Transfemoral endovascular aortic
`graft placement
`
`Timothy A. M. Chuter, BM, BS, Richard M. Green, MD, Kenneth Ouriel, MD,
`William M. Fiore, MD, and James A. DeWeese, MD, Rochester, N.Y.
`
`Purpose: The purpose of this study was to develop an endovascular system for transfemoral
`placement of straight aortic grafts and bifurcated aortoiliac grafts.
`Methods: Both types of graft consist of barbed, self-expanding stents attached to a woven
`polyester fabric. Survival studies of straight-graft function were performed in six large
`mongrd dogs. Digital subtraction fluoroscopic equipment was used to guide insertion and
`record angiograms at 0, 1, and 3 months. Bifurcated grafts were inserted in an additional
`eight dogs, four with distal stents and four without. Straight grafts were inserted into six
`cadaveric aortas (five atherosclerotic and one aneurysmal; age 68.7 + 5.7 years) to assess
`stent attachment.
`Results: Angiograms obtained immediately after straight-graft insertion showed placement
`to be within 4.6 + 1.6 mm of the intended level. Follow-up angiograms at 1 and 3
`months showed no migration, no leakage, and patency of all six grafts. After bifurcated
`graft insertion there were no angiographic signs ofperigraft leakage, with or without distal
`stents. The mean force required to displace straight grafts 10 mm from their original
`position in cadaveric aortas was 1388 + 127g.
`Conclusion: These preliminary results show that straight and bifurcated endovascular
`grafts can be positioned accurately and securely in the abdominal aorta. (J VASC SURG
`1993;18:185-97.)
`
`Endovascular repair of aortic aneurysms is now
`feasible because of advances in vascular imaging,
`catheter delivery systems, and arterial stenting. A
`graft can be introduced through a remote artery and
`anchored to nondilated vessels at the ends of an
`aneurysm to provide protection against rupture and
`a conduit for distal perfusion.
`Graft attachment must be accurate, secure, and
`hemostatic, both proximally and distally. The com-
`bination of graft and introducer must be small
`enough for retrograde insertion through the femoral
`'tory. The system should have sufficient flexibility to
`traverse the often-tortuous iliac vessels.
`Endovascular systems have been used to repair
`small traumatic aneurysms in animals, but these
`
`From the Section of Vascular Surgery, University of Rochester,
`Rochester, N.Y.
`Supported in part by grants from Cook Catheter, Inc., Bloom-
`ington, Ind.
`Presented at the Sixth Annual Meeting of the Eastern Vascular
`Society, New York:, N.Y., April 30-May 3, 1992.
`Reprint requests: Tim Chuter, BM, BS, Department of Surgery,
`Strong Memorial Hospital, 601 Elmwood Ave., Box SURG,
`Rochester, NY 14624.
`Copyright © 1993 by The Society for Vascular Surgery and
`International Sociel~ T for Cardiovascular Surgery, North Amer-
`ican Chapter.
`0741-5214/93/$1.00 + .10 24/6/42587
`
`models lacked the more challenging features of
`human aneurysms. 1,2 Some promising initial results
`have been reported with a balloon-expandable system
`in humans, a
`This report describes our initial laboratory expe-
`rience with an endovascular delivery system ~ for
`straight and bifurcated grafts that was designed
`specifically to meet the demands of clinical use.
`
`MATERIAL AND M E T H O D S
`The technique ofendovascular graft insertion was
`studied in dogs. Graft attachment was assessed
`further in human cadaveric aortas.
`
`Apparatus
`The two systems of endovascular grafting used in
`these studies represent different stages in the evolu-
`tion of the technique. Several components were
`changed in the interval between the straight and
`bifurcated graft insertions, and several have changed
`since then. Differences between these systems also
`reflect the more exacting requirements for bilateral
`distal limb placement and stenting.
`Straight grafts. Straight grafts were constructed
`
`*Patent held by Timothy A. M. Chuter.
`
`185
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-1
`
`

