Atraumatic detection/stimulation microlead

Abstract

An atraumatic detection/stimulation lead is disclosed. The lead includes at least one microcable having a core cable comprising a plurality of elementary metal strands. One of the microcables has provided at its distal end an atraumatic protection device. The atraumatic protection device includes a protective coating on the distal ends of the elementary strands of the microcable, and the protective coating is covered by a protective cap of deformable material. The protective cap may be a conical distal end adapted to deform and axially flatten out. The microcable may have an overall diameter less than or equal to 1.5 French (0.50 mm).

Claims

1. A method of manufacturing a lead, comprising: constructing a microcable comprising a core cable made of a plurality of elementary metal strands, each having a distal end; creating a protective coating on the distal ends of the elementary strands of the core cable; and positioning a protective cap of deformable material over the protective coating at a distal end of the core cable.

2. The method of claim 1, wherein the microcable further comprises a plurality of core cables.

3. The method of claim 1, wherein creating the protective coating comprises melting the distal ends of the elementary strands.

4. The method of claim 3, wherein positioning the protective cap comprises fitting the protective cap over a bulbous shape formed by melting the distal ends of the elementary strands.

5. The method of claim 3, wherein positioning the protective cap comprises adhering a length of a core coating sleeve extending from the protective cap along a length the core cable.

6. The method of claim 1, wherein the protective cap is made of a compressible material such that as the protective cap moves into contact with a venous wall, the protective cap can axially flatten to provide a large surface area for distribution of pressure forces on the venous wall.

7. The method of claim 1, wherein the protective coating has the shape of a sphere.

8. The method of claim 7, wherein the diameter of the sphere is between 0.3 mm and 0.4 mm.

9. The method of claim 1, wherein the protective cap is formed from a material that deforms and axially flattens.

10. The method of claim 1, wherein the protective cap is formed by silicone deposition.

11. The method of claim 1, wherein the protective cap comprises a silicone tube covering the protective coating and is secured at a distal end of the silicone tube by silicone adhesive conformation.

12. The method of claim 11, wherein the protective cap and silicon tube provide a constant coating thickness of silicone along the microcable from the tube to the protective cap.

13. The method of claim 12, wherein the silicone tube is glued to the core cable and is sized having a diameter that is substantially the same as the diameter of the protective coating, and wherein a deformable geometry at the distal end is formed at the end of the silicone tube.

14. The method of claim 13, wherein the deformable geometry of the distal end is a conical portion.

15. The method of claim 1, wherein the core cable comprises a plurality of intermediate strands, each of the intermediate strands comprising a plurality of elementary metal strands.

16. The method of claim 1, further comprising surrounding the core cable with an insulation layer.

17. The method of claim 16, wherein the insulation layer surrounding the core cable of the microcable has at least one exposed area to form a detection or a stimulation electrode.

18. The method of claim 1, wherein the lead comprises seven microcables.

19. The method of claim 1, wherein said deformable material is a material from the group consisting of: silicones, polyurethanes, polyethers, and copolymers and combinations thereof.

20. The method of claim 1, wherein the microcable has an overall diameter less than or equal to 1.5 French (0.50 mm).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a is a partial perspective view of the distal end of a monopolar microlead with a protective device according to the invention.

(2) FIG. 1b is a sectional view of the core cable of the microcable of FIG. 1a.

(3) FIG. 1c is a sectional view of an elementary strand of the core cable of FIG. 1b.

(4) FIG. 2a is a partial perspective view of a multipolar microlead the distal end of a microcable of which bears an atraumatic protection device according to the invention.

(5) FIG. 2b is a cross section of the microlead of FIG. 2a.

(6) FIG. 3a is a side view of a core cable of a microcable with an encapsulation means of elementary strands.

(7) FIG. 3b is a CAD view of FIG. 3a.

(8) FIG. 4a is a side view of the distal end of a core cable of a microcable with a protection cap.

(9) FIG. 4b is a CAD view of FIG. 4a.

(10) FIG. 5a is a side view of the distal end of the core cable of FIG. 4a whose protective cap is distorted.

(11) FIG. 5b is a CAD top view of FIG. 5a.

(12) FIG. 6 is a sectional view showing the distal end of the core cable of FIG. 4a stopped in a vein of the deep coronary network.

(13) FIG. 7 is a sectional view showing the distal end of the core cable of FIG. 5a stopped against a venous wall of the deep coronary network.

(14) FIG. 8 is a sectional view of an alternative embodiment of the atraumatic protection device according to the invention.

