Patent Application
20080306578
1. Field of the Invention
The present invention relates to a cardiac lead of the type having a thermoplastic tubing and an electrode or a pin connector, and to a method for fixing a thermoplastic cardiac lead tubing to a cardiac lead electrode or pin connector.
2. Description of the Prior Art
A cardiac lead may be a bipolar (or unipolar or multipolar) electrode lead used for providing stimulation of cardiac tissue, and/or for sensing heart signals, by means of a pulse generator or some other type of heart stimulation apparatus. The cardiac lead carries the stimulus from the pulse generator to the cardiac tissue, or relays intrinsic cardiac signals back to a sense amplifier of such pulse generator.
In a known cardiac lead, an electrically conducting coil interconnects a cardiac electrode (mounted at a distal end of the lead) and a connector (for connection to a cardiac stimulation device). The coil is surrounded by a tubing (for protection and electrical insulation of the coil) that is attached to the electrode and the connector, respectively, at the ends of the cardiac lead. The tubing material is commonly silicone, which is advantageously fixed to the electrode or connector by a silicone adhesive. Such adhesives are commonly used in medical applications.
A desire for improved tubing properties, such as increased resistance to abrasion and altered flexibility, has lead to the use of other tubing material, such as organic polymeric materials. However, due to their intrinsic properties such polymeric materials cannot be effectively fixed to the electrode or connector by silicone adhesives. Other adhesives which may render effective fixation are known. These are, however, not approved for medical use. As an alternative, the solvent method has been applied for joining the tubing to the electrode. Disadvantageously, joints obtainable by said method are difficult to make accurately and also difficult to inspect.
An object of the present invention is to provide an alternative, improved cardiac lead, wherein a thermoplastic tubing is attached to an electrode or a pin connector.
Another object of the present invention is to provide an alternative and improved method for attaching a thermoplastic tubing to an electrode or a pin connector.
The invention is based on the insight that the intrinsic properties of thermoplastic tubing materials can be utilised for their attachment to electrical contact means, such as an electrode or a pin connector, without the use of glues or adhesives. Hence, improved strength and simple production processes are achieved. Furthermore, no separate adhesive is necessary, thereby reducing costs and avoiding regulatory procedures concerning materials for use in medical devices.
Thus, in accordance with the present invention a cardiac lead has a thermoplastic tubing and an electrode or a pin connector, wherein said electrode or a pin connector is provided with outer thermoplastic fixation means, an end portion of the tubing is coaxially provided around a portion of the fixation means, and a section of the end portion of the tubing is fused to the fixation means, such that the tubing is fixed to the electrode or pin connector.
The fusing of the tubing and the fixation means provides a “seamless” attachment between the tubing and the electrode or pin connector, conferring mechanical strength, as well as an insulating closure.
The fixation means is preferably provided in a recess in the electrode or pin connector. Such fixation means can easily be casted during production of the contact means and provides for a durable attachment. Although not necessary, for the ease of production and quality of the attachment said thermoplastic fixation means may extend essentially around the perimeter of the electrical contact means.
The above object is achieved in accordance with present invention by a method for fixing a thermoplastic cardiac lead tubing to a cardiac lead electrode or pin connector provided with outer thermoplastic fixation means, the method including the steps of
This method results in a cardiac lead according to the first aspect of the present invention. The heating of the thermoplastic tubing and fixation means material to a temperature close to the melting points thereof causes fusing of the materials. The fused materials form a “seamless” connection when allowed to solidify.
The heating can be performed by any conventional means and preferably by conductive, irradiative or ultrasonic heating. More preferably the heating and fusing are performed by heat welding, providing a fast and reliable fixation of the tubing to the electrical contact means. Most preferably, the heat is applied locally to said section of the end portion of the tubing and to the fixation means, so as to avoid possibly negative influence on other parts of the cardiac lead. For example, the distal end of a cardiac lead may comprise a steroid plug, which is sensible to heat. Irradiative heating may be performed by laser. Ultrasonic heating may be performed as ultrasonic welding.
Supplementary heat treatment, such as annealing (e.g. to avoid environmental stress cracking), may additionally be performed.
