The presently described embodiments relate to apparatus for delivering an implantable prosthesis, in particular a stent member, to a desired location in a body of a patient.
Radially expandable prosthetic devices such as stents, stent grafts and valves may be delivered from the distal end of a catheter delivery system. The delivery system typically includes an inner catheter tube member surrounded by a sheath and extending from a proximal end controlled by an operator and a distal end inserted to a point of treatment within a body vessel. The inner catheter houses a wire guide lumen extending along at least a portion of the catheter and terminates at a tapered tip portion. The radially compressed prosthetic device may be positioned around the distal portion of the catheter between the sheath and the inner catheter member adjacent or near the distal tip. The prosthetic device is typically adapted to radially expand to an outer diameter greater than the diameter of the distal tip and inner catheter member when the prosthetic device is not radially restrained by the sheath. The sheath can be translated longitudinally with respect to the inner catheter member by the operator to permit movement of the sheath in a proximal direction, away from the tip. Movement of the sheath away from the distal tip permits the prosthetic device to radially expand away from the inner catheter member as the sheath is moved away from the radially compressed prosthetic device, deploying the prosthetic device within a body vessel. The catheter delivery system is then removed from the body vessel after deployment of the prosthetic device.
Friction between the sheath and the prosthetic device, when the sheath is translated during deployment of the prosthetic device, may hinder the steady release of the device. By requiring application of additional force by the operator, this friction may lead to sudden movement of the sheath relative to the device and/or undesirable sudden radial expansion of all or part of the device. When the outer surface of the device has a drug coating, the friction with the sheath may cause undesirable release of the drug and/or compromise drug coating uniformity. In addition, when the prosthetic device includes material that may tear or fold, such as a stent graft covering or a valve leaflet, the friction with the sheath may compromise the physical integrity of the device during the deployment procedure (e.g., causing a tear in a graft or leaflet material leading to leakage or poor performance). Friction and other deployment issues arise when the stent members are lengthier, such as greater than 100 mm. With piston-type introducers, the pushrod needs to retract at least the length of the stent, or much more for a rolling membrane, roll sock, or everted liner introducer that often require at least twice the length of the stent member for retraction.
Thus, during the deployment procedure for stent members, the need can arise to carefully remove a sheath member from a stent member and/or an inner catheter. A problem can arise in respect to long stent members in that a long handle is needed to enable longitudinal retraction of the associated sheath member.