Endoluminal prostheses are typically used to repair, replace, or otherwise correct a diseased or damaged blood vessel. A prosthesis may therefore be used to prevent or treat a wide variety of vascular ailments such as stenosis of the vessel, thrombosis, occlusion, or an aneurysm.
One type of well-known endoluminal prosthesis used in treatment and repair of diseases in various blood vessels is a stent. A stent is a generally longitudinal tubular device which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures, and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
Stents are generally open ended and are radially expandable between a generally unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded insertion diameter. Stents are often flexible in configuration, which allows them to be inserted through and conform to tortuous pathways in the blood vessel. The stent is generally inserted in a radially compressed state and expanded either through a self-expanding mechanism, or through the use of balloon catheters.
A graft is another type of endoluminal prosthesis which is used to repair and replace various body vessels. Whereas a stent provides structural support to hold a damaged vessel open, a graft provides an artificial lumen through which blood may flow. Grafts are typically tubular devices which may be formed of a variety of materials, including textile and non-textile materials. Grafts also generally have an unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded diameter.
It is known to combine a stent and a graft to form a composite endoluminal prosthesis. Such a composite medical device provides additional support for blood flow through weakened sections of a blood vessel. In endovascular applications the use of a stent/graft combination is important because the combination not only effectively allows the passage of blood therethrough, but also ensures the implant will remain open.
It is also known to provide delivery systems for delivering grafts, stents and composite stent/graft prostheses intralumenally. These delivery systems generally include catheters with the prosthesis removably mounted to the distal end of the catheter. Quite often a catheter, introducer sheath, or other similar retaining means, is disposed over the prosthesis to removably support the prosthesis on the catheter. Once the prosthesis is situated in the target site in the lumen, the catheter is removed from the prosthesis.
In treating an abdominal aortic aneurism, traditional open surgery or minimally invasive endovascular procedures may be employed. Traditional open surgery requires a large incision in the abdominal wall, from just below the breast bone to the top of the pubic bone. The muscles are then divided and the intestines and internal organs of the abdomen are pulled aside the aorta in the back of the abdominal cavity, just in front of the spinal column.
The aorta is clamped and the aneurysm is cut open to reveal any plaque and clotted blood inside. Degenerative tissue is then removed. An aortic graft is then sewn to the healthy aortic tissue above and below the weakened area so that, when finished, it functions as a bridge for the blood flow.
After the aortic graft has been sewn in place and all bleeding spots controlled, the aneurysm sack which has been opened along its length is sewn back up usually over the new graft. This prevents the new graft from rubbing against the intestines, which can damage the intestine wall. The entire procedure is fairly traumatic, is relatively high risk, and requires a long recovery period.
The endovascular procedure utilizes the endoluminal prostheses mentioned above to minimally invasively treat an abdominal aortic aneurysm. The endovascular procedure requires two small incisions in the groin. X-ray imaging typically guides the vascular graft, stent, or stent/graft through a blood vessel in the leg and into the aorta.
While minimally-invasive techniques have been an improvement over prior open surgical techniques, there is still need for improvement. A drawback of systems to deliver endoluminal prostheses is the inability to adjust or retrieve the graft or stent/graft once it has been deployed. Generally, deployment of the graft (or stent/graft) marks a point of no return; if the graft is determined to be in an inappropriate position, or the graft size is inadequate, it is not always easy or possible to cancel the procedure or reposition the stent/graft after passing this point.
Another drawback of a known delivery system for delivering stent/grafts is that the large diameter introducer catheters are needed to deliver such systems. A typical previously known stent/graft system may include a central delivery shaft having a diameter of 1.5-1.75 mm, a deployment balloon having a thickness of 0.5-0.75 mm, an anchoring stent with a thickness of 0.3-0.6 mm, a synthetic graft with a thickness of 0.25-0.5 mm, and a delivery sheath having a thickness of 0.5-0.75 mm. A stacking of these thicknesses results in a combined thickness of 4-7 mm, which must be inserted through a vascular system generally having a diameter in the range of 5-7 mm.
This creates apparent problems in the delivery and trauma which may occur with such a prosthesis.
U.S. Pat. No. 5,824,055 to Spiridigliozzi et al. is directed to providing a solution to many of these problems with the delivery systems. The delivery system employed by Spiridigliozzi et al. entails separate delivery of a stent and graft in order to provide a reduced profile and smaller diameter of the system. There are still, however, drawbacks to the system. In particular, once a graft is delivered first before the stent, because there is no anchoring system prior to the stent's introduction, the graft may migrate in the vascular system. This may result in imprecise location and increased trauma to the area. As such, this system requires the use of the stent to lock the graft in place.
Accordingly, it is desirable to provide a system for treating vascular defects and disorders, such as abdominal aortic aneurysms, that minimizes the overall profile of the prosthesis and delivery system and results in a more secure graft/vessel interface.