IMPLANTABLE MEDICAL LEAD AND METHOD FOR MANUFACTURE THEREOF

Abstract

An implantable medical lead for implantation in a patient which has at least one electrical conductor connected to at least one electrode and/or sensor of said lead. The at least one conductor is arranged within a continuous sheet of a polymer material. A distal portion of the lead is adapted to be located in or at a heart of said patient and a proximal portion of said lead is connectable to an implantable medical device and arranged such that, when connected to the device, at least a part of the proximal portion of the sheet is placed in dose proximity to said medical device. At least the proximal portion of the polymer sheet material is processed in at least a first heat process stage such that an inherent resistance to wear of the polymer sheet material is substantially maintained, and the distal portion of said polymer sheet material is processed in at least a second heat process stage in which a polymer morphology of said polymer material is altered such that an inherent flexibility of the polymer sheet material is substantially increased.

Claims

1. A method for manufacturing of an implantable polymer sheet material for implantation in a patient, wherein a distal portion of said polymer sheet material is adapted to be located in or at a heart of said patient and wherein a proximal portion of said polymer sheet material is connectable to an implantable medical device and arranged such that, when connected to said device, at least a part of said proximal is placed in dose proximity to said medical device, said method comprising the steps of: providing a continuous sheet of a polymer material; processing at least said proximal portion of said polymer sheet material in at least a first heat process stage such that an inherent resistance to wear of said polymer sheet material is substantially maintained; processing said distal portion in at least a second heat process stage in which a polymer morphology of said polymer material s altered such that an inherent flexibility of said polymer sheet material is substantially increased.

2. The method according to claim 1, wherein the step of providing a continuous sheet of a polymer material comprises a step of providing a semi-crystalline copolymer having at least a soft amorphous segment and at least a hard crystalline segment being at least partially crystallized.

3. The method according to claim 1, wherein the step of providing a continuous sheet of a polymer material comprises a step of providing a semi-crystalline copolymer having at least a soft amorphous segment where at least a portion thereof comprises at least one flexible polymeric material from a group containing silicone, polyethers, polyethylene oxide, polyolefins, polycarbonates, or a combination thereof, and having at least a hard crystalline segment where at least a portion thereof comprises at least one crystallizable polymeric material from a group containing aromatic urea, aromatic or aliphatic urethane.

4. The method according to claim 1, wherein the first heat process stage comprises heating within a temperature interval from about 50 to about 100 C. during a period of about 30 minutes to about 5 hours, and wherein the second heat process stage comprises heating at a temperature at least 10 C. above the temperature of the first heat process stage during a period of at least 5 minutes.

5. The method according to claim 4, wherein the second heat process stage comprises heating at a temperature of about 120 C. during a period of about 30 minutes.

6. The method according to claim 1, comprising conducting the first and second heat process stages simultaneously by using a common oven that provides individual heat treatments to individual portions of the polymer sheet material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The features that characterize the invention, both as to organization and to method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawings. It is to be expressly understood that the drawings is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawings.

[0029] FIG. 1 illustrates the general principle of a medical lead in relation to a heart of a patient and a medical device.

[0030] FIG. 2 illustrates the relationship between abrasion resistance and hardness of a silicon elastomer material.

[0031] FIG. 3 illustrates the relationship between abrasion resistance and hardness of a polymer sheet material according to the invention.

[0032] FIG. 4 illustrates the relationship between stiffness as a function of heat treatment temperature of a polymer sheet material according to the invention.

[0033] FIG. 5 shows a block diagram illustrating the principles of a process according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The following is a description of exemplifying embodiments in accordance with the present invention. This description is intended for describing the general principles of the invention and is not to be taken in a limiting sense. Please note that like reference numerals indicate structures or elements having same or similar functions or constructional features.

[0035] Referring first to FIG. 1, there is shown an implantable medical device or heart stimulator 2 in electrical communication with a human heart 1 via an implantable medical lead or cardiac lead 4 arranged for stimulation and sensing. Moreover, the heart stimulator 2 includes electronic, circuitry and a battery contained within a hermetically sealed pacemaker housing 3. The housing 3 has a metallic casing of a biocompatible material, for example, titanium, enclosing the electronic circuitry and battery, and a molded plastic header portion, comprising connector blocks and apertures for receiving the connectors at the proximal ends of the cardiac leads. Also, at the proximal end of the lead, a coil of excess lead 8 is provided, which is to be implanted together with the medical device 2.

