Medical device lead including a unifilar coil with improved torque transmission capacity and reduced mri heating

ES 2 547 713 T3

DESCRIPTION

Medical device lead featuring a single-line coil with improved torque transmission capability and reduced MR heating

Technical field

The present invention relates to implantable medical devices. More particularly, the present invention relates to medical device lead constructions that include a single-line coil with a polymeric coating.

Background

Implantable medical devices for treating various medical conditions with electrical stimuli are well known. Implantable medical devices generally include a medical electrical lead to provide an electrical stimulus to a directed site within the body of a patient such as, for example, the heart or nervous system of a patient. Such leads generally have an elongated flexible insulating body, one or more internal conductors that extend through lumens formed in the body, and one or more exposed electrodes connected to the distal ends of the conductors.

The shunts can be inserted into the patient's vasculature at a venous access site and guided transvenously through the veins to the sites where the bypass electrodes will be implanted or otherwise contacted at the site of the targeted therapy. A pulse generator attached to the proximal ends of the leads applies electrical stimulus therapy to the site directed through said lead (s).

Implantable medical leads used in an MRI environment are discussed in US2009 / 0149920 A1. The influence of the filament diameter, the thread pitch and the diameter of the coil is analyzed. It turns out that the absorbed RF energy increases as a quadratic function with a larger thread pitch of the coil.

MRI compatible medical shunts are also described in US2008 / 0262584. Various embodiments are disclosed in which conductors are provided to inhibit, limit, and / or prevent unwanted heating.

Summary

The present invention is defined in claim 1 and relates to a conductive assembly for a medical device shunt. The conductor assembly includes a spirally wound conductor that includes a plurality of turns having a coil thread pitch and an outer diameter and consisting of a filament having a filament diameter. The thread pitch of the coil is one to about two times the diameter of the filament, and the outer diameter is at least 4.5 times the thread pitch of the coil, to minimize heating of the spiral wound conductor in the presence of an MR field. A polymeric wrap is formed over the spiral wound conductor so that the thread pitch of the single-line spiral wound conductor coil is maintained. The polymeric sheath is configured to increase a torque transmitting ability of the spirally wound conductor. The medical device shunt includes an insulated shunt body that includes at least one electrode, and the spirally wound conductor is electrically coupled to the at least one electrode.

The spiral wound conductor, coil thread pitch, and outer diameter are selected based on the filament diameter to minimize heating of the spiral wound conductor in the presence of an MR field. A polymeric wrap is formed around the spiral wound conductor so that the thread pitch of the one-line spiral wound conductor coil is maintained. The polymeric sheath can be partially ablated in a pattern along the length of the polymeric sheath that improves the torque transmitting ability of the spirally wound conductor.

Although multiple embodiments are disclosed, still other embodiments of the present invention will be apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be considered illustrative and not restrictive.

Brief description of the drawings

Figure 1 is a schematic view of a heart rhythm management system that includes a pulse generator coupled to a lead used in a patient's heart.

Figure 2A is a perspective view of a conductive assembly including a one-line conductive coil and a polymeric sheath in accordance with one embodiment of the present invention.

ES 2 547 713 T3

Figure 2B is a cross-sectional view of the conductor assembly shown in Figure 2A.

Figure 3A is a cross-sectional view of a conductive assembly including a partially ablated polymeric sheath in accordance with another embodiment of the present invention.

Figure 3B is a plan view of the conductor assembly shown in Figure 3A.

Figure 4 is a plan view of a conductive assembly including an ablated polymeric sheath with a stent pattern in accordance with another embodiment of the present invention.

Although the invention responds to various modifications and alternative forms, specific exemplary embodiments have been shown in the drawings and are described in detail below. However, the intention is not to limit the invention to the particular embodiments described. Rather, the invention is as defined in the appended claims.

Detailed description

Figure 1 is a schematic view of a heart rhythm management system 10 that includes an implantable medical device (DMI) 12 with a shunt 14 having a proximal end 16 and a distal end 18. In one embodiment, the DMI 12 includes a pulse generator such as a pacemaker or defibrillator. The DMI 12 can be implanted subcutaneously within the body, typically in a location such as the patient's chest or abdomen, although other implantation sites are possible. Proximal end 16 of shunt 14 may be coupled to or part of DMI 12. In turn, the distal end 18 of the shunt 14 can be implanted at or near the desired location in the heart 20.

