Note: Descriptions are shown in the official language in which they were submitted.
CA 02202476 1997-04-11
W096/12449 PCT~S95/13651
r~ ~ æTENT APPARaTUæ
Field of the Invention
This invention relates to medical implant devices,
and more specifically to a connected implantable stent
apparatus consisting of at least two short stent
segments connected by welding, or by using other
methods producing substantially rigid joints, and
particularly suitable for the treatment of coronary or
peripheral vessels in humans.
Background of the Invention
Cardiovascular diseases, including
atherosclerosis, is the leading cause of death in the
U.S. The medical community has developed a number of
methods and devices for treating coronary heart
disease, some of which are specifically designed to
treat the complications resulting from atherosclerosis
and other forms of coronary arterial narrowing.
An important development for treating
atherosclerosis and other forms of coronary narrowing
is percutaneous transluminal coronary angioplasty,
hereinafter referred to as "angioplasty" or "PTCA".
The objective in angioplasty is to enlarge the lumen of
the affected coronary artery by radial hydraulic
expansion. The procedure is accomplished by inflating
a balloon within the narrowed lumen of the coronary
artery. Radial expansion of the coronary artery occurs
in several different dimensions, and is related to the
nature of the plaque. Soft, fatty plaque deposits are
flattened by the balloon, while hardened deposits are
cracked and split to enlarge the lumen. The wall of
the artery itself is also stretched when the balloon is
inflated.
Angioplasty is typically performed as follows: A
thin walled hollow guiding catheter is introduced into
the body via a relatively large vessel, such as the
femoral artery in the groin area or the brachial artery
CA 02202476 1997-04-11
WO96/12449 PCT~S95/13651
in the arm. Access to the femoral artery is achieved
by introducing a large bore needle directly into the
femoral artery, a procedure known as the Seldinger
Technique. Once access to the femoral artery is
achieved, a short hollow sheath is inserted to maintain
a passageway during the procedure. The insertion of
the flexible guiding catheter involves the negotiation
of an approximately 180 degree turn through the aortic
arch to allow the guiding catheter to descend into the
aortic cusp where entry may be gained to either the
left or the right coronary artery, as desired.
After the guiding catheter is advanced to the
ostium of the coronary artery to be treated by
angioplasty, a flexible guidewire is inserted into the
guiding catheter through a balloon (described infra)
and advanced to the area to be treated. The guidewire
provides the necessary steerability for passage through
the lesion. The guidewire is advanced across the
lesion, or "wires" the lesion, in preparation for the
advancement of a balloon catheter composed of
polyethylene, polyvinyl chloride, polyolefin, or other
suitable substance across the guide wire. The balloon,
or dilatation, catheter is placed into position by
sliding it along the guide wire. The use of the
relatively rigid guide wire is necessary to advance the
catheter through the narrowed lumen of the artery and
to direct the balloon, which is typically quite
flexible, across the lesion. Radiopaque markers in the
balloon segment of the catheter facilitate positioning
- 30 across the lesion. The balloon catheter is then
inflated with contrast material to permit fluoroscopic
viewing during treatment. The balloon is alternatively
inflated and deflated until the lumen of the artery is
satisfactorily enlarged.
Unfortunately, while the affected artery can be
enlarged, in some instances the vessel restenoses
CA 02202476 1997-04-11
WO96/12449 PCT~S95/13651
chronically, or closes down acutely, negating the
positive effect of the angioplasty procedure. In the
past, such restenosis frequently necessitated repeat
PTCA or open heart surgery. While such restenosis does
not occur in the majority of cases, it occurs
frequently enough that such complications comprise a
significant percentage of the overall failures of the
PTCA procedure, for example, twenty-five to thirty-
five percent of such failures.
To lessen the risk of restenosis, various devices
have been proposed for mechanically keeping the
affected vessel open after completion of the
angioplasty procedure. Such mechanical endoprosthetic
devices, which are generally referred to as stents, are
typically inserted into the vessel, positioned across
the lesion, and then expanded to keep the passageway
clear. Effectively, the stent overcomes the natural
tendency of the vessel walls of some patients to close
back down, thereby maintaining a more normal flow of
blood through that vessel than would be possible if the
stent were not in place.
Various types of stents have been proposed,
although to date none has proven completely
satisfactory. One proposed stent involves a tube of
stainless wire braid. During insertion, the tube is
positioned along a delivery device, such as a catheter,
in a compressed configuration which extends the tube
along the catheter, making the tube diameter as small
as possible. When the stent is positioned across the
lesion, it is expanded, causing the length of the tube
to contract and the diameter to expand. Depending on
the materials used in construction of the stent, the
tube maintains the new shape either through mechanical
force or otherwise.
