Simon Nitinol Inferior Vena Cava Filter: Initial Clinical Experience

Morris
Simon,
MD
#{149}
Christos
A. Athanasoulis,
David
H. Porter,
MD
#{149}
Barbara
H. Byse, MD
Dan E. Orron,
MD
#{149}
Arthur
C. Waitman,
MD
Simon
Initial
Work
Nitinol
Clinical
Kim,
Kleshinski,
MD
#{149}
Fred L. Steinberg,
BS #{149}Stuart
Geller,
MD
Cava
MD
#{149}
#{149}
Filter:
in Progress’
Index
terms:
Embolism,
pulmonary,
60.72
nae cavae,
filters
#{149}
Venae
cavae,
interventiona!
procedure,
982.1299
#{149}
Venae
cavae,
stenosis
obstruction,
982.458
1989;
#{149}
Ducksoo
Inferior
Vena
Experience
The Simon
nitinol
filter for percutaneous
interruption
of the vena cava
to prevent
pulmonary
embolism
is
currently
undergoing
a multicenter
clinical
trial. Preliminary
clinical
results
are reported
as work in progress.
The results
in 44 patients
at
two centers
are analyzed
in detail,
and major
events
are reported
from
103 patients
in 17 centers
in the
United
States
during
a 10-month
penod. The filter
was successfully
inserted
via the femoral
or jugular
route in all patients
through
a 9-F
catheter.
The placement
procedure
was easy and without
significant
complications.
Follow-up
studies
included
plain
radiography,
ultrasonography,
magnetic
resonance
(MR)
imaging,
and clinical
evaluation.
No
filter migration
or perforation
occurred
among
the 103 patients.
Symptomatic
occlusions
occurred
in
7%-9%,
comparable
to other
series,
and some asymptomatic
occlusions
were detected
with MR imaging
only.
The implications
of occlusion
of the filter
are discussed.
Radiology
MD
#{149}
Stephen
172:99-103
T
Simon
HE
filter)
nitino!
for
monamy
filter
the
embolism
going
tional
clinical
study
(SNF
prevention
is currently
trial
in the
under-
in a multi-instituUnited
States,
with
17 participating
centers.
At this
time, a total of 103 filters
have been
placed
in patients.
This filter is presently
classified
device
as an
by the
Administration
not include
other
cal
data
cava
since
already
ty and
filter
in current
published
exist
regarding
of these
The SNF exploits
ma! shape-memory
of vena
chinisafe-
ticipating
the unique
properties
themof ni-
into
complex
warmed
alloy
a previously
rigid
(1,2).
this material
to stainless
that
can
man
studies
proved
in animal
(3,4).
of
comparable
and hu-
saline
or
it is warmed
to body temperaassumes
its filter shape,
and
locks
into
lungs.
cm
has
a 28-mm
en overlapping
verging
a
legs
The
hoops,
with
up to a
clinical
trial.
to trap
filter
dome
and
terminal
is 3.8
with
has
hooks
AND
METHODS
population
18 women,
consisted
ranging
of 26
in age
sev-
six dito
the
procedure
Hospital
from
Eighof the
and 26
at Massachu(MCH)
between
February
and November
1988. Appropniate informed
consent
was obtained
from
all
from
the lower
limbs
or pelprevent
the emboli
from
the
hong,
easily
through
for delivery
cava (IVC).
It is designed
study
and
underwent
setts
Ceneral
infu-
Here,
tune,
reaching
to a broad
19 to 96 years (median,
62 years).
teen patients
underwent
placement
SNF at Beth Israel Hospital
(BIH),
when
A cold
place.
in the
The
men
Ve-
emboli
vis and
adapt
widths
Patients
imprinted,
filter shape
Biocompatibility
has
steel
can
cava
PATIENTS
as a soft, straight
set of wires
cooled
but is instantly
trans-
formed
filter
data of the major complications
of fibten placement
that would
be reportable to the study
monitor
in a total of
103 patients
from all 17 centers
par-
did
any
the
The
range
devices.
a nickel-titanium
exist
when
Drug
trial
with
extensive
efficacy
tinol,
and
The
filter.
maximum
of 28 mm.
