Ernst-Peter Nikolaus Panagiotis

Strecker, Freudenberg, Tsikuras,

MD #{149} Dieter Liermann, MD #{149} Klemens H. Barth, MD MD #{149}Georg Berg, DVM #{149} Michael Westphal, MD MD #{149} Michael Savin, MD #{149} Beate Schneider, MD

Expandable of Arterial Experimental Work

Arteries,

extremities,

grafts

#{149} Arteries,

and

stenosis

92.456,

prostheses, or

92.456,

S

types of vascular prostheses have been developed and successfully implanted into the iliac and femoral arteries of patients (1,2). The data published on those devices are very promising, although longEVERAL

1990;

From the Departments Nuclear Medicine (E.P.S.,

nal Medicine (H.R.D.W.), Diakonissenknankenhaus Kanlsnuhe-R#{252}ppunr, Diakonissenstrasse 28, D-7500 Karlsruhe 51, Federal Republic of Germany; the Department of Radiology, Univensity Kliniken Frankfurt, Federal Republic of Germany (DL.); the Department of Radiology, Georgetown University Hospital, Washington, DC (K.H.B.); the Institute of Pathology (N.F.)

and Veterinary

Hygiene

vensity Clinics Freiburg, Germany; the Department Krankenhaus NeukOlln, lic of Germany (MW.); Mass

(MS.).

Institute

(GB.),

Uni-

Federal Republic of of Radiology, St#{227}dt. Berlin, Federal Repuband Medi-tech Inc. WaFrom

the

1988

RSNA

an-

nual meeting. Received April 17, 1989; revision requested May 16; final revision received November 28; accepted December 8. Address reprint requests to E.P.S.

RSNA,

1990

the

There

are,

for in-

stance, self-expandable devices with certain degrees of elasticity and flexibility, and balloon-expandable stents of fixed or flexible shapes when expanded (3-11). The authors have developed a balloon-expandable prosthesis consisting of tantalum wire mesh that is flexible both in the nonexpanded and the expanded states (11). The purpose of the study was to demonstmate the flexibility and reliability of the balloon-prosthesis assembly with regard to introduction through curved arteries and implantation into femoral arteries near the hip joint and the thigh demanding adaption to movements of the treated vessel and surrounding muscular structures.

AND

METHODS

retract

balloon

from

of the

due to friction through

treated.

as well.

obstruction,

of Radiology and PT., B.S.) and Inter-

and

ity differ

the

stent

as they

ex-

angioplasty

during

the

catheter

introduction

introducer

sheath

or the

arteries.

The dimensions of the vascular prosthesis can be adapted to the required diameter

and

length

of the

The achievable

vessel

to be

diameter

of the

prosthesis depends mainly on the ben of loops per stent circumference

numand

the loop length of the metallic knit (Fig lb). The producible diameter of an expanded

prosthesis

ranged

mm, with a maximum Length and expanded prosthesis angioplasty

vascular

are related balloon.

prosthesis

from

2 to 14

length of 8 cm. diameter of the to the size Shortening

secondary

of the of the

to radial

ex-

pansion is minimized by mounting the prosthesis on the balloon with a pnimaniby reduced length (Fig lc). This is achieved by longitudinal prosthesis compression of the loosely connected metal loops.

Animal

Studies

Twelve

prostheses

the femoral

were

arteries

implanted

of 10 dogs

15-30 kg. Each prosthesis and 5-6 mm wide in the

into

weighing

was 2.5 cm bong expanded state

Description

of Prosthesis

(four loops per circumference; loop length, 1.6 mm). To spare the femoral artery from injury rebated to surgery,

The vascular ted of a single

prosthesis is a tube knitmetallic tantalum filament

surgical cutdown of the common carotid artery was performed with general an-

175:97-102

1

tion

curved

MATERIALS

©

#{149}

pand in the radial direction (Medi-tech, Watertown, Mass) (Fig 1). This mechanism prevents stent displacement from

term results are not yet available. The structure and material of those prostheses differ; hence, the method of introduction and their biocompatibil-

98.721

tertown,

MD

in Progress’

Index terms: 98.456 #{149}Arteries,

Radiology

R. D. Wolf,

Tubular Stents for Treatment Occlusive Diseases: and Clinical Results

The balloon-expandable vascular prosthesis consists of a flexible, knitted tantalum wire mesh tube. To demonstrate its pliability, this prosthesis was tested experimentally in 10 mongrel dogs by implanting it into the proximal femoral arteries. The maximum follow-up time was 1 year. On the basis of the experimental results, in which there was no relevant stenosis, occlusion, or mlgration of the vascular prosthesis, nine patients were treated: one with iliac artery occlusive disease and eight with superficial femoral artery (SFA) occlusive disease (four reocclusions after angioplasty and four unsatisfactory primary angioplasty results). One SFA lesion was treated with the crossover method from the contralateral side. All implants remained patent without hemodynamically significant stenoses, with the longest observation time being 6 months. Flexible, expandable vascular prostheses are promising adjuncts to angioplasty.