The Palmaz stent (U.S. Patent No. 4,733,655)
involves what may be thought of as a stainless steel
CA 02202476 1997-04-11
W O96/12449 PCTrUS95/136Sl
-- 4
cylinder having a number of slits in its circumference,
resulting in a mesh when expanded. The stainless steel
cylinder is delivered to the affected area by means of
a balloon catheter, and is then eYp~ed to the proper
size by inflating the balloon.
Significant difficulties have been encountered
with known prior art stents, including failure to
readily conform to the vessel shape, and including lack
of flexibility which is required to track through, and
to be implanted in, tortuous vascular anatomy. In
addition, the relatively long length of most prior art
stents has made it difficult to treat curved vessels,
and has also effectively prevented successful
implantation of multiple stents.
One solution to this problem is to implant short
discrete stent segments that would make up the length
of the stenosis to be stented. However, short stent
segments have proven to be somewhat unstable with
respect to positional stability. These and other
complications have resulted in a low level of
acceptance for such stents within the medical
community, and to date stents have not been accepted as
a practical method for treating chronic restenosis.
Boneau U.S. Patent No. 5,292,331 provides a
unitary wire-like stent structure configured to form a
plurality of upper and lower axial peaks, and is
delivered and expanded in a manner similar to delivery
of the prior art stents described above. The low mass
and relatively short length of the Boneau stent
increased steerability through curved vessels.
Copending U.S. Pat. Application Ser. No.08/326,024
describes methods of connecting one or more Boneau
stents using suture materials, short lengths of wire or
ribbon, and internally or externally mounted sleeves.
CA 02202476 1997-04-11
WO 96/12449 PCT/US95/136Sl
SI~MMARY OF THE INVENTION
A connected stent embodying the principles of the
present invention defines an endoprosthetic device or
single stent comprised of at least two short stent
segments interconnected by welding, or by other methods
producing a substantially rigid joint, to enable
selection of a stent tailored to the dimensions of the
lesion to be treated, and to maintain positional
stability within the vasculature. Interconnection of
discrete stent segments occurs preferably by welding
corresponding axial turns, or crowns, on aligned
adjacent stent segments.
Alternatively, for increasing the flexibility of
three or more welded stent segments, the number of
welds is decreased by welding in a substantially
spiral, or alternating pattern which does not include
welds at all adjacent crowns. In this embodiment, the
stent segments themselves are sufficiently flexible to
enable the connected stent to maneuver through and
conform to the often tortuous vessels requiring
treatment. The preferred embodiment uses stent
segments having four crowns at each end with welds at
each adjacent crown area of the connected stent.
In broadest terms, the connected endovascular
stent apparatus of this invention provides a plurality
of short discrete stent segments each forming a
cylinder, each cylinder having an inside, outside, and
at least one end surface, with at least one set of
axial turns, or crowns, on corresponding end surfaces
on adjacent stent segments connected by a method
producing a substantially rigid joint between crowns.
The inventive stent apparatus may be formed from a
plurality of single pieces of wire, each formed into
sections to define an expandable stent, and joined
together as described herein. The resultant stent
apparatus can then be compressed onto a balloon
CA 02202476 1997-04-11
WO96/12449 PCT~S95113651
catheter, delivered to the affected vessel and expanded
in place, all as described herein. Additionally,
multiple connected stents can be spaced apart and
compressed onto a balloon catheter for delivery to the
affected vessel.
The stent, or endovascular support device, of the
present invention may preferably be comprised of
implantable quality high grade stainless steel or other
implantable material, machined specially for
intravascular applications. The inventive stent
segments may comprise a plurality of circles or
ellipsoids formed to create a plurality of axial bends,
thereby permitting compression of the connected stent
onto a delivery catheter, and subsequent expansion once
in place at the affected area.
The deployment methods for the connected inventive
stent apparatus may include balloon expanding, self-
expanding, self-retracting, and mechanically expanding.
Some of the intended uses include PTCA type stenting,
PTA type stenting, graft support, graft delivery, INR
use, GI tract use, drug delivery, and biliari stenting.
A general object of the present invention is to
provide a connected stent that overcomes the drawbacks
and limitations of the prior art.
A specific object of the present invention is to
provide a connected stent comprised of at least two,
short stent segments connected by a method producing a
substantially rigid joint and having a length
sufficient to maintain positional stability when
implanted.
