Intravascular stents are well known in the field of interventional cardiology for the treatment of arterial stenosis. When placed through the body's vascular system, most stents are mounted onto a balloon angioplasty catheter with or without a cylindrical sheath that covers the stent prior to stent deployment by balloon expansion at the site of a dilated stenosis. Self-expanding stents are almost always contained within a cylindrical sheath which is pulled back to release the stent. If a sheath is not used, the rough surface of the stent can damage or remove endothelial cells from the arterial wall as the outer surface of the stent rubs the inside walls of the curved coronary (or other) arteries. Without a sheath, the stent may also get caught on the guiding catheter during movement into or out of the body which can cause the stent to come off the delivery catheter and embolize into the vasculature. When a sheath is used, it can have a few disadvantages. A first disadvantage is that all prior art sheaths are tubes that have a uniform wall thickness and are secured only at the proximal end to the stent delivery catheter system. Therefore, in order to have a sufficient column strength, the sheath must be relatively thick-walled, throughout its entire length, which makes it stiff and bulky so that passage through tortuous coronary arteries can be difficult. Another disadvantage of prior art sheaths is that they have blunt distal ends which can be caught on an already deployed stent, a calcified piece of intimal dissected tissue or a tight stenosis. Still further, when secured only at the proximal end of a stent delivery catheter, the sheath often either uncovers the stent due to significant bending of the stent delivery catheter or the sheath advances too far distally beyond the distal end of the stent. Finally, because of the larger diameter, blunt end and stiffness of sheathed stent delivery systems or the rough outer surface of unsheathed stent delivery systems, pre-dilatation with another balloon angioplasty catheter is almost always required before stent implantation.
Another disadvantage of existing stent delivery catheter systems that use either a conventional sheath or have stents mounted bare onto an inflatable balloon is that the distally directed push force for such stent delivery catheters comes only from the inner and outer shafts of the balloon angioplasty catheter on which the inflatable balloon is situated. Specifically, in no prior art device does the sheath contribute to the pushability of the stent delivery catheter system.