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813
Review
Inferior Vena Caval Available Devices Clement
Filters:
Analysis
The use of an effective,
safe, and easily introducible
sis. Until recently,
per-
of certain thrombo-
the choice of a vena caval filter was limited
to one device,
the 24-French Greenfleld filter, the sole filter accepted by the Food and Drug Administration (FDA) for use in the United States. Now, several devices are FDA-approved and available in the United States, and other newer filters are currently in use in Europe. These filters feature easier insertion, improved filtering, antitilt abilities, memory-wire properties, and potential retrievability.
The purpose
of this article is to review such newer filters in
terms of their ease of use, efficacy, and associated morbidity, focusing on the five devices available for use in the United
to review the current
indications
ous filters; and to put into likely to occur in the future filters.
The “Ideal”
for use of transven-
perspective the trends that are use of inferior vena caval (IVC)
IVC Filter
The characteristics 1 No caval .
filter,
of the ideal PVC filter are listed in Table to date,
these objectives.
Several
has
July 31
I Department
,
1990:
of Radiology,
accepted Harvard
Some
tancies,
April
for optimal
filter design
may be
the funtional
performance
of the device should be the
achieved
all of
case in point is the Mobin-Uddin
when
and 1977. Although its rate of recurrent pulmonary embolism was very low (0.5%), the prevalence of vena caval occlusion was high, 60-70% [2, 3]. Its use declined when the Greenfield filter became available, primarily because of this morbidity, which resulted in venous stasis and leg edema.
after revision Medical
1991 0361-803X/91/1
criteria
primary consideration. A crucial factor in selecting an IVC filter is how efficiently the filter can trap thrombus in vivo. However, a balance must be created between highly effective clot trapping with the concomitant risk of IVC occlusion and maintenance of high IVC patency with the possible failure to trap thrombus. A
November
School
564-0813
filter, used between
1969
1 , 1990.
and Brigham
and Women’s
Hospital,
Rcentgen
Ray Society
Grassi. AJR 156:813-821,
of these
incompatible within a single filter type. For instance, a filter design that has excellent fixation within the IVC and is secure may be extremely difficult to retrieve. The duration of time after insertion also has an effect. Retrievability of the Amplatz filter is initially satisfactory; however, in dogs, Amplatz filter retrieval at 3 weeks was more difficult and may have caused slight vena caval damage [1]. Given the constraints of thromboembolic protection in most patients, and the known continued endothelialization that occurs at the vena caval wall, the practical usefulness of retrievability may be limited. Although much emphasis has been placed by manufacturers on the small size (Fig. 1) of current introduction systems, the size advantage alone should not overshadow the three major factors mentioned before. Especially in patients with filter placement for prophylaxis, and those with full-life expec-
must be considered
successfully
factors
selecting an IVC filter. The most important factors are a high filtering efficiency (large and small emboli) without impedance of blood flow, stability of positioning, and a low rate of associated morbidity. Received
of Five Currently
J. Grassi1
cutaneous vena caval filter is crucial in the treatment patients with pulmonary embolism or deep venous
States;
Article
0 American
75 Francis
St., Boston,
MA 021 1 5. Address
reprint
requests
to C. J.
GRASSI
814
TABLE
1: Characteristics
of an “Ideal”
Nonthrombogenic, biocompatible, High filtering efficiency (large and
Vena
Caval
long-life material small emboli) without
Filter
AJR:156,
has used the major series by the FDA, supplemented
April 1991
published for each filter approved with updates of these devices.
impedance
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of flow
Older
Secure fixation within the vena cava Rapid percutaneous insertion Small
Filters
Mobin-Uddin
caliber
Release mechanism simple and controlled Amenable to repositioning MR imaging compatibility (e.g., nonferromagnetic) Low cost Retrievability
GF(tilt)
VTF
BNF
TGF
%
nL T
24Fr
P’1
?
%/
fl
#{174} U
.
IA
24Fr
fl
l2Fr
SNF
11 Fr
lOFr
Fig. 1.-Diagram of implanted filters shows cross sections (top ),frontal views (middle), and carrier sizes (bottom). GF = Greenfield filter, GF (tilt) = tilted Greenfield filter, TGF = titanium Greenfield filter, BNF = bird’s nest filter, VTF = Vena-Tech filter, SNF = 5imon nitinol filter. Tilted Greenfield
stainless steel filter, which theoretically
leaves larger unprotected
spaces
for thromboembolism passage, is compared with a centered GF and with other filters. (Modified from a diagram provided by courtesy of Morris Simon.)
Stainless
Exact comparison
of filter device function
can be problem-
show superior and
that
the
sufficiently
tilted
clot trapping stainless
when
[3] (Fig.
for both large and small emboli,
steel
centered,
Greenfield
but
1). However,
allowed
another
filter
trapped
clots
emboli
to pass
when
in vitro
study
in sheep
showed that the Greenfield filter is capable of stopping both large and smaller emboli [4]. This underscores the importance of having in vivo studies to evaluate the clinical there is no substitute
studies
[5]. However,
evaluations
on filter
data is quite variable.
in addition to in vitro testing. In order efficacy of percutaneous IVC filters, for randomized, prospective clinical
even in the currently efficacy,
the quality
For instance,
numbers offilters placed conducted follow-up on pulmonary embolism by mail [7], and still other emboli were verified [8].
published
clinical
of the comparative
some
series
have high
for prophylaxis [6], other series have such important factors as recurrent clinical means, telephone contact, or series do not specify how recurrent Given these limitations, this review
Steel Filter
With its longer period of availability, the Greenfield stainless steel filter (GF; Medi-tech, Watertown, MA; Fig. 2) has had the most numerous clinical evaluations. It first was described in 1 973, and the first clinical series were published in 1977 [6, 1 0-1 6]. The GF design permits filling of 70% of the filter
cone by thrombus
with a reduction
in the filter’s
effective
cross-sectional area of only 50% [1 7]. Its construction consists of six stainless steel wires in a conical shape extending from a central hub, and the tips form a circular base with a maximal diameter of 30 mm (recommended for IVC sizes of 28 mm) [1 8]. Percutaneous insertion is performed via a 24French system from femoral or jugular routes, with specific carrier-introduction
atic. Although in vitro models may be helpful initially, they do not consistently reflect clinical reality and may be misleading. For example, Katsamouris et al. [3] demonstrated in vitro that the bird’s nest, Simon nitinol, Amplatz, and Gunther filters
Filter
This filter is mentioned for historical reasons only, because the Mobin-Uddin filter(MUF) is no longer available in the United States. It is constructed as an inverted umbrella with six flat stainless steel spokes, and covered with a thin Silastic membrane. A 23-mm-diameter size was originally used, but episodes of filter migration led to the development of a larger 28-mm filter[9]. The low rate of recurrent pulmonary embolism (0.5%) was overshadowed by the high prevalence of vena caval occlusion, 60-70%, and lower extremity venous stasis. With this major disadvantage, it is not surprising that the MUF was supplanted by the Greenfield filter when it became available.
Greenfield
7Fr
Umbrella
systems.
Misplacement or malposition of the filter into the renal veins, hepatic veins, or right atrium has been reported [1 9]. Asymptomatic penetration of the filter foot prongs through the vena caval wall occurs with some frequency although therate of clinically symptomatic vena caval perforation is low. Penetration has been described at multiple sites including the ureter, intestine, aorta, and vertebral body [1 5, 20]. The GF has a reported recurrent embolism rate of 5% [16, 21 ] and a vena caval occlusion rate of approximately 3-5% [6, 1 1 1 4-i 6]. Optimal filtration of caval blood flow results with angles less than 1 5#{176} tilt from the vertical; this was a potential long-term problem of the filter. Reduced filtration efficiency with tilting has been a muchpublicized disadvantage of the GF [3]. Subsequently published experiments in sheep, whose vena caval diameters ,
approximate toward
Greenfield
that of humans,
deteriorating
have shown
clot-trapping
that the tendency
performance
when
the
filter is tilted within the vena cava is not as dramatic
as once believed [4]. A possible explanation for this apparent discrepancy between clinical and experimental data may be that not all pulmonary emboli are symptomatic and that the Greenfield
filter
pulmonary
emboli,
protects
whereas
against
small
massive,
emboli
potentially
pass
through
lethal
the
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AJR:156,
Fig. filter.
filter
INFERIOR
April 1991
2.-A
and
and
B, Lateral
remain
(A) and
axial
asymptomatic.
