Source: https://patents.google.com/patent/US8538551B2/en
Timestamp: 2019-10-20 06:17:14
Document Index: 521906870

Matched Legal Cases: ['§119', 'Application No. 60', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16']

US8538551B2 - Leads with high surface resistance - Google Patents
US8538551B2
US8538551B2 US13/592,588 US201213592588A US8538551B2 US 8538551 B2 US8538551 B2 US 8538551B2 US 201213592588 A US201213592588 A US 201213592588A US 8538551 B2 US8538551 B2 US 8538551B2
US13/592,588
US20120323297A1 (en
2007-12-06 Priority to US99291507P priority Critical
2008-12-05 Priority to US12/329,257 priority patent/US8275464B2/en
2012-08-23 Application filed by Cardiac Pacemakers Inc filed Critical Cardiac Pacemakers Inc
2012-08-23 Priority to US13/592,588 priority patent/US8538551B2/en
2012-12-20 Publication of US20120323297A1 publication Critical patent/US20120323297A1/en
2013-09-17 Publication of US8538551B2 publication Critical patent/US8538551B2/en
239000004020 conductor Substances 0 abstract claims description 186
239000011133 lead Substances 0 abstract claims description 288
238000002595 magnetic resonance imaging Methods 0 abstract claims description 45
-1 polyphenylenevinylene Polymers 0 description 1
This application is a continuation of U.S. application Ser. No. 12/329,257, filed on Dec. 5, 2008, now U.S. Pat. No. 8,275,464 which claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/992,915, flied on Dec. 6, 2007, entitled “Leads With High Resistive Surface,” which are incorporated herein by reference in their entirety.
The present invention relates to implantable medical leads having impedance characteristics adapted to dissipate RF electromagnetic energy during medical procedures such as magnetic resonance imaging (MRI). An illustrative implantable medical device (IMD) configured for use in a magnetic resonance imaging environment includes a lead having an inner electrical conductor operatively coupled to an electrode, and at least one resistive shield that radially surrounds the inner electrical conductor along all or a portion of the length of the lead. The inner electrical conductor can comprise a material having a relatively low resistance to facilitate energy transmission of IMD electrical signals through the conductor to the lead electrode. The inner conductor may have a relatively low impedance at the IMD such that it does not attenuate electrical energy transmitted by the IMD (e.g., electrical pulses transmitted by a pulse generator).
A proximal portion 26 of the lead 14 can be coupled to or formed integrally with the pulse generator 12. A distal portion 28 of the lead 14, in turn, can be implanted at a desired location within the heart 16 such as in the right ventricle 20, as shown. Although the illustrative embodiment depicts only a single lead 14 inserted into the patient's heart 16, in other embodiments, however, multiple leads can be utilized so as to electrically stimulate other areas of the heart 16. In some embodiments, for example, the distal portion of a second lead (not shown) may be implanted in the right atrium 18. In addition, or in lieu, another lead may be implanted at the left side of the heart 16 (e.g., in the coronary veins) to stimulate the left side of the heart 16. Other types of leads such as epicardial leads may also be utilized in addition to, or in lieu of, the lead 14 depicted in FIG. 1.
The ZI parameter 32 in the circuit 30 represents the equivalent impedance exhibited by the lead 14 at the RF frequency of the MRI scanner. The impedance value ZI 32 may represent, for example, the inductance or the equivalent impedance resulting from the parallel inductance and the coil turn by turn capacitance exhibited by the lead 14 at an RF frequency of 64 MHz for a 1.5 Tesla MRI scanner, or at an RF frequency of 128 MHz for a 3 Tesla MRI scanner. The impedance ZI of the lead 14 is a complex quantity having a real part (i.e., resistance) and an imaginary part (i.e., reactance).
The circuit represented in FIG. 2 and the associated equation described below are for the purpose of illustrating the concept of lead heating in an MRI environment. At frequencies where the wavelength of induced voltage (or current) is dose to the size of the circuit, a simple lumped sum system such as that illustrated in FIG. 2 may not accurately model the behavior of the lead 14 in the MRI environment. Consequently, in those circumstances, a distributed model should be used along with Maxwell's equation for a proper mathematical description of the circuit. In some cases, the approximating distributed model can be created using field solvers or simulators.
