Method and apparatus for delivering an optimum shock duration in treating cardiac arrhythmias

• US 6,643,545 B2
• Filed: 07/26/2001
• Issued: 11/04/2003
• Est. Priority Date: 10/06/1993
• Status: Expired due to Fees

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation), Duke University
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation), Duke University
• Inventors: Hahn, Stephen J., Ideker, Raymond E., Walcott, Gregory P.
• Primary Examiner(s): GETZOW, SCOTT M
• Application Number:
  US09/915,898
• Publication Number:
  US 20010053925A1
• Time in Patent Office: 831 Days
• Field of Search: 607/5-8
• US Class Current: 607/7
• CPC Class Codes: A61N 1/3937 Monitoring output parameters

Abstract

The present invention provides apparatus and methods for delivering an optimum electrical shock in treating cardiac arrhythmias. The apparatus comprises means for producing an electrical waveform signal at least two electrodes The voltage or current of the signal is then detected to determine the signal time constant. The signal time constant is then used in conjunction with a model time constant to determine when the peak amplitude is reached. The waveform is then interrupted when the peak amplitude is reached. Also provided are methods of selecting a cardiac defibrillator by measuring the impedance of implanted electrodes and then selecting a defibrillator having a capacitor which provides an RC time constant equal to that of a model time constant.

Claims

1. A method for externally delivering electrotherapy to a patient, the method comprising:

generating a multiphasic defibrillation pulse;

monitoring an electrical unit of the multiphasic defibrillation pulse as it is being delivered;

determining the rate of change of the electrical unit; and

adjusting a duration of the multiphasic defibrillation pulse based on the rate of change of the electrical unit.

2. The method of claim 1, wherein the multiphasic defibrillation pulse comprises a first phase of polarity followed by a second phase of opposing polarity.

3. The method of claim 2, wherein monitoring an electrical unit of the multiphasic defibrillation pulse comprises monitoring an electrical unit of the first phase of the multiphasic defibrillation pulse.

4. The method of claim 3, wherein adjusting a duration of the multiphasic defibrillation pulse based on the rate of change of the electrical unit comprises adjusting a duration of the first phase of the multiphasic defibrillation pulse based on the rate of change of the electrical unit.

5. The method of claim 1, wherein the electrical unit is voltage.

6. The method of claim 1, wherein the electrical unit is current.

7. A cardiac arrhythmia treatment method comprising:

delivering a multiphasic waveform signal to a pair of electrodes applied externally to a patient;

detecting a patient-dependent electrical characteristic during delivery of the multiphasic waveform signal; and

calculating a duration of the multiphasic waveform signal based on the patient-dependent electrical characteristic.

8. The method of claim 7, wherein delivering a multiphasic waveform signal to a pair of electrodes comprises delivering a first phase of polarity to the pair of electrodes and delivering a second phase of opposite polarity to the pair of electrodes.

9. The method of claim 8, wherein detecting a patient-dependant electrical characteristic during delivery of the multiphasic waveform signal comprises detecting a patient-dependant electrical characteristic during delivery of the first phase of polarity of the multiphasic waveform signal.

10. The method of claim 9, wherein calculating the duration of the multiphasic waveform signal based on the patient-dependent electrical characteristic comprises calculating a duration of the first phase of polarity of the multiphasic waveform signal based on the patient-dependent electrical characteristic detected during delivery of the first phase of polarity of the multiphasic waveform signal.

11. The method of claim 10, further comprising ceasing delivery of the first phase of polarity of the multiphasic waveform signal when the calculated duration of the first phase is reached.

12. The method of claim 11, wherein calculating the duration for the multiphasic waveform signal based on the patient-dependent electrical characteristic further comprises calculating a duration of the second phase of opposite polarity of the multiphasic waveform signal based on the duration of the first phase of polarity of the multiphasic waveform signal.

13. The method of claim 12, further comprising ceasing delivery of the second phase of opposite polarity of the multiphasic waveform signal when the calculated duration of the second phase is reached.

14. The method of claim 7, wherein the patient-dependent electrical characteristic is voltage.

15. The method of claim 7, wherein the patient-dependent electrical characteristic is current.

16. A method for delivering a defibrillation pulse, the method comprising:

delivering the defibrillation pulse to a pair of electrodes applied externally to a patient;

determining a patient impedance as the defibrillation pulse is being delivered to the electrodes;

determining a duration for the defibrillation pulse based on said patient impedance; and

truncating the pulse when said duration is reached.