This
preliminary
progress
report
focuses
on detailed
early
clinical
mesults
of placement
of the SNF in 44
patients.
We also report
follow-up
investigational
Food
(FDA).
randomization
vena
use,
U.S.
sion allows
it to pass
standard
9-F catheter
into the inferior
vena
#{149}
engage
the vena cava wall (Fig 1).
The legs serve as a coarse
first filter,
while
the dome
forms
a fine second
or
of pul-
patients.
The clinical
indications
for filter
ment were those generally
accepted
IVC filter placement
(5). The major
cations
were pulmonary
embolism
tensive
deep
anticoagulant
venous
thrombosis
or thrombolytic
was contraindicated,
cations,
or failed
resulted
to prevent
bolism.
proportion
The
high
placements
MGH
in neunosurgical
placefor
mdion ex-
when
therapy
in complirecurrent
emof filter
patients
at
is noteworthy.
Methods
I From
the Department
of Radiology,
Beth Israel Hospital.
Harvard
Medical
School,
330 Brookline Ave. Boston,
MA 021 15 (MS.,
D.K., D.H.P.,
5K., D.E.O.),
and the Department
of Radiology,
Massachusetts
General
Hospital,
Boston
(C.A.A.,
F.L.S., B.H.B.,
S.C., A.C.W.).
From the 1988 RSNA
annual
meeting.
Received
December
5, 1988; revision
requested
January
17, 1989; revision
received
February
14; accepted
February
17. Address
reprint
requests
to MS.
Nitinol
Medical
Technologies
(NMT),
Woburn,
Mass, is the manufacturer
of the Simon
nitinol
filter and is responsible
for the conduct
of the clinical
trial under
Food and Drug Administration
Investigational
Device
Exemption
no. G870093.
MS. is the Scientific
Director
of NMT,
and C.A.A.
is a member
of the Board
of Advisors.
All authors
are in full compliance
with established
guidelines at their respective
institutions
for disclosure
of financial
interest
related
to research
projects.
©RSNA,
1989
See also the editorial
by Yune (15-16)
and article
by Epstein
et a! (105-1 10) in this issue.
insertion
dune
line
procedure-Before
is started,
is cooled
at least
catheter
a 500 mL
in a bucket
the procebag of normal
saof ice chips
for
half an hour. The 9-F delivery
is inserted
percutaneously
into
Abbreviations:
FDA = Food
inferior
vena
era! Hospital,
a
BIH = Beth Israel Hospital,
and Drug Administration,
IVC
cava, MGH
Massachusetts
GenSNF = Simon
nitinol
filter.
99
common
or jugular
with the
iliac vein via a standard
femonal
venipunctune,
on either
side,
Se!dingen
technique.
The cathe-
ten is first used
vena cavognam
of the
renal
Table 1
Summary
of Preliminary
Results
of
SNF Placement
in 103 Patients
at 17
to obtain a preliminary
to determine
the position
veins
and
to ensure
that
Centers
the
Results
vena cava does not exceed 28 mm in
width, after correction
for magnification.
The
presence
anatomic
of thrombi
anomalies
on significant
is also shown.
catheter
tip is then repositioned
low the lowest
rena! vein, the
cation
for the filter dome.
The
filter
comes
It is received
tube
section
in the
of the delivery
system
infused
and is
feederThe cold
through
the
stor-
via a sideport
at the rate of about
per second
to cool and soften the
filter.
The storage
tube is then connected
directly
to the 9-F catheter
so that the
cold saline
infuses
into
with
requires
the tip of the catheter.
about
six forward
This
strokes
of the
feeder pump handle.
Finally,
a single
backward
stroke of the storage tube and
catheter
unsheaths
the filter and releases
it into
the
IVC.
