IMPLANTABLE LEAD HAVING A VARIABLE COIL CONDUCTOR PITCH

• US 20090149933A1
• Filed: 12/04/2008
• Published: 06/11/2009
• Est. Priority Date: 12/06/2007
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Ameri, Masoud
• Granted Patent: US 8,731,685 B2
• Time in Patent Office: Days
• US Class Current: 607/119
• CPC Class Codes: A61N 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: A61N 1/086 Magnetic resonance imaging [MRI] compatible leads
• CPC Class Codes: H01F 21/04 by relative movement of turns or parts of windings
• CPC Class Codes: H03H 2001/0092 Inductor filters, i.e. inductors whose parasitic capacitance is of relevance to consider it as filter
• CPC Class Codes: H05K 9/0098 for shielding electrical cables

Abstract

Systems and methods for shielding implantable leads from magnetic fields during medical procedures such as magnetic resonance imaging (MRI) are described. In various embodiments, the lead includes an inner conductor that is helically shaped and radially surrounded, at least in part, by one or more outer shielding conductors. The pitch of the inner conductor, and in some cases also the outer conductor, can be varied (e.g., continuously or at certain points) along the length of the lead, forming a plurality of high impedance points along the length of the lead which result in the dissipation of electromagnetic energy at an interrogation frequency of a magnetic resonance imaging device (e.g., 64 MHz, 128 MHz, or the like). In some embodiments, the variance in the pitch of the inner conductor follows a sinusoidal function, a modified square-wave function, or some other repeating pattern.

Claims

1. A medical device, comprising:

a lead having a proximal section, a distal section, and a length;

wherein the lead includes an inner conductor that is helically shaped; and

wherein the pitch of the inner conductor continuously varies along the length of the lead forming a plurality of high impedance points along the length of the lead, each of the plurality of high impedance points adapted to inhibit transfer of absorbed energy from traveling along the length of the lead at an interrogation frequency of a magnetic resonance imaging device.

2. The medical device of claim 1, wherein the inner conductor is radially surrounded at least in part by one or more outer shielding conductors.

3. The medical device of claim 2, wherein the lead further includes one or more layers of insulating material surrounding the one or more outer shielding conductors.

4. The medical device of claim 2, wherein the one or more outer shielding conductors have a pitch that varies continuously.

5. The medical device of claim 2, wherein the inner conductor has an outer diameter smaller than an inner diameter of the one or more outer shielding conductors and the outer diameter of the inner conductor is increased to the inner diameter of the one or more outer shielding conductors on the proximal section and distal section of the lead.

6. The medical device of claim 1, wherein the variance in the pitch of the inner conductor follows a sinusoidal function, a modified square-wave function, a triangle function, or a saw-tooth function.

7. The medical device of claim 1, wherein the variance in the pitch of the inner conductor follows a repeating pattern of a fixed length equal to ¼

of a wavelength of the interrogation frequency of the magnetic resonance imaging device.

8. The medical device of claim 1, wherein the inner conductor has an average pitch between, and including, five mils and fifty mils.

9. The medical device of claim 1, wherein the inner conductor has a pitch no greater than about five mils.

10. The medical device of claim 1, wherein the length of the lead is between forty centimeters and ninety centimeters.

11. The medical device of claim 2, wherein an impedance of the inner conductor is similar to an impedance of the one or more outer shielding conductors.

12. The medical device of claim 1, wherein the distal section of the lead includes an electrode.

13. The medical device of claim 12, wherein the lead includes a low impedance insulation near the proximal section and the distal section of the lead causing the electromagnetic energy to be dissipated along body tissue adjacent to the length of the lead to reduce energy transfer of the electromagnetic energy to the electrode.

14. The medical device of claim 13, wherein the low impedance insulation is made from a material with a relative dielectric constant of five to ten times the dielectric constant of the inner conductor.

15. An implantable medical device, comprising:

a lead having a proximal section coupled to a pulse generator, a distal section implanted within a heart of a patient, and a length, wherein the lead is configured to convey electrical signals between the heart and the pulse generator through an inner conductor;

the inner conductor having a helix-like shape with a continuously varying inner conductor pitch forming one or more high impedance points along the length of the lead at one or more frequencies; and

an outer conductor having a helix-like shape radially surrounding at least a portion of the inner conductor, wherein the outer conductor has an outer conductor pitch that varies at one or more locations along the length of the lead.

16. The implantable medical device of claim 15, wherein the outer conductor pitch continuously varies.

17. The implantable medical device of claim 15, wherein the inner conductor pitch follows a sinusoidal function or a modified square-wave function.

18. The implantable medical device of claim 15, further comprising shielding with a high impedance along the length of the lead and a low impedance along a cross-section.

19. The implantable medical device of claim 15, wherein an impedance of the inner conductor is substantially similar to an impedance of the outer conductor.

20. The implantable medical device of claim 15, wherein the pulse generator is a pacemaker or a cardiac defibrillator.

21. The implantable medical device of claim 15, further comprising one or more layers of insulating material disposed about the outer conductor and the inner conductor.

22. A medical lead, comprising:

an inner conductor having a helix-like shape with a continuously varying inner conductor pitch forming high impedance points along a length of the lead at an interrogation frequency; and

an outer conductor having a helix-like shape and radially surrounding at least a portion of the inner conductor, wherein the outer conductor has an outer conductor pitch that varies at one or more locations along the length of the lead.

23. The medical lead of claim 22, wherein the outer conductor pitch continuously varies.

24. The medical lead of claim 22, wherein the interrogation frequency is in a range of eight and fifty three hundredths and one-hundred twenty eight megahertz.