As shown in Figure 1, a distal portion of the lead 14 is placed in the heart of a patient 20, which includes a right atrium 22, a right ventricle 24, a left atrium 26, and a left ventricle 28. In the embodiment illustrated in Figure 1, the distal end 18 of the shunt 14 is guided transvenously through the right atrium 22, through the coronary sinus orifice 29, and into a bifurcation of the coronary sinus 31 or the great cardiac vein 33. The illustrated position of lead 14 can be used to detect or provide defibrillation rhythm and / or energy to the left side of the heart 20, or to treat arrhythmias or other cardiac disorders that require the application of therapy to the left side of the heart 20. In addition It will be understood that shunt 14 may also be used to apply treatment to other regions of the heart 20 (eg, the right ventricle 24).

Although the illustrative embodiment only depicts a single implanted lead 14, it should be understood that multiple leads may be used to electrically stimulate other areas of the heart 20. In some embodiments, for example, the distal end of a second lead (not shown) it can be implanted in the right atrium 22, and / or the distal end of a third lead (not shown) can be implanted in the right ventricle 24. Other types of leads such as epicardial leads can also be used in addition to or instead of lead 14 shown in Figure 1.

During operation, lead 14 can be configured to transmit electrical signals between DMI 12 and heart 20. For example, in embodiments where DMI 12 is a pacemaker, lead 14 can be used to apply electrical stimuli to mark the heart rhythm 20. In embodiments where the DMI 12 is an implantable cardiac defibrillator, the shunt 14 can be used to apply electrical shocks to the heart 20 in response to an event such as a heart attack or arrhythmia. In some embodiments, the DMI 12 includes both pacing and defibrillation capabilities.

One or more conductors extending along the shunt 14 transmit the electrical signals between the DMI 12 and the electrodes at the distal end 18. The conductor (s) are electrically coupled to a suitable connector to communicate with the DMI 12 at proximal end 16 of lead 14, and to one or more electrodes at distal end 18. In accordance with the present invention, the conductor or conductors are spirally wound including a plurality of turns having a coil thread pitch and an outer diameter and consisting of a filament having a filament diameter. The coil thread pitch and outer diameter are selected based on the filament diameter to minimize the effects of magnetic resonance imaging (MRI) scans on the functionality and function of the shunt 14. A polymeric envelope is formed around the Spiral wound conductor to maintain the thread pitch of the one-line spiral wound conductor coil. The polymeric sheath is also configured to increase a torque transmitting ability of the spirally wound conductor.

Figure 2A is a perspective view, and Figure 2B is a cross-sectional view, of a conductor assembly 50 in accordance with the present invention. Conductor assembly 50 extends through the interior of lead 14 and includes a coil 52 and a polymeric sheath 54. Coil 52 is coupled to DMI 12 via a connector at the proximal end 16 of lead 14 and to one or more electrodes. at the distal end 18 of shunt 14. Although a single coil 52 is shown in Figure 2A and Figure 2B, the lead assembly 50 can be configured to include multiple coils 52, each capable of signaling between the DMI 12 and the electrodes at the distal end 18.

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Coil 52 includes a single filament 56 that is spirally wound about a longitudinal axis of lead assembly 50. Filament 56 has a diameter d. A lumen 58 extends through the center of coil 52 and is suitable to receive a tool for providing shunt 14, such as a guidewire or stent. Coil 52 includes a plurality of turns having an outside diameter DE and an inside diameter DI. Coil 52 also has coil pitch p that extends from the center of one turn of coil 52 to the center of a proximal turn of coil 52.

Exposure of lead 14 to magnetic resonance (MRI) fields can cause localized heating of the electrodes at distal end 18 due to excitation of lead leads (eg, coil 52). Conductors with high inductance (> 1 pH) are more resistant to excitation in MR fields. The inductance of the conductor is determined based on its geometric properties, including whether the conductor is straight or wound. For a wound or wound conductor, such as coil 52, several parameters influence its inductance, including coil pitch p, outer diameter DE, coil 52 cross-sectional area, and the number of filaments that comprise coil. In this way, the dimensions of the coil 52 can be selected to minimize the effects of magnetic resonance (MR) fields on the performance and response of lead 14. In accordance with the invention, for a conductor assembly 50 such as the one shown that includes a single, single-line coil 52, a coil pitch p in the range of one to about two times the filament diameter d, and a diameter Outer DE of at least about 4.5 times coil pitch p increases coil inductance enough to minimize the energy collected by coil 52.

Table 1 below provides examples of dimensions for coil 52 to minimize electrode heating caused by MR fields. The dimensions listed are for a coil 52 that has a length (extending from the connector to the distal end 18) in the range of about 450mm to about 600mm.

