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Technique
Access is obtained through popliteal vein puncture under ultrasound guidance and the
device is advanced through the thrombosed veins to unclot them. Most catheters are used
in association with chemical thrombolytic agents.
One of the technical aspects is the need for IVC filter. This technique has a risk of PE
due to intrathrombus maneuvers and particulate embolization, mainly in the absence of
thrombus aspiration. Thus retrievable filters are commonly used while performing mechanical
thrombolysis.
Results
So far, published reports are few and are summarized in Table 4 (29,53–56).
Table 4 Published Results of Percutaneous Mechanical Thrombectomy for DVT
Study Thrombus removal
Adjunctive
techniques Complication rate Results
Gandini 75% complete Filter 100% Death 12.5% 75% patency at
24 months
12.5% partial
Kasirajan 24% O90% TL: 53% Improvement
82%
35% 50–90%
Delomez 83% partial Filter 100% Death 6% 91% minimal
sequelae at
30 months
Stent 11%
Bush 65% complete Filter 35% Death 0% Improvement
74% at D1
35% partial TL: 35% Bleeding 13%
Stent 61%
Vedantham 83% O50% TL: 100% Bleeding 6% Improvement
96%
Abbreviations: DVT, deep venous thrombosis; TL, thrombolysis.
Source: From Refs. 50–54.
Table 3 Devices Used for Mechanical Thrombolysis
Incomplete wall contact Complete wall contact
Angiojet Arrow trerotola
Oasis Cragg brush
Gelbfish endovac MTI-castaneda brush
Thrombex PMT Prolumen
Amplatz thrombectomy device Solera/Fino
Hydrolyser Cleaner
X-Sizer Prolumen
Rotarex
Trellis reserve
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Indications
These are the same as for thrombolysis due to the fact that use of thrombolytic agents is
commonly associated with the technique.
RESPECTIVE INDICATIONS
To date, mechanical thrombectomy has yet to be proven effective and no device has FDA
approval in the treatment of DVT.
According to the literature, thrombolysis should be the preferred method due to its
lower invasiveness compare to surgical thrombectomy.
In cases of femoral-popliteal DVT, thrombolysis should be performed whenever
there is no contraindication.
In caseof iliofemoral DVT,an algorithm was proposed bythe AmericanVenous Forum
guidelines (13). According to this, thrombolysis should be the method of choice.
Nevertheless, thrombolysis has non negligible rates of complications mainlydue to bleeding.
Moreover, contraindications are limiting its applicability (75% in our experience), and long
term patency and valve preservation rates are unknown, but mid-term results do not reach
those of surgical thrombectomy. Thus,we believed thatvenous thrombectomy with AVF and
stenting in case of residual lesions remains the best option to treat iliofemoral DVT when
performed by trained teams and while respecting strict indications.
KEY POINTS
† The primary aim of DVT treatment is to avoid progression and prevent
pulmonary embolism and the postthrombotic syndrome.
† Heparin prevents progression but does not remove thrombus.
† Surgical thrombectomy should be considered for recent and proximal DVT in
patients with a good life expectancy.
† The thrombosis should be less than 7 days old.
† Pregnancy, post-delivery, and thrombolytic treatment failure are not contraindi-
cations to venous thrombectomy.
† CT angiography is the investigation of choice to delineate the thrombus and
exclude malignancy.
† At completion of surgical thrombectomy, an arterio-venous fistula is constructed
to aid patency.
† Thrombolysis can be considered in patients with normal life expectancy and
thrombosis of !10 days duration.
† Major bleeding occurs in 11% of patients, mostly at the puncture site.
† Thrombolysis offers advantages in reducing postthrombotic syndrome and
maintaining venous patency.
† Adjunctive techniques to both surgical thrombectomy and thrombolysis include
venous angioplasty +/K stenting for residual stenosies.
† Surgical insertion of IVC filters or interruption of the IVC is rarely required
since the development of percutaneous filters.
Surgery and Endovascular Therapies in DVT 219
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17
Inferior Vena Cava Filters
Sumaira Macdonald
Northern Vascular Centre and the Department of Radiology, Freeman Hospital,
Newcastle upon Tyne, U.K.
THE SCOPE OF THE CLINICAL PROBLEM
Venous thromboembolism (VTE), defined as including any thromboembolic event occur-
ring within the venous system, encompassing deep venous thrombosis (DVT) and pulmo-
nary embolism (PE), continues to pose a major health problem.