(B)
radiographs
Significant
VENA
which
are
vein placement derived
from
is necessary.
limited
numbers
FILTERS
815
of Greenfield
thrombus
has
been observed on both sides of the filter on follow-up venacavography [21 ], yet may not be apparent on subsequent examinations. Possibly, these thrombi are lysed in situ by the flow of blood, or fragment further into sufficiently small sizes that they may pass through the GF and cause no clinical symptoms on reaching the lungs. Other thrombi are symptomatic, and for any patient with clinical or radiologic evidence of pulmonary emboli despite the presence of a Greenfield IVC filter, there should be a high suspicion for recurrent thrombus on the filter itself (Fig. 3). The GF’s established rate of high vena caval patency (9598%) is an advantage in those uncommon situations in which
a suprarenal
CAVAL
Fig. 3.-Venacavogram
obtained
proach shows thrombus tilted within vena cava.
(arrows)
with right superior
internal
to Greenfield
jugular filter,
vein apwhich is
These indications, of patients,
include
caval thrombosis extending above the renal veins, renal vein thrombosis, thromboemboli despite prior IVC interruption, or recurrent thromboemboli with a large, patent left ovarian vein (with or without thrombus itself) [22]. The large 24-French size of the stainless steel Greenfield filter system is its principal disadvantage. A 1 0-24% prevalance of sonographically identified femoral vein thrombosis
[23], most likely related injury
Newer Bird’s
locally,
is another
to venous important
dilatation
and endothelial
consideration. Fig. 4.-A configuration
Filters Nest and Modified
and
axial
(B)
venacavograms
of mesh
Filter (four
The bird’s nest filter (BNF; Cook,
Bloomington,
IN; Fig. 4)
was first tested clinically in 1 982 and has the advantage of a small sheath size, 1 2-French internal diameter in the modified version. Its mesh configuration consists of a series of pre-
shaped
and B, Lateral (A) of bird’s nest filter.
wires that are formed
by the operator
in a series of
maneuvers with a special applicator, and the wires assume an original shape that resembles a bird’s nest [24]. Initially, the mesh was affixed by a series of V-struts 0.25 mm in diameter, intended to hold the BNF securely within the IVC. However, in the original BNF model, five of 422 filters migrated
to
the
right
atrium
without
fatality,
and
one
to
the
pulmonary embolism)
artery with death 1 0 days later due to pulmonary [7]. The design of the BNF was modified, and a second-generation device with stiffer securing struts, 0.46 mm
in diameter,
has
had
no reported
episodes
of migration
[7]. The rate of recurrent pulmonary embolism reported is 2.7%, and the rate of caval occlusion is 2.9% [7]. However, this follow-up was largely clinical and consisted of telephone or questionnaire contact in 400 of the 440 patients after 6 months; sonography, venacavography, or pulmonary angiog-
GRASSI
816
Titanium
radiologic
The titanium Greenfield filter (TGF; Medi-tech; Fig. 7), actually a significantly modified design of the stainless steel GF, was created to provide a smaller introduction size for percutaneous insertion. Its design lacks a central apical hole for
follow-up
[25].
Additionally,
vena
caval
occlusion
perforation
of the caval
An advantage
wall has also been
identified
of the bird’s nest filter is its free-form
[25].
config-
uration within the IVC, because it is not subject to the need for centering as are several other filters. It can be inserted in vena cavas up to 40 mm in diameter. In very large vena cavas, it can eliminate the need to use bilateral iliac vein filters (Figs. 5A and SB), because a single bird’s nest filter will suffice
(Figs. 5C and SD). The free-form the filter mesh to include
alous veins (Fig. 6).
unexpected
nature allows positioning collateral
of
veins or anom-
Greenfield
April 1991
raphy was infrequently performed. Vena caval occlusion was documented in 1 9% of a subset of 40 patients who underwent
with phlegmasia cerulean dolens has been reported in one case that led to the patient’s death [26], and a significant Downloaded from www.ajronline.org by 117.255.237.195 on 10/09/15 from IP address 117.255.237.195. Copyright ARRS. For personal use only; all rights reserved
AJR:156,
Filter
guidewire insertion, and once the sheath and dilator are placed, the TGF carrier is passed directly under fluoroscopic
control. pressed ences
Its elastic properties permit the TGF to be corninto a 12-French carrier. The TGF has several differfrom
the stainless
Greenfield
filter:
it is broader
at the
base (38 mm vs 30 mm), lighter (0.25 g vs 0.56 g), and it exerts a force of fixation on the wall of the vena cava that is greater than the stainless steel Greenfield filter’s force at diameters
over
22 mm,
but less at diameters
under
22 mm
Fig. 5.-A-D, Venacavograms of large vena cava (A) that necessitated bilateral iliac vein filters when Greenfield filter was sole device available (B). A more recent case with a large vena cava (C) of 39 mm diameter was more easily managed with bird’s nest filter alone (D).
INFERIOR
April 1991
AJR:156,
VENA
CAVAL
FILTERS
817
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Fig. 6.-A and B, Venacavograms show large left-sided anomalous vein (A ) or collateral vein contiguous with left renalvein (B). By positioning a portion of the bird’s nest mesh well caudad (faintly seen on radiograph, small arrows in B), filtration of this extra vein was included.
A
[27].
TGF
filter,
is recommended
placement,
exceeding This
as for for
the
stainless-steel
caval
diameters
Greenfield up
to
but
not
28 mm.
filter
was
available
at selected
centers
for clinical
trials,
of vena caval perforation by the filter legs [27] (Belmont M, personal communication). One in vitro study published at a participating center in the clinical trials attributed this higher rate of caval wall perforation to the possibility of filter splaying associated with the physical design ofthe TGF, clot retraction, and the possibility of changes in intracaval pressures [28]. The design of the filter hooks has been changed to avoid but
these
were
terminated
caval wall perforation,
because
of a high
frequency
and the TGF is now available for clinical
use.
Vena-Tech
radiograph
and B, Lateral
of titanium (A) and axial
alloy version
of Greenfield
(B) photographs
filter.
of Vena-Tech
Filter
The Vena-Tech filter (VTF; Fig. 8) is the American-marketed and FDA-approved version of the LGM filter (L. 0. Medical, Chasseneuil, France). It has been accepted for use under a
510(K) application, that is, as a modification of a previously accepted device, the stainless steel Greenfield filter. Constructed
Fig. 7.-Lateral Fig. 8.-A filter.
of a cone
with
six flat,
metallic
diagonal
struts
and
side rails that run parallel to the walls of the IVC, additional small barbs hold the filter in place. The VTF comes prepack-
aged in a 1 0-French diameter
sheath.
inverted
when
carrier
and requires
Filter orientation transjugular
with the transfemoral
within
placement
a 1 2-French
outer
the carrier syringe is is used as compared
approach. The Vena-Tech filter has been evaluated in a series of 100 patients abroad reported in two different journals [29, 30], and clinical usage in the United States is under way. Of the 100 attempts at insertion, the internal jugular route had an
of 2% (two cases) and a 1 6% rate of (eight filters tilted 15#{176} or more, five filters opened and correctly aligned, and three filters opened and tilted) [30]. Follow-up at 1 year, including an abdominal radiograph, showed migration of the filter in 1 3% (nine cases inferiorly not exceeding the height of initial
failure
rate
malpositioning incompletely incompletely
one vertebral
body,
and four
superiorly
toward
the renal
veins). Clinical follow-up shows a rate of recurrent pulmonary embolism of 2%, and vena caval occlusions in 7% during 1year follow-up. An advertised advantage of the VTF design is the feature of “positive positioning” by means of the barbed side rails.
