T wave with respect to time that occurs when the first derivative of T wave with respect to time is not zero,

(vi) delivering a test shock to the patient at the test-shock strength and at a test-shock time corresponding to the base time interval plus one of the offset times;

(vii) sensing for an induction of cardiac fibrillation for a predetermined sensing time period; and

(viii) if fibrillation is not sensed in step b(vii), then repeating sub steps b(i-vii), at the same test-shock strength, up to the fourth test shock, each test shock member of the set of test shocks having a different test-shock time corresponding to a base time interval plus an offset time; and

(c) if fibrillation is not sensed in step (b) by the fourth test shock, then repeating step (b) at a lower test-shock strength corresponding to the shock strength decrement, to deliver at least one additional set of up to four test shocks; and

(d) if fibrillation is sensed in step (b), then;

(i) defibrillating the patient; and

(ii) setting the programmed first-shock strength of the implantable cardioverter defibrillator at a predetermined higher level than the weakest test-shock strength at which fibrillation was not induced, which test-shock strength represents the upper limit of vulnerability.

49. A method for determining a cardiac shock strength, comprising the steps of:

(a) sensing at least two changes with respect to time in a T wave of an electrical cardiac signal, the at least two changes being selected from the group of changes consisting of two different changes with respect to time of a single cardiac electrical signal, at least two different cardiac electrical signals, or a combination thereof;

(b) delivering a test shock by;

(i) delivering a test shock at a test-shock strength and at a test-shock time relating to at least one of the sensed changes with respect to time in the T wave; and

(ii) sensing for cardiac fibrillation; and

(c) if fibrillation is not sensed, repeating step (b) at the test-shock strength and at a different test-shock time relating to the change in the T wave; and

(d) if fibrillation is sensed, setting the cardiac shock strength as a function of the test-shock strength.

50. An apparatus for determining a cardiac shock strength, comprising:

(a) a sensor for sensing the electrical activity of the heart, including at least two changes in the T wave with respect to time of a cardiac signal and including fibrillation; and

(b) a controller, connected to the sensor, which provides a test shock of a test-shock strength and at a test-shock time relating to the change in the T wave with respect to time, and to determine the cardiac shock strength as a function of the test-shock strength.

51. An apparatus for determining and delivering a therapeutic cardiac shock, comprising:

(a) a plurality of electrodes, at least one electrode being adapted for sensing cardiac signals and at least one electrode being adapted for delivering shocks to the heart;

(b) a shock subsystem connected to the at least one electrode for delivering shocks and which is capable of generating test shocks and therapeutic cardiac shocks; and

(c) a ULV subsystem connected to the shock subsystem and for providing test-shock information to the shock subsystem, the test-shock information including test-shock strength and test-shock time relating to at least two changes in one or more cardiac signals with respect to time, and for determining the shock strength of the therapeutic cardiac shocks as a function of the test-shock strength.

52. A method for determining a cardiac shock strength, comprising the steps of:

(a) sensing the T wave of an electrical cardiac signal recorded from a subcutaneous electrode;

(b) delivering a test shock by;

(i) delivering a test shock at a test-shock strength and at a test-shock time relating to a timing interval selected utilizing one, some, or all points in time in the T wave of the derived signal and

(ii) sensing for cardiac fibrillation;

(c) if fibrillation is not sensed, repeating step (b) at the test-shock strength and at a different test-shock time relating to the change in the T wave; and

(d) if fibrillation is sensed, setting the cardiac shock strength as a function of the test-shock strength.

53. A method for determining a cardiac shock strength for a medical device connected to a patient and capable of delivering a shock, comprising the steps of:

(a) delivering a set of test shocks with the device to the patient, each member of the set comprising the sub steps of;

(i) sensing a cardiac electrical signal from the patient;

(ii) differentiating the T wave of the cardiac electrical signal;

(iii) digitally processing the differentiated signal

(iv) integrating the processed, differentiated signal

(iii) delivering a test shock to the patient at a test-shock strength and at a test-shock time relating to the maximum the T wave of the integrated signal;

(iv) sensing for induction of cardiac fibrillation; and

(v) if fibrillation is not sensed in step a(iv), then repeating sub-steps a(i-iv) at the test-shock strength up to a predetermined maximum set number, each member of the set having a different test-shock time relating to the maximum derivative of the T wave; and

(b) if fibrillation is not sensed in step (a) after the maximum set number, then repeating step (a) at a lower test-shock strength; and

(c) if fibrillation is sensed in step (a), then defibrillating the patient and setting the cardiac shock strength as a predetermined function of the test-shock strength that induced fibrillation.

54. The method of claim 53 in which the cardiac electrical signal is recorded from a subcutaneous Laplacian electrode.