There are no reliable studies of the incidence or prevalence of VTE in the United
Kingdom. A prospective Scandinavian study found an annual incidence of 1.6/1000
people in the general population (1). In another longitudinal Scandinavian study, the
incidence of DVT was 2 per 100,000 observation-years, with corresponding incidence
rates of 98 for nonfatal PE, 107 for fatal PE and 387 for all venous embolic events (2).
In the United States, the incidence of VTE exceeds 1 per 1000. Over 200,000 new cases
occur annually. Of these, 30% of patients die within 30 days, one-fifth suffering sudden
death as a result of PE (3). Of those surviving VTE, 30% will develop recurrent disease
within 10 years. Around 28% will develop venous stasis syndrome within 20 years (3).
One postmortem study estimated that 600,000 people develop PE each year in the
United States, of whom 60,000 die as a result (4).
The calculated prevalence of DVT depends on the extent to which all laboratory
records are searched and misclassification of patients represents a major problem for
investigators working exclusively from ICD-9-CM coded data. If records of patients who
have undergone venous ultrasound or contrast venography are reviewed in addition to
discharge summaries, the overall prevalence of DVT in adults over 20 years of age in a
general hospital setting in the United States has been found to be 0.78% (271 of 34,567
patients) (5). Twenty-one percent of this population suffer PE. This figure included those
patients treated prophylactically with low molecular weight heparin (LMWH).
Anticoagulation remains the treatment standard for venous thromboembolic disease
with satisfactory outcomes in 90% of treatment cases. Heparin has been shown to decrease
the risk of fatal PE by 75% and to reduce the risk of recurrent PE from 25% to 2% (6).
Long-term warfarin therapy reduces the incidence of documented DVT from 47% to 2%.
Patients with VTE who receive adequate anticoagulation generally do not die of recurrent
disease. However, it should be noted that patients who are treated for PE are almost four
times more likely (1.5% versus 0.4%) to die of recurrent VTE in the next year than are
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patients who are treated for DVT (7), indicating that this population is at the higher-risk
end of the spectrum of diseases that characterize VTE.
Recurrence rates however, may be surprisingly high; as many as 33% of patients
develop a second PE while receiving adequate anticoagulation therapy. This fact supports
an alternative treatment strategy, namely caval filtration.
INFERIOR VENA CAVA INTERRUPTION: AN EVOLUTION
One of the earliest techniques for the prevention of PE in the setting of proximal DVT was
pioneered by John Hunter, when he ligated the femoral vein at the level of the thrombus.
Homans later addressed the problem by the ligation of both femoral veins. When it became
clear that neither of these approaches would reliably prevent recurrent PE, vena caval
interruption, involving laparotomy under general anesthesia was performed. These
methods were used in parallel with anticoagulation once heparin and warfarin became
available in 1935 and 1948 respectively. These procedures were associated with
substantial morbidity from lower extremity edema, venous stasis ulceration and the post-
thrombotic syndrome. Furthermore, the potential benefits of these early procedures were
negated by the fact that retroperitoneal collaterals subsequently developed, exposing the
patients to the risk of recurrent PE in upto 15% of cases. Mortality following ligation
was also unacceptably high, ranging from 4% in low-risk cases to 39% in those with
significant cardiorespiratory co-morbidities (8). Ligation of the inferior vena cava (IVC)
was performed initially in patients with clot burden above the level of the superficial
femoral veins. Eventually, this replaced lower-level venous ligation. The operative
mortality was not significantly different but a lower rate of recurrent PE was reported.
The optimal level for ligation was located immediately below the renal veins to prevent
thrombosis due to venous stasis between the interrupted IVC and the renal veins.
Immediate lower limb swelling occurred in 10–16% of cases.
External caval clips (Moretz clip, Miles clip, Adams-DeWeese clip) and sutures or
staple grids were subsequently used in an attempt to provide channels to allow unhindered
venous return while preventing PE. These procedures also required laparotomy and
general anesthesia. The incidence of limb edema was reduced but the rates of recurrent PE
and operative mortality were unchanged. Despite the partial interruption of venous return,
caval occlusion rates of 30%–40% were reported.
In the late 1960s, methods were developed that allowed caval interruption devices to
be placed directly into the vena cava through the femoral or jugular vein via a small
surgical incision under local anesthesia. The first endoluminal filter was devised in 1967,
the Mobin-Uddin umbrella (9).