`

`186 Chuter et al.
`
`JOURNAL OF VASCULAR SURGERY
`August 1993
`
`Guid
`
`Barb
`
`barb
`
`Graft -
`
`-
`
`
`
`Stent--
`
`Carrier
`
`A
`
`le wire
`
`Introducer
`
`~
`
`Hemostatic
`
`seal
`
`Injection
`port
`
`Fig. 1. A, Straight graft mounted on central carrier shows stems protruding from graft orifices.
`B, Proximal stent of straight graft and attachment to central carrier. C, Delivery system during
`insertion shows how dilator head combines with introducer sheath to create smooth, featureless
`external profile.
`
`of the heavy, crimped fabric used in conventional
`aortic bypass grafts. The fabric was cut and sutured
`into tubes with the crimps nmning longitudinally to
`provide an element of transverse elasticity. Three
`stents occupied the lumen of the graft: one in the
`middle and one protruding from each end (Fig. 1,A).
`Stents measured 23 mm in length and 20 mm in
`diameter in their nondeformed state. At normal
`canine aortic diameters
`(approximately 9 mm)
`
`stents exerted a constant outward force, which
`served to press the graft and the barbs against the'
`aortic wall. The stent at the cranial end of the
`graft carried four barbs to enhance attachment to the
`aorta.
`The narrow portion of a central carrier traversed
`the lumen of the graft. Splits in the catheter of the
`central carrier were traversed by short loops of
`monofilament suture, which connected stents at both
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-2
`
`

`

`JOURNAL OF VASCULAR SURGERY
`Volume 18, Nmnber 2
`
`Chuter et al.
`
`187
`
`ends of the graft to a guide wire in the lumen of the
`carrier (Fig. 1,B). As long as the guide wire remained
`within the lumen of the delivery system, the loops
`could not retract and the graft remained attached to
`the central carrier. Removal of the guide wire released
`the graft.
`The graft, its stents, and the carrier were com-
`pressed into an introducer sheath, before insertion. A
`dilation at the distal end of the carrier matched the
`diameter of the sheath orifice. With the sheath in
`place around the terminal dilation, the apparatus had
`a smooth external prone (Fig. 1, C). A seal at the
`outer end of the sheath ensured hemostasis.
`Bifurcated grafts. Bifurcated grafts (13 mm by
`6 mm) were constructed of thin, uncrimped, woven
`polyester. Two lines of very fine gold chain ran the
`length of the 1eft limb of file graft. These served as
`radiopaque markers, indicating the axial orientation
`,~ 2 the graft limb. Only one stent was attached to the
`graft before insertion. This stent carried small coils on
`6 of its 12 limbs, to which the proximal orifice of the
`graft was sutured. The outer angles of the stent
`carried Caudally directed barbs (Fig. 2).
`A central carrier traversed the lumen of the graft
`through the mink and one of the distal limbs (Fig.
`3, A). The narrow portion of the central carrier
`consisted of two coaxial catheters instead of the single
`catheter used in straight-graft insertion. The outer
`catheter was split at the sites of graft attachment.
`,Suture loops from both ends of the graft traversed
`these splits to ,encircle the inner catheter, thereby
`attaching the graft to the central carrier. A Luer lock
`between the hubs of the inner catheter and the outer
`catheter prevented premature graft release (Fig. 3, B).
`Graft attachmenl: to the carrier was dependent on the
`presence of the inner catheter instead of the guide
`wire alone. This permitted insertion of the delivery
`system by guide wire exchange. Removal of the
`g ide wire also permitted the lumen of the inner
`°catheter to be used as a conduit for radiographic
`contrast.
`Only one limb of the graft was attached to the
`central carrier in this way. The other was attached to
`a small (3F) catheter by a loop of free monofilament
`suture that ran through the lumen of the catheter
`t"rom one end to the other. The graft remained
`attached to the catheter as long as the suture was
`intact. Graft release was accomplished by severing the
`outer end of the suture, whereupon one arm of the
`loop slid up the lumen of the catheter and out of the
`graft. The outer end of this catheter was attached to
`file central carrier where it was accessible after
`removal of the innroducer sheath.
`
`Barb ~ Graft
`~ ~ ~hment
`
`Fig. 2. Segment of proximal stent used with bifurcated
`graft shows apical barb and point of graft attachment.
`
`A small dilator with a fish-mouth split at its end
`served as a graft straightener. The graft was pulled
`into the jaws of the dilator by traction on the small
`catheter attached to the orifice (Fig. 4).
`In this series of experiments, distal stents were not
`attached to the graft but were inserted separately once
`the graft was in position. A stent delivery system (Fig.
`5) was directed into the lumen of the graft by a guide
`wire (right side) or a catheter (left side).
`
`Technique
`Straight grafts. Canine studies were approved
`by the institutional committee on animal research
`and conformed to guidelines of the National Insti-
`tutes of Health. All procedures were performed
`under general (barbiturate) anesthesia. Animals were
`placed in the supine position on a radiolucent
`operating table for graft insertion. The right common
`femoral artery and its branches were exposed through
`a longitudinal incision in the groin. All animals
`received 2000 units heparin by intravenous injection
`before the application of noncrushing clamps to the
`superficial and deep femoral arteries. Silicone rubber
`bands around the common femoral arteries provided
`hemostasis proximally. Access to the arterial tree
`was through a longitudinal common femoral arteri-
`otomy.
`Our vascular imaging system (OEC-Diasonics,
`Inc., Salt Lake City, Utah) recorded real-time fluo-
`roscopy on videotape. Images obtained after intraar-
`terial injection of contrast material (Conray 60) were
`enhanced digitally and transferred to photographic
`films as angiograms. Another useful feature of the
`digital subtraction imaging system was the "road-
`mapping" function, which combined real-time fluo-
`roscopic images with static angiograms. The corn-
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-3
`
`

