Monitoring physiological signals during external electrical stimulation

• US 20060178706A1
• Filed: 02/10/2005
• Published: 08/10/2006
• Est. Priority Date: 02/10/2005
• Status: Active Grant

• Current Assignee: Zoll Medical Corporation (Asahi Kasei Corporation)
• Original Assignee: Zoll Medical Corporation (Asahi Kasei Corporation)
• Inventors: Bures, Martin E., Lisogurski, Daniel M., Lopin, Michael, Butler, Gideon D. H., Parascandola, Michael, Freeman, Gary A., Cordaro, Marc, Dupelle, Michael R., Geheb, Frederick J., Craige, David N. III, Jones, Deborah T.
• Granted Patent: US 8,185,199 B2
• Time in Patent Office: Days
• US Class Current: 607/10
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/327 Generation of artificial ECG signals based on measured signals, e.g. to compensate for missing leads
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/7217 of noise originating from a therapeutic or surgical apparatus, e.g. from a pacemaker
• CPC Class Codes: A61N 1/0408 Use-related aspects
• CPC Class Codes: A61N 1/046 Specially adapted for shock therapy, e.g. defibrillation
• CPC Class Codes: A61N 1/0476 Array electrodes (including any electrode arrangement with more than one electrode for at least one of the polarities)
• CPC Class Codes: A61N 1/048 Electrodes characterised by a specific connection between lead and electrode
• CPC Class Codes: A61N 1/0488 Details about the lead
• CPC Class Codes: A61N 1/0492 Patch electrodes A61N1/0412, A61N1/0428 take precedence

Abstract

Electrodes and circuitry for monitoring and stimulating the exterior of the human body, comprising delivering stimulation pulses to stimulation electrodes applied to the exterior of the body, detecting an electrical potential at monitoring electrodes applied to the exterior of the body, positioning at least a first and second monitoring electrode at locations at which an electrical artifact caused by the electrical stimulation pulses is substantially cancelled in a signal formed from the electrical potentials detected at the first and second monitoring electrodes.

Claims

1. A device-implemented method of monitoring and stimulating the exterior of the human body with electrodes, comprising

delivering stimulation pulses to stimulation electrodes applied to the exterior of the body;

detecting an electrical potential at monitoring electrodes applied to the exterior of the body,

positioning at least a first and second monitoring electrode at locations at which an electrical artifact caused by the electrical stimulation pulses is substantially cancelled in a signal formed from the electrical potentials detected at the first and second monitoring electrodes.

2. The method of claim 1 wherein the signal formed from the electrical potentials comprises a difference signal that comprises a difference between the electrical potentials detected at the first and second monitoring electrodes.

3. The method of claim 2 wherein the first and second monitoring electrodes are at locations at which the electrical artifact is substantially equal.

4. The method of claim 2 or 3 wherein the stimulation pulses comprise cardiac stimulation pulses, and the difference signal comprises an ECG signal.

5. The method of claim 4 wherein the cardiac stimulation pulses comprise pacing pulses.

6. The method of claim 2 wherein there are at least three monitoring electrodes applied to the exterior of the patient, and the first and second monitoring electrodes are selected from among the at least three monitoring electrodes, with the selection being made so as to reduce the effect of the electrical artifact on the difference signal.

7. The method of claim 6 wherein the selection of first and second monitoring electrodes is made automatically by the device rather than manually by the user.

8. The method of claim 7 wherein the automatic selection of the first and second monitoring electrodes varies over time.

9. The method of claim 6 wherein the at least three monitoring electrodes comprise at least two monitoring electrodes positioned at different distances from one of the stimulation electrodes, and wherein the selection of the first monitoring electrode comprises choosing between the two electrodes positioned at different distances.

10. The method of claim 9 wherein the choosing between the two electrodes varies over time.

11. The method of claim 2 further comprising at least a third monitoring electrode applied to the exterior of the patient, and wherein the difference signal comprises the difference between the electrical potential detected at the first electrode and a combination of the electrical potential detected at the second and third electrodes.

