Tubular endoprosthesis or “stents” have been suggested for dilating or otherwise treating stenoses, occlusions, and/or other lesions within a patient's vasculature or other body lumens. For example, a self-expanding stent may be maintained on a catheter in a contracted condition, e.g., by an overlying sheath or other constraint, and delivered into a target location, e.g., a stenosis within a blood vessel or other body lumen. When the stent is positioned at the target location, the constraint may be removed, whereupon the stent may automatically expand to dilate or otherwise line the vessel at the target location.
Alternatively, a balloon-expandable stent may be carried on a catheter, e.g., crimped or otherwise secured over a balloon, in a contracted condition. When the stent is positioned at the target location, the balloon may be inflated to expand the stent and dilate the vessel.
Balloon-expanded stents tend to be relatively stiff and straight, as are the balloons used to deliver them, which reduces the ability of the stents to conform to the shape of vessels that are curved and/or angulated. Curved connectors between rings of certain stent designs may allow bending of the unexpanded stent, but such connectors rarely provide enough differential lengthening to allow significant bending of the expanded stent because the connectors are made from the same inelastic material used throughout the stent. Moreover, if such a fully expanded stent were capable of bending easily, e.g., to accommodate a bend in the artery, the stent may be capable of bending repeatedly in response to arterial motion, increasing risk of the stent becoming work-hardened and/or breaking, e.g., after deployment within a body lumen, such as a cardiac vessel, within which the stent may experience significant dynamic forces. The interface between the end of a substantially stiff, straight balloon-expanded stent and a relatively soft, otherwise curved artery may also become the focus of stress. The resulting micro-trauma may cause inflammation, scarring, and/or flow-limiting narrowing, especially when the artery stretches or bends repeatedly with the cardiac cycle, respiratory excursion, and/or flexion/extension of a joint.
One solution involves the implantation of many short unconnected stents, so that the stented artery can bend, just as a long train bends. The simultaneous delivery of multiple short balloon-expanded stents is complicated by the tendency of individual stents to migrate relative to the balloon during inflation. When a conventional balloon on a balloon catheter is expanded, one end of the balloon may initially expand before the other, which may cause the stent to migrate away from the initially expanding end and/or compress the stent axially, or both ends may expand initially before a central region carrying the stent, which may cause the stent to compress or otherwise deform undesirably. If this occurs, the actual position of the stent may be difficult to control, which risks the stent being deployed misaligned relative to a desired location. This aspect of balloon expansion may be particularly problematic when deploying many short stents.
Accordingly, an improved apparatus and methods for delivering stents would be useful.