Graft stent and method of repairing blood vessels

A method and apparatus for repairing a weakened section of a vessel. A pair of expandable stents are placed at either end inside a prosthetic graft of a length sufficient to span the weakened section. The graft and stents are inserted into the vessel. The stents are positioned on either side of the weakened section and expanded to a stable, increased diameter for securing by friction the graft in situ inside the vessel.

BACKGROUND OF THE INVENTION 
This invention relates generally to stents for holding in situ vascular 
grafts and, more specifically, to such stents and a method using such 
stents for repairing diseased or damaged sections of a vessel. 
A common health problem is diseased or damaged blood vessels which may 
weaken, develop into an aneurysm, and rupture. Conventional techniques for 
the repair of damaged or diseased sections of vessels include invasive 
surgery to expose to a surgeon the section of the artery to be repaired. 
The weakened section is resected and replaced either by a section of 
healthy vessel removed from a remote site of the patient's vascular system 
or by a tubular synthetic graft. Either graft is sutured into place. This 
prior art technique is traumatic to the patient, frequently requires major 
surgery, and may be hazardous or impossible to perform if, as is not 
infrequent, the health of the patient is poor. 
A large number of patient admissions and procedures performed each year are 
due to aneurysms of the aorta that are distal of the renal arteries, i.e., 
infra-renal abdominal aortic aneurysms. In addition to the resection and 
replacement procedure, aortic aneurysms are currently repaired by the 
axillobifemoral bypass method, which method also requires major, invasive, 
and risky surgery. Recently, a promising new apparatus and procedure for 
the repair of aortic aneurysms was described in U.S. Pat. No 4,577,631. 
This procedure is accomplished via a small incision in a femoral artery of 
the patient and relies on an occlusion catheter to block the arterial flow 
of blood through the aneurysm site during adhesion of a tubular synthetic 
graft over the diseased or damaged section of the aorta. 
SUMMARY OF THE INVENTION 
The present invention is a stent for holding a tubular synthetic graft in 
place to replace and repair a damaged or diseased section of a vessel. The 
stent is formed of a generally rectangular section of semi-rigid material. 
The rectangular section is rolled so that an inside longitudinal edge is 
overlapped by the opposite longitudinal edge. In its relaxed state, the 
stent is generally cylindrical, having a relatively small diameter and a 
cross section that is a section of a spiral. The stent can be expanded 
from its smaller diameter to a larger diameter by partially unrolling the 
stent, with the result that the cross section is now a shorter section of 
a spiral having a larger inner and outer diameter. The inner surface of 
the stent includes a retaining means which acts to restrain the expanded 
graft from returning to its relaxed, smaller diameter condition. 
To repair a section of vessel, a tubular synthetic graft is positioned in 
place inside the vessel overlapping the weakened section to adjoining 
healthy sections of the vessel. A stent in its relaxed, smaller diameter 
condition is positioned at one end inside of the graft and expanded to its 
enlarged, larger diameter condition, a diameter which is somewhat greater 
than the inner diameter of the vessel. The retaining means prevents the 
stent from returning to the small diameter condition. Friction between the 
stent, the graft, and the inner wall of the vessel prevents displacement 
of the stent and graft once expanded. Similarly, a stent is positioned and 
expanded at the other end inside of the graft. If necessary, a tie or 
other means can be placed over the vessel in the region of the stents 
further to prevent displacement thereof.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Illustrated in FIG. 1 at 10 and 12 are a pair of stents that are used to 
hold a tubular synthetic graft 14 in place inside a vessel 16 to replace 
and repair a damaged or diseased section 18 of the vessel. The stents 10 
and 12 are identical in construction and may be identical in size. For the 
purposes of describing the stents 10 and 12, reference will be made to 
stent 10 only with the understanding that the same description applies to 
stent 12. 
The stent 10 has a relaxed, smaller diameter condition (FIG. 2 and an 
expanded, larger diameter condition (FIG. 3). The stent 10 is described 
fully in U.S. Pat. No. 4,740,207, which patent is incorporated herein by 
this reference. Briefly, the stent 10 is made of a semi-rigid, generally 
rectangular piece of material that is rolled so that an inside 
longitudinal edge 20 is overlapped by the opposite longitudinal edge 22. 