`

`188 Chuter et al.
`
`JOURNAL OF VASCULAR SURGERY
`August 1993
`
`Guide wire
`
`graft limb
`
`Suture loop
`
`I ~
`
`Inner catheter
`
`Luer lock
`connector
`
`jection port
`
`Carrier
`
`a
`All
`Fig. 3. A, Bifurcated graft mounted on central carrier shows catheter used to control left limb.
`B, Outer end of central carrier used in bifurcated graft insertions shows locking inner and outer
`catheters.
`
`de wire
`
`posite image facilitated guidance of the apparatus
`through the vascular tree.
`After initial angiography the delivery system was
`inserted to a predetermined position within the aorta,
`where the graft was released. Fluoroscopic visualiza-
`tion was relatively easy because most of the apparatus
`was radiopaque. Bony landmarks served as reference
`points for graft placement. The object was to position
`the proximal (upstream) stent at the caudal end of the
`third lumbar vertebra. The position of the prosthesis
`was controlled by manipulation of the central carrier,
`as the introducer sheath was withdrawn slowly.
`Expansion of the distal stent was taken as a sign that
`graft extrusion was complete. Removal of the guide
`wire released the graft from the central carrier, which
`was removed. Arteriography was repeated before
`closure of the femoral artery.
`Angiograms were obtained at i and 3 months by
`
`intraarterial injection of contrast material through an
`angiographic catheter introduced percutaneously.
`Angiographic measurements of distance were cali-
`brated by reference to the known length of sten~.
`The ability of a graft to isolate the adjacent segment ~
`of aortic wall from the circulation was assessed by
`examining angiograms for opacification of aortic
`branches in the region of the graft. Visualization of
`lumbar or middle sacral arteries was indicative of
`leakage of contrast material, either through the walls
`of the graft or between the ends of the graft and the'
`aorta.
`Bifurcated grafts. Placement, straightening, and
`stenting of the left limb of bifurcated grafts required
`some additional maneuvers. In this series of experi-
`ments access to the left femoral artery was obtained
`by direct surgical exposure and longitudinal arteri::
`otomy.
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-4
`
`

