Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1999-08-13
2001-04-24
Weiss, John G. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S096010, C604S103060, C604S916000, C606S108000, C606S194000
Reexamination Certificate
active
06221043
ABSTRACT:
FIELD OF USE
This invention is in the field of devices for delivering stents into a vessel of a human body. More specifically, this invention is an angioplasty balloon that has an inflated shape that is ideally suited for delivering a stent into a stenosis of an artery or for performing balloon angioplasty.
BACKGROUND OF THE INVENTION
Balloon expandable stents have for many years been mounted on angioplasty balloons situated at a distal portion of a balloon angioplasty catheter. When the balloon is inflated at the site of an arterial stenosis, the stent is expanded radially outward thus acting as a scaffold to keep the stenosis from closing after the balloon is deflated and removed from the body. To accomplish this objective, prior art balloons utilize a cylindrical section that extends along most of the longitudinal length of the balloon. A stent is then co-axially mounted at the longitudinal center of this cylindrical section. Because there is typically more resistance to the expansion of the stent at its longitudinal center (as compared to the ends of the stent where there is comparatively little plaque) a deployed stent tends to have an undesirable hourglass shape. That is, pressure from excessive plaque at the longitudinal center of the stent causes that region of the stent to have a reduced diameter.
This problem was addressed in the invention by M. Crocker et al that is disclosed in U.S. Pat. No. 5,843,116. The Crocker et al invention has a longitudinally centered, comparatively short, cylindrical segment that has an increased diameter as compared to the diameter of the balloon cylindrical segments situated both proximal and distal to that central cylindrical segment. Thus, a stent deployed on such a balloon would have an increased diameter at the longitudinal center of the stent. However, it would be extremely rare for a stenosis to have a longitudinal distribution of plaque that is exactly cylindrical for about one third of the longitudinal length of the stent and then becomes a cylindrically shaped, uniformly reduced extent of the plaque both proximal and distal to that center segment. More typically, the plaque has its greatest volume at a central region of a stenosis and then rather uniformly decreases in the extent of the plaque as one moves away from that central region in either a proximal or a distal direction. Thus the Crocker et al invention that has discontinuous (i.e. abrupt) changes in balloon compliance along the length of the balloon is not ideally suited for the placement of a stent in a typical arterial stenosis.
Another problem associated with stents is called “balloon overhang”. Balloon overhang is the length of an inflated balloon that extends beyond the edge of the radially expanded balloon. For example, if a radially expanded stent is 17 mm long and mounted on a balloon that has a length when inflated of 20 mm, then the balloon overhang at each end of the stent is 1.5 mm. It has been found in actual practice that a large percentage of restenosis after stent implantation occurs in the region just proximal and just distal to the edge of the stent. This phenomenon, which is known as the “edge effect”, is even more pronounced with a radioisotope stent such as described in U.S. Pat. No. 5,059,166 by Fischell et al. One explanation for the edge effect is that trauma to the arterial wall caused by the balloon results in late vascular contraction at that region; and there is no stent structure in that region of balloon overhang to act as a scaffold to prevent the late vasculature contraction.
Prior art balloons all have a conical segment placed at each end of the balloon. The proximal conical end segment is joined at its proximal end to the outer shaft of a stent delivery catheter or balloon angioplasty catheter. The distal conical end segment is joined at its distal end to the distal end of the inner shaft of a balloon angioplasty catheter which balloon angioplasty catheter can also be used for delivering a stent. Early designs for conical end segments had half-angles that were about 45 degrees. Although this half-angle provides a desirable sharp corner where the conical segment joins the cylindrical segment of the balloon, this comparatively high 45 degree half-angle makes it somewhat more difficult for the balloon to be advanced through tortuous coronary vasculature. Therefore, more recent balloon designs have a half-angle for the conical segments that is typically less than 20 degrees. Although this decreased half-angle provides for improved tracking through small curved arteries, the exact length of the cylindrical segment of the balloon onto which a stent would be mounted is more difficult to ascertain. This can lead to a greater length of balloon overhang that results in an increased level of trauma and restenosis beyond the edges of the stent. That is, this can lead to the undesirable result of an increased edge effect.
SUMMARY OF THE INVENTION
The objectives of this invention are to overcome several of the shortcomings of prior art balloons as used for balloon angioplasty or as used for delivering a stent into a vessel of a human body.
In a first embodiment of the present invention, a balloon is disclosed that has a longitudinally centered central segment that has a substantially cylindrical shape. The length of this central segment is less than one third of the nominal length of the expanded balloon. Immediately proximal to the central segment of the balloon is a proximal segment of the balloon in the form of a prolate spheroid having a distal end that is the same diameter as the diameter of the cylindrical central segment and a proximal end that has a slightly reduced diameter. Immediately distal to the central segment is a distal segment in the form of a prolate spheroid that has the same diameter as the central segment at its proximal end and a slightly decreased diameter at its distal end. Thus, the section of the balloon onto which the stent is mounted has a central segment that is substantially cylindrical in shape that is centered between two prolate spheroids. This shape for a balloon for a stent delivery catheter provides a more cylindrical shape for the stent after it is implanted in an artery that has a typical distribution of plaque, which distribution of plaque is greatest for some limited length at a central region of the stent and then decreases somewhat uniformly as one approaches the edges of the stent. This balloon shape would also be suitable for the balloon of a balloon angioplasty catheter.
In what could be considered a second embodiment of the present invention, the length of the cylindrical central segment is zero. That is, the distal end of the proximal prolate spheroid balloon segment is fixedly joined to the proximal end of the distal prolate spheroid segment with no cylindrical segment in between. This design is particularly suitable for stent delivery or for balloon angioplasty if the plaque in a stenosis that is being treated has a greatest extent at the center of the stenosis and decreases somewhat uniformly in the extent of the plaque as one approaches the ends of the balloon.
Another embodiment of the present invention, is similar to the first or second embodiment except that the segments that have a prolate spheroid shape are replaced with conical segments whose actual shape is a frustrum of a cone.
Another embodiment of the present invention is a balloon having the same general shape as described for the first two embodiments described above. However, the third embodiment has a central, substantially cylindrical segment having a thinner wall thickness as compared to the average wall thickness of the prolate spheroid segments. In a particular embodiment, where the prolate spheroid segments join the cylindrical central segment, both prolate spheroid segments have the same wall thickness at their junction points with the central segment. Then, as one approaches the ends of the balloon, the wall thickness of both the proximal and distal prolate spheroid segments increase continuously to a maximum wall thickness whe
Fischell David R.
Fischell Robert E.
Fischell Tim A.
IsoStent, Inc.
Thanh Loan H.
Weiss John G.
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