The temperature at the tip of the lead 14 where contact is typically made to the surrounding tissue is related in part to the power dissipated at 38 (i.e., at “Zb”), which, hi turn, is related to the square of Vb. To minimize temperature rises resulting from the power dissipated at 38, it is thus desirable to minimize Vi (34) and Zc (38) while also maximizing the impedance of the lead ZI (32). In some embodiments, the impedance ZI (32) of the lead 14 can be increased at the RF frequency of the MRI scanner, which aids in reducing the power dissipated into the surrounding body tissue at the point of contact 38.
In the embodiment of FIGS. 10-11, the lead 80 further includes a layer of insulation 86 disposed between the outer resistive shield 84 and the inner conductor core 82. The layer of insulation 86 is configured to electrically isolate the inner conductor core 82 from RF energy received on the outer resistive shield 84. An example of a layer of insulation 86 suitable for electrically isolating the inner conductor core 80 is a thin layer less than or equal to about 10 mils. If another insulation layer or coating is paced about the resistive shield 84, then the layer of insulation 86 employed may be thinner, in some embodiments less than or equal to about 1 mil thickness. In certain embodiments, the outer diameter of the lead 80, including the inner coil conductor 82, the resistive shield 84, and the insulation 86 is about 50 to 100 mils.
The outer resistive shields 94 a,94 b,94 c each extend along a portion of the length of the lead 88, and are separated from each other via a number of small gaps G, as shown. The gap G between each longitudinally adjacent shield 94 a,94 b,94 c can be sufficient such that each shield 94 a,94 b,94 c is electrically isolated from the other shields 94 a,94 b,94 c. In some embodiments, for example, the outer resistive shields 94 a,94 b,94 c can be separated from each other by a gap G of approximately 4 mm to 5 mm. In other embodiments, the gap G separating each of the outer resistive shields 94 a,94 b,94 c may be greater or lesser depending on the electrical characteristics of the shields 94 a,94 b,94 c (e.g., the material and thickness of the shields 94 a,94 b,94 c), the amount of RF energy received on the lead 88, as well as other factors.
In the embodiment of FIG. 16, the outer resistive shield 112 comprises a helically-shaped resistive coil that radially surrounds the inner conductor coil 108 and the layer of insulation 110. The resistive coil 112 has a relatively high resistance in comparison to the resistance of the inner conductor coil 108 to facilitate dissipation of RF energy received on the lead 106 into the surrounding body tissue along the length of the lead 106. In some embodiments, for example, the ratio of the resistance of the resistive coil 112 to the resistance of the inner conductor coil 108 may be in the range of between about 2 to 10. In one embodiment, the inner conductor coil 102 is fabricated from a silver filled MP35N wire containing approximately 28% to 30% saver whereas the outer resistive member 84 comprises different, more resistive material such as a pure MP35N.
1. An implantable medical lead for use in a magnetic resonance imaging (MRI) environment, the lead comprising:
a lead having a proximal portion configured to be coupled to a pulse generator, a distal portion having an electrode, and a conductor wire that extends from the proximal portion to the distal portion to electrically connect with the electrode for conducting energy between the electrode and the pulse generator;
the lead having a resistivity that increases across a width of the lead between a center portion of the conductor wire and an outer portion of the lead such that the resistivity is greatest at the outer surface of the lead; and
wherein the outer portion of the lead is configured to dissipate RF electromagnetic energy received by an MRI device along a length of the lead.
2. The lead of claim 1, wherein the resistivity increases at a plurality of finite locations across the width of the lead.
3. The lead of claim 1, wherein the lead comprises a plurality of conductive layers radially surrounding the conductor wire.
4. The lead of claim 3, wherein the conductive layers successively increase in resistivity across the width of the lead.
5. The lead of claim 3, wherein the plurality of conductive layers comprises a first outer conductor layer with a first resistivity, a second outer conductor layer with a second resistivity greater than the first resistivity, and a third outer conductor layer with third resistivity greater than the first and second resistivities.
6. The lead of claim 1, wherein the conductor wire is surrounded radially by a plurality of outer resistive shields that successively increase in resistivity.
7. The lead of claim 1, wherein the conductor wire is the only conductor wire that extends along the length of the lead, the conductor wire having a variable resistivity across its width that increases from the center portion of the conductor wire.
8. The lead of claim 7, wherein the conductor wire continuously increases in resistivity from the center portion of the conductor wire.
9. The lead of claim 1, wherein the outer surface of the conductor wire is the outer surface of the lead.
10. The lead of claim 1, wherein the lead is configured to attenuate RF energy from an MRI scan by the increasing resistivity across the width of the lead inhibiting alternating currents from being transmitted to the center portion of the conductor wire and to the electrode on the distal portion of the lead.