`

`JOURNAL OF VASCULAR SURGERY
`Volume 18, Ntm~ber 2
`
`Chuter et al. 189
`
`Straightener
`
`Distal graft limb
`
`Catheter
`Fig. 4. Graft straightener engaging left limb of graft.
`
`PJacement of a cross-femoral catheter preceded
`graft insertion. A wire basket, inserted through the
`right femoral artery, was opened in the aorta at the
`orifice of the left common iliac artery (Fig. 6). A
`,~ ,theter was threaded through the left femoral artery,
`up the left iliac artery, and into the open wire basket,
`which was ther~ closed and withdrawn. After cross-
`femoral cathete:: insertion, a prelimina W angiogram
`"was obtained by injection of contrast material into
`1:he proximal aorta. To ensure that the angiographic
`catheter could not become tangled with the cross-
`femoral catheter, the two were inserted through
`separate lumina of a double-lumen introducer. The
`angiographic catheter was guided into the proximal
`aorta by manipulation of its curved tip. After initial
`angiography, care was taken to ensure that neither the
`C arm nor the table moved. The angiographic
`catheter was removed, leaving a guide wire in place,
`over which the graft delivery system was inserted.
`When the graft reached the desired position, the
`introducer sheath was withdrawn slowly. The ex-
`posed graft expanded onto the aorta under the action
`of the proximal stent and the force of flowing blood.
`Removal of the sl~eath exposed the small catheter on
`t' : left limb of the graft (Fig. 3,A). This catheter was
`:freed of its attachment to the central carrier and
`sul~red to the cross-femoral catheter. Traction on the
`cross-femoral catheter pulled the small catheter back
`into the right femoral artery through the iliac arteries
`and out of the left femoral arteriotomy. The attached
`limb of the graft fallowed the catheter into the left
`~ommon iliac artery.
`The small catheter was also used to apply the
`limb-straightening device to the left limb of the graft
`(Fig. 4). Twists were corrected by reference to the
`two radiopaque lines on the graft. During introduc-
`tion of the distal stents, tension was maintained on
`ehe end of the gra_fir limb to prevent graft displace-
`ment. The stent insertion apparatus (Fig. 5) was
`
`ide wire
`
`stent
`
`Fig. 5. Longitudinalsecdon of distal stent delivery system
`used with bifurcated grafts shows stent maintained in
`compressed state by sheath.
`
`guided into the graft lumen over a catheter on one
`side and a wire on the other. Catheters were released
`from the graft by severing the loops of suture that ran
`through the lumina.
`The bifurcated graft was released from the carrier
`by removing the inner catheter and guide wire. The
`guide wire was replaced before removal of the carrier
`to act as a guide for the insertion of the right-limb
`stent-delivery system and as a guide to the insertion
`of an angiographic catheter.
`
`Canine studies
`Preliminary experiments in 12 dogs were used
`to refine the techniques and apparatus for both
`tubular and bifurcated graft insertion. Definitive
`studies used standardized methods in two sets o£
`sequential experiments. Straight grafts were inserted
`in six mongrel dogs (weight 29.2 + 1.3 kg) and
`monitored for 3 months. Acute studies of bifurcated
`grafts were performed
`in eight mongrel dogs
`(weight 33.4 +_ 1.0 kg). Four of the bifurcated
`grafts were inserted with distal stents and four
`without.
`
`Cadaveric studies
`The apparatus for insertion of a straight graft was
`reproduced on a human scale. The graft measured 25
`mm in diameter and 100 mm in length. An eight-
`pointed stent, attached to each end of the graft,
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-5
`
`

