Patent Application
20080077223
A novel feature of the stent delivery system 10 is the front section that has an inner core wire 14D which is a shape memory alloy such as Nitinol that has a transition temperature higher than body temperature. Specifically, for Nitinol, the front section of the core wire should have an austenitic transition start temperature above body temperature so that the distal core wire will remain malleable at body temperature and an austenitic transition finish temperature such that the distal core wire will be heat memory shape recoverable at a temperature well above body temperature (e.g., 120° F.). Thus, any curvature that the interventional cardiologist places into the front section prior to placement into a human body will be retained. If the front section becomes inadvertently bent after placement in the human body, then exposure to a temperature of about 120° F. or higher will return the front section to its pre-set memory shape. When the front section then cools below body temperature, the front section can be reshaped by the interventional cardiologist and advanced again through the human body. The distal wire section 14D of the core wire 14 that lies within the front section of the stent delivery system 10 will, as described above, have a transition temperature that is higher than body temperature. However, that portion of the core wire section 14D that lies within the balloon 12 will have a transition temperature that is below body temperature. Thus, the portion of the distal wire section 14D within the balloon 12 will automatically remain straight as it is pushed through the human body because it will be at body temperature. The section of the core wire 14D that lies within the balloon connector 13 can be that portion of the core wire where the transition temperature changes from higher than body temperature for the core wire 14D distal to the distal end of the balloon connector 13 and lower than body temperature for that portion of the core wire 14D that lies proximal to the proximal end of the balloon connector 13.
The core wire 14 has a proximal wire section 14P that extends for most of the length of the stent delivery system 10. This entire proximal wire section 14P has a transition temperature that is just below body temperature so that it always remains straight as it is pushed through the human body. The diameter D4 of the distal wire section 14D should be approximately 0.007±0.003 inches. This smaller diameter D4 is necessary so that the balloon 12 can be tightly wrapped around the distal wire section 14D and the outside diameter of the balloon 12 will be smaller than if the distal wire section 14D was (let us say) 0.014 inches which is the typical diameter of a coronary guide wire. A smaller outside diameter for the balloon 12 allows for a smaller outside diameter for the stent 15. This smaller outside diameter for the stent 15 (that is, a lower profile) is one of the most important objectives of this invention.
The proximal core wire section 14P would typically have an outside diameter D5 that is typically 0.014±0.005 inches. This increased diameter provides additional pushability for the stent delivery system 10. Just distal to the distal end of the proximal wire section 14P is the proximal radiopaque marker band 19P and just proximal to the balloon connector 13 lies the distal radiopaque marker band 19D. The stent 15 is centered between these two marker bands so the interventional cardiologist can accurately place the stent 15 across an arterial stenosis. It should be noted that the marker bands do not lie directly under the stent 15 which would be a more conventional design The reason for this is that the outside diameter of the marker bands 19P and 19D would be large enough so as to increase the profile of the stent 15. Maintaining the lowest possible profile for the stent 15 is one of the most important objectives of this invention.
Although the core wire 14 is shown to have a distal wire section 14D and a proximal wire section 14P each with a different diameter, it should be understood that the core wire 14 could have three or more different diameters along its length. Also it is envisioned that different sections of the core wire 14 could be made from a tube into which other sections of the core wire could be inserted and fixedly attached. This tube could be very short and made from (for example) steel or Nitinol. Also, it may be less expensive to make the proximal wire section 14P from stainless steel or another material and that would still be an adequate structure to provide good pushability for the stent delivery system 10. Still further, it should be understood that the entire core wire 14 could be made in one or more sections from a metal that does not have a shape memory characteristic.
The balloon 12 is fixedly attached at its cylindrical proximal portion 12P to the cylindrical tube 11 and is joined at its cylindrical distal portion 12D to the balloon connector 13. The balloon connector 13 would typically be made from a polymer cylinder that is joined with a shrink fit or thermally or adhesively bonded to the distal wire section 14D. The outside diameter of the balloon connector 13 would typically be approximately the same diameter as the outside diameter of the cylindrical tube 11. One goal of the design of the stent delivery system 10 is to have an outside diameter of the stent 15 that is equal to or smaller than 0.030 inches. Therefore, the outside diameter of the proximal balloon connector 13 and the cylindrical tube 11 should be less than approximately 0.026 inches.