98.456 92.721,

#{149} Helimut

0.1 mm in diameter. Since the knitting is a series of loosely connected loops, this stent design tic and very

is, within certain limits, elasflexible, both in the longitu-

dinal and radial directions. Initially, the prosthesis was wrapped around an angioplasty balloon catheter and held there by means of its own radial tension. Then a new design for fixation of the prosthesis on the angioplasty catheter balloon was

developed.

The prosthesis

by thin-walled silicone end of the balloon that

and proximal

ends

is held

firmly

sleeves at either cover the distal

of the tubular

esthesia

(pentobarbital,

venously). Then the with a stent mounted

mm in diameter

25 mg/kg,

a

intra-

angioplasty catheter on a balloon 5-6

was introduced

over

a

guide wire through a 10-F introducer sheath. Under fluoroscopic control, the balloon was inflated for stent expansion

and placement near the hip joint into the common femoral artery (Fig 2) or into the proximal part of the superficial femoral artery (SFA). Two animals received implants

on

the animals

both

sides.

were

After

allowed

the

procedure,

to bend

and

ex-

stent.

During balloon expansion, the vascular prosthesis is released because the silicone sleeves shorten in the longitudinal direc-

Abbreviation:

SFA

superficial

femoral

artery.

97

c.

b.

a. Figure

1. Catheter-stent assembly. (a) The knitted wire-mesh tube is mounted on the expansion site of the its ends by thin silicone sleeves to prevent backsliding during introduction. (b) Draft view of an expandable distended tantalum wire ioops, which are without firm connection at their junction sites. (c) After complete sis becomes unlocked by minimal foreshortening of the prosthesis and the silicone sleeves.

5-F balloon catheter and held at metallic knit demonstrates the balloon distention, the prosthe-

tend their lower extremities freely; their moving habits outside or within the kennels

were

not

restricted.

During

the

pro-

cedume, the animals received 5,000 hepanin intraarterially. Thereafter, day for 5 weeks, the dogs received

IU of every 325 mg

of acetylsalicybic

acid for platelet-aggre-

gation inhibition mole to prevent

and 75 mg of dipyridaplatelet activation and

thrombosis.

Clotting

parameters

were

not

monitored (12). Control angiography was performed 1, 2, 6, 10, 20-30, and 54 weeks after implantation. One day and 1, 2, 6, 8 (two dogs), 9, 11, 15,

and

54 weeks

after

stent

implantation,

the experimental animals were killed to perform pathologic gross and microscopic examinations (Fig 3). For this purpose, the arterial segments treated with the prosthesis, distal

their parts,

adjacent

and

their

proximal

and

corresponding

con-

tmabateral arterial segments were memoved, longitudinally opened, and attached to cork plates with corrosion-resistant stainless steel needles, with their inner

vessel

surface

turned

fixation in 4% buffered least 2 days, the arterial

ed into thesis

3 X 4-mm struts

were

magnification to the

tic-van

On

the

standard

aid of

damage

a.

Paraffin

Figure

conditions slices

hip

of 5 jm and elas-

basis

arterial

of the

information

ob-

experiments,

20 patients

atherosclerotic

disease

were

had

lesions

of ili-

Eleven

patients mean

b. 2.

joint

Animal into

nine loops

lesions in those per circumference;

mm;

stent

these cases (11). In (seven

age,

stenotic

(arrows).