[0036] The electronic circuitry includes at least one pulse generator for generating stimulation pulses, sensing circuitry for receiving cardiac signals sensed by the cardiac lead 2, and a controller. The controller controls both the sensing of cardiac signals and the delivery of stimulation pulses, for instance as to the duration, energy content and timing of the stimulation pulses.

[0037] The stimulation pulses generated by the pulse generator are transmitted via the cardiac lead 4 and delivered to the cardiac tissue by the use of tip electrodes positioned at the distal end 5 of the cardiac lead. Generally, the tip electrode acts as the cathode when the cardiac pulse is delivered. Furthermore, in unipolar cardiac systems, the casing 3 acts as the anode, while in bipolar cardiac systems, the anode is provided by an annular or ring electrode 7 arranged on the cardiac lead at a small distance from the tip electrode.

[0038] It should be noted that even though a ring electrode 7 is illustrated in the greatly simplified drawing of FIG. 1, the present invention is equally applicable to unipolar, bipolar, and multipolar systems. Thus, implantable leads with or without ring electrodes are equally contemplated without departing from the scope of the invention. Furthermore, even though only one lead 4 for attachment and stimulation in the right ventricle is illustrated in the drawing, the medical implant 2 may be connected to further leads, for instance for stimulation of the right atrium, the left atrium, and/or the left ventricle.

[0039] The implantable medical lead 4 according to the present invention preferably includes at least one electrical conductor connected to at least one electrode and/or sensor of the lead, the at least one conductor being arranged within a continuous sheet of a polymer material. It should be noted that such a polymer sheet material may have the shape of a tube or the like provided with at least one lumen. In other words, the at least one electrical conductor is situated within a polymer sheet material, e.g. an isolating polymer tube.

[0040] At least a portion of the proximal end of the lead has a maximized resistance to wear, or at least those parts which may be in contact with the device 2 when implanted. For example, that part of the lead that is implanted into the subcutaneous pocket is preferably subjected to a heat treatment such that the wear resistance of the polymer sheet material is substantially maintained. In FIG. 1, the lead 4 is provided with a wear or abrasion resistance surface property, which more or less equals a part of the lead 8 being located in the subcutaneous pocket and in proximity to the pocket, i.e. the proximal end portion. Preferably, the part of the lead that is less flexible, i.e. the proximal end, has a high resistance to wear. However, as is understood, the wear resistant property may also be arranged in other ways. For example, only the part of the lead being placed within the pocket may be processed such the inherent wear resistance property is maintained. Similarly, the distal end or a distal portion of the lead is subjected to heat treatment such that the inherent flexibility property of the polymer sheet material is increased. In other words, the distal end, or at least a portion thereof, is more flexible than the proximal end, or at least a portion thereof. In FIG. 1, about 10 cm is flexible, (not shown) of the about 50 cm long lead. The distal treatment should be applied to at least about 5 cm of the distal end, and preferably about 10 to about 25 cm, which is the distal portion of the lead that is situated within the heart.

Experiment 1

[0041] FIG. 2 presents experimental information showing that the hardness property and abrasion resistance property are related. The test result which relates to a silicone elastomer shows that within a group of otherwise chemically identical, the abrasion resistance increases with increasing hardness. The silicone elastomer or rubbers were cured and post-cured to achieve a specific hardness (Shore A). These were then tested in an abrasion test apparatus, which by St. Jude Medical internally is designated ES 1907 rev X1, designed for measuring the abrasion resistance of pacemaker lead bodies. For this type of abrasion, it has thus been demonstrated that harder materials, of otherwise identical composition as that of the present invention, have greater resistance to abrasion. Thus, it is beneficial to provide softness in the tip for flexibility, but retain hardness in the proximal end to optimize abrasion resistance.

Experiment 2

[0042] In FIG. 3, test results for a material according to an embodiment of the present invention, similar to that of the experiment 1, is shown. The graph in FIG. 3 presents abrasion resistance results on a pacemaker lead body made of an Elast-Eon material, more specifically an Elast-Eon 2A material. This material is provided by Aor-Tech. The purpose of such an experiment is to simulate the wear situation of a medical lead in abutment with a medical device can when implanted. The experiment was similarly performed as experiment 1 in the way that the material was first subjected to heat treatment followed by an abrasion test. The abrasion test was performed according to a St. Jude Medical internal test method called 60010764 rev P02. The result shows that the lower hardness material, i.e. less stiff as indicated by lower Young's modulus, from a heat treatment at 120 C/6 hrs has a lower abrasion resistance compare to material treated at 85 C/4 h that has higher stiffness/hardness/modulus, and thus higher abrasion resistance.

