Medical electrical device including novel means for reducing high frequency electromagnetic field-induced tissue heating

• US 20060009819A1
• Filed: 07/12/2004
• Published: 01/12/2006
• Est. Priority Date: 07/12/2004
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Przybyszewski, Piotr
• Granted Patent: US 7,912,552 B2
• Time in Patent Office: Days
• US Class Current: 607/63
• CPC Class Codes: A61N 1/056 Transvascular endocardial electrode systems
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: A61N 1/3754 Feedthroughs

Abstract

A medical device including an elongate lead connected to a pulse generator connector further includes a passive lossy circuit electrically connected in between a distal portion of the lead conductor and the high frequency-grounded surface. The passive lossy circuit has a high frequency impedance approximately equal to a characteristic impedance of the lead when implanted in a body and dissipates energy of an incident wave formed along the lead, thereby diminishing a reflection of the incident wave, the incident wave being induced by exposure of the medical device to a high frequency electromagnetic field. The passive lossy circuit further has low pass properties allowing for normal device operation.

Claims

1. A medical device, comprising:

an electrical lead including an elongate insulative body, an elongate lead conductor extending within the body, a connector element electrically connected to the lead conductor and terminating a proximal end of the lead conductor;

a housing containing electronic circuitry and including a feedthrough;

the feedthrough including a signal conductor electrically connected to the electronic circuitry and extending out from the housing through the feedthrough;

a connector module attached to the housing and including a conductive contact electrically connected to the signal conductor and adapted to electrically connect to the connector element of the lead;

a high frequency-grounded surface electrically connected in between a distal portion of the lead conductor and the electronic circuitry when the conductive contact is connected to the connector element; and

a passive lossy circuit electrically connected in between the distal portion of the lead conductor and the high frequency-grounded surface when the conductive contact is connected to the connector element;

wherein the passive lossy circuit has a high frequency impedance approximately equal to a characteristic impedance of the lead when implanted in a body;

the passive lossy circuit dissipating energy of an incident wave formed along the lead, thereby diminishing a reflection of the incident wave, the incident wave being induced by exposure of the medical device to a high frequency electromagnetic field; and

the passive lossy circuit has low pass properties allowing for normal device operation when the conductive contact of the connector module is electrically connected to the connector element of the lead.

2. The device of claim 1, wherein the high frequency-grounded surface has a high frequency impedance less than the characteristic impedance of the lead

3. The device of claim 1, wherein the high frequency-grounded surface is an outer surface of the housing.

4. The device of claim 1, wherein the high frequency-grounded surface is formed as an outer surface of the lead body.

5. The device of claim 1, wherein the passive lossy circuit is positioned along the lead conductor in proximity to the connector element.

6. The device of claim 1, wherein the passive lossy circuit is positioned within the connector module.

7. The device of claim 1, wherein the passive lossy circuit is positioned in the housing, the passive lossy circuit being formed in part by the feedthrough.

8. The device of claim 1, wherein the high frequency-grounded surface has a high frequency impedance an order of magnitude less than the characteristic impedance of the lead.

9. The device of claim 1, further comprising:

a lead connector joined to the insulative body and on which the connector element is mounted; and

a connector sleeve extending from the lead connector to the body;

wherein the passive lossy circuit is positioned in proximity to the connector sleeve.

10. The device of claim 1, further comprising:

a lead connector joined to the insulative body and on which the connector element is mounted; and

a connector sleeve extending from the lead connector to the body;

wherein the passive lossy circuit is positioned within the lead connector.

11. The device of claim 1, wherein the passive lossy circuit comprises a parallel resistor and inductor.

12. The device of claim 1, wherein the passive lossy circuit comprises a series resistor and capacitor in parallel with an inductor.

13. The device of claim 12, wherein:

the feedthrough includes an insulator surrounding the signal conductor, the insulator including a first part and a second part surrounding the first part; and

the capacitor is formed by the first part of the insulator and the resistor is formed by the second part of the insulator.

14. The device of claim 12, wherein:

the feedthrough includes an insulator surrounding the signal conductor, the insulator including a first part and a second part surrounding the first part; and

the resistor is formed by the first part of the insulator and the capacitor is formed by the second part of the insulator.

15. The device of claim 1, wherein:

the lead further includes an electrode connected to and terminating a distal end of the lead conductor and a passive non-lossy circuit electrically connected between the conductor and the electrode and positioned in proximity to the electrode;

the passive non-lossy circuit has a high frequency impedance such that a combined impedance of the non-lossy circuit and an electrode-to-tissue interface impedance, when the lead is implanted in the body, is different from the characteristic impedance of the lead in order to enhance a reflection of a second incident wave and thereby minimize energy of the second incident wave dissipated at the electrode-to-tissue interface;

the second incident wave being induced by exposure of the medical device to the high frequency electromagnetic field; and

the passive non-lossy circuit has low pass properties allowing for normal device operation when the conductive contact of the connector module is electrically connected to the connector element of the lead.

16. The device of claim 15, wherein the passive non-lossy circuit comprises an inductor in series with the electrode.

17. The device of claim 15, wherein the passive non-lossy circuit comprises a capacitor in parallel with the electrode and further comprising a conductive surface in contact with a portion of tissue.

18. The device of claim 16, wherein the passive non-lossy circuit further comprises a capacitor in parallel with the electrode and further comprising a conductive surface in contact with a portion of tissue.

19. The device of claim 15, wherein the electrode is a tip electrode terminating a distal end of the lead body.

20. The device of claim 19, wherein the passive non-lossy circuit comprises a capacitor in parallel with the electrode and further comprising a conductive surface formed about the lead body in contact with a portion of tissue.