(b)

knitted Control

tantalum

stent

angiogram

years;

cm

[in

previously

2.5

and

lapse in one patient. One had an eccentric, high-degree

range,

two

stenoses

three

wom-

45-81

patients

5). That

stents

flexible The

residual

(Fig

Eighteen

patients (five loop length, 1.6

required

were

per

placed

patient

in

one

case,

8

Four patients had nestenoses of the after a previous angioplasty. Four pashowed an unsatisfactory result immediately after angioplasty of the SFA:

of

were

nine

cm]). SFA tients

plasty

prostheses

Radiology

(a) A 2.5-cm-long artery

were pubthe remaining

men

65.6

length,

four

#{149}

femoral

implantation.

the

98

the

after

years) with severe life-style-limiting claudication, the introduction of the prostheses or the anatomic site of implantation required a flexible intravascular implant. The length of the stenoses ranged from 1 to 8 cm (mean, 4.2 cm), and one to

(Table).

experiment.

of

implanted

the

near

same

animal

of its to be using

tortuosity. treated routine

the

2 weeks

staining.

ac arteries, and lished previously en;

layers.

to obtain hematoxylin-eosin

in animal

treated.

nine

the

to prevent

Treatment

tamed with

with

under

Patient

was

removed tissue

Gieson

at divid-

and the pros-

surrounding

was performed thickness for

After for

particles,

glasses

embedment

upward.

fonmalin tissue

and

proximal

access

by

due

right the

an

to

wall

dissection

arterial

SFA

wall

cob-

retrograde

arterial

lateral side 2-cm-long

(Fig 4). Another patient had stenosis due to a wall dissec-

tion,

which

occurred the

right

particular

puncture

of

4 days common

the

after iliac

vessel

a

10-F

a

ameter

on

angio-

mm

a

the

were less

than

stent,

the

a diameter

the

di-

equal

to

angioplasty of

more

than

completely

balloon

a a

with

balloon was

Since

expand

in-

through

arteries

expansion

diameter. not

the implant.

In

6 mm,

stent with

restenosis

implanted

sheath.

for

mounted

or

justified

wall-supporting

introducer

will

(x-ray magniOnly unsatis-

results

prostheses

artery

overdilation

angioplasty

for

were an-

diameter was artery diameter

image

angioplasty

balloons

artery

balloon to the

the film disregarded).

previous

diameter

the

without

The equal

was

dication

contra-

required

artery. to be

measured fication

All

with

because lesions dilated by

technique

of the chosen

after

necessitated

technique,

gioplasty

factory

of these patients stenosis of

that

crossover

in

stent arterial

with

diameter

April

6 the

was

1990

b. Figure

3.

specimen

(a) Gross

specimen

demonstrates

chosen

to be

the

1 mm

arterial

diameter

priate

fixation

of the

insertion

tmolled

formed

than

the

appro-

stent.

prosthesis

was

of fluonoscopy.

When

con-

the balloon-prosthesis assembly reached the arterial area to be treated, the introducem sheath was pulled backward to permit inflation of the balloon with thesis. In cases in which the site

treated

was beyond

the length

the prosto be

of the in-

troducer sheath (distal SFA), the balloonprosthesis assembly was moved, without protection of the sheath, through the amtemial lumen, even around the aortic bifurcation. Five thousand international units of hepamin were applied intraarterially before balloon inflation for angioplasty, and an additional 5,000 IU were given after insertion of the 10-F introducer sheath. Thereafter, an intravenous hepanfl

infusion

to increase

was

administered

for

the thrombin

time

3 days

to three

to

four times normal (with monitoring of the thrombin time). In addition, 325 mg

of aspirin

and

day

given

were

plantation

75 mg orally

of dipynidamole during the

follow-up

thrombosis

by

period

per postim-

to prevent

platelet-aggregation

inhi-

bition. The therapeutic effect of aspirin and dipynidamole was not monitored. According to the experimental protocol, penipheral arterial foot pressures were monitored before and after the procedure, at 4 weeks, and at 3 and 6 months (Fig 6). Foblow-up angiography was performed 3-7 days and 6 months after prosthesis implantation.

RESULTS Animal The

of the

affirmed

that

could be insertion

correctly at the

and

migration

All

that the

Volume

tantalum

175

animal

the

holes,

femorab mained

expeni-

manipulated chosen arterial

artery patent.

did

not

Number

1

take

place.

in the

removal

defects were or distally.

fects

appeared

implantation The

wire

after

mesh

in the pathologic

up to 2 weeks

me-

observed in These de-

first

and

few

weeks

resolved

after-

examinations

after

is covered

of tantalum

near the hip joint With angiography,

after wand.

knitted

channel

small filling the prostheses

implantation

me-

by neointima. struts

from

following months

tenial

neocclusion

remained

deformation

the

prosthesis,

as was Nine

ob-

later, a thin fibrous layer filled the openings of the wine mesh, while the stent was neointima. em, a thin,

layer

completely Eight and transparent

covered

the

covered with 12 months latendothelial

buminal

surface

of de-

the prosthesis fects, which

(Fig 3). The were observed

filling angio-

graphically,

corresponded

to thin

thrombus formations in the first few weeks, and later on, to an intimab layer. There was no significant foreign-body reaction to the tantalum implant. In general, theme was a mesomptive reaction in the tissue sunrounding the stent, with healed scar formation. In most cases, the inner third of the media was involved in this process.