The major complications associated with this device included IVC thrombosis in up
to 60% of cases and device migration at a rate of 0.4%. As a result of these complications,
this device was withdrawn from the market. The first percutaneous insertion of
a Greenfield conical filter was performed in 1984 (10,11). Perhaps as a result of its
unique cone geometry, the long-term patency rate has been shown to be over 95% for over
three decades (12). Mathematical modeling and in-vitro studies have demonstrated that the
unique design allows upto 70% of the cone volume to be filled with thrombus before
significant reductions in blood flow occur.
First generation filters were delivered through a 24 French (8 mm) delivery system
resulting in a high incidence of insertion site complications. Naturally, this prompted
technical refinements and the development of modern low-profile filters delivered through
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6 to 10 French introducer systems, which have reduced the incidence of access site
complications. Most of the newer generation filters are made of titanium, nitinol or
stainless steel alloys that have low ferromagnetic properties, rendering them safe in
magnetic resonance imaging (MRI) scanners although imaging may be somewhat
degraded by artefact.
FILTER TYPES AND DESIGN
IVC filters are designed for their physical properties, efficacy at trapping clots, ability to
preserve flow in the IVC, and ease of placement. Each of the currently available filters
achieves some, but not all, of the following ideal properties:
† The filter should maximize clot capture in order to prevent new or recurrent PE.
† The filter should be nonthrombogenic and maintain caval patency
† The filter should be made of a biocompatible material that is durable
and noncorrosive
† The shape and structural integrity of the filter should be durable
† The delivery system of the filter should have a low profile and promote
easy placement
† Clot trapping should be reasonably effective even if filter deployment is
suboptimal, for example, many deployed filters assume a tilted angle in the cava
† Migration after deployment should be minimal
† The filter should not cause caval perforation
a
† Preferably, the filter should be nonferromagnetic to allow safe subsequent
MRI imaging.
The most frequently used filters at the current time are permanent and
retrievable models.
Temporary Filters
Temporary filters, which are attached to catheters that protrude from the access site and
can be secured in the subcutaneous tissues (much as would an untunneled central venous
line), are much less frequently used. Temporary filters include the Tempofilter, (B Braun
Medical Inc, Bethlehem, Pensylvania, U.S.A), the Gu
¨
nther temporary filter, (Cook,
Leechburg, Pennsylvania, U.S.A.), the Prolyser (Cordis Corporation, Warren, New Jersey,
U.S.A.), and the Antheor filters (Boston Scientific, Natick, Massachusetts, U.S.A.). These
filters can be left in situ for around six weeks. In an in-vitro study, temporary filters
demonstrated better clot capture efficiency than permanent filters (13) but they are
associated with an appreciable risk of migration (fatalities have been reported with the
Tempofilter) (14), filter thrombosis and a potential risk of sepsis.
a
Extension of the filter struts beyond the IVC, which is suggestive of perforation, has been noted in
high incidence on CT. Recent animal studies evaluated the apparent vena caval penetration
following placement of the Greenfield filter (15). All filters appeared to penetrate the IVC on
cavography and CT. Laparoscopy failed to demonstrate penetration, and histology revealed
remodelling of the intimal surface of the IVC and thinning of the adventitia. The authors further
hypothesized that IVC adaptation and remodelling occurred due to the presence of the filter.
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Permanent Filters
Currently available permanent filters include; the stainless steel Greenfield, the titanium
Greenfield (Boston Scientific), the LGM VenaTech (B. Braun Medical Inc), the Simon
Nitinol (CR Bard, Murray Hill, New Jersey, U.S.A.), the Bird’s Nest filter (Cook), and
the TrapEase (Cordis Corporation). Currently, only the Bird’s Nest filter is licensed for
use in mega-cava (over 30 mm in diameter), and is sufficient to provide adequate
filtration up to 40 mm. The other filters have a working range between 28 mm and
32 mm. The caveat is that the IVC is flattened on an anteroposterior image taken during
venography for filter placement and this measurement is likely to represent the largest
caval diameter. A measurement taken perpendicularly is likely to be much smaller and
this can be readily appreciated on axial computed tomography (CT). All the filters named
are United States Food and Drug Administration (FDA) approved and Conformity
European (CE) marked.
Currently there are no prospective data comparing the clinical efficacy and
complications of these devices. There are a number of retrospective case series for each
device but heterogeneity in patient selection, indications for treatment and definitions of
technical and clinical success make meaningful comparison difficult (16).
