Abstract:
A medical lead includes a first wire coil having an outer diameter and a marker coil having an inner diameter. The marker coil is assembled over the first wire coil. The outer diameter first wire coil is smaller than the inner diameter of the marker coil thereby defining a gap. A second wire coil substantially fills the gap between the first wire coil and the marker coil. A ball weld is formed at an end of the medical lead adjacent each of the first and second wire coils and adjacent the marker coil.

Description:
BACKGROUND 
     One aspect relates to a medical lead having a filler layer. More particularly, a medical lead having a filler layer includes a marker coil. Medical leads and intravascular guidewires are used in conjunction with intravascular devices such as catheters to facilitate navigation through the vasculature of a patient. Such guidewires are typically very small in diameter and some include marker bands for in-vivo radiographic visualization. A wide variety of radiopaque marker bands have been developed for intracorporal medical devices. Some of the devices that include marker bands are guidewires and catheters. Of the known marker bands and intracorporal medical devices with marker bands, each has certain advantages and disadvantages. There is an ongoing need to provide alternative designs and methods of making and using marker bands and medical devices with marker bands. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a medical lead in accordance with one embodiment. 
         FIG. 2A  illustrates a stranded coil of a medical lead in accordance with one embodiment. 
         FIG. 2B  illustrates a stranded coil of a medical lead in accordance with one embodiment. 
         FIG. 3  illustrates a filler layer over the stranded coil of a medical lead in accordance with one embodiment. 
         FIG. 4A  illustrates a perspective view of a medical lead in accordance with one embodiment. 
         FIG. 4B  illustrates a sectional view of a medical lead in accordance with one embodiment. 
         FIG. 4C  illustrates a cross sectional view of a medical lead in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
       FIG. 1  illustrates medical lead  10  in accordance with one embodiment. In one embodiment, lead  10  has a proximal section  12  and a distal section  14 . In some applications, medical lead  10  is a guide catheter. In such an application, a hub or other mechanism is attached to proximal section  12  for guiding or controlling the medical lead  10 . Although medical lead  10  is in one embodiment a guide catheter, medical lead  10  could be any other type of catheter including diagnostic or therapeutic catheters such as angioplasty balloon catheters, atherectomy catheters, stent delivery catheters, and the like, or any other suitable device. Furthermore, medical lead  10  can generally include any device designed to pass through an opening or body lumen. For example, medical lead  10  may comprise an endoscopic device, laproscopic device, embolic protection device, guidewire, and the like, or any other suitable device. 
     In one embodiment, distal section  14  of medical lead  10  includes marker coil  18 , which is assembled over an inner coil (not visible in  FIG. 1 ) adjacent lead tip  20 . In one embodiment, marker coil  18  of medical lead  10  is used to aid in the visualization of medical lead  10  in accordance with any number of known visualization techniques, while the medical device is in use within the body. Typically the visualization techniques used rely on marker coil  18  being made from or otherwise including a radiopaque material. Radiopaque materials are materials capable of producing a relatively bright image on a fluoroscopy screen or another imaging technique during a medical procedure. This relatively bright image aids the user of medical lead  10  in determining its location. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, platinum-iridium, palladium, tantalum, tungsten alloy, plastic material loaded with a radiopaque additive, and the like. 
     In one embodiment, marker coil  18  is assembled about the distal section  14  of medical lead  10  adjacent lead tip  20 . Securing the position of marker coil  18  may be important for a number of reasons. For example, if marker coil  18  is properly secured, the clinician can rely on the known position of marker coil  18  in order to accurately assess the position of the remainder of medical lead  10 . This may include the clinician being able to know the precise location of the lead tip  20  of medical lead  10  by virtue of visualizing marker coil  18  and knowing that marker coil  18  is adjacent the distal tip  20  of medical lead  10 . 
     Knowing the precise location may be important when medical lead  10  is being used in a particular sensitive location, such as the central nervous system, because errantly positioning the medical lead  10  could damage sensitive areas. It can be appreciated that given the small scale of catheters and blood vessel, even a very small shift in the position of marker coil  18  can have real impact on a medical intervention. 
       FIG. 2A  illustrates a portion of distal section  14  of medical lead  10  during assembly. In one embodiment, medical lead  10  is formed starting with its inner coil  16 . In one embodiment, inner coil  16  is a stranded coil. In one example, inner coil  16  is a miltifiler coil, that is, a coil with multiple wires stranded together, the combination of which is then helically wound. In one embodiment, the helical winding of inner coil  16  forms an inner lumen, which can be useful in many embodiments. In one example, inner coil  16  can be helically wound over a mandrel that is then subsequently removed. In the illustration, inner coil  16  has an outer diameter OD 16 . 