Table 1

<td>Filament diameter (d) mm (inches)</td><td>Coil Thread Pitch (p) mm (inches)</td><td>Coil Outside Diameter (OD) mm (inches)</td>

<td> 0,013 (0,0005)</td><td> 0,013 (0,0005)-0,020 (0,0008)</td><td> 0,051 (0,002)</td>

<td> 0,025 (0,001)</td><td> 0,025 (0,001)-0,051 (0,002)</td><td> 0,102 (0,004)</td>

<td> 0,051 (0,002)</td><td> 0,051 (0,002)-0,076 (0,003)</td><td> 0,229 (0,009)</td>

<td> 0,076 (0,003)</td><td> 0,076 (0,003)-0,102 (0,004)</td><td> 0,330 (0,013)</td>

<td> 0,102 (0,004)</td><td> 0,102 (0,004)-0,127 (0,005)</td><td> 0,508 (0,020)</td>

<td> 0,127 (0,005)</td><td> 0,127 (0,005)-0,178 (0,007)</td><td> 0,559 (0,022)</td>

<td> 0,152 (0,006)</td><td> 0,152 (0,006)-0,203 (0,008)</td><td> 0,686 (0,027)</td>

<td> 0,178 (0,007)</td><td> 0,178 (0,007)-0,229 (0,009)</td><td> 0,787 (0,031)</td>

<td> 0,203 (0,008)</td><td> 0,203 (0,008)-0,254 (0,010)</td><td> 0,914 (0,036)</td>

<td> 0,229 (0,009)</td><td> 0,229 (0,009)-0,279 (0,011)</td><td> 1,016 (0,040)</td>

<td> 0,254 (0,010)</td><td> 0,254 (0,010)-0,305 (0,012)</td><td> 1,143 (0,045)</td>

<td> 0,279 (0,011)</td><td> 0,279 (0,011)-0,330 (0,013)</td><td> 1,245 (0,049)</td>

These dimensions are suitable for a conductor assembly 50 that includes a single, single-line coil 52. The dimensions listed for filament diameter d, coil pitch p, and coil outside diameter DE are shown for guidance only. For example, other dimensions are also contemplated that reduce electrode heating due to MR fields to suitable levels. In addition, for embodiments of conductor assembly 50 that include multiple coaxial one-wire coils, these dimensions may change to account for the interaction of the coils with each other in the presence of an MR field.

Coil 52 with a small diameter DE and having a small thread pitch may be prone to damage during construction and use. For example, in actively locking leads, coil 52 is designed to rotate relative to the lead body and drive torque to extend the locking helix into heart tissue 20. Single-wire coils, such as coil 52, tend not to conduct torque well, and the forces typically encountered by shunt 14 can cause coil 52 to experience stress concentrations in parts of coil 52, which can cause a premature coil fatigue 52. In order to improve the torque transmission capacity of coil 52, as well as to maintain the integrity of the thread pitch of coil p, polymeric sheath 54 is formed around coil 52 so that polymeric sheath 54 cover or wrap coil 52.

The polymeric wrap 54 may be formed on the coil 52 so that the portions of the polymeric wrap 54 extend between the turns of the coil 52 in order to maintain adequate spacing of the turns of the coil from each other. In some embodiments, polymeric wrap 54 is a sleeve that mounts on top of coil 52 during manufacture. In other embodiments, polymeric wrap 54 is extruded onto, molded around, adhered to, or heat shrunk onto coil 52. Polymeric wrap 54 can be formed on coil 52

ES 2 547 713 T3 with an open lumen 58. Alternatively, coil 52 can be wound around a tube or cylinder of insulating material, and polymeric wrap 54 can be formed around coil 52 thereafter.

The polymeric sheath 54 is sufficiently thick and is composed of a material that is sufficiently rigid to increase the torque transmission capacity and maintain the pitch of the coil p of the coil 52, while still allowing the conductor assembly 50 bends sufficiently during operation. In some embodiments, the thickness g of the polymeric shell 54 is less than about 0.051 mm (0.002 inches) and is manufactured from a material selected from the group consisting of expanded polytetrafluoroethylene (PTFEe), coated PTFEe, polytetrafluoroethylene (PTFE), copolymer of ethylene-tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), silicone, polyurethane, silicone-polyurethane copolymer, and a porous polymer. It will be understood that other materials and other thicknesses g are also possible.

