Stent crimping device and method of use

A pivotally-engageable device for enabling uniform and tight crimping of an intravascular stent onto a balloon catheter assembly. The stent crimping device includes at least one releasable loop portion that enables the stent and catheter assembly to be supported therein. The ends of the loop portion are moved in opposite directions thereby reducing the size of loop radially inwardly to uniformly and tightly crimp the stent onto the balloon catheter assembly.

BACKGROUND OF THE INVENTION 
This invention relates to a stent crimping device of the type that will 
enable the user to uniformly and tightly crimp a stent onto the distal end 
of a catheter assembly, for example of the kind used in a typical 
percutaneous transluminal coronary angioplasty (PTCA) procedure or 
percutaneous transluminal angioplasty (PTA) procedure. 
In a typical PTCA procedure, for compressing lesion plaque against the 
artery wall to dilate the artery lumen, 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 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 lesion. Once in 
position across the lesion, a flexible, expandable, preformed balloon is 
inflated to a predetermined size 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withdrawn from the patient's vasculature and blood flow resumed through 
the dilated artery. While this procedure is typical, it is not the only 
method used in angioplasty. Other methods for compressing plaque or 
removing it are known, such as atherectomies or use of plaque dissolving 
drugs. 
In angioplasty procedures of the kind referenced above, a restenosis of the 
artery may develop over several months, which may require another 
angioplasty procedure, a surgical bypass operation, or some method of 
repairing or strengthening the area. To reduce the likelihood of the 
development of restenosis and strengthen the area, a physician can implant 
an intravascular prosthesis for maintaining vascular patency, typically 
called a stent. A stent is a device used to hold tissue in place in a 
vessel or to provide a support for a vessel to hold it open so that blood 
flows freely. A variety of devices are known in the art for use as stents, 
including expandable tubular members, in a variety of configurations, that 
are able to be crimped onto a balloon catheter, and expanded after being 
positioned intraluminally on the balloon catheter, and that retain their 
expanded form. Typically, the stent is loaded and crimped onto the balloon 
portion of the catheter, and advanced to a location inside the artery at 
the lesion. The stent is then expanded to a larger diameter, by the 
balloon portion of the catheter, to implant the stent in the artery at the 
lesion. Examples of stents and delivery catheters of the type described 
herein are disclosed in more detail in U.S. Pat. No. 5,102,417 (Palmaz); 
U.S. Pat. No. 5,569,295 (Lam); and U.S. Pat. No. 5,514,154 (Lau et al.). 
If the stent is not effectively crimped onto the catheter balloon portion 
when the catheter is advanced in the patient's vasculature, the stent may 
move or possibly slide off the catheter balloon portion in the coronary 
artery prior to expansion, and may block the flow of blood, requiring 
procedures to remove the stent. 
In procedures where the stent is placed over the balloon portion of the 
catheter, the stent must be compressed or crimped onto the balloon portion 
to prevent the stent from sliding off the catheter when the catheter is 
advanced in the patient's vasculature. In the past this crimping was often 
done by hand, which does not provide optimum results due to the uneven 
force being applied, resulting in non-uniform crimps. In addition, it was 
difficult to judge when a uniform and reliable crimp had been applied. 
Though some tools, such as ordinary pliers, have been used to crimp the 
stent, these tools have not been entirely adequate in achieving an 
effective crimp. Moreover, an ineffectively crimped stent may result in an 
ineffectively expanded stent in the vessel or artery, which is 
undesirable. 
SUMMARY OF THE INVENTION 
The invention is directed to a crimping tool and method of use for enabling 
effective crimping of a stent onto the balloon portion of a catheter in 
order to better secure a stent onto the catheter for low-profile delivery 
of the stent through the patient's vascular system. The present invention 
attempts to solve several problems associated with crimping stents onto 
balloon catheters. 
In an exemplary embodiment ofthe present invention, the stent crimping tool 
includes a pair of handles pivotally engaged such that a first handle 
member receives within it a second handle member. The invention further 
includes a cylindrical loop crimping member comprising a flexible sheet or 
film of material, such as a thin piece of Mylar material, in the form of a 
loop. The ends of the loop are attached respectively to the first handle 
and the second handle. An application of force on the handles causes the 
prospective ends of the cylindrical loop to move in opposite directions 
thereby providing a tension force which results in reducing the opening of 
the cylindrical loop. 
The invention further provides for mounting a stent on the balloon portion 
of a catheter, and positioning the stent and balloon portion of the 
catheter within the cylindrical loop. As the handles of the stent crimping 
tool are compressed, the ends of the cylindrical loop are pulled in 
opposite directions thereby reducing the size of the loop and tightly 
compressing the stent in a uniform manner on the balloon portion of the 
catheter. 
