Metal working – Method of mechanical manufacture – Assembling or joining
Reexamination Certificate
2001-04-26
2003-11-04
Vidovich, Gregory (Department: 3726)
Metal working
Method of mechanical manufacture
Assembling or joining
C029S516000, C029S282000, C029S283500
Reexamination Certificate
active
06640412
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for loading a tubular graft, such as a stent, onto the distal end of a catheter assembly of the kind used, for example, in percutaneous transluminal coronary angioplasty (PTCA) or percutaneous transluminal angioplasty (PTA) procedures.
Prior art stents typically fall into two general categories of construction. A first type of stent is expandable upon application of a controlled force, for example, through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. A second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from expandable heat sensitive materials allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent.
Generally, in typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the ostium. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient's coronary vasculature and the dilatation catheter is advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, a flexible and expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient's vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the development of restenosis and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery at the lesion. The stent is transported through the patient's vasculature to the implant site where it is to be deployed. At the implant site, the stent is expanded to a larger diameter. For a self-expanding sent, deployment is achieved by allowing the stent to be released from a delivery catheter where upon freedom from the constraints of the delivery catheter the stent self-expands. Alternatively for a balloon expandable stent, deployment is achieved by inflating a balloon portion of a dilatation catheter forcing expansion of the stent.
Because the catheter and stent must travel through the patient's vasculature, and possibly through the coronary arteries, the stent must have a small delivery diameter and must be firmly secured within a delivery catheter until the physician is ready to implant it. Thus, the stent must be loaded onto the catheter so that it does not interfere with delivery, and it must not come off the catheter until it is implanted.
In procedures where a self-expanding stent is utilized, the stent is placed within a protective delivery sleeve of the delivery catheter. It is necessary to properly collapse the stent for loading into the protective delivery sleeve. This collapsing of the stent has proven to be a particular challenge where it is necessary to load the stent into a small diameter delivery catheter. Because of the inherent tendency for a self-expanding stent to resist compression, it is difficult to ensure a uniform collapse of the stent during the loading process without possible damage to or improper orientation of the stent. The resistance to compression is especially pronounced where it is necessary to load the stent into a small diameter delivery catheter because the stent must be collapsed down to an extremely small profile.
In procedures where a balloon expandable stent is utilized, the stent is placed over the balloon portion of the catheter, it is necessary to crimp the stent onto the balloon portion to reduce its diameter and to prevent it from sliding off the catheter when the catheter is advanced through the patient's vasculature. Nonuniform crimping can result in sharp edges being formed along the now uneven surface of the crimped stent. Furthermore, non-uniform stent crimping may not achieve the desired minimal profile for the stent and catheter assembly. Where the stent is not reliably crimped onto the catheter, on rare occasions it is possible that the stent may slide off the catheter and into the patient's vasculature prematurely as a loose foreign body, possibly causing blood clots in the vasculature, including thrombosis. Therefore, it is important to ensure the proper crimping of a stent onto the balloon portion of a catheter in a uniform and reliable manner.
It is generally the case that the collapsing or crimping of a stent is often done by hand, which can be unsatisfactory due to the uneven application of force resulting in non-uniform collapsing or crimps. In addition, it is difficult to visually judge when a uniform and reliable crimp has been applied.
As mentioned above, the problem often encountered with hand loading self-expanding stents into a delivery catheter is that given the natural tendency of self-expanding stents to expand back to an expanded profile. Upon compressing the stent for loading onto a catheter, the stent will quickly spring out of a compressed state thereby making it a cumbersome ordeal. Unlike balloon expandable stents that hug or grip the balloon in which the stent has been crimped, in order to successfully load a compressed self expanding stent a need exists for a collapsing device that will maintain the compressed state of the stent until it is successfully loaded within a protective delivery sleeve of a delivery catheter. Again, the difficulty in loading such a stent is increased where it is desirous to further reduce the stent's compressed profile for loading onto smaller diameter catheters. Furthermore, the more the stent is handled the higher the likelihood of human error. Accordingly, there is a need in the art for a device that will reliably collapse a stent and allow it to be loaded into a smaller low profile delivery catheter.
There have been attempts at devising a tool for compressing a stent, most of which have been directed to the crimping of a balloon expandable stent onto a balloon delivery catheter. An example of such a tool embodies a series of plates having substantially flat and parallel surfaces that move in a rectilinear fashion with respect to each other. A stent carrying catheter is disposed between these surfaces, which surfaces crimp the stent onto the outside of the catheter by their relative motion and applied pressure. The plates have multiple degrees of freedom and may have force-indicating transducers to measure and indicate the force applied to the catheter during crimping of the stent.
Another stent loading tool design includes a tubular member housing a bladder. The tubular member and bladder are constructed to hold a stent that is to be crimped onto a balloon catheter assembly. Upon placemen
Cozart Jermie E.
Endovascular Technologies, Inc.
Fulwider Patton Lee & Utecht LLP
Vidovich Gregory
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