`

`190 Chuter et al.
`
`IOURNAL OF VASCULAR SURGERY
`August 1993
`
`S
`
`7
`
`basket
`
`ross femoral ~
`- catheter/~
`
`/
`
`Fig. 6. Cross-femoral catheter placement shows how basket was used to pull catheter from one
`side to other.
`
`carried four barbs that resembled those used in canine
`studies of straight grafts.
`Human abdominal aortas were obtained at au-
`topsy from six cadavers (age 68.7 +--6.0 years).
`Specimens included proximal segments of renal and
`iliac arteries. The youngest cadaver (age 47 years) had
`had diabetes and a history of peripheral vascular
`disease. All cadaveric specimens showed signs of
`atherosclerosis. One aorta contained a 6 cm aneu-
`rysm. Specimens were stored at - 20 ° C and thawed
`before use. Specimens were then mounted on a stand.
`Hooks and damps held both ends in place. Grafts
`were inserted through the stump of the right iliac
`artery. No fluoroscopy was used in cadaveric studies.
`Instead, grafts were positioned by reference to
`markings on the outside of the introducer sheath.
`Otherwise the insertion procedure was similar to that
`used in canine studies of straight grafts.
`Graft attachment was tested by applying traction
`to the distal stent. The force required to displace the
`graft was measured with a simple gravity tensometer
`(Fig. 7). An inelastic suture was passed over a pulley
`from the downstream stent to a light plastic con-
`tainer. Movement of a knot in the suture was used to
`detect displacement of the graft relative to a linear
`scale, marked in millimeters. Measurements of dis-
`placement force were performed after three separate
`insertions for each specimen. Water was added to the
`container of the tensometer until the graft moved 10
`
`mm from its original position or the maximum
`capacity of 2000 ml was reached.
`
`RESULTS
`Canine studies
`Straight grafts. The distances between actual
`and intended positions of straight grafts decreased
`with increasing operator experience (Table I). No
`graft migration was seen at 1 and 3 months. Fig. 8
`shows the relation of the upstream stent of a straight
`graft to the lumbar vertebrae and the angiographic
`appearance of the same straight graft at 3 months.
`All straight grafts remained patent by angiogra-
`phy and all animals had palpable femoral pulses at 1
`and 3 months. Completion angiograms of e ~
`straight grafts showed perigraft flow of contrast
`material into lumbar arteries. These vessels were not
`apparent at 1 and 3 months.
`The luminal diameter of the graft (5.5 +_ 0.4
`ram) at
`the narrowest point was significantly
`(p < 0.005) less than at the narrowest point in the
`ungrafted aorta (8.7 +-0.5 mm) on completiofi
`angiography. The difference represented the space
`occupied by the wall of the graft, which retained a
`high degree of crimping at canine aortic diameters.
`At 1 month the corresponding luminal diameter was
`4.2 _+ 0.3 mm (p < 0.05, from 0-monthvalue), and
`at 3 months it was 4.8 +_ 0.7 ram. These change~
`were attributed to the presence of mural thrombus at
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-6
`
`