By releasing the handles, which are biased open, the cylindrical loop 
returns to its original size, thereby permitting the stent and balloon 
portion of the catheter to be removed from the cylindrical loop. 
In one embodiment of the invention, the cylindrical loop is formed from a 
substantially non-stretchable plastic material having a high tensile 
strength and a low modulus. 
One of the handles of the stent crimping tool includes reference indicia 
relative to the other handle member so that the reference indicia 
correspond to the crimping diameter of the cylindrical loop. As the two 
handles are compressed one into the other, the reference indicia will 
indicate the size or diameter of the cylindrical loop, and thereby 
determine the ultimate travel and thus, the resultant crimped diameter of 
the stent onto the balloon portion of the catheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides for a crimping tool which uniformly and 
tightly crimps an expandable stent onto a catheter, such as a balloon 
catheter, so that the stent remains removably attached to the catheter 
until the stent and catheter are positioned in a body lumen. In keeping 
with the invention, device 10 comprises crimping tool 20 for enabling 
effective crimping of an intravascular stent 11 onto the collapsed balloon 
portion 12 adjacent the distal end 13 of a balloon catheter assembly 14. 
In the exemplary embodiment of device 10, as shown in FIGS. 1-5, crimping 
tool 20 is adapted to be held in the hand of the user, so as to enable 
stent 11 and catheter 14 to be supported in tool 20, and to enable the 
user to apply compressive force to tool 20 to crimp stent 11 on catheter 
14. 
Crimping tool 20 includes first handle member 22, second handle member 24 
pivotally movable into engagement with first handle member 22 in a 
generally pendulum-like movement, and pin 26 pivotally connecting the 
upper portions of first handle member 22 and second handle member 24. 
First handle member 22 and second handle member 24 are engageable and 
generally complementary and preferably somewhat triangular in shape to 
ergonomically fit the hand, and include slots 28 and 30 therein which are 
preferably somewhat arcuate-shaped. Preferably, first handle member 22 is 
configured to receive second handle member 24. 
Crimping tool 20 further includes crimping member 32 which is disposed 
within slots 28,30 which is adapted to receive stent 11 mounted on balloon 
portion 12 of the catheter assembly 14. Crimping member 32 includes 
cylindrical loop 34 having first end 36 and second end 38. First end 36 of 
cylindrical loop 34 is attached to first attachment member 40 on first 
handle member 22. Second end 38 of cylindrical loop 34 is attached by 
second attachment member 42 to second handle member 24. First attachment 
member 40 and second attachment member 42 can be of any design which can 
removably attach first end 36 and second end 38 respectively to the first 
and second handle members. As an example, first attachment member 40 and 
second attachment member 42 can include a snap or jaw-like member which 
grips first end 36 and second end 38 of cylindrical loop 34. It is 
intended, for example, that cylindrical loop 34 be replaceable when it 
wears out. 
While cylindrical loop 34 can have various configurations to suit 
particular needs, a preferred embodiment is shown in FIG. 11. Thus, first 
end 36 of the cylindrical loop is attached to first attachment member 40 
on first handle member 22 and second end 38 is attached by second 
attachment member 42 to second handle member 24. As indicated, the first 
and second attachment members can be of any design which can removably 
attach the first and second ends of the cylindrical loop to the handle 
members. In the FIG. 11 embodiment, apertures 44,46 are provided as 
convenient attachment means to correspond with a snap or jaw-like member 
on the handle members to help grip and removably attach first and second 
ends 36,38. A slot 48 is provided in the cylindrical loop to receive first 
end 36 to form the loop. Flanges 49 are provided to prevent the loop 
overtravel. The width 45 of the cylindrical loop should coincide with the 
length of the stent which typically is from about 6 mm to 30 mm. The width 
can be selected to accommodate either shorter or longer stents as 
necessary. Preferably, width 45 is selected so that the full length of the 
stent is covered by the cylindrical loop since it generally is undesirable 
to crimp less than the entire stent length at one time. The cylindrical 
loop can be formed of any non-stretchable material, and preferably is 
formed of Mylar or a similar flexible, but non-stretchable plastic 
material. 
In a manufacturing context, the crimping tool can be used repeatedly to 
crimp stents onto the balloon portion of catheters. Repeated use will 
result in the cylindrical loop wearing out, whereby it should be replaced. 
Thus, it is contemplated that first attachment member 40 second attachment 
member 42 provide means for releasing the ends of the cylindrical loop and 
accepting ends of a replacement cylindrical loop for further use. 
Additionally, an adhesive may be used to permanently attach first end 36 
and second end 38 to the handle members, for use in those situations where 
the crimping tool 20 is designed for a single-use application, as will be 
described. 