It is instantaneously
trans-
formed
into its expanded
filter shape
locks into place. The catheter
is then
and
pulled
ye-
back
nogram
slightly,
and
is obtained
is removed
pressed
and
in the
dune
requires
skills
and
complete,
and
the
only
including
grams,
if cine
ing is used.
the final
po-
manner.
routine
takes
both
site
is com-
The
proce-
vena
and jugular
minutes
and
plain
radiography
ly after
placement
angiography.
to
cavoimag-
delivery
sys-
that the jugular
and its filter is
be performed
through
Follow-up-The
initial
and
follow-up
examinations
were directed
toward
the
detection
of complications
at the venipuncture
site, such as venous
thrombosis
hemorrhage,
and at the filter
site, in-
cluding
filter migration,
penetration
or
perforation
of the vena cava wall, misplacement,
filter tilting,
or crossing
of the
filter legs. Possible
recurrent
pulmonary
embolism
and systemic
effects
of the nitinol
material
were
also
evaluated
with
clinical
and laboratory
methods.
In addition, partial
on complete
occlusion
of the
filter due to trapped
embohi,
an anticipated sequela
of filter placement,
was also
diagnosed
clinically
on by means
of noninvasive
imaging,
including
magnetic
resonance
(MR) imaging.
100
#{149}
Radiology
of the
again
and
Chest
ti!ation/perfusion
Migrations
Cranial
0
Caudal
0
Recurrent
pulmonary
embolism
Symptomatic
0(1)
2
Asymptomatic
filter
shortat 3 and
6
also
optional
studies.
enhanced
with
formed
only
The clinical
when
and
scanning
Vena
contrast
yen-
were
was
clinically
bolytic
were
requires
therapy
medications
prescribed.
of anticoagulant
at the
time
that major
or other
The
use or
on throm-
of filter
place-
in-
RESULTS
ic recurrent
in progress
and
thus, only limitreported.
Of the 103
centers,
there
were
and no deaths
me(Table
1). There
was
case of symptomat-
pulmonary
embolism,
and two patients
had confirmed
asymptomatic
pulmonary
embolism.
Theme were seven
cases of confirmed
symptomatic
IVC occlusion
and two
possible
IVC occlusions
detected
on
the basis of clinical
findings
only.
Of the 44 patients
studied
in Boston,
10 have
undergone
in parentheses
with
clinically
represent
suspected
Table 2
Summary
of Preliminary
Results
SNF Placement
in 44 Patients
of
No.
of Patients
Results
Entry
a 3-month
complications
site thrombus
Hemorrhage
Failuretointroduce
Major
misplacement
Leg penetration
Migration
Tilting
of dome*
Spindle formationt
Leg crossingl
5
0
0
0
0
0
24
1
4 (2)
IVC patency
Patent
with
Occlusion
Occlusion
require-
ment or subsequently
was based
purely
on clinical
considerations
and was not
fluenced
by the protocol.
The trial is now
data are incomplete;
ed trends
can be
patients
at all 17
no filter
migrations
bated to the filter
one unconfirmed
to filter
Note-Numbers
additional
patients
findings
only.
Perioperative
complications
at all centers
be reported
immediately
to the study
monitor.
These
included
filter migrations,
recurrent
pulmonary
embolism,
IVC occlusions,
and
filter-related
deaths.
follow-up
7 (2)
3
0
indicated.
at 3 and 6
but was not a protocol
therapies
withholding
related
per-
months
included
history,
physical
examination
of the puncture
site and lower
limbs,
plain radiography
of the filter negion, and laboratory
tests of blood
and
urine
for liven and kidney
function
and
blood
clotting.
Autopsy
examination
of
the vena cava and filter of patients
who
died during
the course
of the 6-month
study or later, due to any cause,
was en-
protocol
Deaths
cavography
material
examination
Symptomatic
Asymptomatic
ultrasite
radiography
lung
the same catheter
by means of a retrograde injection
of contrast
medium
just
above the filter.
and
(top)
from
months.
Optional
studies
included
sound
(US) imaging
of the puncture
The study
preloaded
for a feet-first
delivery
from
above. After a jugular
delivery,
follow-up
can
a 9-F catheter
form
viewed
the side (night).