Another specific object of the present invention
is to provide a connected stent comprised of short
stent segments of low mass formed of straight segments
integrally joined at axial bends (crowns) wherein
individual, adjacent short segments are welded together
at one or more adjacent crowns.
CA 02202476 1997-04-11
W O96/12449 PCTrUS951136Sl
One more specific object of the present invention
is to provide a connected stent comprised of at least
three short stent segments wherein the welds form a
spiral or alternating pattern around the generally
circular, or elliptical, connected stent thereby
welding at a single adjacent crown area in each plane
of the stent.
An additional object of the present invention is
to provide a connected, welded stent having stent
segments sufficiently flexible so that a spiral or
alternating pattern of rigid welds allows the connected
stent to be maneuvered through and implanted in highly
curved vessels.
Yet another object of the present invention is to
provide a connected stent made from a plurality of
short stent segments to enable a single connected
stent, or multiple connected stents, to be tailored to
the dimensions of the particular area to be treated.
These and other objects, advantages and features
of the present invention will become more apparent upon
considering the following detailed description of a
preferred embodiments, presented in conjunction with
the accompanying drawings.
Brief Description of the Drawings
Fig. 1 is a side sectional view of a stent segment
in its expanded configuration taken along lines 2-2 in
Fig. 2.
Fig. 2 is a side elevational view of a connected
stent embodying principles of the present invention and
showing two, short, discrete stent segments of Fig. 1
- connected at adjacent axial turns, or crowns, by welds.
Fig. 3A is an enlarged side sectional view of the
assembled connected stent of Fig. 1, prior to
deployment and expansion, taken along lines 2-2 and
showing the welded crown areas. Fig. 3B shows the
section view in its deployed configuration.
CA 02202476 1997-04-11
WO96/12449 PCT~S95/13651
Fig. 4A is an end view of the connected stent
prior to deployment and expansion, and Fig. 4B is an
end view of the deployed and expanded connected stent.
Fig. 5 is a side view of a preferred connected
stent having four stent segments connected by a pattern
of welds spiraling around the connected stent.
Detailed Description of Preferred Embodiments
Fig. l is a side sectional view of a preferred
stent segment lO for forming a connected stent
embodying the principles of the present invention. The
stent segment lO comprises a single wire 12 bent into a
plurality of straight sections 13 integrally joined by
discrete axial turns, or crowns 14 and forming a
cylinder 16, as best shown in Fig. 2. In the preferred
lS stent segment lO, the straight sections 13 and the
crowns 14 have substantially the same cross-sectional
dimensions.
The stent segment lO is preferable formed from
implantable materials having good mechanical strength,
such as implantable quality stainless steel wire. The
outside of the stent segment may be selectively plated
with platinum or other radiopaque materials to provide
improved visibility during fluoroscopy. The cross-
sectional shape of the finished stent segment lO may be
circular, ellipsoidal, rectangular, hexagonal, square,
or another polygon, although at present it is believed
that circular or ellipsoidal may be preferable.
Referring now to Figs 2 and 3A, a connected stent
20 is formed from two or more stent segments lO by
aligning the stent segments lO end to end so that
corresponding crowns 14 are adjacent. The connected
stent 20 is formed by a weld 30 between at least one
set of corresponding axial turns 14 or crowns on the
adjacent stent segments lO. Any welding or rigid joint
forming material suitable for implantation into the
body may be used, and it is preferred to use the same
CA 02202476 1997-04-11
WO96/12449 PCT~S95113651
stainless steel for both the stent segments lO and the
welds 30. The welds 30 are approximately the same
width as the cross-sections of the crowns 14 and
sections 13. The length of the welds 30 is selected so
that approximately one quarter of the diameter of the
crown 14 is not welded. The welds 30, which are
substantially rigid, are made as small as possible to
reduce the mass and maintain the flexibility of the
connected stent 20, the segments lO thereof which are
inherently somewhat flexible.
As shown in Fig. 2, welds 30 may be placed at each
adjacent crown 14 area around the cylindrical connected
stent, and four welds 30 are shown. Alternatively as
best shown in Fig. 5, welds 30 may be placed at only
one adjacent crown pair between two adjacent stent
sections lO. Fig. 5 shows a connected stent 20' having
four stent segments lO. The welds 30 form a spiral
pattern around the cylindrical stent 20'. The spiral
pattern shown in Fig. 5, or an alternating pattern,
reduces the number of welds 30 thereby maintaining the
flexibility of the connected stent 20'.