Patient

Studies

All mectly

tantalum implanted

sites,

and

no

prostheses into the difficulties

during cases, were

an 8-cm-long penficial

insertion

and

by

were

con-

could

(Figs

4,

be further

the support of tubular (Fig 4). In one case, after

neocclusion

femomab

artery

of the occurred

opened support

su-

was

seen

due

were

by means provided

after

arterial

of the mechanical by the stents. No

stress

course

extremities tients were

tubular

wire

compression caused

of the

observed. to protect

The their

per extremities from severe mechanical stress (eg, blood cuffs).

traction

filling or with

digital subtraction which was performed after stent implantation. intravenous digital angiograms

are

lower paup-

outside pressure

No significant intrabuminab defects were observed within proximal or distal to the stent

intravenous ognaphy, in 1 week Six-month

or

by a curved

or motion

was told

me-

An 8afterpatent. that had

to a vascular

to external

mechanical

6 an-

completely

of the

due

angiwithsub-

available

for

two patients. In the first patient, with a stent in the proximal part of the SFA,

the

angiogmam

smooth filling defect thick) that probably en of neointima (Fig

ond patient, defects can common

en-

the stenosed arterial not fully opened

angioplasty

dilated prostheses

were arterial

collapse

mesh

weeks

performed immediate

an

stenotic

covered

microscopically.

microscopic

tissue.

peat balloon dilation therapy. cm-long prosthesis implanted ward held the arterial lumen In general, arterial segments wall

served

(b) The

the

angioplasty previously,

vealed a thin layer of thrombus spread over the stent. Six weeks after implantation, a complete neointima

by

after site,

The

and

5). In all segments

prosthesis

prostheses

#{149}

implantation.

countered

Experiments results

ments

after

neointima,

pa-

to achieve

of the

by means

newly

wider

tient’s The

of the SFA 1 year

depicts

no intraluminal be seen in the

iliac

artery.

a thin,

(0.5-1.0 mm represents a lay4e). In the sec-

The

filling treated ankle-arm

indexes remained unchanged during the follow-up period in those two patients. In the other seven patients, the ankle-arm indexes improved by the placement of the arterial prostheses and did not decrease within the first

4 weeks

sunements). improved

to 3 months

The ankle-arm in all patients

(four

mea-

indexes by more Radiology

99

#{149}

a.

b.

C.

Figure 4. (a) Severe short stenosis of the proximal part of the right SFA (arrow). (b) No significant improvement after angioplasty performed with the crossover technique from the contralateral side (arnow). (c) The catheter-stent assembly is introduced with the crossover technique oven the aortic bifurcation. (d) The lumen of the SFA is held completely patent after implantation of a vascular prosthesis

(e)

(arrows).

Intravenous

digital

subtraction

angiogram,

months after implantation, demonstrates patency. rows) is covered by a smooth layer corresponding

obtained

6

The prosthesis to neointima.

(ar-

d. 10%. The change in ankle-arm from before to after treatment was significant (P < .001 by the Wilcoxon signed rank test) (Fig 6). Clini-

recoil of the arterial loon dilation, which stenosis on occlusion

cal symptoms

treated arteries may than with angioplasty arterial flow through increase. Furthermore, regular inner surface

than index

with

an

in all but improved only.

improved

unlimited

one

permanently

walking

patient,

maximal

who walking

distance

had

an

distance

fore,

with

Intraarterial stent placement optimizes the mechanical alterations caused by angioplasty. The mechanical support of the distended tantalum

100

prosthesis

.

Radiology

prevents

the

luminal

an elastic

wall after can result (1,11,13).

cross

prosthesis

irregularities vessel lumen.