Protocol
requirements
included
clinical
history
and physical
examination,
documentation
of the placement
procedure,
No
The femoral
in its extended
ment.
angiognaphic
30-45
or digital-subtraction
tems are identical,
except
catheten
system
is longer
venognaphy
form
for passage
through
and in its fully
expanded
the end (left)
and from
counaged
whether
there
is
Finally,
the catheter
puncture
usual
typically
a follow-up
to check
sition
of the filter
any leg penetration.
is shown
and filter region, computed
tomography
(CT), MR imaging,
or digital-subtraction
the IVC for a few
seconds.
Typically,
less than 150 mL of saline is required
for filter delivery,
an insufficient
amount
to affect patient
temperatune.
The filter is then advanced
napidly through
the catheter
until its tip
aligns
The SNF
of Patients
IVC occlusion
storage-
with a telescoping
and pusher
wire.
is briefly
age tube
10 drops
just beoptimal
lo-
1.
to be delivered.
preloaded
preassemb!ed
pump
section
saline
ready
Figure
The
No.
thrombus
(symptomatic)
(asymptomatic)
Recurrent
pulmonary
embolism
Symptomatic
Asymptomatic
Deaths
5 [11J
3 (2)[7-1
3 [7]
1]
0(1)
1
Related to filter
Unrelated
to filter
0
7
Note-Numbers
in parentheses
represent
patients
with
clinically
suspected
findings
only. Numbers
in brackets
are percentages.
* Dome
tilting of up to 30#{176}
occurs as a normal
adaptation
to a small
IVC lumen.
It does not
affect filtering
efficiency,
since the dome hole
sizes are unaffected.
t Spindle
formation
is an intermediate
stage
of dome recovery
that may occur in very small
venae cavae.
I Leg
crossing
occurred
in the first four patients
due to a pusher
wire problem
that has
been corrected.
follow-up
6-month
abdominal
were
and four
have
completed
follow-up
(Table
2). Initial
madiogmaphs
of the filter
obtained
in all 44 patients;
en underwent
abdominal
phy at 3 months,
and
four
months.
Ultrasound
studies
a
sev-
madiograat 6
of the
puncture
patients
3 months
sites
were
performed
in 18
soon
after
placement,
five at
and two at 6 months.
US
studies
of the IVC and filter
region
proved
technically
difficult
due to
wide
variations
in build
and bowel
contents
in individual
patients
but
July 1989
were attempted
in nine patients
in
the early period
after placement,
in
five patients
at 3 months,
and in two
The filter
tip was properly
positioned
within
3 cm of the lowest
menal vein
in all patients,
except
three
at 6 months.
three
patients.
in whom
it was delivered
slightly
lower
than
planned
due to early
opemator
inexperience.
In two cases,
the
dome
appeared
to engage
the infemior edge
of the lowest
renal
vein
without
affecting
renal
venous
meturn.
It should
be noted
that in large
aging
CT
was performed
Twenty-five
MR
examinations
Ti-weighted
gradient-echo
formed
with
sequences
sequence
nongated
or a new
fast
were
per-
in 21 patients.
MR
imaging
appears
to be a promising
sive method
for determining
tency
of the vena
cava and
menting
thrombi
captured
tem or complete
cava
was
the
occlusion
(6). In seven
only
by
referring
One
patient
in
im-
noninvathe pafor docuin the filof the
patients,
telephone
physician
vena
follow-up
interview
or patient.
refused
of
all follow-up
ex-
aminations.
Seven
patients
hated to the filter
died of causes
unmeplacement
during
the trial
period.
None
tients
died
of pulmonary
One
autopsy
study
of these
paembolism.
was
obtained
dun-
ing the study
period
and showed
no
thrombus
in the filter.
A second
autopsy
was performed
on a patient
aften the 6-month
study
period
and
showed
an organized
thrombus
attached
to the legs-a
result
that confirmed
findings
of an earlier
followup MR imaging
study-as
well
as a
more
recent
thrombus
captured
in
the filter
dome.
Forty-one
filters
were
delivered
by
the
femomal
route,
29 on the
right
and
12 on the left, and three
were
delivened
by the jugular
route,
two on
the might,
and
one via the left extemnal jugular
vein.
The filter-placement
procedume
was well
tolerated
by all
44 patients.