The stent 15 could be made from stainless steel or from a cobalt-chromium alloy such as L605 or from tantalum or from any other metal that has reasonably high radiopacity. It is also possible to place a bioabsorbable stent 15 onto the balloon 12. If the alloy L605 is used, then optimally it should be heat treated to have a smaller grain size. Also, it is envisioned that the stent 15 would elute a drug that prevents restenosis such as Taxol, sirolimus or a sirolimus analog. Still further, an antithrombogenic coating for the stent 15, using for example heparin or phosphorylcholine, would be useful to prevent acute and subacute thrombosis. A combination of an antithrombogenic coating and elution of an anti-restenosis drug is also envisioned.
A very important novel feature of this invention is the design of the front section of the stent delivery system 10. Specifically, the distal wire section 14D is at the center of the front section surrounded by a polymer material that is designed to be, or by its coating to be extraordinarily lubricious. For example, the polymer of the cone 17 could be made from polyurethane, polyethylene, Nylon, PTFE, polypropylene, PeBax, etc. Furthermore, as is well known in the art of lubricious polymer surfaces, whatever polymer material is used for the cone 17 could have a hydrophilic coating applied such as polyvinyl-pyrrolidone (PVP). Such a hydrophilic coating would aid significantly in improving the lubricity of the cone 17 and/or the elastomer band 16. Ideally the coefficient of friction for the small angle cone 17 becomes even lower in the presence of blood.
The front portion of the front section having a length L1 can be of uniform diameter or it can have a tapered shape with a distal diameter D1 of approximately 0.012±0.002 inches and a proximal diameter D2 of approximately 0.014±0.002 inches. The distal diameter of the small angle cone 17 is the same D2 but the proximal diameter of the small angle cone 17, D3, should be approximately equal to the outside diameter of the stent 15. For an outside diameter of 0.030 inches for the stent 15, the diameter D3 would be equal to 0.030 inches. If the outside diameter of the stent 15 would be less than 0.030 inches, then the diameter D3 would also be less than 0.030. In any case, the diameter D3 for the cone 17 would be essentially equal to the outside diameter of whatever stent 15 is placed on the balloon 12.
If the diameter D2 is its nominal value of 0.014 inches and the diameter D3 is 0.030 inches, then the apex angle “A” of the small angle cone 17 would be 1.55 degrees which is indeed a very small angle. The combination of a very small apex angle “A” and a very lubricious surface for the cone 17 allows the stent delivery system 10 to be readily pushable through even a very tight stenosis. The apex angle “A” should certainly be less than 10 degrees and preferably less than 3 degrees in order to most easily slide through a tight stenosis. By being extraordinarily pushable, the stent delivery system can avoid pre-dilitation of the stenosis and allow direct stenting, thus saving considerable cost and reducing the time for the stenting procedure. The length L1 is approximately 1.0 cm and the length L2 is approximately 1.5 cm. It should be understood however that either of these lengths could be somewhat shorter or longer. Also, the front section of the stent delivery system 10 could be a single cone rather than two conical shapes of different cone angles as shown in
Although a single elastomer band 13 is shown in
It should also be understood that the distal end of the elastomer band 16 would have a circular shape. However, the proximal end of the elastomer band 16 would have a shape that conforms with essentially zero clearance to the shape of the strut at the proximal end of the stent 15. This design provides a continuous and smooth surface for the outer surface of the stent delivery system 10 so that it can most easily penetrate a tight stenosis. If an elastomer band is also used (though not shown) at the proximal end of the stent 15, then its distal edge would conform to the curvature of the proximal end of the most proximal strut of the stent 15. Another advantage of the elastomer band 16 (and any elastomer band at the proximal end of the balloon 12) is that it would tend to fold the balloon 12 when deflation is required in order to remove the balloon 12 from the deployed stent 15.
A valve 22 is mounted into the handle body 21 as shown in
Although this specification and drawings describe a stent delivery system 10 that can be used for placing a stent within a stenosis of a human body, it should also be understood that many of the features of the stent delivery system 10 would be valuable as an angioplasty catheter without a stent. Specifically, the lubricious cone 17 that lies distal to the balloon 12 would aid in placing an angioplasty catheter through a tight stenosis for any use for which angioplasty catheters are now used. Also, the core wire 14 would add to the pushability of an angioplasty catheter used for dilatation of a stenosis.
Various other modifications, adaptations and alternative designs are of course possible in light of the teachings as presented herein. Therefore it should be understood that, while still remaining within the scope and meaning of the appended claims, this invention could be practiced in a manner other than that which is specifically described herein