21. The device of claim 20, wherein the passive non-lossy circuit further comprises an inductor in series with the electrode.

22. A medical electrical lead comprising:

an elongate insulative body;

an elongate lead conductor extending within the body;

a connector element electrically connected to the lead conductor and terminating a proximal end of the lead conductor, the connector element adapted to electrically connect with a pulse generator for forming a medical device; and

a passive lossy circuit electrically connected in between a distal portion of the lead conductor and the connector element;

wherein the passive lossy circuit has a high frequency impedance approximately equal to a characteristic impedance of the lead when implanted in a body;

the passive lossy circuit dissipating energy of an incident wave formed along the lead, thereby diminishing a reflection of the incident wave, the incident wave being induced by exposure of the medical device to a high frequency electromagnetic field; and

the passive lossy circuit has low pass properties allowing for normal device operation when the lead is electrically connected to the pulse generator.

23. The lead of claim 22, further comprising a high frequency-grounded surface electrically connected to the lead conductor, the surface being connected in between the passive lossy circuit and the connector element.

24. The lead of claim 23, wherein the high frequency-grounded surface has a high frequency impedance less than the characteristic impedance of the lead.

25. The lead of claim 22, wherein the passive lossy circuit is positioned along the lead conductor in proximity to the connector element.

26. The lead of claim 22, further comprising:

a lead connector joined to the insulative body and on which the connector element is mounted; and

a connector sleeve extending from the lead connector to the body;

wherein the passive lossy circuit is positioned in proximity to the connector sleeve.

27. The lead of claim 22, further comprising:

a lead connector joined to the insulative body and on which the connector element is mounted; and

a connector sleeve extending from the lead connector to the body;

wherein the passive lossy circuit is positioned within the lead connector.

28. The lead of claim 22, wherein the passive lossy circuit comprises a parallel resistor and inductor.

29. The lead of claim 22, wherein the passive lossy circuit comprises a series resistor and capacitor in parallel with an inductor.

30. The lead of claim 23, wherein the high frequency-grounded surface is formed as an outer surface of the lead body.

31. The lead of claim 23, wherein the high frequency-grounded surface has a high frequency impedance an order of magnitude less than the characteristic impedance of the lead.

32. The lead of claim 22, further comprising:

an electrode connected to and terminating a distal end of the lead conductor; and

a passive non-lossy circuit electrically connected between the passive lossy circuit and the electrode and positioned in proximity to the electrode;

wherein passive non-lossy circuit has a high frequency impedance such that a combined impedance of the non-lossy circuit and an electrode-to-tissue interface impedance, when the lead is implanted in the body, is different from the characteristic impedance of the lead in order to enhance a reflection of a second incident wave and thereby minimize energy of the second incident wave dissipated at the electrode-to-tissue interface;

the second incident wave being induced by exposure of the medical device to the high frequency electromagnetic field; and

the passive non-lossy circuit has low pass properties allowing for normal device operation when the lead is electrically connected to the pulse generator.

33. The lead of claim 32, wherein the passive non-lossy circuit comprises an inductor in series with the electrode.

34. The lead of claim 32, wherein the passive non-lossy circuit comprises a capacitor in parallel with the electrode and further comprising a conductive surface in contact with a portion of tissue.

35. The lead of claim 33, wherein the passive non-lossy circuit further comprises a capacitor in parallel with the electrode and further comprising a conductive surface in contact with a portion of tissue.

36. A medical pulse generator comprising:

a housing containing electronic circuitry and including a feedthrough;

the feedthrough including a signal conductor electrically connected to the electronic circuitry and extending out from the housing through the feedthrough;

a connector module attached to the housing and including a conductive contact electrically connected to the signal conductor and adapted to electrically connect to a connector element of a medical lead in order to form a medical device;

a high frequency-grounded surface electrically connected in between conductive contact and the electronic circuitry; and

a passive lossy circuit electrically connected in between the conductive contact and the high frequency-grounded surface;

wherein the passive lossy circuit has a high frequency impedance approximately equal to a characteristic impedance of the medical lead when the lead is electrically connected to the conductive contact and implanted in a body;

the passive lossy circuit dissipating energy of an incident wave formed along the lead, thereby diminishing a reflection of the incident wave, the incident wave being induced by exposure of the medical device to a high frequency electromagnetic field; and

the passive lossy circuit has low pass properties allowing for normal device operation when the conductive contact of the connector module is electrically connected to the lead.

37. The pulse generator of claim 36, wherein the high frequency-grounded surface has a high frequency impedance less than the characteristic impedance of the lead.

38. The pulse generator of claim 36, wherein the high frequency-grounded surface is an outer surface of the housing.

39. The pulse generator of claim 36, wherein the high frequency-grounded surface has a high frequency impedance an order of magnitude less than the characteristic impedance of the lead.

40. The pulse generator of claim 36, wherein the passive lossy circuit is positioned within the connector module.

41. The pulse generator of claim 36, wherein the passive lossy circuit is positioned within the housing, the passive lossy circuit being formed in part by the feedthrough.

42. The pulse generator of claim 36, wherein the passive lossy circuit comprises a parallel resistor and inductor.

43. The pulse generator of claim 36, wherein the passive lossy circuit comprises a series resistor and capacitor in parallel with an inductor.

44. The pulse generator of claim 43, wherein:

the feedthrough includes an insulator surrounding the signal conductor, the insulator including a first part and a second part surrounding the first part; and

the capacitor is formed by the first part of the insulator and the resistor is formed by the second part of the insulator.

45. The pulse generator of claim 43, wherein:

the feedthrough includes an insulator surrounding the signal conductor, the insulator including a first part and a second part surrounding the first part; and

the resistor is formed by the first part of the insulator and the capacitor is formed by the second part of the insulator.