It will be recognized by those skilled in the art
that the number of axial turns (crowns 14) in each
stent segment lO may vary, generally between two and
ten with the optimum being three to five, and that the
number of welds 30 may vary accordingly. At least one
weld 30 is required to connect two stent segments lO,
and it is preferable to space welds in a balanced
fashion in the spiral or alternating configuration.
Alternatively, the welds 30 may be selectively placed
- to more easily selectively configure a connected stent
to the contours of the vessel to be treated.
Fig. 3B shows the increased spacing between the
straight sections 13 following application of a
radially expansive force to expand the connected stent
20 into its deployment position. A comparison of Fig.
CA 02202476 1997-04-11
W O96/12449 PCT~US95/13651
-- 10 --
3A and 3B shows that expansion causes the angle of the
crown 14 to increase, and causes the distance between
welds 30 to increase. The comparison between the non-
expanded and the e~p~ed configuration may also be
seen in Fig. 4A (non-expanded) and Fig. 4B (expanded).
The crowns 14 can be seen to permit each stent segment
10 to be compressed or expanded over a wide range while
still maintaining a significant mechanical force, such
as required to prevent a vessel from restenosing.
The minimum length of the connected stent 20 or
20' is determined in large measure by the size of the
vessel into which the stent 20 will be implanted. The
connected stent 20 will preferably be of sufficient
length to maintain its axial orientation with the
vessel without shifting under the hydraulics of blood
flow (or other fluid flow in different types of
vessels), while also being long enough to extend across
at least a significant portion of the affected area.
At the same time, the connected stent should be short
enough as to not introduce unnecessarily large amounts
of material as might cause undue thrombosis. Typical
cardiovascular vessels into which the connected stent
20 might be implanted range from 1.5 millimeters to six
millimeters in diameter, and corresponding connected
stents 20 may range from approximately 4 millimeters to
four centimeters in length.
Due to the conformability of the single weld
connected stent, not only can varying lesion lengths be
treated, but curved vessels and multi-curved vessels
may also be treated.
Once the configuration of the connected stent has
been selected and the stent is welded to form the
selected configuration, the connected stent may be
crimped onto a balloon of a balloon catheter device for
delivery to the affected region of a vessel such as a
coronary artery. Once the balloon is in place across
CA 02202476 1997-04-11
Wo96/12449 PCT~S95/13651
the lesion, using conventional imaging techniques and
radiopaque dyes, the balloon may be inflated, again
substantially in a conventional manner, to deploy the
connected stent. In selecting a balloon, it is helpful
to ensure that the balloon will provide radially
uniform inflation so that the connected stent will
expand equally along each of the segments. The
inflation of the balloon causes the expansion of the
stent. The amount of inflation, and commensurate
amount of expansion of the connected stent, may be
varied as dictated by the lesion itself, making the
connected stent of the present invention particularly
flexible in the treatment of chronic restenosis.
Because of the inflation of the balloon, the
lesion in the vessel is compressed, or cracked, and the
lumen is expanded accordingly when the wall of the
vessel to pressed outwardly radially. At the same
time, the plaque deposited within the intima of the
vessel is displaced and thinned, and the stent is
embedded in the plaque or other fibrotic material
adhering to the intima of the vessel.
Following inflation of the balloon and expansion
of the connected stent within the vessel, the balloon
is deflated and removed. The exterior wall of the
vessel attempts to return to its original shape through
elastic recoil. The stent, however, remains in its
expanded form within the vessel, and prevents further
restenosis of the vessel. The stent maintains an open
passageway through the vessel, so long as the tendency
toward restenosis is not greater than the mechanical
strength of the stent. Because of the low mass of the
support device of the present invention, thrombosis is
less likely to occur. Ideally, the displacement of the
plaque deposits and the implantation of the stent will
result in a smooth inside diameter of the vessel.
-
CA 02202476 1997-04-11
W096/12449 PCT~S95/13651
- 12 -
While the primary application for the connected
stent is presently believed to be treatment of
cardiovascular disease such as atherosclerosis or other
forms of coronary narrowing, the stent of the present
invention may also be used for treatment of narrowed
vessels in the kidney, leg, carotid, or elsewhere in
the body. In such other vessels, the size of the
connected stent may need to be adjusted to compensate
for the differing sizes of the vessel to be treated.
While this invention has been described in
connection with preferred embodiments thereof, it is
obvious that modifications and changes therein may be
made by those skilled in the art to which it pertains
without departing from the spirit and scope of the
invention. For instance, other stents may be axially
aligned and connected by welds without departing from
the spirit and scope of the invention. Accordingly,
the aspects discussed herein are for illustration only
and should not limit the scope of the invention herein
which is defined by the claims.