However,
as these
data indicate,
the prevalence
of initial
malpositioning is significant, and the rate of later migration is lower. It is likely that several of these malpositionings were operator-related, occurring early in the VTF experience. 5ev-
GRASSI
818
AJR:156,
April 1991
eral other malpositionings have been associated with jugular insertion. For best insertion, a technique of rapid deployment from the introducer should be used, with a quick motion of
release into the IVC. Downloaded from www.ajronline.org by 117.255.237.195 on 10/09/15 from IP address 117.255.237.195. Copyright ARRS. For personal use only; all rights reserved
In the United
States,
have reported Recently,
F.C. Taylor
65 successful
investigators
et al. (unpublished
placements
have
data)
with low morbidity.
cautioned
against
placement
above the renal veins and have avoided using the VTF from the left femoral vein because of malpositioning (Vogelzang AL, unpublished data). Several thousand LGM filters have been placed in Europe, and although United States experience is growing, further data will be necessary.
Simon
Nitinol
Filter
The Simon nitinol filter (SNF; Nitinol Medical Technologies, Woburn,
MA;
Fig.
9) is made
composed
of nickel and titanium,
properties.
The filter
wires
of a thermal
memory
alloy
which gives the filter unique
are in straightened
form
at cooled
temperatures (4-i 0#{176}C) and these re-form into a predetermined filter shape at body temperature [31]. The filter shape is that provide
of an umbrella dome with seven petal loops, which the major filtering, and six legs for fixation to the caval
wall. Insertion
is performed
with a cold saline infusion through
the plastic filter holder [32], and the device is easily inserted through a 7-French carrier with a 9-French outer diameter sheath. Both transfemoral and jugular insertion sets are available. The Simon nitinol filter has been accepted by the FDA (April 1 990) for clinical use. The multicenter clinical trials show a
Fig. 9.-Photographs of Simon nitinol filter in straight form (left), lateral view (lower right), and axial view (upper right).
within
carrier
symptomatic recurrent pulmonary embolism rate of 1.1%, and asymptomatic pulmonary embolism of 0.7%, detected by ventilation/perfusion
lung
scan,
or pulmonary
arteriogram,
added in select cases. The vena caval occlusion is 7.8%
(symptomatic)
and
1 .9%
rate reported
(asymptomatic),
with
the
latter detected by additional sonography, CT, or MR imaging (Simon M, Grassi CJ, Kim D, unpublished data). The SNF has a unique design and very appealing small introduction
size.
Its
memory-wire
properties
enable
it to
achieve the smallest introduction size of all the filters. The “SNF 7/6” (seven dome loops and six legs) rate of vena caval occlusion necessary
appears to be slightly higher; however, to see how its long-term caval patency
it will be compares
with those of the bird’s nest and Vena-Tech
filters with more
clinical
be made.
Current
usage,
before
a final
comparison
can
Indications
With the increase in percutaneous filter placement by using small French systems, and greater experience with the natural
outcome
of venous thrombosis, the indications for vena caval filters have been expanded. There are now three major cate-
gories for filter placement
in venous
thromboembolism:
con-
traindication to anticoagulation, failure of adequate anticoagulation therapy, and prophylactic placement in high-risk patients. Of these, the first two categories are well established [10, 1 7, 33] and apply to the older and newer filters. However, the
role of vena cava filter placement in patients thrombosis that develops despite adequate
with deep venous anticoagulation is
less clear. Most agree that the presence of iliofemoral thrombosis is a high-risk factor for pulmonary embolus, and they will place a filter when anticoagulation 33]. This risk is significant particularly floating femoral or iliac vein thrombus
is contraindicated
in patients greater
[10,
with free-
than
S cm in
length [34]. The third category, prophylaxis for high-risk patients (e.g., before neurologic, spine, or hip surgery, and patients with paraplegia or pelvic fractures), has evolved largely because the percutaneous IVC filter is such an attractive therapy that its placement in patients without established pulmonary embolism or deep venous thrombosis has been advocated [10, 35]. It is my belief that the ease of insertion should not lead to an uncontrolled situation in which technology becomes the motivating force for IVC filter placement. Rather, firm medical
indications should be the prime determinant of which patients receive vena caval filters [36, 37]. One indication for prophylactic filter use is in the setting of cor pulmonale in patients with severe sion. These patients may not tolerate nary embolus [38], and filter placement
Additionally, when a previous has migrated, or has functionally embolus,
a second
vena caval
pulmonary hypertena subsequent pulmohas a valuable role. IVC filter has been misplaced,
failed to prevent
pulmonary
filter can be added
(Fig. 10).
AJA:156,
INFERIOR
April 1991
VENA
Contraindications Contraindications
to percutaneous
filter
placement
of all
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types include the relatively uncommon situations in which surgical venotomy and closure may be preferred. Patients with severe blood coagulopathy predisposing them to bleeding from the puncture site, patients who cannot comply with postprocedure rest orders (especially
or will not with older
24-French system), and those with obstructing thrombus along all available routes of transvenous insertion are included. Traditionally, placement of a permanent IVC filter has been discouraged
in the
expectancy.
There
gevity
of these
young,
and
are no strict
filters
in patients guidelines,
in the human
with
a long
life
the
Ion-
because
body
can only
be esti-
should
be ob-
mated. Technique
Before
filter placement,
a venacavogram
tamed, which is another reason why percutaneous filter placement should be performed by interventional radiologists who
are prepared
to perform
venacavography
by means
of cut
CAVAL
FILTERS
819
The newer IVC filters require careful percutaneous technique, as do all filter devices. For punctures of the femoral or jugular
vein,
a single-wall
puncture
technique,
preferably
with
a percutaneous entry needle, is recommended. During the insertion of this open-ended needle, continuous suction is applied with an attached syringe, and a visual check is made for any arterial blood. If arterial blood is obtained, the needle is removed, and the puncture is performed again. I prefer a single-wall technique in order to avoid the complication of arteriovenous fistula [39]. Puncture of the right internal jugular vein is performed with a similar technique [1 1 ], by using a venous puncture midway between the mastoid tip and the sternal notch, after visualization of the venous pulsation. The use of mild Trendelenberg positioning of the patient at the start of the procedure aids in a jugular venous distention, and having the patient sitting when the venous introducer is withdrawn facilitates hemostasis at the puncture site on the right side of the neck. For the choice of access route, just as percutaneous transvenous access has become favored over surgical venotomy, so has the transfemoral vein route become popular with the newer filters because it is well tolerated by the patient and
film, digital subtraction angiography, or cineangiography. Venacavography is necessary [36] for obtaining information (1) to check IVC patency and the extent of thrombus, if any, within the vena cava or along the route of intended filter
vein is most commonly used. The left femoral vein route can be used; however, greater resistance in filter passage due to the angle of the common iliac vein into the inferior vena cava
delivery;
can be encountered
(2) to determine
the caval diameter
and the suitability
of the intended filter device; and (3) to delineate the anatomy, including location of the renal veins, possible
anomalies,
and any significant
collateral
vessels.
IVC IVC
straightforward
for the
physician
operator.
[13], especially
The
right
with the 24-French
femoral
intro-
duction system. Some have avoided the left femoral vein approach in 97% of patients [25], yet others have experienced no more difficulty from the left side than from the right [1 1].