In its relaxed condition (FIG. 2), the stent 10 requires an expansile 
force to increase its diameter (FIG. 3). That is, the material comprising 
the stent 10 is resilient and will attempt to return to its relaxed 
condition (FIG. 2) unless restrained. 
If an expansile force is exerted on the interior of the relaxed stent 10, 
it will unroll. As it unrolls, the inner longitudinal edge 20 approaches 
the edge of an inwardly projected restraining tooth 24. A maximum diameter 
condition is defined wherein the inner longitudinal edge 10 is between the 
edge of the tooth 24 and the outer longitudinal edge 22. If the expansile 
force is now released, the resiliency of the stent 10 will cause it to 
move toward its relaxed condition. The tooth 24, however, captures the 
inner longitudinal edge 20 and the stent 10 is restrained in its expanded, 
larger diameter condition (FIG. 3). 
Repair of a weakened section of a vessel proceeds by insertion of the 
tubular synthetic graft 14 into the vessel 16 (FIG. 1). The graft 14 is a 
conventional tubular graft made of Dacron or Gore-Tex.RTM. 
(polytetrafluoroethylene) and is of a length sufficient to span the 
weakened section 18 of the vessel to overlap healthy sections of the 
vessel 16 on either side of the weakened section 18. 
Once the graft 14 has been appropriately positioned in the vessel 16, the 
stent 10 is its relaxed condition is inserted into the graft 14 (FIG. 5) 
and the vessel 16 and properly positioned on one side of the weakened 
section 18. It is then expanded to its maximum diameter and released to 
its expanded, larger diameter condition (FIG. 1). Similarly, the stent 12 
is positioned inside the graft 14 and vessel 16, appropriately positioned, 
and expanded to its expanded-larger diameter condition. The stents 10 and 
12 are chosen to be of an expanded, larger diameter that is larger than 
the ordinary inside diameter of the vessel 16 in the areas where the 
stents will be placed. The stents, accordingly, will be expanding somewhat 
the natural diameter of the vessel 16. The combination of stent, vessel, 
and intervening graft will be held relatively stationary by the friction 
between the different elements A raised lip 26 (FIGS. 1-3) is provided at 
either end of the stents 10 and 12 to further increase the holding ability 
of the stents. If additional security against movement is desired, a tie 
28 (FIG. 6) may be applied outside the vessel 16 in the area of the 
stents. Alternatively, a clamp or suitable tape could be applied to 
further secure the stents and graft. Further, the stents could be held 
captive to the graft, e.g., in sleeves or pockets at either end of the 
graft. 
While the stents 10 and 12 can be used instead of sutures in the 
conventional resection procedure, a less invasive method of repairing the 
weakened section is preferred. One such method is a modification of the 
aneurysm repair method described in U.S. Pat. No. 4,577,631, which patent 
is incorporated herein by this reference. The stent 10 of the present 
invention is placed inside the graft of the '631 patent and the balloon 
catheter thereof is used to expand the stent to hold the graft in place. 
The stent 10 thus takes the place of the '631 patent of the adhesive for 
securing the graft to the vessel. 
A second less invasive method would-make use of a double balloon catheter 
that is similar to the triple balloon catheter (50) of the '631 patent 
except that only two balloon sections are required. In this method, a 
graft of the appropriate length and diameter is selected. Two stents 
having the appropriate expanded, larger diameter are received about the 
noninflated balloons of the catheter that have been positioned a distance 
apart sufficient to span the weakened section of the vessel to be 
repaired. The graft is then received about the stents and catheter. It may 
be desirable to secure the graft to the exterior of the stent or stents so 
that it is not displaced therefrom during the procedure. 
An incision is made in the vessel at a site remote from the weakened 
section. In the case of an infra-renal aortic aneurysm, the incision may 
be made into a femoral artery in the leg of the patient. The catheter 
carrying the stents and graft is inserted into the incision and fed to the 
site of the weakened section. As described in the '631 patent, a 
radio-opaque equator on the balloons may assist in placement of the 
catheter. Once the catheter is in position, the balloons are inflated to 
expand the stents to their maximum diameter and then deflated. As 
described above, the stents will be restrained in their expanded, larger 
diameter condition and will hold the graft in place thereby repairing the 
weakened section of vessel. This method can, of course, be adapted (as can 
the other methods herein described) to make use of a bifurcated or 
Y-shaped graft for use, for example, in performing an axillobifemoral 
bypass.