`

`j'OUKNAL OF VASCULAR SURGERY
`Volume 18, Nmnber 2
`
`Chuter et eL
`
`191
`
`Aneurysm
`
`r
`
`lilac a
`~,~ ~:,/.....~
`
`~ T h r o m b u s
`
`t
`
`~
`
`~
`
`Proximal aorta
`
`
`
`Renal artery
`
`Fig. 7. Experimental apparatus for measuring force required to displace graft 10 mm from
`initial position in cadaveric aorta.
`
`1- and 3-month follow-up, which was confirmed at
`autopsy.
`Bifurcated grafts. All eight bifurcated grafts
`were placed successfully. None of the lmnbar or
`middle sacral arteries at the level of the graft was
`apparent on completion angiography (Fig. 9).
`All grafts were widely patent into the iliac arteries.
`None of the distal limbs contained a twist of more
`than 90 degrees, and routine straightening of the
`contralateral limb produced no noticeable change in
`the femoral arterial pulse or blood flow. There were
`no angiographic or hemodynamic signs of significant
`kinking. In two of the unstented grafts the bifurca-
`tion was placed ~.'ight on top of the aortic trifurcation,
`producing an oblique fold in the surface of the graft.
`This fold was apparent at autopsy and on angiogra-
`phy but had no noticeable effect on blood flow.
`Comparison of completion and preliminary angio-
`grams (Fig. 9) in bifurcated graft insertions showed
`r_., measurable difference between the diameters of
`the proximal graft lumen (nonbifurcated portion)
`and the corresponding segment of the aorta, in
`contrast to the ¢:arrowing seen with straight grafts.
`The accuracy of bifurcated graft placement is
`difficult to quantify because grafts were not targeted
`to bony landmarks. However, the location of distal
`~limb angulation on completion angiograms (indicat-
`ing the position of the iliac artery origin) suggests
`thLat approximately half of the graft was placed in the
`aorta and half in the iliac arteries, as intended.
`
`Cadaveric studies
`The force required to displace a graft 1 cm (or
`more) from its initial position in a cadaveric aorta was
`
`Table I. Distance between actual and
`intended graft positions on
`completion angiography
`Distance from target (ram)
`Calibration
`factor
`
`Measured
`
`Dog
`
`7
`8
`9
`10
`11
`12
`
`9
`16
`7
`4
`1
`2
`
`2.3/3.3
`2.3/3.2
`2.3/3.5
`2.3[3,2
`2,3/3.3
`2.3/3.1
`
`Corfected
`
`6.3
`I1.5
`4.6
`2.9
`0.7
`1.5
`
`1388 _ 127 gm (Table II). Measurements could not
`be repeated more than three times for each specimen
`because graft displacement occurred only when the
`aortic wall began to tear. The less severely diseased
`vessels appeared to withstand less force, although the
`degree of atherosclerosis was not quantified.
`
`DISCUSSION
`We have developed a transfemoral system that
`satisfies many of the prerequisites for endovascular
`repair of human abdominal aortic aneurysms. Graft
`attachment is accurate, hemostatic, and secure; the
`delivery system is small, flexible, and smooth. Both
`straight and bifurcated endovascular grafts channel
`unimpeded blood flow through the distal aorta,
`isolating the aortic wall from the circulation.
`Two elements of our delivery system had pro-
`found effects on function. One is the carrier head,
`which engaged the orifice of the introducer sheath
`giving the whole a smooth, featureless external
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-7
`
`

`

`192 Chuter et al.
`
`JOURNAL OF VASCULAR SURGERY
`August 1993
`
`Fig. 8. A, One-month angiogram of straight graft shows position of proximal stent (arrow) in
`relation to spine and adjacent visceral arteries. B, More caudal view of same graft at 3 months
`demonstrates that graft remains patent and four lumbar arteries, in region of graft, do not fill.
`
`profile. Without the carrier head or a conventional
`dilator, the open end of the introducer sheath would
`snag on any bends or lumenal irregularities. Because
`the carrier head occupied only the terminal portion of
`the proximal introducer sheath, there was room for
`the prosthesis. The presence of a conventional dilator
`would have prevented simultaneous introduction of
`the prosthesis, necessitating additional maneuvers
`and possibly a second sheath. The other important
`feature of the delivery system was the attachment of
`the cranial (upstream) end of the prosthesis to the
`central carrier. Through this attachment the prosthe-
`sis was pulled, not pushed, into position. Because the
`prosthesis did not have to withstand compressive
`loading, it could be soft and flexible enough to
`negotiate the often-tortuous path through the iliac
`arteries to the proximal end of the aneurysm.
`Several elements of the apparatus improved in the
`interval between straight and bifurcated graft inser-
`tions. The first, and most important, change was the
`substitution of a smooth, lightweight cloth for the
`standard graft material used in straight grafts. Lon-
`gitudinal crimping was used in straight grafts as a
`means of eliminating graft redundancy. However,
`preliminary experiments during the design of a
`bifilrcated prosthesis showed that a small amount of
`redundancy in a thin-walled graft caused no leaking
`or luminal narrowing. Crimped grafts produced
`
`both. It is perhaps remarkable that all straight grafts
`remained patent because their heavy, crimped walls
`occupied more than half of the aorta and subsequent
`accumulation of thrombus narrowed the lumen still
`more. Thrombus deposition on the walls of straight
`grafts may be attributable to characteristics of the
`graft material or to associated flow disturbances.
`Mural thrombus did not accumulate in two prelim-
`inary studies, in which smooth, thin-walled grafts
`were followed for I month.
`Changing to a thin fabric also allowed a reduction
`in sheath size to 14F, the use of a more advanced
`stent, and less compression of the prosthesis. A less
`tightly packed prosthesis generated less fricti~,
`resulting in a smoother, more accurate extrusion. The ~
`proximal stent became shorter, more elastic, and
`easier to attach to the graft. The improvement in stent
`design may have contributed to the elimination of
`leakage around the ends of the graft, as evidenced by
`the nonvisualization of aortic branches adjacent to
`bifurcated grafts.
`The main advantage of the two-catheter central
`carrier, used in bifurcated graft insertions, is the
`ability to insert the delivery system over a previously
`positioned guide wire. The manipulation required to
`negotiate the often-tortuous iliac arteries can then be
`accomplished with standard angiographic techniqueg"
`before the delivery system is inserted. The basic
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-8
`
`

