Surgery – Instruments – Means for inserting or removing conduit within body
Reexamination Certificate
1997-08-15
2001-04-17
Buiz, Michael (Department: 3731)
Surgery
Instruments
Means for inserting or removing conduit within body
C606S198000
Reexamination Certificate
active
06217585
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to systems for percutaneously delivering and deploying vascular stents and grafts, and more particularly to devices for positioning a stent or graft within a target vessel, then radially expanding the stent or graft into intimate contact with vessel tissue.
Stenosed vessels traditionally have been opened by angioplasty, with a balloon placed into the stenosed vessel and expanded radially to open the vessel. A frequently recurring problem with angioplasty is the eventual restenosis of the vessel. One approach to counteract restenosis involves positioning radially expandable stents within treated vessels. Typically, balloons are used to open the vessel wall and to expand the stent. However, size and burst pressure considerations limit the efficacy of balloons in expanding the stent. Multiple balloons typically are used to expand a single stent, due to the tendency of balloons to burst during stent expansion.
Another vessel condition requiring treatment, the aneurysm, results from weak blood vessel walls which can balloon due to the intrinsic pressure in the vessel. Aneurysms can apply pressure on adjacent anatomic structures, producing abnormal function. In addition, vessels have a potential to rupture, causing internal bleeding and potentially life threatening conditions. Grafts are used to isolate aneurysms or other blood vessel abnormalities from the blood pool, reducing pressure on the weakened vessel wall. Grafts reduce blood loss in the event of vessel rupture. Currently, grafts are expanded into place using balloon catheters. Some large diameter vessels, e.g. the aorta, require large diameter balloons to fully expand the graft into place. At the same time, the balloon must be collapsible into a low delivery profile during introduction and withdrawal, a factor that limits balloon diameters and wall thicknesses.
Frequently, calcified lesions result in weakened blood vessel wall sections, where a stent or graft must be radially expanded at a gradual rate to minimize the risk of further injury to the vessel. However, the paramount concern of maintaining blood flow through the vessel necessitates either providing a profusion lumen, or periodic evacuations of the balloon to allow blood flow, thus prolonging the radial expansion procedure.
Thus, a need exists for a mechanical delivery system which, in the non-linear environment found within blood vessels, is capable of expanding into an enlarged, predetermined configuration to cause an accompanying stent or graft to fully expand. The delivery system must facilitate introduction of a stent or graft into the target vessel, permit enlargement of the stent or graft within small vessels, and facilitate continuous profusion of blood around the expanding device during the procedure. The system also must be capable of exerting large radial forces to expand stents or grafts having excessive stiffness, or more generally to expand any grafts or stents within excessively stenosed vessels.
Particularly, there is a need for a delivery system which can expand stents or grafts without the need of an inflation medium. The delivery system must be capable of targeting large vessels such as the aorta, or small vessels such as the arteries or arterioles. Although the delivery system and particularly its stent or graft expansion region can be scaled to different sizes, preferably a single device or system is usable over a wide range of vessel and prosthesis sizes.
SUMMARY OF THE INVENTION
To address the above and other objects, there is provided an apparatus for deploying expandable prostheses within body lumens. The apparatus includes an elongate and flexible catheter having a proximal end and a distal end. The catheter is body insertable to position the distal end within a body lumen, with the proximal end remaining outside the body. A control device is disposed along the catheter. The apparatus further includes an expansion framework comprising a plurality of elongate compliant strands. The strands are coupled at a first location that is axially fixed with respect to the catheter, and further are coupled at a second location that is axially fixed with respect to the control device. The elongate strands cooperate to determine a profile of the expansion framework. The control device is operable from the proximal end to increase an axial distance between the first and second locations to reduce the framework to a reduced-radius state for intravascular delivery of an unexpanded tubular prosthesis in surrounding relation to the framework. Alternatively, the control device is operable to reduce the axial distance to radially expand the framework, thereby to radially expand an expandable prosthesis surrounding the framework.
The apparatus or system enables a physician to accurately position a stent or graft within a target vessel of a patient, and to expand the stent or graft without the need for an inflation medium. The system permits percutaneous access, requiring a smaller puncture site than a surgical cut-down. The delivery system expands the stent or graft after accurate positioning.
According to one aspect of the invention, the apparatus is composed of a number of strands bound proximally to the catheter, and distally to a stylet that functions as the control device. The stylet runs the length of the catheter body, disposed within a lumen of the catheter. When retracted, the stylet causes the strands to exert a radial force for expanding a stent or graft. When advanced distally, the stylet moves the strands into their reduced-radius state, in which they extend axially, parallel to and adjacent the stylet. The aspect ratio of the maximum expanded radius to the minimum or collapsed radius depends on movement of the stylet. The expansion of the wire strands may be regulated by stylet motion.
If desired, an elastomeric sleeve can surround the strands at least over medial regions of the strands. As the stylet is retracted, the strands are increasingly curved and extend increasingly radially outward, causing the elastomeric covering or sleeve to radially expand. The elastomeric covering may incorporate slits to permit sustained perfusion through the vessel, thus to enable prolonged expansion of the delivery system without compromising cardiac output through the vessel.
According to one desired enhancement, the strands are preformed to exert a radially outward force throughout a larger region of the stent or graft. The stiffness of the strands can be controllably varied over their respective lengths, to produce a more uniform expansion profile. This can involve varying the thickness or the width of the strands, or both.
According to another embodiment, the strands are electrically conductive and connected to a radio frequency (RF) signal generator. RF energy is applied to one or more of the strands, causing ohmic or resistive heating near the graft or stent. This is believed to help secure the graft to the vessel, and also may promote quicker formation of an endothelial layer over the prosthesis. As an alternative, a DC power source can be coupled to opposite ends of the strands for resistive heating.
According to a further embodiment, the strands may support balloon chambers which are porous or microporous to permit their use to deliver a drug to the target vessel. Perfusion is maintained between the balloon chambers to permit longer inflation durations for diffusing the maximum amount of the desired drug to the target vessel wall.
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Fleischman Sid D.
Houser Russell A.
Whayne James G.
Buiz Michael
Converge Medical Inc.
Morrison & Foerster / LLP
Ngo Lien
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