Retrievable Filters
The newer generation of retrievable filters have potential benefits in that they may be
utilized to prevent PE during the time when the patient is at increased risk, for example in
a multiple trauma setting, thereby harvesting the benefits of shorter-term survival benefit
from PE, while avoiding the risks associated with permanent placement (which includes
filter thrombosis, caval thrombosis and lower limb edema). Retrievable devices may be
retrieved percutaneously after varying periods, without the requirement for an
indwelling catheter.
Retrievable filters include:
† Gu
¨
nther Tulip (Cook). This may be retrieved upto 14 days following placement.
It must be retrieved via the jugular vein although it may be initially placed via
the femoral or jugular routes
† OptEase (Cordis). This may be retrieved up to 14 days post-placement.
The Optease can be deployed from either the femoral or the jugular approach
using the same system. Currently, it is the only retrievable filter that can be
recovered from a femoral approach. One potential benefit of the femoral
approach over the jugular approach during retrieval is the avoidance of the heart,
thus lessening possible myocardial injury or arrhythmia
† The ALN (Pyramed, Surbiton, Surrey, United Kingdom) can be removed after
an indefinite period of time
† The Recovery (Bard) also has no upper limit on time to safe removal. A small
prospective analysis of the Recovery filter in 32 patients, indicated a mean
implantation period of 53 days (range: 5–134 days) (17).
INDICATIONS FOR USE
It must be appreciated that unlike anticoagulant therapy, vena caval interruption is an
incomplete treatment of venous thromboembolic disease. Caval filtration has no beneficial
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effect on the prevention of DVT, or on the prevention of DVT extension, recurrence, and
subsequent postphlebitic syndrome. As anticoagulant therapy effectively prevents PE in
the majority of patients with DVT, only absolute contraindications to and documented
failures of anticoagulant therapy in patients with acute VTE represent obvious and widely
accepted indications for caval interruption (18). It may be considered that controled trials
would be unethical in these settings. However, in certain populations, most patients may
have neither of the two main indications (19).
Use of filters in a prophylactic sense, in patients at high risk of but with no
documented evidence for VTE, or adjuvant caval filtration for patients with VTE who can
receive anticoagulant therapy remain a matter of debate (18,20). The prevailing
uncertainties in clinical use of caval filters is highlighted spectacularly in the huge
variation in practice between countries; from 3 to 140 per million inhabitants per year in
Sweden and the United States, respectively (21).
Although categorical indications for filter placement have been given, as
recommended by the Vena Cava Filter Consensus Conference (Table 1) (22), various
thresholds exist among clinicians, and there is scarce level-1 evidence to support practice.
The rate of prophylactic placement appears to be increasing. Greenfield has reported
a summary of 642 placements over 27 years (23). Of note is the increasing use of caval
filters in the prophylactic setting (11% of placements in 1977 and 32% in 1999), and the
reduction in number of placements for failure of anticoagulation (38% in 1977 and 10%
in 1999).
Free-floating iliofemoral thrombus is a relatively rare entity but it comprises
a commonly proposed indication for caval filtration (24). A retrospective review of
78 patients with documented iliofemoral DVT treated with anticoagulation concluded
that there was an extremely high rate of PE, i.e., 60% among those with free-floating
thrombi (25).
Several other retrospective studies have reported similar outcomes but a prospective
analysis of 95 patients reported no significant differences in the rates of PE between
patients with (3.3%) or without (3.7%) free-floating iliofemoral thrombi treated with
anticoagulation (26). Differences in study populations may explain the conflicting
conclusions but the use of caval filters in this clinical scenario remains controversial.
Table 1 Categorical Indications for Filter Placement
†Contraindication to anticoagulation (absolute or relative), e.g., thrombocytopenia
†Complication of anticoagulation
Hemorrhage: major or minor
Skin necrosis
Drug reaction
†Failure of anticoagulation, i.e., objectively documented extension of existing DVT or a new
DVT or PE while therapeutically anticoagulated
†Evidence/probability of poor compliance with anticoagulation therapy
†Prophylaxis: no thromboembolic disease, i.e., multiple trauma
†Prophylaxis in patients with thromboembolism in addition to anticoagulation, e.g., those
scheduled for major orthopedic or pelvic surgery
†Failure of previous device to prevent PE; central extension of thrombus through an existing filter
or recurrent PE
†In association with another procedure: thrombectomy, embolectomy, or lytic therapy
Source: From Ref. 22.
Inferior Vena Cava Filters 227
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