DETAILED DESCRIPTION

(15) The microleads of the invention are detection/stimulation microleads intended to be implanted in venous, arterial and lymphatic networks. The leads can be either monopolar microleads with a single microcable or multipolar microleads having a plurality of microcables.

(16) In some implementations, these microleads may be intended for cardiac pacing applications, including resynchronization of the cardiac rhythm, which can involve positioning the stimulation electrodes in the coronary venous system, which means veins of small diameter can be reached (and hence it supposes a small thickness). Therefore at least one microcable of the microleads may have an overall diameter of not more than 1.5 French (0.50 mm).

(17) The microlead 50 shown in FIG. 1a is a monopolar microlead with one microcable 40 whose conductor core cable 11, as shown in FIG. 1b, consists of seven intermediate strands of seven elementary metal strands 10 assembled into strands. The diameter of an elementary strand is, for example, 0.033 mm. The diameter of the core cable 11 of the microcable 40 is then 0.3 mm.

(18) FIG. 1c illustrates an elementary strand 10. Strand 10 includes a core 1 in a structural material such as stainless steel, cobalt alloy of the MP35N series, a noble metal, titanium, or a NiTi alloy, of high fatigue resistance, the diameter of 0.033 mm averagely providing a maximum resistance to fatigue tensile strength in the extreme stress conditions to which such structures can be submitted.

(19) Strand 10 may include an amount of radiopaque material 2 in a composite structure providing both fatigue resistance of the cable and radiopacity. Material 2 may be or include any suitable material having X-ray visibility features (e.g., tantalum (Ta), tungsten (W), iridium (Ir), platinum (Pt) and gold (Au)). With modern medical imaging techniques such as Mill, given the small diameter of the strands, this favors heat dissipation and reduces the heating effects of MRI. The thermal energy stored by the material, already limited in volume, can be further reduced if the individual strands are coated with an outer layer of material of low magnetic susceptibility (magnetic susceptibility is the ability of a material to be magnetized by the action of an external magnetic field). The most favorable materials in this application are those whose magnetic susceptibility is less than 2000.Math.10-12.Math.m.sup.3.Math.mole.sup.−1, including tantalum (Ta), titanium (Ti), rhodium (Rh), molybdenum (Mo), tungsten (W), palladium (Pd) and gold (Au).

(20) The microlead 50′ shown in FIG. 2a is a multipolar microlead and includes a plurality of seven microcables 40.sub.1, 40.sub.2, 40.sub.3, 40.sub.4, 40.sub.5, 40.sub.6, 40.sub.7 assembled in a strand especially shown in FIG. 2b in cross section, each microcable constituting for the microlead 50′ a conduction line connected to a pole of the generator.

(21) As shown in FIG. 2b, a microcable includes a core cable 12 surrounded by an insulation layer 20 so as to provide electrical insulation between the microcables. In the embodiment shown in FIG. 2b, each core cable 12 is formed by a bundle of seven elementary strands 10 having a diameter of also, for example, 0.033 mm. The diameter of a core cable 12 is then 0.1 mm.

(22) To achieve the insulation layer 20, materials with high chemical inertness which also have very good insulation, such as fluoropolymers, may be used. One particular example is ETFE (ethylene tetrafluoroethylene).

(23) As can be seen in FIG. 2a, the insulation layers 20 surrounding the core cables 12 of the microcables have at least an exposed area 30 to form a detection/stimulation electrode for the microlead 50′, such as electrodes 52 in FIG. 2a. The exposed areas 30 are notably obtained by laser ablation technique.

(24) In this embodiment, one can observe that the central microcable 40.sub.7 extends beyond the other microcables of the microlead 50′, such that one can install one or more electrodes at its distal end. Of course, the distal end of the microcable 40 of the microlead 50 of FIG. 1a can also be equipped with one or more electrodes.

(25) There may be a risk of perforation of the deep veins of the coronary network due to irregularities that may appear at the distal ends of the microcables during manufacturing. Indeed, the use of a cutter to cut the microcables can lead to the formation of offensive edges (e.g., having pointed and/or sharp angles). One alternative is the use of a laser shot. In this case, the observed risk is that the winding of the strands is damaged and that one or more strands deviate from the nominal isodiameter and become hurtful.