Theme
introduction.
with
material
starting
the
Some
early
problems
caused
difficulty
in
filter
movement
out of
the
storage
tube,
were
and
no failures
some
leg
of
cross-
venae
cavae,
mally
descends
aging
or CT. Theme
embolism
for
venotomy
femonal
vein
Theme was no clinical
evidence
matoma
formation
at the venous
tion
or new
ed subsequently
in one
developed
disseminated
agulation.
formation
Volume
patient
who
vascular
co-
No arteriovenous
or air embolism
172
devel-
#{149}
Number
fistula
occurred.
1
filter
mito secure
who
has been
frequency.
of
cannot
be
In
the
the
have
chanical
track
(measured
raised
passage
has
of
been
been
large
in
with
recurrent
bohism
(10).
Other
tilting,
misplacement,
Ques-
the
me-
Greenfield
shown
emboli
filled
resulting
about
(9).
fil-
to allow
once
clot,
its
the
apex
a condition
em-
pulmonary
problems
included
caudal
or
cranial
migration,
perforation
and fracture
of
the Greenfield
filter,
and thrombosis
at
the entry
site (11,12).
IVC occlusion
is
reported
to occur
in about
5% of patients
For
tigatons
(13).
these
have
reasons,
attempted
a number
to
of invesdevelop
sembhed.
The
through
delivery
is accomplished
a 9-F (3-mm
outside
catheter;
thus,
angiographic
phications
at the puncture
mized.
The clinical
trial
femonal
then
or
side,
jugular
but
com-
site are
is limited
vein
access
diameter)
local
approach
to
the
minito a
on
central
ei-
ye-
nous
system
may eventually
via a number
of alternative
veins.
The external
jugular
been
used in one patient.
cial
requirement
cold
saline
be gained
peripheral
vein
has
The only speinfusion
of a
is the
solution
during
the
brief
passage
of the filter
through
the catheter.
During
the clinical
trial a number
of
new observations
and insights
have
emerged
about
the filter
placement
and
the capture
of embo!i
en route
to the
lungs.
These
relate
to tenting
of the
vena
cava wall,
tilting
of the dome,
and
occlusion
of the filter
by thrombus.
Local tenting
of the vena
cava wall
due to pressure
by the rim of the filter
dome
was observed
frequently,
particulanly
in
venae
smaller
cavae,
but ap-
peared
to have
no significant
hemodynamic
impact
or ill effects.
The tented
portion
fills in within
a few months
due to development
of a slightly
thicker
neointima
at the points
of contact just within
the outer
rim so that the
rim may appear
to lie just outside
the
main
column
of contrast
medium
on
follow-up
venograms.
Similarly,
though
rarely,
the distal
end of a filter
leg may appear
to lie alongside
the lumen.
Earlier
animal
experiments
have
documented
that this effect
is due to a
longitudinal
crease
formed
by the legs
in
the
vena
cava
wall
and
covered
with
endothelium.
The leg ends
have
not
penetrated
the vena
cava wall.
The dome
of the filter
frequently
was
observed
to be tilted
about
20#{176}-25#{176}
toward
the wall of the vein,
particularly
outside
about
of the
dila-
to ac-
sheath,
efficacy
which
filter
increasing
requires
diameter
been
the
percuta-
Greenfield
venipuncture
in outside
large
houses
with
this
a 29-F
or
the
years,
introduction
9.6 mm
has
recent
of
jugular
to insert
that
performed
However,
diameter)
ten,
the
capsule
commodate
tions
of
in order
insertion
thrombosis
in paanticoagulant
thrombus
was not-
patients
surgical
neous
withdrawal,
no instances
given
anticoagulant
on thrombolytic
drugs
or for whom
such drugs
have
failed
(7). In the United
States,
the only
device
currently
available
for clinical
use is the Gmeenfield
filter
(8). At the
time of its introduction
in 1973, placement
of the Gneenfield
filter
required
filter.
of venous
not receiving
Femomal
were
It is now widely
accepted
that vena
cava filters
have
become
the method
of
choice
for the prevention
of pulmonary
folded
opment
tients
therapy.
nor-
during
DISCUSSION
ing resulted
in the first four
patients,
without
clinical
effect.