     In one embodiment, inner coil  16  is coated with a plastic coating, such as a polytetrafluoroethylene (PTFE) or the like. In one embodiment, the plastic coating on inner coil  16  is removed such that when lead tip  20  is welded to coil  16 , the strands of coil  16  are electrically coupled together. In one embodiment, inner coil  16  of medical lead  10  thus functions as a conductor and electrode. 
     In removing the plastic coating from inner coil  16 , however, the outer diameter OD 16  is decreased to a smaller outer diameter OD 16′ , in the region where the coating is removed.  FIG. 2B  illustrates a portion of distal section  14  of medical lead  10  after the plastic coating is removed from inner coil  16 , thereby causing the smaller outer diameter OD 16′ . 
     When inner coil  16  has a smaller outer diameter OD 16′ , such as can occur after its plastic coating is removed, securing marker coil  18  over it and securing lead tip  20  adjacent to it, can be compromised in some embodiments. Accordingly, in one embodiment, filler layer  17  is assembled over inner coil  16  before securing marker coil  18  over it, and before securing lead tip  20  adjacent to it. In one embodiment, filler layer  17  is assembled over the area where plastic coating is removed from inner coil  16  and has a smaller outer diameter OD 16 . 
       FIG. 3  illustrates filler layer  17  is assembled over a portion of distal section  14  of medical lead  10  over inner coil  16 . In one embodiment, filler layer  17  is a single inner strand, and in others it is a multifiler coil and in another is a ribbon or similar form. In one embodiment, filler layer  17  ends adjacent the end of inner coil  16 , and in other embodiments the two ends can be offset from each other. 
     Marker coil  18  is then assembled over filler layer  17 , as illustrated in  FIG. 4A . In one embodiment, providing filler layer  17  between inner coil  16  and marker coil  18  provides a more stable and secure medical lead  10 . 
       FIGS. 4B and 4C  respectively illustrate cross sections taken parallel and perpendicular to the axis running along the length of medical lead  10 . Inner coil  16  is illustrated defining lumen  22  ( FIG. 4C ). Filler layer  17  is assembled over inner coil  16  and marker coil  18  is assembled over inner coil  16 . In one embodiment, lead tip  20  is a ball weld that is welded to each of the ends of inner coil  16 , filler layer  17 , and marker coil  18 . In one embodiment, the overall outer diameter OD 10  of medical lead  10 , along with the ends of the three coils—inner coil  16 , filler layer  17 , and marker coil  18 —is such that a good weld is made between lead tip  20  and the coils  16  and  18 . 
     Where only a inner coil  16  and a marker coil  18  are used, occasionally the lead tip  20  does not weld well to the ends of the coils  16  and  18 . In some applications, dimensional requirements for the various components of medical lead  10  can degrade these welds. For example, where the outer diameter OD 10  of medical lead  10  and thickness of marker coil  18  establish a marker coil inner diameter ID 18  that is significantly larger than the inner coil outer diameter OD 16 , this leaves a gap between inner coil  16  and a marker coil  18 . With such as gap, there may be a degraded weld of the lead tip  20  to inner coil  16  and marker coil  18 . Adding filler layer  17  can increase the surface area to which lead tip  20  is welded, and can improve the look and strength of the weld. 
     In one embodiment, inner coil  16  is stainless steel, such as SS316L, filler layer  17  is stainless steel, such as SS304 and marker coil  18  is one of gold, platinum, platinum alloy, platinum-iridium, palladium, tantalum, tungsten alloy, and a plastic material loaded with a radiopaque additive. 
     In one example, the pull strength was tested for a weld on a lead tip in a lead where only an inner coil and a marker coil were used. In that case, the pull strength for the weld was approximately 1.4667 lbs. The pull strength was also tested for the weld on lead tip  20  welded to each of the ends of inner coil  16 , filler layer  17 , and marker coil  18  in medical lead  10  in accordance with one embodiment. In that case, the pull strength for the weld was approximately 1.71033 lbs, or approximately a 15% improvement with filler layer  17 . 
     In one embodiment, medical lead  10  is configured for applications of very small dimensions. In one example, inner diameter of inner coil  16 , and thus the inner diameter ID 10  of the central lumen  22  of medical lead  10 , is approximately 0.009 inch, the thickness of inner coil  16  is approximately 0.006 inch, the thickness of filler layer  17  is approximately 0.0025 inch, and the thickness of marker coil  18  is approximately 0.004 inch. As such, the outer diameter OD 10  of medical lead  10  is approximately 0.034. 
     In one application, providing a medical lead  10  having the inner diameter ID 10  of the central lumen  22  of approximately 0.009 inch and having an outer diameter OD 10  of approximately 0.034 is workable for the application. As such, if filler layer  17  is not used in such an application, either or both of inner coil  16  or marker coil  18  must have larger thicknesses or the outer diameter OD 10  cannot be maintained. Filler layer  17  allows maintaining the outer diameter OD 10  to be maintained while still allowing the above given thicknesses of the coils to be maintained. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.