Fig. 10-68-year-old woman with a Greenfield filter in place who had recurrent shortness of breath. A, Abdominal radiograph shows abnormal widening of filter base (arrows) to 38 mm (normal, 28 mm); this is virtually infrarenal cava by foot process of filter. B, Venacavogram confirms perforation of caval wall and shows filling defect of thrombus within filter (arrow). C, Radiograph shows Simon nitinol filter that was added within true vena caval lumen inferioriy (arrowheads) for treatment.
diagnostic
of perforation
of
820
GRASSI
TABLE
2: Comparison
Filter
of Five Inferior
Type
Vena
Caval
Carrier
Size
Size in French
(OD)
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29 14
24 12
Bird’snest
14
11
Vena-Tech
12
10
9
7
Greenfield
stainless
Greenfield
titanium
Simon
steel
nitinol
Note.-OD = outer diameter. Manufacturer’s recommendation
a
before
surgical
procedures
At our institution, the left femoral vein approach has been useful in the past, even with the 24-French Greenfield system (six [9%] of 68 patients in 1 year). With the new, smaller introduction systems (outer diameter 1 4-, 1 2-, 9-French), the past sequence of access choice (first, right femoral vein;
internal jugular vein; third, left femoral vein) is chang-
ing, with a trend toward more transfemoral placements from either the right or left side. The advantages of femoral, compared with jugular vein, puncture do include avoidance of the risks of air embolism, pneumothorax, and inadvertent puncture of the carotid artery, as well as the fact that radiologists
generally are more familiar with puncture of the femoral vein. External jugular [40], subclavian, and even brachial vein insertions formed.
(Brown
A, personal
Filter Advantages
communication)
have
been
per-
and Disadvantages
As shown in Table 2, the smaller introduction size is a significant advantage for the newer generation filters available for clinical use. The versatility of accommodating larger vena
caval sizes up to 40 mm is an added advantage
of the bird’s
nestfilter since the titanium Greenfield, Vena-Tech, and Simon nitinol types are limited to caval sizes up to 28 mm. Because of this size versatility, a radiology department that can afford to keep only one filter on inventory for all patients should logically choose the bird’s nest filter. However, the bird’s nest filter’s stainless steel construction
poses a relative disadvantage, MR imaging construction.
(IVC)
Introducer in French
second,
AJR:156,
because
has introduced Those devices
are ferromagnetic,
whereas
the increased
composed
Maximum
IVC Diameter
requiring
Yes Yes No Yes
28 (24)
No
anesthesia.
rapidly
and effectively
data) [43]. In the future, constructed
of high-strength,
The 24-French
(Grassi
CJ et al., unpublished
it is likely that all IVC filters
Greenfield
nonferromagnetic
will be
materials.
filter has one relative advantage,
that is, its well-documented rate of high vena caval patency. It is indicated for use in the uncommon situation of suprarenal vein placement [22] with the attendant risk of thrombosis and renal compromise, at least until more experience can be accumulated with suprarenal placement of the newer IVC filters to confirm their patency in this position. At our institution, the bird’s nest and Simon nitinol devices are used. The Simon nitinol filter is valuable when the smaller
9-French
percutaneous
puncture
is advantageous,
or where
the longitudinal distance between the renal veins and iliac bifurcation is reduced, favoring the shorter 3-cm length of the Simon nitinol over the bird’s nest. The bird’s nest filter is used routinely. Specifically, it is the only filter device suitable at this time for vena caval sizes between 29 and 40 mm diameter.
Conclusions A group of new, now available, each
will
by, nitinol, or beta-Ill titanium alloy are less ferromagnetic [41 42]. Although the heat or torque effects on the filter or adjacent structures do not appear to be detrimental to patient’s safety during routine clinical imaging [41], filters fabricated from stainless steel are highly ferromagnetic and create marked magnetic susceptibility artifact on MA. This artifact
Significant?
28 28 40 28
general
formed
existing
of elig-
Tilting
Recommended (mm)
Further prospective
a new consideration for filter fabricated from stainless steel
those devices
Filters
as described.
use of
April 1991
smaller percutaneous with its advantages
filter devices are and disadvantages,
The ideal vena caval filter is not yet available.
clinical study
trials of these are necessary,
devices with randomized, in order to further refine the
filters and to assist in the development
be superior
for
the
prevention
of a filter that
of pulmonary
embolism.
Until that time, the choice of an IVC filter from those available should be based not only on the interventional radiologist’s
preference, filter’s
but also on the specific
clinical situation
and the
performance.
,
degrades
abdominal
imaging.
noninvasive method of assessing presence of intracaval thrombus,
a nonferromagnetic intracaval
filters
As MR imaging
filter is clear. Gradient-echo and
trapped
provides
a
vena caval patency and the the potential advantage of thromboemboli
imaging can
be
of per-
REFERENCES Hunter DW, Lund G, Rysavy JA, et al. Retrieving the Amplatz retrievable vena cava filter. Cardiovasc lntervent Radio! 1987:10:32-36 2. McIntyre AB, McCready RA, Hyde GL, Mattingly W. A ten year followup study of the Mobin-Uddin filter for vena cava interruption. Surg Gyneco! Obstet 1984;158:513-516 3. Katsamouris AA, Waltman AC, Delichatsios MA, Athanasoulis CA. Inferior vena cava filters: in vitro comparison of clot trapping and flow dynamics. Radiology 1988;166:361-366 4. Thompson BH, Cragg AH, Smith TP, Barenieweski H, Bamhart WH, Dc
1.
AJR:156,
INFEAIOA
April 1991
Jong SC. Radiology 5. Yune HY. 1989;172:
Thrombus-trapping
efficiency
of the
filter
in vivo.
1989:172:979-981 Inferior vena cava filter: search for an ideal device. Radiology
JOF, Johnsrude
insertion patients.
of Greenfield J Vasc Surg
filter placement
by femoral
vein
puncture.
AJR
1985:145:
692-698 Wingerd M, Bernhard VM, filters in the management 1978:113:1264-1270
Maddison F, Towne JB. Comparison of caval of venous thromboembolism. Arch Surg
16. Greenfleld U, Michna BA. Twelve-year clinical experience field vena caval filter. Surgery 1988;104:706-712
with the Green-
1 7. Simon M, Palestrant AM. Transvenous devices for the management of pulmonary embolism. Cardiovasc lntervent Radio! 1980:3:308-318 18. Messmer JM, Greenfleld U. Greenfleld filters: long-term radiographic follow-up study. Radiology 1985:156:613-618 1 9. Yakes W. Percutaneous retrieval of a Kimray Greenfleld filter from right atrium and placement in the inferior vena cava. Radiology 1988:169: 849-851 20. Kim D, Porter DH, Siegel JB, Simon M. Perforation of the inferior vena cava with aortic and vertebral penetration by a suprarenal Greenfleld filter. Radiology 1989;172:721-723 21 . Geisinger MA, Zelch MG, Aisius B. Recurrent pulmonary emboli after Greenfield filter placement. Radiology 1987:165:383-384
22. Orsini AA, Jarrell BE. Superarenal tions,
inferior 25.
GS.
Percutaneous
inferior
vena
cava
transcatheter filters.
Radiology
26. Aruny JE, Kandarpa
K. Phlegmasia cerulea dolens, a complication after placement of a bird’s nest vena cava filter. AJR 1990:154:1105-1106 Greenfleld U, Cho KJ, Pais SO, Van Amen M. Preliminary clinical experience with the titanium Greenfleld filter. Arch Surg 1989:124:657-659 Teitelbaum GP, Jones DL, van Breda A, et al. Vena caval filter splaying: potential complication of use of the titanium Greenfield filter. Radiology
placement of vena caval filters: indica-
and results. J Vasc Surg 1984;1 :124-135 23. Mewissen MW, Erickson SJ, Foley WD, et al. Thrombosis insertion sites after inferior vena caval filter placement.
28.
1989:173:809-814 29.
at venous Radiology
Crochet
D, Petitier
H, Ricco
JB, et al. Le nouveau
fitre cave LEM
de l’ebolie pulmonaire. J Radio! 1988;69:431-436 30. Ricco JB, Crochet D, Seibilotte P, et al. Percutaneous
31
.
preventif
transvenous
interruption with the LGM filter: early results of a multicenter Vasc Surg 1988;3:242-247 Simon M, Kaplow A, Salzman E, Friedman D. A vena cava thermal shape memory alloy: experimental aspects.