DISCUSSION

mesh

the

ment treated in reflected

section

babin meThemeof the

become widen alone, and the the vessels will a smooth and is achieved, diminishing

wall

protruding into the This reduces pressure

gradients (1,11) and, lence as well. However, noncompliance

e.

of the

probably, the arterial

by the stent wave patterns

turburelative seg-

may result that could

disrupt

normal

The

design

sis offers

flexibility. even with

flow

patterns.

of the

a high

degree

Therefore, a length

can be introduced sertion through

knitted

prosthe-

of mechanical

this implant, of 8 cm (one case),

into curved

the SFA. arteries

oven the aortic bifurcation The prosthesis can maintain figuration after expansion,

Inand

is possible. its consince the

loosely connected loops, made of tantalum wire filaments, are elastic within certain limits. The maximum radial compression tolerated by the prosthesis amounts to 40% of its oniginal shape. Therefore, it becomes evident

that

the

knitted,

semiebastic April

1990

corrosion sue fluids are

caused (16-17).

covered

by

tantalum electrically preventing

by surrounding tisTantalum implants a thin

layer

pentoxide, negative adhesion

are negatively A mechanical and stainless the same diameter strength) resistance

of inert

which creates an surface charge, of platelets that

charged

as well

(18).

evaluation of tantalum steel stents knitted in pattern (wines of the same and the same tensile revealed no difference in to compression.

Animal tests not yet published meveal that tantalum, like medicalgrade stainless steel alloys, can be megarded as thrombotic resistant. Our tantalum implants are chemically electropolished to achieve a smooth surface, preventing uncontrolled thrombus formation. Immediately af-

ten implantation, b. Figure 5. (a) Severe dissection of the common planted flexible stents open the curved arterial travasation due to the dissection is seen.

iliac artery after angioplasty. segment completely. A small

(b) Two

im-

amount

of ex-

long

SFA

with multiple any angiographic changes

the

stents

related Since

movement

osseous a knitted

of

or muscular wire-mesh

prosthesis consists of loosely connected loops forming a nonrigid elastic structure radially, arterial compliance will probably be only minimalby disturbed, reducing the tendency of thrombus formation. According animal experiments performed to study various vascular graft mateni-

als, by using ance

preoperative

measurements

oxine-labeled good before

immediately

1 MOnth

Stent

after

after

Stent

Stent

Figure 6. Doppler pressure ankle-arm indexes as percentages in all patients before, immediately after, and 1 month after stent placement (M mean, ±1 standard deviation).

prosthesis

opposes

cient

and

force

compression

itself

with

elasticity

suffi-

to outside

to prevent

the

conforms

hip,

because

to arterial

the

prosthesis

curves

induced

by flexion

or extension

extremities. alterations prosthesis

Secondary intraluminal due to the bending of the were not observed. In pa-

Volume

175

Number

#{149}

of the

1

lower

indium-i

there

between

11-

is a

elastic

properties and graft patency (14). Our dog study results demonstrate that the percutaneously inserted prosthesis will initially be covered a thin layer of thrombus that will almost completely endothelialized

by be

nied

by

a small,

hemodynamicalby

degree

of luminal

oroscopy

due

to its high

proton number. ed as biologically

Tantalum inert

density

is regardand shows

me-

intimal

by platelet-de-

of a self-expandable

femoral

into

tenies. reveal should animals duced taneously stents balloon nience

Our animal experiments promising results, although it be noted that we used healthy without experimentally inatherosclerotic disease. Percuimplanted expandable may extend the indications for angioplasty, and more expeis necessary to determine the

indications the

iliac

and

pros-

thesis

for this

popliteal

new

atherosclerotic

and

femomab

an-

therapy

for

disease

in

arteries.

U

References Palmaz

CJ, Richter

Intraluminal

no

from

induced

plantation

1.

and

of

not observe any occlusion developing after a follow-up of 18 months (11). Tmiller et al (20) reported a patency mate of 87% 9 months after im-

nan-

rowing. Tantalum is better suited to the specific needs of arterial stents. This metal is superior to stainless steel or other alloys because it is very radiodense and is well visualized with flu-

layer

nived growth factors (4,10,20). The mesults of our patient series are very promising; however, the follow-up time is still relatively short. In anothen patient group treated with this prosthesis in iliac arteries, we could

occlusive

within 2 weeks, as unpublished ebectron-micnoscopic examinations in dogs have revealed. This is accompainsignificant

collapse.

The results of animal experiments have confirmed that the prosthesis can be implanted into arterial sites

near

platelets,

correlation

to

compli-

and

on occlusion

hyperplasia

treated

did not reveal or mechanical

to the

surrounding

tissue.

segments

thin

to cover the metendothelial coven that may formation on the

prosthesis wall thereafter (19). Thrombosis remains a problem, causing acute occlusion and later stenosis

tients,

a very

thrombus develops al material, allowing cells to form a thin prevent thrombus

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Deen HG, Sundt TM. The effect of combined aspirin and dipyridamole therapy on thrombus formation in an arterial

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