17. The method of claim 16, wherein the defibrillation pulse is a biphasic defibrillation pulse having a first phase of a first polarity and a second phase of second polarity.

18. The method of claim 17, wherein the first phase of the biphasic defibrillation pulse is truncated when a first duration is reached, wherein the first duration is determined based on said patient impedance.

19. The method of claim 18, wherein the second phase of biphasic defibrillation pulse is truncated when a second duration is reached, wherein the second duration is determined based on the first duration of the first phase of the biphasic defibrillation pulse.

20. The method of claim 16, wherein said patient impedance is indirectly determined by measuring a change in a patient-dependent electrical characteristic as the defibrillation pulse is being delivered to the electrodes.

21. The method of claim 20, wherein the patient-dependent electrical characteristic is voltage.

22. The method of claim 20, wherein the patient-dependent electrical characteristic is current.

23. A method of delivering a defibrillation pulse comprising:

discharging energy in a defibrillation pulse from an energy storage device;

during the energy discharge, measuring an electrical characteristic related to the energy discharge;

based on the measurement of the electrical characteristic, conserving an amount of energy discharged in the defibrillation pulse.

24. The method of claim 23, wherein the amount of energy discharged in the defibrillation pulse is conserved by truncating the discharge at a duration determined as a function of the electrical characteristic measured during the energy discharge.

25. The method of claim 24, wherein the energy is discharged in a multiphasic defibrillation pulse.

26. The method of claim 23, wherein the electrical characteristic is voltage.

27. The method of claim 23, wherein the electrical characteristic is current.

28. A method for treating a cardiac arrhythmia comprising:

discharging energy in a defibrillation pulse through a set of electrodes externally applied to a patient;

detecting an electrical unit related to discharging energy;

extending the duration of the energy discharge for a period of time that is determined based on the detected electrical unit.

29. The method of claim 28, wherein the energy is discharged in a multiphasic defibrillation pulse.

30. The method of claim 29, wherein the multiphasic defibrillation pulse has an earlier phase and a later phase, and a duration of the energy discharge in the earlier phase is extended for the period of time that is determined based on the detected electrical unit.

31. The method of claim 30, wherein a duration of the energy discharge in the later phase is extended for a period of time that is determined based on the duration of the energy discharge in the earlier phase.

32. The method of claim 28, wherein the electrical unit is voltage.

33. The method of claim 28, wherein the electrical unit is current.

34. A method for delivering a defibrillation pulse comprising:

delivering a multiphasic waveform signal to a patient until a condition for truncating the multiphasic waveform signal is met;

monitoring an electrical parameter related to the multiphasic waveform signal while the multiphasic waveform signal is being delivered to the patient; and

determining the condition for truncating the multiphasic waveform signal based on the electrical parameter.

35. The method of claim 34, wherein the condition for truncating the multiphasic waveform signal is a voltage condition.

36. The method of claim 34, wherein the condition for truncating the multiphasic waveform signal is a current condition.

37. The method of claim 34, wherein the condition for truncating the multiphasic waveform signal is an energy condition.

38. An external defibrillator comprising:

(a) an energy storage device;

(b) electrodes in electrical communication with the energy storage device; and

(c) a controller configured to cause the energy storage device to discharge energy in a defibrillation pulse through the electrodes, the controller further being configured to;

(i) determine a patient impedance as the energy in the defibrillation pulse is being discharged through the electrodes;

(ii) determine a duration for the discharge of energy in the defibrillation pulse based on said patient impedance; and

(iii) cease the discharge of energy in the defibrillation pulse when said duration is reached.

39. The defibrillator of claim 38, wherein the energy is discharged in a biphasic truncated exponential defibrillation pulse having a first phase and a second phase.

40. The defibrillator of claim 39, wherein the first phase of the biphasic truncated exponential defibrillation pulse ceases when a first duration is reached, wherein the first duration is determined based on said patient impedance.

41. The defibrillator of claim 40, wherein the second phase of biphasic truncated exponential defibrillation pulse ceases when a second duration is reached, wherein the second duration is determined based on the first duration of the first phase of the biphasic truncated exponential defibrillation pulse.

42. The defibrillator of claim 38, wherein said patient impedance is indirectly determined by measuring a change in a patient-dependent electrical characteristic as the energy in the defibrillation pulse is being discharged.

43. The defibrillator of claim 42, wherein the patient-dependent electrical characteristic is voltage.

44. The defibrillator of claim 42, wherein the patient-dependent electrical characteristic is current.