1977:125:89-94 32. Simon M, Athanasoulis
caval
trial. Ann filter using Radiology
CA, Kim D, et al. Simon nitinol inferior vena cava
filter: initial clinical experience. Radiology 1989:172:99-103 33. Alexander J, Gewerk B, Lu C, Zarins C. New criteria for placement of a prophylactic vena cava filter. Surg Gynecol Obstet 1986:163:405-409 34. Norris C, Greenfleld L, Hermanson J. Free-floating iliofemoral thrombus: a risk of pulmonary embolism. Arch Surg 1985:120:806-808 35. Goluek PJ, Garrett WV, Thompson JE, Smith BL, Talkington CM. Interruption of the vena cava by means of the Greenfleld filter: expanding the indications. Surgery 1988:103:111-117 36. Grassi CJ, Goldhaber SZ. Interruption of the inferior vena cava for prevention of pulmonary embolism. Herz 1989:14:182-191 37. Goldhaber SZ, Grassi CJ. Management of pulmonary embolism. In: Sabiston DC Jr, ed. Textbook of surgery, Update 8. Orlando, FL: Saunders, 1990:115-127 38. Stewart JA, Greenfleld U. Transvenous vena caval filtration and pulmonary embolectomy. Surg Clin North Am 1982:62:411-430 39. Grassi CJ, Bettmann MA, Rogoff P, Reagan K, Hamngton DP. Femoral arteriovenous fistula after placement of a Kimray-Greenfield filter. AJR I988;151 :681 -682 40. McCowan TC, Ferris EJ, Carver DK, Harshfleld DL. Use of extemal jugular vein as a route for percutaneous inferior vena cava filter placement. 41
42.
techniques,
1989:173:155-157
filter: a new percutaneous vena cava filter. J Vasc Surg 1984:1 :498-501
Dorfman
IS, Barth
1 3. Rose BS, Simon DC, Hess ML, van Amen ME. Percutaneous transfemoral placement of the Kimray Greenfleld filter. Radiology 1987:165:373-376 14. Greenfield U, Zocco J, Wilk J, Schroeder TM, Elkins AC. Clinical experience with the Kimray-Greenfleld vena caval filter. Ann Surg 1977:185: 15.
24. Roehm JOF. The Bird’s nest
27.
MH, Gianturco C. The bird’s nest inferior vena cava filter: progress report. Radiology 1988;168:745-749 8. Aicco J, Crochet D, Sebilotte P, et al. Percutaneous transvenous caval interruption with the “LGM” filter: early results of a multicenter trial. Ann Vasc Surg 1988;3:242-247 9. Mensoian JO, LoGerfo FW, Weitzman AF, Ezpleta M, Sequeira JC. Clinical experience with the Mobin-Uddin vena cava umbrella filter. Arch Surg 1980;115:1179-1181 1 0. Jones T, Bames A, Greenfield L. Greenfield vena caval filter: rationale and current indications. Ann Thorac Surg 1986;42:S48-S55 1 1 . Pais SO, Tobin KD. Percutaneous insertion of the Greenfleld filter. AJR 1989:152:933-938 12. Denny DF, Cronan JJ, Dorfman GS, Esplin C. Percutaneous Kimray-
Greenfleld 827-829
821
FILTERS
1990:174:987-992
I988;8:460-464 7. Aoehm
CAVAL
15-16
6. Pais 5, Tobin K, Austin C, Queral L. Percutaneous inferior vena cava filter: experience with ninety-six
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Greenfield
VENA
43.
.
Radiology 1990;176:527-530 Teitelbaum GP, Bradley WG, Klein BD. MA imaging artifacts, ferromagnetism, and magnetic torque of intravascular filters, stents and coils. Radiology 1988:166:657-664 Teitelbaum GP, Ortega HV, Vinitski 5, et al. Low-artifact intravascular devices: MA imaging evaluation. Radiology 1988:168:713-719 Teitelbaum GP, Ortega HV, Vinitski S, et al. Optimization of gradient-echo imaging parameters for intracaval filters and trapped thromboemboli. Radiology 1990:174: 101 3-1 019
813
Review
Inferior Vena Caval Available Devices Clement
Filters:
Analysis
The use of an effective,
safe, and easily introducible
sis. Until recently,
per-
of certain thrombo-
the choice of a vena caval filter was limited
to one device,
the 24-French Greenfleld filter, the sole filter accepted by the Food and Drug Administration (FDA) for use in the United States. Now, several devices are FDA-approved and available in the United States, and other newer filters are currently in use in Europe. These filters feature easier insertion, improved filtering, antitilt abilities, memory-wire properties, and potential retrievability.
The purpose
of this article is to review such newer filters in
terms of their ease of use, efficacy, and associated morbidity, focusing on the five devices available for use in the United
to review the current
indications
ous filters; and to put into likely to occur in the future filters.
The “Ideal”
for use of transven-
perspective the trends that are use of inferior vena caval (IVC)
IVC Filter
The characteristics 1 No caval .
filter,
of the ideal PVC filter are listed in Table to date,
these objectives.
Several
has
July 31
I Department
,
1990:
of Radiology,
accepted Harvard
Some
tancies,
April
for optimal
filter design
may be
the funtional
performance
of the device should be the
achieved
all of
case in point is the Mobin-Uddin
when
and 1977. Although its rate of recurrent pulmonary embolism was very low (0.5%), the prevalence of vena caval occlusion was high, 60-70% [2, 3]. Its use declined when the Greenfield filter became available, primarily because of this morbidity, which resulted in venous stasis and leg edema.
after revision Medical
1991 0361-803X/91/1
criteria
primary consideration. A crucial factor in selecting an IVC filter is how efficiently the filter can trap thrombus in vivo. However, a balance must be created between highly effective clot trapping with the concomitant risk of IVC occlusion and maintenance of high IVC patency with the possible failure to trap thrombus. A
November
School
564-0813
filter, used between
1969
1 , 1990.
and Brigham
and Women’s
Hospital,
Rcentgen
Ray Society
Grassi. AJR 156:813-821,
of these
incompatible within a single filter type. For instance, a filter design that has excellent fixation within the IVC and is secure may be extremely difficult to retrieve. The duration of time after insertion also has an effect. Retrievability of the Amplatz filter is initially satisfactory; however, in dogs, Amplatz filter retrieval at 3 weeks was more difficult and may have caused slight vena caval damage [1]. Given the constraints of thromboembolic protection in most patients, and the known continued endothelialization that occurs at the vena caval wall, the practical usefulness of retrievability may be limited. Although much emphasis has been placed by manufacturers on the small size (Fig. 1) of current introduction systems, the size advantage alone should not overshadow the three major factors mentioned before. Especially in patients with filter placement for prophylaxis, and those with full-life expec-
must be considered
successfully
factors
selecting an IVC filter. The most important factors are a high filtering efficiency (large and small emboli) without impedance of blood flow, stability of positioning, and a low rate of associated morbidity. Received
of Five Currently
J. Grassi1
cutaneous vena caval filter is crucial in the treatment patients with pulmonary embolism or deep venous
States;
Article
0 American
75 Francis
St., Boston,
MA 021 1 5. Address
reprint
requests
to C. J.
GRASSI
814
TABLE
1: Characteristics
of an “Ideal”
Nonthrombogenic, biocompatible, High filtering efficiency (large and
Vena
Caval
long-life material small emboli) without
Filter
AJR:156,
has used the major series by the FDA, supplemented
April 1991
published for each filter approved with updates of these devices.
impedance
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of flow
Older
Secure fixation within the vena cava Rapid percutaneous insertion Small
Filters
Mobin-Uddin
caliber
Release mechanism simple and controlled Amenable to repositioning MR imaging compatibility (e.g., nonferromagnetic) Low cost Retrievability
GF(tilt)
VTF
BNF
TGF
%
nL T
24Fr
P’1
?
%/
fl
#{174} U
.
