Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
2000-03-31
2001-11-13
Lacyk, John P. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
Reexamination Certificate
active
06315708
ABSTRACT:
FIELD OF USE
This invention is in the field of medical devices to maintain the patency of vessels of the human body.
BACKGROUND OF THE INVENTION
Self-expanding stents, particularly those made from the shape-memory alloy Nitinol, are well known in the art of intravascular stents. These stents are typically placed within a sheath-like stent delivery system for placement into a stenosis of a vessel such as an artery of a human body. When the sheath of the stent delivery system is pulled back, the self-expanding stent will deploy radially outward against the wall of a vessel of a human body such as a coronary artery. After they are deployed, it is typically necessary to remove the sheath-like catheter that delivered the stent and then insert a balloon angioplasty catheter for the purpose of further expanding the stent at the site of an arterial stenosis. This results in additional time and cost for performing this procedure. The balloon that is used for further expansion of the stent is typically longer than the stent itself. Therefore, the regions of the artery just beyond the distal and proximal edges of the stent undergo some trauma caused by the expansion of the balloon. This trauma caused by the balloon expansion beyond the stent edges also occurs with balloon expandable stents.
One disadvantage of existing delivery systems for self-expanding stents (i.e., sheath-like catheters) is that they have a larger diameter as compared to a stent delivery system that does not use a sheath. Another disadvantage is that they have less flexibility and are therefore more difficult to deliver into highly curved arteries such as the coronary arteries. All stent delivery systems that have an expandable balloon extending beyond the edges of the stent can cause an “edge effect” which is a narrowing of the artery just beyond the edges of the stent. The edge effect is particularly pronounced when a radioisotope stent is placed into an arterial stenosis. Still another disadvantage of using a sheath to deploy a self-expanding stent is that it is more difficult to exactly position the stent within a stenosis as compared to the accurate positioning that is achievable with balloon expandable stents.
Because balloon expandable stents have the inflated balloon extending beyond the edges of the stent, arterial wall edge dissections are sometimes encountered. These dissections typically require an additional stent implantation to repair the dissection in order to decrease the possibility that acute or subacute thrombosis or restenosis will occur.
SUMMARY OF THE INVENTION
The goal of the present invention is to overcome several of the potential shortcomings of the existing stents and stent delivery systems. The present invention is a hybrid stent that is defined as having a central section that is balloon expandable and end sections that are self-expanding. The entire stent is mounted by nesting onto a balloon of a balloon angioplasty catheter, such as that described in U.S. patent application Ser. No. 09/444,105, incorporated herein by reference. An advantage of nesting is that the stent is retained on the balloon of the balloon angioplasty catheter, allowing more reliable insertion of a stent into tortuous vessels of a human body and a decreased probability of stent embolization.
A major difference between the present state of the art of stent nesting and the present invention is that existing nested stents are all of the balloon expandable type, but the present invention is a hybrid stent that is part balloon expandable and part self-expanding. One way to retain the self-expanding portion of the stent onto a balloon onto which it has been nested is to place a cylindrical elastomer tube around each of the self-expanding end sections of the stent. Another way to retain a hybrid stent onto a stent delivery system is to use a conventional sheath that is pulled back to initiate stent deployment.
An advantage of non-sheath embodiment of the present invention is that the stent can be delivered to a stenosis without a sheath-like stent delivery system. By using nesting and an elastomer tube over each end section of the stent, the need to employ a sheath can be eliminated. Thus, a more flexible and smaller outer diameter for the distal section of the stent delivery system can be produced. This allows for easier and more accurate placement of the stent as it is advanced through curved vessels of the human body and positioned within a stenosis. Therefore, the present invention is ideally suited for direct stenting, which precludes the need for pre-dilatation of an arterial stenosis.
Still another feature of the present invention is that the stent delivery system described herein uses a stent dilation balloon that has a cylindrical central section that is shorter in length as compared to the total length of the stent. Thus the end sections of stent are self-deployed against the vessel wall without the need for balloon expansion. However, the central portion of the stent is capable of being pushed under high pressure radially outward against the stenosis by inflating the balloon to a high pressure such as 16 atmospheres. The end sections of the stent are deployed by their own shape-memory characteristic outward into comparatively normal (i.e., non-stenosed) sections of an artery that are situated on either side of a stenosis. The lack of a high-pressure balloon deployment at the end sections of the stent reduces the trauma experienced by those sections of the artery into which the end sections are placed. Most importantly, having no inflated balloon extending beyond the edges of the stent will drastically reduce the incidence of arterial wall edge dissections. The high-pressure inflation of the balloon is used only to cause the balloon expandable central section of the stent to deploy radially outward against the typically high resistance of a stenosis. By this technique, the artery will not experience balloon trauma at the regions of the artery at and just beyond the edges of the stent. Thus the artery will have a decreased propensity for arterial wall dissections and edge stenoses. This is particularly important for a radioisotope stent that has an increased propensity to exhibit arterial narrowing just proximal and just distal to the edges of the radioisotope stent.
An object of the present invention is to have a hybrid stent that has a balloon expandable central section and self-expanding end sections.
Another object of the invention is to have a stent made from a shape-memory alloy that has a transition temperature for its central section that is distinctly higher than body temperature and a transition temperature for its end sections that is below normal body temperature.
Still another object of the invention is to have a stent that has a central section formed from a conventional metal such as stainless steel that is balloon expandable and also has end sections that are formed from a shape-memory metal having a transition temperature that is less than body temperature.
Still another object of the present invention is to obviate the need for a sheath when delivering a stent having self-expanding end sections into a vessel of a human body thereby providing a smaller outside diameter for the stent delivery system.
Still another object of this invention is to use a stent delivery system that has a distal section that includes the hybrid stent, which stent delivery system has greater longitudinal flexibility as compared to a sheathed stent.
Still another object of the invention is to use a hybrid stent in order to decrease the likelihood of balloon trauma to the vessel walls that are at and beyond the edges of the stent.
Still another object of the invention is to have a hybrid stent that has self-expanding end sections and an inflatable balloon that does not extend beyond the edges of the stent, the combination being capable of drastically reducing the incidence of arterial wall dissections resulting from stent implantation.
Still another object of the invention is to use a sheath as part of the stent delivery s
Fischell David R.
Fischell Robert E.
Fischell Tim A.
Salmon Sean
Stockel Dieter
Cordis Corporation
Lacyk John P.
Szmal Brian
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