12. The method of claim 11 wherein the manner in which the combination is made varies over time to compensate for variation over time of the relative magnitude of the electrical artifact at the second and third electrodes.

13. The method of claim 11 further comprising at least a fourth monitoring electrode applied to the exterior of the patient, and wherein the difference signal comprises the difference between a combination of the electrical potential detected at the first and fourth electrodes and a combination of the electrical potential detected at the second and third electrodes.

14. The method of claim 13 wherein one or both of the combination of the electrical potential detected at the first and fourth electrodes and a combination of the electrical potential detected at the second and third electrodes varies over time.

15. The method of claim 2 wherein the edge-to-edge separation between the active areas of the at least first and second monitoring electrodes and the active area of one of the stimulation electrodes is less than 10 centimeters.

16. The method of claim 2 wherein the at least first and second monitoring electrodes are positioned at the same separation from one of the stimulation electrodes.

17. The method of claim 16 further comprising a third monitoring electrode positioned at the same separation as the first and second electrodes from one of the separation electrodes.

18. The method of claim 16 wherein the first and second monitoring electrodes and the one stimulation electrode are fixed in position on a common substrate.

19. The method of claim 2 wherein the at least first and second monitoring electrodes are positioned so that they are at approximately the same electrical potential in an electric field formed between the two stimulation electrodes when the stimulation electrodes are polarized following a stimulation pulse.

20. The method of claim 2 wherein the at least first and second monitoring electrodes are positioned along approximately the same field line in an electric field formed between the two stimulation electrodes when the stimulation electrodes are polarized following a stimulation pulse.

21. The method of claim 2 wherein the first and second monitoring electrodes are supported on a first substrate that is separate from a second substrate supporting one of the stimulation electrodes.

22. The method of claim 21 wherein the first substrate supporting the first and second monitoring electrodes substantially surrounds the second substrate.

23. The method of claim 22 wherein the first substrate is annular in shape and the second substrate is circular in shape, and the two substrates are positioned approximately concentrically, so that the separation between the two is approximately an equal radial distance.

24. The method of claim 2 wherein the at least first and second monitoring electrodes and the at least one stimulation electrode form one assembly.

25. The method of claim 24 wherein the positions of the at least first and second monitoring electrodes and the stimulation electrode are fixed on the assembly, so that the separation between each of the monitoring electrodes and the stimulation electrode is fixed.

26. The method of claim 5 wherein electrical artifact potential in the ECG difference signal is less than about 10 millivolts measured within 100 milliseconds after termination of the cardiac pacing pulse.

27. The method of claim 5 wherein the electrical artifact potential in the ECG difference signal is less than five times the QRS amplitude when the pacing pulses are of sufficient amplitude to capture the heart.

28. The method of claim 1 wherein the detecting an electrical potential at monitoring electrodes comprises an impedance matching circuit to which at least the first and second monitoring electrodes are connected.

29. The method of claim 28 wherein the impedance matching circuit creates an imbalance in the electrode impedances to compensate for variation in the electrical artifact potential in the two monitoring electrodes.

30. The method of claim 2 wherein there are a plurality of difference signals, and the difference signals are used in a transformation to derive ECG signals that resemble standard 3-lead ECG signals.

62. The method of claim 1 further comprising having a monitoring device automatically identify a nonstandard monitoring configuration from one or more of the electrodes or from a connector used to the connect the electrodes to the monitoring device, and in the event of identifying the nonstandard monitoring configuration automatically modifying signal processing of the detected electrical potentials.

63. The method of claim 1 further comprising positioning a third electrode on the body, and wherein the signal formed from the electrical potentials comprises a summation of electrical potentials measured at the first and second electrodes with respect to the third electrode, and wherein the electrical artifact is substantially cancelled in the signal as a result of the electrical artifact being of similar magnitude but of opposite polarity in the electrical potentials measured.

64. The method of claim 63 wherein there are at least first and second stimulation electrodes, and the first monitoring electrode is positioned in the vicinity of the first stimulation electrode, and the second monitoring electrode is positioned in the vicinity of the second stimulation electrode.