(26) Therefore, as can be seen in FIGS. 1a and 2a, the distal ends 40 and 40.sub.7 of the microcables that may reach veins of the deep coronary network are equipped with an atraumatic protection device 60. This device 60 essentially consists of two main parts, namely a coating means 61 for the distal ends of the elementary strands of the core cable 11, 12, and a protective cap 62 made of a deformable and incompressible material, wrapping the coating means 61. By its mechanical deformability of incompressibility properties and its biocompatibility, the silicone may be a material of choice for the tip 62.

(27) The coating means 61 is designed to eliminate the disadvantages associated with irregularities in the cutting of the microcables. In the embodiment illustrated in FIGS. 3a and 3b, the coating means is made by melting by a laser shot from the distal ends of the elementary metal strands 10 forming the core cables 11, 12. The transformation of the end of the microcable in a homogeneous spherical surface thus eliminates the risk of perforation due to irregularities in the core cables 11, 12.

(28) The protective cap 62, shown in FIGS. 4a and 4b with a conical distal end, is intended to address problems related to the rigidity of the metal sphere forming the coating means 61. Indeed, this non-deformable structure cannot adapt the distal end of the microcables to the geometry of deep coronary vessels. The deformability of the tip 62 solves this first problem. Furthermore, the pressures applied by the coating sphere on the venous walls, during insertion of the microlead for example, may be relatively large because the sphere/walls contact surfaces are small. As shown in FIGS. 5a and 5b, the distal end of the tip 62 is able to deform and axially flatten while retaining the area of the contact surfaces. Deformability and incompressibility of the cap 62 ensures that the forces exerted by the physician are spread over a maximum surface area and thus limit the pressure on the walls of the veins.

(29) Note that the metal sphere 61 at the end of the microcable can also mechanically hold the silicone cap 62. To increase the holding force, the protective cap 62 extends along the core cable in the form of a core coating 621. Preferably, the silicone is glued on the entire length of the core coating 621.

(30) Regarding the dimensional aspects, for a monopolar version (with a single microcable as the microcable 40 of FIG. 1a), the sphere 61 may have a diameter between 0.3 and 0.4 mm. So that the tip 62 can move in an implantable catheter of inner diameter 1.6 French (0.53 mm), it is appropriate that the thickness of the silicone cladding is of the order of 0.1 mm or less, or an overall diameter about 0.5 mm, along the length of the cable, and locally of 0.6 mm at the sphere 61, in view of the possibility of local deformation permitted at this location of the silicone sheathing and of the thin catheter tube at the passage of the distal end of the lead.

(31) For a multipolar version (with several microcables 40.sub.1-40.sub.7 as shown in FIG. 2a), only the central 40.sub.7 microcable of 0.1 mm diameter supports a distal end with the sphere 61 and the silicone cap 62. In this configuration, the thickness of the cover may vary from 0.2 to 0.5 mm maximum, the limitation being that of the passage in the catheter.

(32) Finally, it is contemplated having a steroid such as dexamethasone in the silicone cap 62, for example by mixing silicon powder with dexamethasone, a method commonly used in the manufacture of cardiac leads.

(33) FIG. 6 illustrates a first example of a situation with a potential risk of perforation wherein the microcable of the microlead faces a vein of reduced diameter.

(34) In the case of a microcable without an atraumatic device, the vein wall alone should withstand the deformation produced by the force exerted by the microlead. The risk of perforation is then dependent on the force applied by the physician and the resistance of the vein walls in contact.

(35) As shown in FIG. 6, the protective cap may help guide the microlead in a vein of the coronary network of smaller diameter, making contact with the walls of the vein and stopping the progression of the microlead. In this case, the area of the silicon surface in contact with the vein wall is preserved, and ensures a better distribution of pressures on the walls (the involved vein surfaces are indicated by the references A, B and C).

(36) In the example of FIG. 7, the end of the cap 62 is blocked by a front contact with a vein wall of the deep coronary network. The vein and the cap 62 deform to absorb the pressing force. The cap then adopts a distorted geometry as that shown in FIGS. 5a and 5b. The deformation of the silicone defines surfaces A′, B′ and C′ having a total contact area much larger than that corresponding to a microcable departed of the atraumatic system of the invention. The result is again a better distribution of pressures applied to the walls.

(37) FIG. 8 shows an advantageous embodiment that ensures a constant coating thickness of silicone along the microcable.

(38) In this embodiment, the connector 62 includes a protective silicone tube 62b glued to the core cable 11, 12 and exactly covering the coating metal sphere 61. The deformable geometry in the distal end 62a is formed at the end of the silicone tube 62b, for example by manual conformation of silicone glue.