11. An implantable medical lead for use in a magnetic resonance imaging (MRI) environment, the lead comprising:
the conductor wire having a resistivity that increases across a width of the conductor wire between a center portion of the conductor wire and an outer portion of the conductor wire such that the resistivity is greatest at the outer portion of the conductor wire; and
wherein the outer portion of the conductor wire is configured to dissipate RF electromagnetic energy received by an MRI device.
12. The lead of claim 11, wherein the resistivity increases along the width of the conductor wire at a plurality of finite locations.
13. The lead of claim 11, wherein the conductor wire comprises a plurality of conductive layers radially surrounding the center portion of the conductor wire.
14. The lead of claim 13, wherein the conductive layers successively increase in resistivity across the width of the conductor wire.
15. The lead of claim 13, wherein the plurality of conductive layers comprises a first outer conductor layer with a first resistivity, a second outer conductor layer with a second resistivity greater than the first resistivity, and a third outer conductor layer with third resistivity greater than the first and second resistivities.
16. The lead of claim 11, wherein the conductor wire comprises an inner wire core surrounded radially by a plurality of outer resistive shields that successively increase in resistivity.
17. The lead of claim 11, wherein the conductor wire is the only conductor wire that extends along the length of the lead.
18. The lead of claim 11, wherein the conductor wire continuously increases in resistivity from the center portion of the conductor wire to an outer surface of the conductor wire.
19. The lead of claim 11, wherein an outer surface of the conductor wire defines an outer surface of the lead.
20. The lead of claim 11, wherein the conductor wire is configured to attenuate RF energy from an MRI scan by the increasing resistivity across the width of the conductor wire inhibiting alternating currents from being transmitted to the center portion of the conductor wire and to the electrode on the distal portion of the lead.
US13/592,588 2007-12-06 2012-08-23 Leads with high surface resistance Active US8538551B2 (en)
US99291507P true 2007-12-06 2007-12-06
US12/329,257 US8275464B2 (en) 2007-12-06 2008-12-05 Leads with high surface resistance
US13/592,588 US8538551B2 (en) 2007-12-06 2012-08-23 Leads with high surface resistance
US14/027,678 US8788058B2 (en) 2007-12-06 2013-09-16 Leads with high surface resistance
US12/329,257 Continuation US8275464B2 (en) 2007-12-06 2008-12-05 Leads with high surface resistance
US14/027,678 Continuation US8788058B2 (en) 2007-12-06 2013-09-16 Leads with high surface resistance
US20120323297A1 US20120323297A1 (en) 2012-12-20
US8538551B2 true US8538551B2 (en) 2013-09-17
US12/329,257 Expired - Fee Related US8275464B2 (en) 2007-12-06 2008-12-05 Leads with high surface resistance
US13/592,588 Active US8538551B2 (en) 2007-12-06 2012-08-23 Leads with high surface resistance
US14/027,678 Active US8788058B2 (en) 2007-12-06 2013-09-16 Leads with high surface resistance
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JPS58192205A (en) 1982-04-22 1983-11-09 Siemens Ag Multipolar coaxial conductor
2008-12-05 US US12/329,257 patent/US8275464B2/en not_active Expired - Fee Related
2008-12-17 JP JP2011539494A patent/JP5430671B2/en not_active Expired - Fee Related
2008-12-17 EP EP08876509.4A patent/EP2355890B1/en not_active Not-in-force
2008-12-17 WO PCT/US2008/087068 patent/WO2010065049A1/en active Application Filing
2012-08-23 US US13/592,588 patent/US8538551B2/en active Active
2013-09-16 US US14/027,678 patent/US8788058B2/en active Active
International Search Report and Written Opinion issued in PCT/US2008/085533, mailed Aug. 26, 2010.
International Search Report and Written Opinion issued in PCT/US2008/087068 on Aug. 3, 2009.
WO2010065049A1 (en) 2010-06-10
US20120323297A1 (en) 2012-12-20
JP2012510854A (en) 2012-05-17
US20140018896A1 (en) 2014-01-16
JP5430671B2 (en) 2014-03-05
EP2355890B1 (en) 2014-09-03
EP2355890A1 (en) 2011-08-17
US8275464B2 (en) 2012-09-25
US8788058B2 (en) 2014-07-22
US20090149920A1 (en) 2009-06-11
Bottomley et al. 2010 Designing passive MRI‐safe implantable conducting leads with electrodes