`

`JOURNAL OF V'ASCULAR SURGERY
`Volume 18, Nmnbcr 2
`
`Chuter et cd. 193
`
`Fig. 9. A, Angiogram of canine aortic trifurcation shows large middle sacral artery. B,
`Angiogram of same dog after insertion of bifurcated graft shows position of distal srents (arrows)
`and absence of flow' into middle sacral artery.
`
`mechanism of graft attachment was the same in
`straight and bifurcated studies, despite the substitu-
`i:ion of a catheter for the guide wire as the control
`mechanism for graft release. In both series of experi-
`ments loops of suture remained on the graft after
`insertion. The mechanism has since been modified to
`allow these sutures to be removed with the carrier.
`The accuracy of graft placement is attributable to
`a combination of external control and continuous
`fluoroscopic visualization. Straight graft insertions
`targeted bony landmarks, whereas bifurcated graft
`insertions targeted reference points in the vascular
`tree, with the ":roadmapping" capabilities of the
`digital subtraction vascular imager. In clinical use the
`b-;al would be to ensure that the ends of the graft
`engage nondilated vessels on either side of the
`~Leurysm withoul> encroaching on the origins of vital
`aortic branches. The proximal neck between the renal
`arteries and the aRaeurysm is usually long enough to
`be suitable for graft attachment, but the distal cuff is
`often very short. In such patients
`transfemoral
`"insertion of a straight graft may be difficnk, danger-
`ous, or impossible.
`We believe that all straight grafts should be
`stented against the arterial wall distally. It is unlikely
`that the direction of blood flow alone would be
`sufficient to prevent extravasation of blood around a
`"Free distal grfft orifice given the paucity of the distal
`cuff in the majority of cases.
`
`Table II. Displacement force in cadaveric
`aortas, after each of three
`successive insertions
`
`Specimen
`1
`2
`3
`4
`5
`6
`
`Sex
`M
`M
`F
`M
`M
`F
`
`Age
`(yr)
`75
`61
`75
`88
`47
`67
`
`Weight (gin)
`Mean
`2
`3
`l
`1200
`1750 1200
`650
`1950 2000 1350 1767
`2000 1400 1200 1533
`1750
`1230 1950 1643
`950
`980
`900
`943
`2000
`880
`850
`1243
`
`The role of distal stents in bifurcated grafts is
`more open to question. Completion angiograms
`showed no signs of leakage around the distal ends of
`any bifurcated graft, with or without distal stents.
`Leakage would have been apparent as visualization of
`the aortic branches in the region of the graft,
`including the middle sacral, which is the largest
`closest to the distal graft orifices. Graft displacement
`during stent insertion was prevented by applying
`traction to the distal ends of bifurcated grafts. There
`were no complications of stent insertion in four
`experiments (eight stents). This system of distal stent
`placement was probably safe, but it was also complex.
`We have since developed a system in which distal
`stents are attached to the limbs of bifurcated grafts
`before insertion. With this system, fully stinted
`
`W.L. Gore & Associates, Inc.
`Exhibit 1027-9
`
`