IA
24Fr
fl
l2Fr
SNF
11 Fr
lOFr
Fig. 1.-Diagram of implanted filters shows cross sections (top ),frontal views (middle), and carrier sizes (bottom). GF = Greenfield filter, GF (tilt) = tilted Greenfield filter, TGF = titanium Greenfield filter, BNF = bird’s nest filter, VTF = Vena-Tech filter, SNF = 5imon nitinol filter. Tilted Greenfield
stainless steel filter, which theoretically
leaves larger unprotected
spaces
for thromboembolism passage, is compared with a centered GF and with other filters. (Modified from a diagram provided by courtesy of Morris Simon.)
Stainless
Exact comparison
of filter device function
can be problem-
show superior and
that
the
sufficiently
tilted
clot trapping stainless
when
[3] (Fig.
for both large and small emboli,
steel
centered,
Greenfield
but
1). However,
allowed
another
filter
trapped
clots
emboli
to pass
when
in vitro
study
in sheep
showed that the Greenfield filter is capable of stopping both large and smaller emboli [4]. This underscores the importance of having in vivo studies to evaluate the clinical there is no substitute
studies
[5]. However,
evaluations
on filter
data is quite variable.
in addition to in vitro testing. In order efficacy of percutaneous IVC filters, for randomized, prospective clinical
even in the currently efficacy,
the quality
For instance,
numbers offilters placed conducted follow-up on pulmonary embolism by mail [7], and still other emboli were verified [8].
published
clinical
of the comparative
some
series
have high
for prophylaxis [6], other series have such important factors as recurrent clinical means, telephone contact, or series do not specify how recurrent Given these limitations, this review
Steel Filter
With its longer period of availability, the Greenfield stainless steel filter (GF; Medi-tech, Watertown, MA; Fig. 2) has had the most numerous clinical evaluations. It first was described in 1 973, and the first clinical series were published in 1977 [6, 1 0-1 6]. The GF design permits filling of 70% of the filter
cone by thrombus
with a reduction
in the filter’s
effective
cross-sectional area of only 50% [1 7]. Its construction consists of six stainless steel wires in a conical shape extending from a central hub, and the tips form a circular base with a maximal diameter of 30 mm (recommended for IVC sizes of 28 mm) [1 8]. Percutaneous insertion is performed via a 24French system from femoral or jugular routes, with specific carrier-introduction
atic. Although in vitro models may be helpful initially, they do not consistently reflect clinical reality and may be misleading. For example, Katsamouris et al. [3] demonstrated in vitro that the bird’s nest, Simon nitinol, Amplatz, and Gunther filters
Filter
This filter is mentioned for historical reasons only, because the Mobin-Uddin filter(MUF) is no longer available in the United States. It is constructed as an inverted umbrella with six flat stainless steel spokes, and covered with a thin Silastic membrane. A 23-mm-diameter size was originally used, but episodes of filter migration led to the development of a larger 28-mm filter[9]. The low rate of recurrent pulmonary embolism (0.5%) was overshadowed by the high prevalence of vena caval occlusion, 60-70%, and lower extremity venous stasis. With this major disadvantage, it is not surprising that the MUF was supplanted by the Greenfield filter when it became available.
Greenfield
7Fr
Umbrella
systems.
Misplacement or malposition of the filter into the renal veins, hepatic veins, or right atrium has been reported [1 9]. Asymptomatic penetration of the filter foot prongs through the vena caval wall occurs with some frequency although therate of clinically symptomatic vena caval perforation is low. Penetration has been described at multiple sites including the ureter, intestine, aorta, and vertebral body [1 5, 20]. The GF has a reported recurrent embolism rate of 5% [16, 21 ] and a vena caval occlusion rate of approximately 3-5% [6, 1 1 1 4-i 6]. Optimal filtration of caval blood flow results with angles less than 1 5#{176} tilt from the vertical; this was a potential long-term problem of the filter. Reduced filtration efficiency with tilting has been a muchpublicized disadvantage of the GF [3]. Subsequently published experiments in sheep, whose vena caval diameters ,
approximate toward
Greenfield
that of humans,
deteriorating
have shown
clot-trapping
that the tendency
performance
when
the
filter is tilted within the vena cava is not as dramatic
as once believed [4]. A possible explanation for this apparent discrepancy between clinical and experimental data may be that not all pulmonary emboli are symptomatic and that the Greenfield
filter
pulmonary
emboli,
protects
whereas
against
small
massive,
emboli
potentially
pass
through
lethal
the
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AJR:156,
Fig. filter.
filter
INFERIOR
April 1991
2.-A
and
and
B, Lateral
remain
(A) and
axial
asymptomatic.
(B)
radiographs
Significant
VENA
which
are
vein placement derived
from
is necessary.
limited
numbers
FILTERS
815
of Greenfield
thrombus
has
been observed on both sides of the filter on follow-up venacavography [21 ], yet may not be apparent on subsequent examinations. Possibly, these thrombi are lysed in situ by the flow of blood, or fragment further into sufficiently small sizes that they may pass through the GF and cause no clinical symptoms on reaching the lungs. Other thrombi are symptomatic, and for any patient with clinical or radiologic evidence of pulmonary emboli despite the presence of a Greenfield IVC filter, there should be a high suspicion for recurrent thrombus on the filter itself (Fig. 3). The GF’s established rate of high vena caval patency (9598%) is an advantage in those uncommon situations in which
a suprarenal
CAVAL
Fig. 3.-Venacavogram
obtained
proach shows thrombus tilted within vena cava.
(arrows)
with right superior
internal
to Greenfield
jugular filter,
vein apwhich is
These indications, of patients,
include
caval thrombosis extending above the renal veins, renal vein thrombosis, thromboemboli despite prior IVC interruption, or recurrent thromboemboli with a large, patent left ovarian vein (with or without thrombus itself) [22]. The large 24-French size of the stainless steel Greenfield filter system is its principal disadvantage. A 1 0-24% prevalance of sonographically identified femoral vein thrombosis
[23], most likely related injury
Newer Bird’s
locally,
is another
to venous important
dilatation
and endothelial
consideration. Fig. 4.-A configuration
Filters Nest and Modified
and
axial
(B)
venacavograms
of mesh
Filter (four
The bird’s nest filter (BNF; Cook,
Bloomington,
IN; Fig. 4)
was first tested clinically in 1 982 and has the advantage of a small sheath size, 1 2-French internal diameter in the modified version. Its mesh configuration consists of a series of pre-
shaped
and B, Lateral (A) of bird’s nest filter.
wires that are formed
by the operator
in a series of
maneuvers with a special applicator, and the wires assume an original shape that resembles a bird’s nest [24]. Initially, the mesh was affixed by a series of V-struts 0.25 mm in diameter, intended to hold the BNF securely within the IVC. However, in the original BNF model, five of 422 filters migrated
to
the
right
atrium
without
fatality,
and
one
to
the
pulmonary embolism)
artery with death 1 0 days later due to pulmonary [7]. The design of the BNF was modified, and a second-generation device with stiffer securing struts, 0.46 mm
in diameter,
has
had
no reported
episodes
of migration
[7]. The rate of recurrent pulmonary embolism reported is 2.7%, and the rate of caval occlusion is 2.9% [7]. However, this follow-up was largely clinical and consisted of telephone or questionnaire contact in 400 of the 440 patients after 6 months; sonography, venacavography, or pulmonary angiog-
GRASSI
816
Titanium
radiologic
The titanium Greenfield filter (TGF; Medi-tech; Fig. 7), actually a significantly modified design of the stainless steel GF, was created to provide a smaller introduction size for percutaneous insertion. Its design lacks a central apical hole for
follow-up
[25].