65. The method of claim 2 wherein the signal is formed in a manner that is varied over time.

66. The method of claim 65 wherein the signal is formed by forming a combination of the electrical potentials at the first end and second monitoring electrodes, and the manner in which the combination is made varies over time.

31. A device-implemented method of external monitoring and external stimulating the heart, comprising

delivering stimulation pulses between a first polarity stimulation electrode and a second polarity stimulation electrode applied to the exterior of the body, wherein at least the first polarity stimulation electrode comprises a plurality of smaller electrodes, through which the stimulation pulses are applied,

wherein the aggregate area of the smaller electrodes is sufficient for stimulation;

and

monitoring an ECG potential by forming a difference signal that comprises the difference between the electrical potentials detected at two of the smaller electrodes,

wherein the two smaller electrodes used to form the difference signal are positioned and configured so that the stimulus artifact from polarization is approximately equal on both of the smaller electrodes, so that the stimulus artifact is approximately cancelled in the difference signal.

32. The method of claim 31 wherein the stimulation pulses comprise cardiac pacing pulses applied to the exterior of the chest.

33. An electrode assembly for external cardiac pacing and external cardiac monitoring, comprising

at least one external stimulation electrode for delivering a pacing pulse;

at least first and second external monitoring electrodes;

at least one positioning element to which the stimulation and first and second monitoring electrodes are connected,

wherein the positioning element, stimulation electrode, and first and second monitoring electrodes are configured so that the first and second monitoring electrodes are located in positions in which an electrical artifact caused by the pacing pulses is substantially cancelled in a difference signal formed by taking a difference between the electrical potentials detected at the first and second monitoring electrodes.

34. The electrode assembly of claim 33 wherein the positioning element comprises a common substrate that supports the stimulation electrode and the first and second monitoring.

35. The electrode assembly of claim 33 wherein the positioning element comprises elements such as wires that prescribe the separation of the first and second monitoring electrodes from the stimulation electrode.

36. The electrode assembly of claim 33 wherein the edge-to-edge separation between the active areas of the at least first and second monitoring electrodes and the active area of one of the stimulation electrodes is less than 10 centimeters.

37. The electrode assembly of claim 33 wherein the at least first and second monitoring electrodes are positioned at the same separation from one of the stimulation electrodes.

38. The electrode assembly of claim 37 further comprising a third monitoring electrode positioned at the same separation as the first and second electrodes from one of the separation electrodes.

39. The electrode assembly of claim 33 wherein the at least first and second monitoring electrodes are positioned so that they are at approximately the same electrical potential in an electric field formed between the two stimulation electrodes when the stimulation electrodes are polarized following a stimulation pulse.

40. The electrode assembly of claim 33 wherein the at least first and second monitoring electrodes are positioned along approximately the same field line in an electric field formed between the two stimulation electrodes when the stimulation electrodes are polarized following a stimulation pulse.

41. The electrode assembly of claim 33 wherein the first and second monitoring electrodes are supported on a first substrate that is separate from a second substrate supporting one of the stimulation electrodes, and the first and second substrates are shaped to facilitate their being applied to the patient in a desired relative position.

42. The electrode assembly of claim 41 wherein the first substrate is annular in shape and the second substrate is circular in shape, and the two substrates are positioned approximately concentrically, so that the separation between the two is approximately an equal radial distance.

43. The electrode assembly of claim 33 wherein the first and second monitoring electrodes and the stimulation electrode form one assembly.

44. The electrode assembly of claim 43 wherein the positions of the at least first and second monitoring electrodes and the stimulation electrode are fixed on the assembly, so that the separation between each of the monitoring electrodes and the stimulation electrode is fixed.

45. An electrode assembly for external cardiac pacing and external cardiac monitoring, comprising

at least one external stimulation electrode for delivering a pacing pulse, the stimulation electrode comprising a stimulation conductive plate;

at least one external monitoring electrode, the monitoring electrode comprising a monitoring conductive plate;

a backing layer supporting the stimulation and monitoring electrodes,

wherein the stimulation conductive plate and monitoring conductive plate are spaced apart;

a common gel layer in electrical contact with both the stimulation electrode and the monitoring electrode.