These
early
problems
were
resolved
by minor
design
changes
of the feeder
system.
catheter
filter
2 cm
of either
cranial
or caudal
gmation.
The device
appears
itself
well.
delivery
puncture
site. Five of the 18 patients
studied
with
US in the days
following the procedure
showed
some
local
thrombosis.
Three
patients
were
symptomatic.
This
finding
could
represent
local
thrombus
formation
due
to intimal
injury,
thrombus
peeled
off of the catheter
surface
during
tip of the
about
dome
formation
as the catheter
is being withdrawn.
It is possible
to readvance
the filter
upward
to its optimal
position
before
the legs are released,
but this is not recommended
because
of the risk of damage
to the venous
endothelium.
In smaller
venae
cavae,
the filter
dome
commonly
assumed
a
slightly
tilted
position.
Penetration
of the vena
cava wall
by the filter
legs did not occur.
Theme
was no clinical
evidence
of metropemitoneal
hemorrhage,
nor was any seen
in patients
followed
up with
MR im-
metal
of he-
the
proved
filter
devices
that are easier
to
insert,
have
lower
complication
rates,
and produce
a more
effective
mechanical filtering
action.
The SNF is one of
these.
Others
include
the bird’s
nest filten, the Amplatz
filter,
and the Gunther
filter
(14-16).
The SNF is distinguished
by its ease
of insertion
and mechanical
effectiveness.
The device
is pmehoaded
to eliminate
handling
of the filter
device, and the delivery
system
is preas-
im-
in
small
is due
venae
to
the
cavae
dome
(Fig
2).
geometry,
This
result
which
is
more
easily
accommodated
in a confined
space
if the dome
is slightly
indined
rather
than perfectly
transverse.
However,
such sloping
does not impair
the filtering
efficiency
of the filter
because
the size of the openings
in the
dome
remain
unchanged.
Fewer
openings
of a given
size are required
to subdivide
a smaller
IVC cross section.
This
contrasts
with
the Greenfield
filter,
in
which
tilting
enlarges
the size of the
openings
between
some
of the legs and
Radiology
.
101
thus reduces
of the device,
the mechanical
an effect
well
ed in in vitro
studies
(17).
efficiency
document-
Portions
of
the dome
loops
or legs that are in contact with
the wall of the vena
cava become
covered
by a neointimal
layer
within
2 weeks
(3).
Traditionally,
cava
occlusion
filter
has been
ous complication.
designed
to trap
order
to prevent
of a vena
regarded
as a semi-
However,
the SNF is
embohi
in the IVC in
them
from
reaching
the lungs.
We would
therefore
argue
that filter occlusion
should
be considered an unfortunate
but expected
event
in a small
but
the patients
significant
percentage
in our study.
Occlusion
of
is
certainly
preferable
to pulmonary
embohism,
the potentially
fatal alternative.
Partial
or complete
occlusion
may be
associated
with
obstructive
symptoms
of variable
severity,
depending
on the
size
of the emboli,
the completeness
obstruction,
and the state
of the
eral venous
return.
The symptoms
usually
transient,
with
recovery
weeks
or months
ization
collateral
the
as lysis
and
of occlusion
recanal-
thus
of
that
pnimar-
ily reflects
the recurrence
rate of pulmonamy
embolism
and the size of the
embohi
in a given
patient
population
rather
than
any defect
of filter
design
or performance.
The frequency
of recurrent
pulmonary
embolism
in patients
such
as ours
who cannot
receive
anticoagulant
ment, and thus the potential
clot
treatcap-
ture rate
determine
indirectly.
of the filter,
is difficult
to
and can be estimated
only
Before
the use of anticoagumortality
due
to pulmonary
emwas reported
to be about
30%
lants,
bolism
(18),
while
the
current
tients
treated
with
py is only
8% (19).
b.
Figure
2.
monly
assumed
Radiographs
of filter
dome
venae
cavae
in smaller
in a central
mortality
in
anticoagulant
This difference
pa-
theraof
seems
that some
large
single
embohi
or
several
smaller
embohi
can be massive
enough
to cause
a symptomatic
occlusion when
captured
in the filter.