Polymeric wrap 54 can be adhered to portions of coil 52 to prevent polymeric wrap 54 from delaminating from coil 52. This can often be accomplished by applying an adhesive material to coil 52 prior to forming polymeric wrap 54 thereon. However, in some cases, the material used for the polymeric wrap 54 does not adhere well to the material used for the coil 52. In order to ensure good adhesion, coil 52 can be coated with a material that binds well to polymeric wrap 54. For example, filament 56 can be coated in a suitable polymer prior to winding filament 56 onto coil 52. Alternatively, coil 52 may be etched, such as laser etching, with a pattern that allows good bonding to polymeric wrap 54.

In some cases, portions of the polymeric wrap 54 may be modified to increase the flexibility of the polymeric wrap 54. For example, in a J-shaped lead, the lead has a steep curve in place of the J-shaped portion. The interaction between certain materials for polymeric shell 54 and conductive coil 52 in this steep curve can cause conductive assembly 50 to remain J-shaped, which can prevent manipulation of the J-shaped portion during implantation.

Figure 3A is a cross-sectional view and Figure 3B is a plan view of a conductor assembly 60 in accordance with another embodiment of the present invention that includes elements that enhance the flexibility of the conductor assembly 60. Conductor assembly 60 includes coil 62 and polymeric sheath 64 with material and dimensional characteristics substantially similar to coil 52 and polymeric sheath 54, respectively, discussed above in connection with Figures 2A and 2B. In this embodiment, polymeric sheath 64 is partially ablated with an ablation pattern 70 along a length of at least a portion of conductive assembly 60. Polymeric wrap 64 is partially ablated while polymeric wrap 64 is not completely removed (ie, coil 52 is not exposed) at ablated portions of polymer wrap 64. For example, in a bypass in J-shaped, polymeric shell 64 can be partially ablated along the inner radius of the steep curve in the J-shaped portion. By improving the flexibility of the conductor assembly 60, the remaining thickness of the polymeric sheath 64 at the partially ablated locations serves to maintain the thread pitch p of the coil 62 and improve the torque transmitting ability of the coil 62 .

In the embodiment shown, ablation pattern 70 is a spiral pattern that wraps around polymeric wrap 64, and approximately 20% of polymeric wrap 64 is partially ablated. However, it will be understood that the ablation pattern 70 may comprise any shape, and any percentage of the polymeric shell 64 may be partially ablated, to improve the flexibility of the lead assembly 60 while maintaining the thread pitch of the coil p and se improves the torque transmission capacity of the driver assembly 60.

Polymeric wrap 64 can be partially ablated with ablation pattern 70 using various techniques. In some embodiments, an unmodified polymeric wrap 64 is formed on coil 62 and then modified into the desired pattern. Ablation pattern 70 can be formed by, for example, laser ablation of ablation pattern 70 within polymeric envelope 64. Ablation pattern 70 may alternatively be formed by etching or forging ablation pattern 70 into polymeric envelope 64.

Figure 4 is a plan view of a conductor assembly 80 in accordance with another embodiment of the present invention. Conductor assembly 80 includes coil 82 and polymeric sheath 84 having material and dimensional characteristics substantially similar to coil 52 and polymeric sheath 54, respectively, discussed above in connection with Figures 2A and 2B. In this embodiment, the polymeric sheath 84 is ablated with a stent pattern 90 along a length of at least a portion of the conductive assembly 80. The stent pattern 90 includes substantially shaped ablated portions 92 rhombus and non-ablated portions 94. In some embodiments, the ablated portions 92 are partial ablations that do not extend completely through the thickness g of the polymeric shell 84. In other embodiments, the ablated portions 92 are fully ablated through the thickness g of the polymeric shell 84.

In summary, the present invention relates to a lead assembly for a medical device shunt that includes a spirally wound lead that includes a plurality of turns with a coil thread pitch and

ES 2 547 713 T3 an outer diameter and consisting of a filament having a filament diameter. The coil thread pitch and outer diameter are selected based on the filament diameter to minimize heating of the spiral wound conductor in the presence of an MR field. In some embodiments, the thread pitch of the coil is one to about two times the diameter of the filament, and the outer diameter is at least 4.5 times the thread pitch of the coil. A polymeric wrap is formed around the spiral wound conductor so that the thread pitch of the one-line spiral wound conductor coil is maintained. The polymeric sheath is configured to increase a torque transmitting ability of the spirally wound conductor. In some embodiments, the polymeric sheath is partially ablated in a pattern along a length of the polymeric sheath that improves the torque transmitting ability of the spirally wound conductor 10. In an exemplary embodiment, the medical device shunt includes an insulated shunt body that includes at least one electrode, and the spirally wound conductor is electrically coupled to the at least one electrode.