The design of said electrode or pin connector is preferably as defined in relation to the first aspect of the invention.
In both aspects of the invention, the material of the thermoplastic tubing, as well as the material of the thermoplastic fixation means, preferably comprises a thermoplastic polymer. Such a material allows for heating to cause melting and for fusing, respectively. Property-wise such materials should preferably be rigid or flexible thermoplastic materials suitable for extrusion or injection molding and be biocompatible. Common materials fulfilling these requirements are polyurethanes, polyolefins (such as UHMWPE, HDPE, LDPE, etc.), polycarbonates (plexiglass), polyesters (such as PET, Dacron), polyamides (such as Nylon), polyimides, etc., the common characteristics being that the materials can be melted, reformed while in the molten state, and then become solid again in the new form upon cooling.
Generally, to facilitate fusing and to allow a durable joint, the melting point, melt index and/or hardness of the thermoplastic polymer of the two materials should preferably be close to each other. Furthermore, both materials should preferably be free from impurities. In particular, moisture and soot (resulting from e.g. insufficient cleaning of equipment used) should be avoided.
With regard to the above-mentioned general guidelines for the choice of materials and for fusing of thermoplastic polymers, preferred materials are characterized by having soft and hard segments in the polymer backbone, joined by reaction of isocyanates. Hence, any type of modified thermoplastic polyurethane material, such as a polyether polyurethane, a polycarbonate polyurethane, a poly(siloxane-carbonate) polyurethane, or a poly(ether-siloxane) polyurethane, may preferably be used for either of the thermoplastic tubing or the thermoplastic fixation means.
Depending on the general properties required for the tubing, such as resistance to abrasion, flexibility, durability and surface properties, a preferred thermoplastic polymer is a polyether polyurethane comprising soft segments and hard segments or a poly(ether-siloxane) polyurethane comprising soft segments and hard segments. In a polyether polyurethane, the soft segments may comprise polytetramethyleneoxide (PTMO) (such as in Pellethane™, Dow Chemical Company) or polyhexamethyleneoxide (PHMO). A preferred polyether polyurethane is a Pellethane™, more preferred is Pellethane™ 2363-55D. In a poly(ether-siloxane) polyurethane, the soft segments may comprise polyhexamethyleneoxide (PHMO) and polydimethylsiloxane (PDMS) (such as in Elast-Eon™). A preferred poly(ether-siloxane) polyurethane is an Elast-Eon™, more preferred is Elast-Eon™ 2A. The hard segments of the polyether polyurethane or the poly(ether-siloxane) polyurethane, respectively, may comprise be a diisocyanate, such as methylenediphenyldiisocyanate (MDI), and a diol, such as butanediol (BDO), as a chain extender.
Depending on the properties required for the fixations means, such as compatibility with the tubing, castability, melting point etc., a preferred thermoplastic polymer is a polyether polyurethane comprising soft segments and hard segments. The soft segments may comprise polytetramethylenedioxide (PTMO) (such as in Tecothane®, Thermedics Polymer Products) or polyhexamethylenedioxide (PHMO). The hard segments may be a diisocyanate, such as methylenediphenyldiisocyanate (MDI) and a diol, such as butanediol (BDO), as a chain extender. A preferred polyether polyurethane is a Tecothane®, more preferred is Tecothane® 1075D.
In a cardiac lead according to
Another embodiment of a tubing 1 fixed to an electrode 2 provided with a fixation element 3 is shown in
Tensile testing of cardiac leads according to the embodiment shown in
Three tubing materials were tested:
A) Two stage process including
Safe cardiac lead performance requires (EN45502-2-1 CEN/CENELEC)) the cardiac lead to withstand 5 N pull force during 1 minute. All samples complied with this requirement. Furthermore, the pull force mean value at fracture was ≧9 N. All samples present a small standard deviation, thus being suitable for accurate production.
Although modifications and changes may be suggested by those skilled in the art, it is the invention of the inventor to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of his contribution to the art.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE04/01738 | 11/24/2004 | WO | 00 | 11/16/2007 |