[0043] According to an embodiment of the present invention, the at least proximal portion of the polymer sheet material has a hardness ranging from Shore 60A to Shore 80D. Thus, the at least proximal portion of the medical lead is provided with an inherent wear resistance property.

Experiment 3

[0044] FIG. 4 shows the relationship between stiffness, indicated by Young's Modulus, and treatment temperature of a polymer sheet material according to an embodiment of the invention. The experiment was performed by first heat treating an Elast-Eon 2A material in a conventional oven. In FIG. 4, the name Optim is used which is a name of the Elast-Eon 2A material used at St. Jude Medical. Thereafter, the stiffness was then measured by a conventional apparatus for measuring tensile properties of stress versus strain. Lloyd Instruments LRX plus ExT with 10N load cell tested on tubing in a mandril clamp with 100 mm gauge length. The graph shows that a higher treatment temperature results in a lower stiffness of the polymer material or Elast-Eon 2A provide by Aor-Tech.

Heat Treatment Process

[0045] As is understood by the skilled person in the art, the heat treating process according to the present invention may he performed in number of alternative ways. In an example method for manufacturing of an implantable polymer sheet material which is to be implanted into a patient according to the present invention, first a continuous sheet of a polymer material is provided. Thereafter, at least a proximal portion of the polymer sheet material is processed in at least a first heat process stage. Thereby, an inherent resistance to wear of the polymer sheet material is substantially maintained. Thereafter, a distal portion in at least a second heat process stage is processed. The polymer morphology of this polymer material is altered such that an inherent flexibility of said polymer sheet material is substantially increased.

[0046] In FIG. 5, there is shown a schematic block diagram of a preferred process. First, at step S100, at least one polymer tube is placed in an oven having a temperature of about 85 C. The at least one polymer tube is annealed in a batch process over the full length of the tube to stabilize. its dimensions for 4 hours. The temperature and/or time parameter may he varied within the interval of the present invention, i.e. a temperature interval from about 50 C. to about 100 C. during a period of about 30 minutes to about 5 hours, to achieve a desired stabilizing effect of the dimensions. However, a preferred first process steps is, as mentioned above, to subject the tube to a first heat treatment step S100 at a temperature of about 85 C. for about 4 hours. Thereafter, at step S110, a lead is assembled using a processed polymer tube as an outer tube. This is not described in detail since is conventional practice within the art. After assembly of a lead, the lead is heat treated in a second heat treatment step S120. Preferably, a heating mantle or other suitable localized controlled temperature heat source is used to treat the sections of the lead, preferably about 10-25 cm of the distal lead end, where a higher degree of flexibility is desired. Temperatures selected influence the modulus or stiffness of the material in a controlled fashion. However, the second heat treatment is preferably performed at a temperature of about 120 C. for about 30 minutes.

[0047] As is understood, the tube or polymer sheet material may be gradually heated to attain a mechanical property gradient, i.e. the flexibility at the distal end is gradually decreased towards the proximal end, or at least up to that part of the lead that is not be wear or abrasion resistant.

[0048] Also, as is understood by those skilled in the art, the method may also comprise the step of providing at least one electrical conductor adapted to be connected to at least one electrode and/or sensor of the lead. Also, the step of assembling the medical lead may be done in a number of alternative ways. For example, the assembly of the lead may be performed after completion of the first and second heat treatment steps, or may be performed before the heat treatment. However, a preferred embodiment is to assemble the medical lead after the first heat treatment. During the first heat treatment stage, relaxation of internal stresses can occur which may alter the dimensions of the polymeric component slightly. Thus, it is useful to treat the entire tube prior to the assembly in order to control tolerances of components of the medical lead and device. Moreover, the assembling may also be performed in a number of alternative ways. For example, the conductors may be positioned within the polymer sheet material after the first heat treatment step, followed by the second heat treatment step. However, this assembling may or may not include mounting the sensor and/or electrode to the lead and also the medical device or control unit may also be mounted in the same assembly step.

[0049] Although an exemplary embodiment of the present invention has been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications, or alterations to the inventions as described herein may be made. Thus, it is to be understood that the above description of the invention and the accompanying drawings is to be regarded as a non-limiting example thereof and that the scope of protection is defined by the appended patent claims.