46. The electrode assembly of claim 45 wherein the common gel layer comprises solid gel or hydrogel.

47. An electrode assembly for external cardiac pacing and external cardiac monitoring, comprising

at least one external stimulation electrode for delivering a pacing pulse, the stimulation electrode comprising a stimulation conductive plate;

at least one external monitoring electrode, the monitoring electrode comprising a monitoring conductive plate;

a backing layer supporting the stimulation and monitoring electrodes,

wherein the stimulation conductive plate and monitoring conductive plate are spaced apart;

a first gel layer in electrical contact with the stimulation electrode;

a second gel layer in electrical contact with the monitoring electrode,

wherein the first and second gel layers are spaced apart;

wherein one of the first gel layer or the second gel layer comprises a solid gel or hydrogel, and

wherein the other one of the first gel layer or the second gel layer comprises a liquid gel.

48. An electrode assembly for external stimulation and/or monitoring of a patient, the assembly comprising

at least a first and second electrode supported within the assembly;

a first gel layer positioned adjacent the first electrode;

a second gel layer positioned adjacent the second electrode;

the first and second gel layers having different levels of moisture content; and

a moisture vapor barrier layer sized and positioned to retard moisture vapor from migrating from one of the first and second gel layers to the other of the gel layers.

49. The electrode assembly of claim 48 wherein the electrode assembly is configured for cardiac stimulation, and the first electrode comprises a stimulation electrode and the second electrode comprises a monitoring electrode.

50. The electrode assembly of claim 49 wherein the first gel layer comprises a liquid gel and the second gel layer comprise a solid gel.

51. The electrode assembly of claim 49 wherein the first gel layer comprises a solid gel of one moisture content, and the second gel layer comprises a solid gel of a second moisture content greater than the first content.

52. The electrode assembly of claim 49 wherein the vapor barrier comprises a polyester film.

53. The electrode assembly of claim 49 wherein the vapor barrier comprises an aluminum film.

54. A multi-electrode assembly for cardiac stimulation and monitoring, the assembly comprising:

a monitoring electrode configured to monitor electrical potential on the chest of a patient;

a stimulation electrode configured to deliver one or more stimulating pulses to the chest of a patient;

an electrode cable having first and second cable ends, the first cable end configured for connection to an external cardiac device and the second cable end configured for connection to the monitoring electrode and to the stimulation electrode; and

a non-linear circuit element electrically interposed between the second cable end and the stimulation electrode, the non-linear circuit element being configured to conduct during delivery of the stimulating pulses and to block conduction in the presence of a residual potential on the stimulating electrode following delivery of a stimulation pulse.

55. The electrode assembly of claim 54 wherein the non-linear circuit element comprises one or more diodes or gas discharge tubes.

56. The electrode assembly of claim 54 wherein the non-linear circuit element comprises at least two non-linear circuit elements forming parallel paths between the cable and the stimulation electrode, and with the polarity of the elements being opposite along the two paths, so that a biphasic stimulation waveform can be delivered to the stimulation electrode, with current flowing through one of the paths in one polarity of the waveform and through the other of the paths in the other polarity of the waveform.

57. The electrode assembly of claim 56 wherein conductance in the presence of a residual potential on the stimulation electrode is blocked along one of the parallel paths by setting the net offset potential of the one or more elements in that path to greater than the expected residual potential.

58. The electrode assembly of claim 54 wherein the non-linear circuit element comprises one or more transistors.

59. The electrode assembly of claim 54 wherein the non-linear circuit element generally blocks current flow in one direction and permits current flow in the opposite direction.

60. The electrode assembly of claim 54 wherein the electrode cable comprises a single conductor, and the first and second cable ends are first and second ends of the single conductor.

61. The electrode assembly of claim 54 further comprising a high-impedance element that is positioned in the electrical path between the electrode cable and the monitoring electrode and configured to reduce the level of current flowing to the monitoring electrode during delivery of a stimulation pulse to the stimulating electrode.