Additionally,
vena
caval
occlusion
perforation
of the caval
An advantage
wall has also been
identified
of the bird’s nest filter is its free-form
[25].
config-
uration within the IVC, because it is not subject to the need for centering as are several other filters. It can be inserted in vena cavas up to 40 mm in diameter. In very large vena cavas, it can eliminate the need to use bilateral iliac vein filters (Figs. 5A and SB), because a single bird’s nest filter will suffice
(Figs. 5C and SD). The free-form the filter mesh to include
alous veins (Fig. 6).
unexpected
nature allows positioning collateral
of
veins or anom-
Greenfield
April 1991
raphy was infrequently performed. Vena caval occlusion was documented in 1 9% of a subset of 40 patients who underwent
with phlegmasia cerulean dolens has been reported in one case that led to the patient’s death [26], and a significant Downloaded from www.ajronline.org by 117.255.237.195 on 10/09/15 from IP address 117.255.237.195. Copyright ARRS. For personal use only; all rights reserved
AJR:156,
Filter
guidewire insertion, and once the sheath and dilator are placed, the TGF carrier is passed directly under fluoroscopic
control. pressed ences
Its elastic properties permit the TGF to be corninto a 12-French carrier. The TGF has several differfrom
the stainless
Greenfield
filter:
it is broader
at the
base (38 mm vs 30 mm), lighter (0.25 g vs 0.56 g), and it exerts a force of fixation on the wall of the vena cava that is greater than the stainless steel Greenfield filter’s force at diameters
over
22 mm,
but less at diameters
under
22 mm
Fig. 5.-A-D, Venacavograms of large vena cava (A) that necessitated bilateral iliac vein filters when Greenfield filter was sole device available (B). A more recent case with a large vena cava (C) of 39 mm diameter was more easily managed with bird’s nest filter alone (D).
INFERIOR
April 1991
AJR:156,
VENA
CAVAL
FILTERS
817
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Fig. 6.-A and B, Venacavograms show large left-sided anomalous vein (A ) or collateral vein contiguous with left renalvein (B). By positioning a portion of the bird’s nest mesh well caudad (faintly seen on radiograph, small arrows in B), filtration of this extra vein was included.
A
[27].
TGF
filter,
is recommended
placement,
exceeding This
as for for
the
stainless-steel
caval
diameters
Greenfield up
to
but
not
28 mm.
filter
was
available
at selected
centers
for clinical
trials,
of vena caval perforation by the filter legs [27] (Belmont M, personal communication). One in vitro study published at a participating center in the clinical trials attributed this higher rate of caval wall perforation to the possibility of filter splaying associated with the physical design ofthe TGF, clot retraction, and the possibility of changes in intracaval pressures [28]. The design of the filter hooks has been changed to avoid but
these
were
terminated
caval wall perforation,
because
of a high
frequency
and the TGF is now available for clinical
use.
Vena-Tech
radiograph
and B, Lateral
of titanium (A) and axial
alloy version
of Greenfield
(B) photographs
filter.
of Vena-Tech
Filter
The Vena-Tech filter (VTF; Fig. 8) is the American-marketed and FDA-approved version of the LGM filter (L. 0. Medical, Chasseneuil, France). It has been accepted for use under a
510(K) application, that is, as a modification of a previously accepted device, the stainless steel Greenfield filter. Constructed
Fig. 7.-Lateral Fig. 8.-A filter.
of a cone
with
six flat,
metallic
diagonal
struts
and
side rails that run parallel to the walls of the IVC, additional small barbs hold the filter in place. The VTF comes prepack-
aged in a 1 0-French diameter
sheath.
inverted
when
carrier
and requires
Filter orientation transjugular
with the transfemoral
within
placement
a 1 2-French
outer
the carrier syringe is is used as compared
approach. The Vena-Tech filter has been evaluated in a series of 100 patients abroad reported in two different journals [29, 30], and clinical usage in the United States is under way. Of the 100 attempts at insertion, the internal jugular route had an
of 2% (two cases) and a 1 6% rate of (eight filters tilted 15#{176} or more, five filters opened and correctly aligned, and three filters opened and tilted) [30]. Follow-up at 1 year, including an abdominal radiograph, showed migration of the filter in 1 3% (nine cases inferiorly not exceeding the height of initial
failure
rate
malpositioning incompletely incompletely
one vertebral
body,
and four
superiorly
toward
the renal
veins). Clinical follow-up shows a rate of recurrent pulmonary embolism of 2%, and vena caval occlusions in 7% during 1year follow-up. An advertised advantage of the VTF design is the feature of “positive positioning” by means of the barbed side rails.
However,
as these
data indicate,
the prevalence
of initial
malpositioning is significant, and the rate of later migration is lower. It is likely that several of these malpositionings were operator-related, occurring early in the VTF experience. 5ev-
GRASSI
818
AJR:156,
April 1991
eral other malpositionings have been associated with jugular insertion. For best insertion, a technique of rapid deployment from the introducer should be used, with a quick motion of
release into the IVC. Downloaded from www.ajronline.org by 117.255.237.195 on 10/09/15 from IP address 117.255.237.195. Copyright ARRS. For personal use only; all rights reserved
In the United
States,
have reported Recently,
F.C. Taylor
65 successful
investigators
et al. (unpublished
placements
have
data)
with low morbidity.
cautioned
against
placement
above the renal veins and have avoided using the VTF from the left femoral vein because of malpositioning (Vogelzang AL, unpublished data). Several thousand LGM filters have been placed in Europe, and although United States experience is growing, further data will be necessary.
Simon
Nitinol
Filter
The Simon nitinol filter (SNF; Nitinol Medical Technologies, Woburn,
MA;
Fig.
9) is made
composed
of nickel and titanium,
properties.
The filter
wires
of a thermal
memory
alloy
which gives the filter unique
are in straightened
form
at cooled
temperatures (4-i 0#{176}C) and these re-form into a predetermined filter shape at body temperature [31]. The filter shape is that provide
of an umbrella dome with seven petal loops, which the major filtering, and six legs for fixation to the caval
wall. Insertion
is performed
with a cold saline infusion through
the plastic filter holder [32], and the device is easily inserted through a 7-French carrier with a 9-French outer diameter sheath. Both transfemoral and jugular insertion sets are available. The Simon nitinol filter has been accepted by the FDA (April 1 990) for clinical use. The multicenter clinical trials show a
Fig. 9.-Photographs of Simon nitinol filter in straight form (left), lateral view (lower right), and axial view (upper right).
within
carrier
symptomatic recurrent pulmonary embolism rate of 1.1%, and asymptomatic pulmonary embolism of 0.7%, detected by ventilation/perfusion
lung
scan,
or pulmonary
arteriogram,
added in select cases. The vena caval occlusion is 7.8%
(symptomatic)
and
1 .9%
rate reported
(asymptomatic),
with
the
latter detected by additional sonography, CT, or MR imaging (Simon M, Grassi CJ, Kim D, unpublished data). The SNF has a unique design and very appealing small introduction
size.
Its
memory-wire
properties
enable
it to
achieve the smallest introduction size of all the filters. The “SNF 7/6” (seven dome loops and six legs) rate of vena caval occlusion necessary
appears to be slightly higher; however, to see how its long-term caval patency
it will be compares
with those of the bird’s nest and Vena-Tech
filters with more
clinical
be made.
Current
usage,
before
a final
comparison
can
Indications
With the increase in percutaneous filter placement by using small French systems, and greater experience with the natural
outcome
of venous thrombosis, the indications for vena caval filters have been expanded. There are now three major cate-
gories for filter placement
in venous
thromboembolism:
con-
traindication to anticoagulation, failure of adequate anticoagulation therapy, and prophylactic placement in high-risk patients. Of these, the first two categories are well established [10, 1 7, 33] and apply to the older and newer filters. However, the
role of vena cava filter placement in patients thrombosis that develops despite adequate
with deep venous anticoagulation is
less clear. Most agree that the presence of iliofemoral thrombosis is a high-risk factor for pulmonary embolus, and they will place a filter when anticoagulation 33]. This risk is significant particularly floating femoral or iliac vein thrombus
is contraindicated
in patients greater
[10,
with free-
than
S cm in
length [34]. The third category, prophylaxis for high-risk patients (e.g., before neurologic, spine, or hip surgery, and patients with paraplegia or pelvic fractures), has evolved largely because the percutaneous IVC filter is such an attractive therapy that its placement in patients without established pulmonary embolism or deep venous thrombosis has been advocated [10, 35]. It is my belief that the ease of insertion should not lead to an uncontrolled situation in which technology becomes the motivating force for IVC filter placement. Rather, firm medical
indications should be the prime determinant of which patients receive vena caval filters [36, 37]. One indication for prophylactic filter use is in the setting of cor pulmonale in patients with severe sion. These patients may not tolerate nary embolus [38], and filter placement
Additionally, when a previous has migrated, or has functionally embolus,
a second
vena caval
pulmonary hypertena subsequent pulmohas a valuable role. IVC filter has been misplaced,
failed to prevent
pulmonary
filter can be added
(Fig. 10).