Furthemmore,
since
improved
imaging
methods
indicate
that complete
occlusion may occur
without
symptoms
if
good
venous
collaterals
exist,
the total
number
of complete
occlusions
is probably higher
than
previously
reported.
In the BIH/MGH
subseries,
five of the
nized
with
44 patients
collateral
(11%)
had
lower-limb
swell-
ing. MR imaging
showed
filling
defects
in the filters
in these
patients,
which
could
represent
captured
embohi.
Three
of 44 patients
(7%) showed
complete
occlusion
(Table
2). In addition,
two patients
had clinical
findings
that may
have been
due to IVC occlusion,
but
this
aging
sion
result
was
studies.
rate
in
not
confirmed
The
the
with
symptomatic
BIH/MGH
im-
occluseries
is thus
Since
less than
one-third
of significant
pulmonary
embohi
are lethal,
there
must
be at least three
times
this number of clinically
significant
recurrent
embohi,
or more
than
66%. It seems
clear
that once a patient
has had a single episode
of embolism
and remains
untreated
with
anticoaguhants,
the
probability
of a recurrence
is very high.
This is supported
by autopsy
studies
of
pulmonary
embolism
(20, 21) and a
7%-11%
(three
plus a possible
two of 44
patients),
and the overall
symptomatic
occlusion
rate is 7%-9%
(seven
plus a
possible
two of 103 patients
in all 17
participating
centers),
findings
comparable
to those
previously
reported
by
other
investigators.
Another
three
completely
asymptomatic
patients
also
showed
complete
occlusion,
which
would
not have
been
detected
without
a routine
MR imaging
follow-up
study.
To our knowledge,
this is the first chinical study
in which
it has been
possible
to use noninvasive
MR imaging
to assess the presence
of thrombus
in a vena
clinical
cava
22%
thus
represents
the
recurrence
rate
hism,
anticoagulants
when
study
probable
of pulmonary
of the Gunther
fatal
emboare not used.
filter
with
contrast
material-enhanced
CT, which
showed
thrombi
in 39% of the filters
studied
at an arbitrary
point
of time in
the follow-up
period
(22).
Clinical
reports
of patients
with
filtens in place
indicate
that 5%-10%
experience
symptoms
and signs
of IVC occlusion
(22). In view
of the estimated
high
embolism
recurrence
rate, it
102
.
Radiology
position
(a) and
in a tilted
position
corn-
(b).
of
cohlatare
in
of the IVC or enlargement
vessels
occur.
We believe
frequency
a.
filter,
since
the SNF
is nonfemro-
as filling
defects
when
contrast
material-enhanced
digital-subtraction
or
complete
with
total
US
also
veins
will
not
generally
with
mild
asymptomatic
leg swelling,
or associated
can be recog-
multiple
allow
sionally,
may
be large.
plain
recurrent
or
large
that
clusion
MR
five
of the
of
were
obstruction
pathways
Thus,
to
of
of
have
been
studies
of
an
of
through
be missed
to
collateral
the
ye-
rate
the
rate
selection
clots
filter.
clinically,
filter
of
the
in
(22).
do not
cannot
In
fact,
beto
too
raise
or,
perhaps,
allowed
to
and
van-
We
indicate
be used
should
These
fil-
at a rate
reported
being
me-
popu-
receive
efficiency.
patient
of
various
filters
occlusion
the
prone
prevalence
occlusions
and
thus
filter
tions
more
occlusions
other
low
that
complete
thrombosis
who
5%-10%
compare
three
patients.
the
in
patients
these
failure
with
that
Symptomatic
hieve
filter
in
be
the
embolism
lations
with
(27).
reflects
current
for
interest
venous
it is likely
occlusion
images
neurosurgical
extensive
nous
persist
occlusion.
signs
of oc-
patients
tend
with
can
MR
patients
It is of
were
ex-
veins
be severe
confirmed
eight
patients
develop
our
complete
clinical
imaging.