Crimping tool 20 also is adapted for a single-use application, for example, 
by a cath lab physician or cath lab personnel. In that situation, crimping 
tool 20 can be discarded after the stent is crimped onto the balloon 
portion of the catheter. Further, first attachment member 40 and second 
attachment member 42 can be a permanent attachment, as opposed to a 
removable attachment to attach the ends of the cylindrical loop to the 
handle members. 
In the preferred method of use, as shown in FIGS. 6-10, stent 11 is first 
positioned over balloon portion 12 by hand, and then catheter assembly 14 
is moved within cylindrical loop 34 to receive the crimping procedure. For 
ease of illustration, FIGS. 6-10 depict loop 34 as having no or very 
little width, however, loop 34 should preferably have a width that 
approximates the length of the stent, which typically may be 20 mm or more 
as previously described for thc FIG. 11 embodiment. First handle member 22 
and second handle member 24 are compressed together thereby moving ends 
36, 38 in opposite directions as depicted in FIGS. 6-9. As the opening of 
cylindrical loop 34 becomes smaller, the loop tightens around stent 11 
thereby crimping it onto the balloon portion of the catheter. Reference 
indicia 50 on second handle member 24 corresponds to the size or diameter 
of cylindrical loop 34. Thus, one using the crimping tool can easily 
determine the crimping force, and importantly, the crimped diameter of the 
stent on the balloon portion of the catheter. Thus, the reference indicia 
correspond to the final diameter, or crimped diameter of the stent, 
thereby taking the guesswork out of the crimping procedure as it relates 
to the amount of force applied to the stent and the final crimped 
diameter. 
The first and second handle members are biased open, such as by a coil 
spring or other biasing means, so that when the compressive force of the 
user's hand is released, the handles will move open and away from each 
other. When the handles move open, cylindrical loop 34 has enough 
resiliency in the material that it naturally will open, allowing the 
crimped stent and balloon catheter assembly to be withdrawn. 
In each of the embodiments of the crimping tool, sheath 60 can be 
positioned over the stent, preferably prior to crimping the stent. The 
sheath can have various configurations such as those shown in FIGS. 
12A-12C, and preferably has sufficient length and wall thickness to cover 
the stent and uniformly distribute the crimping forces applied to the 
stent by crimping tool 20. As the crimping tool applies force to the 
sheath, the force is evenly distributed over the sheath and hence to the 
stent. The sheath can be left on the stent after crimping and provide a 
cover to protect the stent in a safe manner until just before the stent is 
implanted in the patient. 
In one preferred embodiment of sheath 60, slots 61 are formed in the sheath 
so that strips 62 in between the slots cover specific portions of the 
stent to prevent fish scaling during the crimping process. Fish scaling, 
which results from portions of the stent moving radially outwardly due to 
uneven crimping forces, can occur during the crimping process with some 
stent configurations. Thus, strips 62 are positioned over portions of the 
stent susceptible to fish scaling to counteract the effect and maintain a 
cylindrical geometry in the stent. 
The sheath can be formed from an elastic material known in the art and can 
have various thicknesses depending on the particular stent configuration. 
Slots 51 or other apertures 54 are formed in the sheath using a laser or 
by other means known in the art. The sheath is removed prior to implanting 
the stent in the patient. 
It is contemplated that the present invention crimping tool 20 can be used 
in a manufacturing facility having a sterile environment to be used 
multiple times to crimp multiple stents on catheter assemblies. It is also 
contemplated that the crimping tool 20 will be used for single use 
applications by cath lab personnel, where a stent is crimped onto the 
balloon portion of a catheter, and the tool is then discarded, since there 
is no assurance that the tool can be sterilized after the single use 
application in the cath lab. 
While certain dimensions and materials of manufacture have been described 
herein, modifications can be made without departing from the scope and 
spirit of the invention. 
While in the preferred embodiment the stent described is intended to be an 
intraluminal vascular prosthesis for use within a blood vessel, such as a 
saphenous vein, coronary artery, carotid artery, etc., and the balloon 
delivery catheter is of the same or similar to that used in therapeutic 
coronary angioplasty, it will be appreciated by those skilled in the art 
that modifications may be made to the present invention to allow the 
present invention to be used to crimp any type of stent onto any catheter. 
The present invention is not limited to stents that are deployed in a 
patient's vasculature, but has wide applications to loading any type of 
graft, prosthesis, liner or similar structure. Furthermore, the stent may 
be delivered and implemented not only into coronary arteries, but into any 
body lumen. Other modifications can be made to the present invention by 
those skilled in the art without departing from the scope thereof.