AJA:156,
INFERIOR
April 1991
VENA
Contraindications Contraindications
to percutaneous
filter
placement
of all
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types include the relatively uncommon situations in which surgical venotomy and closure may be preferred. Patients with severe blood coagulopathy predisposing them to bleeding from the puncture site, patients who cannot comply with postprocedure rest orders (especially
or will not with older
24-French system), and those with obstructing thrombus along all available routes of transvenous insertion are included. Traditionally, placement of a permanent IVC filter has been discouraged
in the
expectancy.
There
gevity
of these
young,
and
are no strict
filters
in patients guidelines,
in the human
with
a long
life
the
Ion-
because
body
can only
be esti-
should
be ob-
mated. Technique
Before
filter placement,
a venacavogram
tamed, which is another reason why percutaneous filter placement should be performed by interventional radiologists who
are prepared
to perform
venacavography
by means
of cut
CAVAL
FILTERS
819
The newer IVC filters require careful percutaneous technique, as do all filter devices. For punctures of the femoral or jugular
vein,
a single-wall
puncture
technique,
preferably
with
a percutaneous entry needle, is recommended. During the insertion of this open-ended needle, continuous suction is applied with an attached syringe, and a visual check is made for any arterial blood. If arterial blood is obtained, the needle is removed, and the puncture is performed again. I prefer a single-wall technique in order to avoid the complication of arteriovenous fistula [39]. Puncture of the right internal jugular vein is performed with a similar technique [1 1 ], by using a venous puncture midway between the mastoid tip and the sternal notch, after visualization of the venous pulsation. The use of mild Trendelenberg positioning of the patient at the start of the procedure aids in a jugular venous distention, and having the patient sitting when the venous introducer is withdrawn facilitates hemostasis at the puncture site on the right side of the neck. For the choice of access route, just as percutaneous transvenous access has become favored over surgical venotomy, so has the transfemoral vein route become popular with the newer filters because it is well tolerated by the patient and
film, digital subtraction angiography, or cineangiography. Venacavography is necessary [36] for obtaining information (1) to check IVC patency and the extent of thrombus, if any, within the vena cava or along the route of intended filter
vein is most commonly used. The left femoral vein route can be used; however, greater resistance in filter passage due to the angle of the common iliac vein into the inferior vena cava
delivery;
can be encountered
(2) to determine
the caval diameter
and the suitability
of the intended filter device; and (3) to delineate the anatomy, including location of the renal veins, possible
anomalies,
and any significant
collateral
vessels.
IVC IVC
straightforward
for the
physician
operator.
[13], especially
The
right
with the 24-French
femoral
intro-
duction system. Some have avoided the left femoral vein approach in 97% of patients [25], yet others have experienced no more difficulty from the left side than from the right [1 1].
Fig. 10-68-year-old woman with a Greenfield filter in place who had recurrent shortness of breath. A, Abdominal radiograph shows abnormal widening of filter base (arrows) to 38 mm (normal, 28 mm); this is virtually infrarenal cava by foot process of filter. B, Venacavogram confirms perforation of caval wall and shows filling defect of thrombus within filter (arrow). C, Radiograph shows Simon nitinol filter that was added within true vena caval lumen inferioriy (arrowheads) for treatment.
diagnostic
of perforation
of
820
GRASSI
TABLE
2: Comparison
Filter
of Five Inferior
Type
Vena
Caval
Carrier
Size
Size in French
(OD)
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29 14
24 12
Bird’snest
14
11
Vena-Tech
12
10
9
7
Greenfield
stainless
Greenfield
titanium
Simon
steel
nitinol
Note.-OD = outer diameter. Manufacturer’s recommendation
a
before
surgical
procedures
At our institution, the left femoral vein approach has been useful in the past, even with the 24-French Greenfield system (six [9%] of 68 patients in 1 year). With the new, smaller introduction systems (outer diameter 1 4-, 1 2-, 9-French), the past sequence of access choice (first, right femoral vein;
internal jugular vein; third, left femoral vein) is chang-
ing, with a trend toward more transfemoral placements from either the right or left side. The advantages of femoral, compared with jugular vein, puncture do include avoidance of the risks of air embolism, pneumothorax, and inadvertent puncture of the carotid artery, as well as the fact that radiologists
generally are more familiar with puncture of the femoral vein. External jugular [40], subclavian, and even brachial vein insertions formed.
(Brown
A, personal
Filter Advantages
communication)
have
been
per-
and Disadvantages
As shown in Table 2, the smaller introduction size is a significant advantage for the newer generation filters available for clinical use. The versatility of accommodating larger vena
caval sizes up to 40 mm is an added advantage
of the bird’s
nestfilter since the titanium Greenfield, Vena-Tech, and Simon nitinol types are limited to caval sizes up to 28 mm. Because of this size versatility, a radiology department that can afford to keep only one filter on inventory for all patients should logically choose the bird’s nest filter. However, the bird’s nest filter’s stainless steel construction
poses a relative disadvantage, MR imaging construction.
(IVC)
Introducer in French
second,
AJR:156,
because
has introduced Those devices
are ferromagnetic,
whereas
the increased
composed
Maximum
IVC Diameter
requiring
Yes Yes No Yes
28 (24)
No
anesthesia.
rapidly
and effectively
data) [43]. In the future, constructed
of high-strength,
The 24-French
(Grassi
CJ et al., unpublished
it is likely that all IVC filters
Greenfield
nonferromagnetic
will be
materials.
filter has one relative advantage,
that is, its well-documented rate of high vena caval patency. It is indicated for use in the uncommon situation of suprarenal vein placement [22] with the attendant risk of thrombosis and renal compromise, at least until more experience can be accumulated with suprarenal placement of the newer IVC filters to confirm their patency in this position. At our institution, the bird’s nest and Simon nitinol devices are used. The Simon nitinol filter is valuable when the smaller
9-French
percutaneous
puncture
is advantageous,
or where
the longitudinal distance between the renal veins and iliac bifurcation is reduced, favoring the shorter 3-cm length of the Simon nitinol over the bird’s nest. The bird’s nest filter is used routinely. Specifically, it is the only filter device suitable at this time for vena caval sizes between 29 and 40 mm diameter.
Conclusions A group of new, now available, each
will
by, nitinol, or beta-Ill titanium alloy are less ferromagnetic [41 42]. Although the heat or torque effects on the filter or adjacent structures do not appear to be detrimental to patient’s safety during routine clinical imaging [41], filters fabricated from stainless steel are highly ferromagnetic and create marked magnetic susceptibility artifact on MA. This artifact
Significant?
28 28 40 28
general
formed
existing
of elig-
Tilting
Recommended (mm)
Further prospective
a new consideration for filter fabricated from stainless steel
those devices
Filters
as described.
use of
April 1991
smaller percutaneous with its advantages
filter devices are and disadvantages,
The ideal vena caval filter is not yet available.
clinical study
trials of these are necessary,
devices with randomized, in order to further refine the
filters and to assist in the development
be superior
for
the
prevention
of a filter that
of pulmonary
embolism.
Until that time, the choice of an IVC filter from those available should be based not only on the interventional radiologist’s
preference, filter’s
but also on the specific
clinical situation
and the
performance.
,
degrades
abdominal
imaging.
noninvasive method of assessing presence of intracaval thrombus,
a nonferromagnetic intracaval
filters
As MR imaging
filter is clear. Gradient-echo and
trapped
provides
a
vena caval patency and the the potential advantage of thromboemboli
imaging can
be
of per-
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