occlusion
could
embolism
that
three
that
with
size
(25,26).
had
had
Occaveins
if the collateral
there
may
no symptoms
Five patients
and
embohi.
collateral
swelling
showed
of
of
collat-
small
pulmonary
or months
tens.
and
This
lower-limb
Such
if adequate
Generally,
two
(24). However,
are compromised,
weeks
occlusion
passage
one
significant
emboli,
are
may
of the vena
of flow on MR
asymptomatic
exist.
em-
embohi
occlusion
absence
veins
imaging
within
a large
small
A complete
be
eral
contrast,
of
images.
may
thai
Small
In
cause
cava
ous
problems.
weeks.
on cluster
on
or
or with
MR
Recovery
occurs
bolus
magnetic
(23). This suggests
that the
true total occlusion
rate for other
IVC
filters
may be greater
than
previously
reported
without
MR imaging.
Partial
or complete
filter
occlusion
may cause
various
transient
but nonleclinical
angiography,
vena
cavography
or duplex
US.
days
imaged
CT,
quesof
pass
emboli
may
routine
fol-
July
1989
low-up
ventilation
/perfusion
chide studies
are rarely used
radionu(28). Even
deaths
due to pulmonary
embolism
may be ascribed
to the known
undemlying cardiac
disease
or malignancy,
as
autopsies
are performed
in only a small
percentage
of fatalities
in hospitals.
The possibility
of local thrombosis
occurring
tion
on the
filter
to a metallic
itself
device
as a reac-
in the blood-
stream
is difficult
to rule out with
certainty.
This would
be difficult
or impossible
to distinguish
from
captured
emboli
from
the veins
of the lower
limb or even
from
the catheter
surface
during
withdrawal.
The nitinol
matemiah of the SNF has been
shown
to have
low thrombogenicity
ments
(3). Furthermore,
jomity
of SNFs
free,
in animal
expemisince the ma-
in humans
inherent
remain
thrombogenicity
anticoagulation
high
probability
remains
the most
occlusion.
All attempts
to
successful.
There
tion
one
or significant
filter dome
pletehy
in an
In this
SNFs and
treatment,
of recurrent
likely
cause
the
embolism
of filter
small
the surface
livery
catheter
of recurrent
thrombus
the
(29).
was very low. Pulmonary
embowas suspected
in one of 103 paon the basis of clinical
findings
a change
in the pattern
of abnorfindings
on ventilation/perfusion
Another
patient
was asympto-
pulmonary
embo-
matic, but new perfusion
defects
observed
on a routine
follow-up
In conclusion,
with
the
cedure
is simple,
significant
puncture
SNF
were
perfu-
weeks.
A vena
cavogmam
a thin
thrombus
extendfilter
from
clot contained
deaths
were
attributable
embolism
of filter
our
initial
for percutaneous
pleted
one
and
detailed
11.
to 39% in a contrast
CT study of another
14.
and
15.
complete
report
trial
study
of the
is com-
bird’s
Ind)
16.
U
for clinical
since this
nest
has
filter
been
(Cook,
18.
19.
Bloom-
20.
panel
21.
recommended
approval
by an FDA
article
was submitted.
Acknowledgments:
We are indebted
to the
many
unnamed
investigators
currently
participating
in the clinical
trial of the SNF at numerous centers
in the United
States.
Their
interest
and dedication
in the exploration
of new interventional
developments
and in the pursual
of
the demanding
protocols
necessary
to obtain
meaningful
data have been
remarkable.
We
thank
Anne
Maloney,
RT, Beth Israel Hospital,
and Joseph
DeBenedeto,
RT, Massachusetts
Genera!
Hospital,
and their staff for technical
assistance,
and Claire
Martinez,
BA, for manuscript
preparation.
1.
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A
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pro-
insertion
quick,
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free of
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Simon
3.
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M, Kaplow
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symptomatic
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to those
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marked
clinical
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or
months.The
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ly rare after
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at the venipunc-
of the
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and
requires
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in the fil-
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or occlusions
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shape
was considered
satisfactory.
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of the filter legs was extreme-
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#{149}
Number
1
Radiology
.
103