`

`194 Chuter et aI.
`
`JOURNAL OF VASCULAR SURGERY
`August 1993
`
`bifurcated grafts are deployed with the same series of
`maneuvers as for unstented grafts.
`Our initial concern that barbs would not pene-
`trate the typical elderly diseased aorta was not borne
`out. Straight grafts were found to attach securely to
`the walls of cadaver aortas, which contained athero-
`sclerosis, calcification, and luminal debris. Indeed,
`the force required to displace a graft experimentally
`(1388 + 127 gm) was far more than the expected
`stresses. For example, the sheer force on a 20 mm by
`100 mm tubular graft is less than 1 gm, assuming that
`the graft is held in dose apposition to the aortic wall
`by low-profile stents and flow remains laminar. 4
`All our grafts were constructed of woven polyes-
`ter, which is known to be strong and durable. A
`lightweight knitted construction was avoided be-
`cause the very fine yarns and loose knits necessary to
`achieve a low volume might predispose to progres-
`sive dilation, 5 It is doubtful that the aneurysm wall
`can be relied on to generate a high-pressure environ-
`ment around the graft and thereby limit transmural
`pressure.
`Suitable candidates for endovascular repair of
`aortic aneurysm would be selected on the basis of
`preliminary angiography and cross-sectional imag-
`ing. Specific contraindications would include supra-
`renal extension of the aneurysm and iliac occlusive
`disease. Angiographic evidence that inferior mesen-
`teric flow is an indispensable source of intestinal
`perfusion would be another contraindication to
`endovascular repair, because the endovascular tech-
`nique does not offer the oppommity to restore flow
`through the inferior mesenteric artery. The inability
`to reimplant the inferior mesenteric artery has special
`implications for graft selection when the bifurcated
`technique is used. Ideally internal iliac arterial flow
`should be maintained as a source of intestinal and
`spinal perfusion.
`Any instrumentation of an aneurysm risks injury
`to mural thrombus and plaque, which might frag-
`ment and embolize to distal arteries. The risk of
`mural injury has been minimized by using a delivery
`system with a smooth, tapered external profile and a
`tip that is guided through the iliac arteries and the
`aneurysm over a wire. The relatively low incidence of
`embolism after angiography alone suggests that
`mural thrombus is smoother and less prone to
`fragmentation than it appears at operation. More-
`over, the risk of embolism is transitory because the
`thrombus lining an aneurysm cannot enter the
`circulation once the graft is in place.
`
`The eventual indications for straight and bifur-
`cated grafts will depend largely on the architecture of
`the distal cuff and the effect of mural thrombus on
`graft attachment. Compared with conventional sur-
`gical repair, endovascular techniques require longer
`segments of nondilated aorta for graft attachment,
`particularly at the distal end. Examination of corre-
`sponding angiographic and tomographic studies
`reveals that mural thrombus often produces long
`cylindric segments of lumen at both ends of the
`aneurysm, even when the outer wall of the aneurysm
`extends from the renal arteries to the aortic bifurca-
`tion. However, a reliance on mural thrombus for
`hemostatic graft attachment is probably not war-
`ranted in early clinical studies. Bifurcated grafts will
`be required in most cases, because the distal cuff is
`rarely long enough to permit straight graft repair by
`endovascular means.
`With this system, at least one femoral artery mu~
`be exposed. The delivery system is too large (5.5 mm)
`to be introduced percutaneously. The other femoral
`artery was also exposed in this series of bifurcated
`graft insertions. However, the small catheters and
`sheaths inserted on that side could easily pass through
`a percutaneously placed sheath.
`The main advantages of the transfemoral ap-
`proac h to aortic aneurysm repair are the avoidance of
`abdominal o