Surgery – Instruments – Internal pressure applicator
Reexamination Certificate
1998-11-10
2001-10-30
Buiz, Michael (Department: 3731)
Surgery
Instruments
Internal pressure applicator
C606S194000, C623S001110, C623S017120
Reexamination Certificate
active
06309402
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to medical implant devices. More specifically, the invention relates to a stent encapsulated by an expandable balloon for delivery and deployment in narrowing coronary or peripheral vessels in humans.
DESCRIPTION OF THE PRIOR ART
Cardiovascular disease, 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 in the arm. Once access to the femoral artery is achieved, a short hollow sheath, or guiding catheter, is inserted to maintain a passageway during the procedure. The flexible guiding catheter must negotiate an approximately 180 degree turn through the aortic arch 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 area to be treated by angioplasty, a flexible guidewire is inserted into the guiding catheter through an expandable balloon (described infra) and advanced to the area to be treated. The guidewire is advanced across the lesion, or “wires” the lesion, in preparation for the advancement of a balloon catheter having an expandable balloon portion composed of polyethylene, polyvinyl chloride, polyolefin, or other suitable substance, across the guide wire. Currently, most balloons utilize two folded wings wrapped around the hollow catheter tube. The balloon catheter is placed into position by sliding it along the guide wire. The use of the relatively rigid guide wire is necessary for steerability 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 across the lesion. The balloon catheter is then inflated with contrast material to permit fluoroscopic viewing during treatment. The balloon is alternately inflated and deflated until the lumen of the artery is satisfactorily enlarged.
Unfortunately, while the affected artery generally can be enlarged, in some instances the vessel restenoses chronically, or closes down acutely, negating the positive effect of the angioplasty procedure. In the past, such restenosis has 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, including self-expandable and expandable stents, although to date none has proven completely satisfactory. Expandable stents generally are conveyed to the area to be treated on balloon catheters or other expandable devices. For insertion, the stent is positioned in a compressed configuration along the delivery device, such as a balloon catheter defining a balloon with two folded and wrapped wings, to make the stent diameter as small as possible. After the stent is positioned across the lesion, it is expanded by the delivery device, causing the length of the stent to contract and the diameter to expand. Depending on the materials used in construction of the stent, the stent maintains the new shape either through mechanical force or otherwise.
One such expandable stent for delivery on a balloon catheter is the Palmaz stent (U.S. Pat. No. 4,733,665) which may be thought of as a stainless steel cylinder having a number of slits in its circumference, resulting in a mesh when expanded. The stainless steel cylinder is compressed onto the outside of a non-expanded balloon catheter which includes stent retainer rings at each end of the stent to help to maintain the stent on the balloon. Also, it is advisable to place a sheath over the compressed stent and balloon assembly to retain the stent on the balloon and to create an even outer surface on the assembly for negotiation through the narrowed vessels. Boneau U.S. Pat. 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 similar manner.
Significant difficulties have been encountered with deployment of known prior art stents, including difficulty in maintaining the stent on the balloon and in achieving symmetrical expansion of the stent when deployed. Currently, some stent delivery systems retain the stent on the delivery catheter by means of either (a) plastically deforming the stent so that it is crimped onto the balloon, or (b) having the stent exhibit a small enough internal diameter to act as an interference fit with the outside diameter of the balloon catheter. The disadvantage with these methods is that the limited amount of securement between the stent and the balloon is not always adequate to insure that the stent will properly stay in place while advancing the stent to and through the target lesion. Additionally, the outer surface of the delivery device is uneven because the stent generally extends outwardly beyond the balloon and may contact a narrowed vessel wall and be displaced while the catheter negotiates a narrowed vessel. Most known expandable stent delivery systems utilize a removable sheath system on the outside of the stent, with or without retainer rings, that is removed once the stent is at the delivery site. This method protects the stent and provides a smooth surface for easier passage through vessels, but the method increases the crossing profile of the delivery device thereby decreasing the device's ability to track through narrowed and tortuous vasculature. This 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.
A long felt need exists for a delivery and deployment method for stents which ensures positional stability of the stent during delivery without the need for an external sheath, thereby substantially decreasing the cross sectional profile of the balloon delivery device, and ensures symmetrical expansion of the stent at deployment.
SUMMARY OF THE INVENTION WITH OBJECTS
The stent delivery and deployment method of this invention provides a frozen-in balloon i
Bonneau Michael D.
Jendersee Bradley A.
Lashinski Robert D.
Buiz Michael
Lewis William
Medtronic Ave Inc.
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