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There are four main categories of patients who could be at high risk for
thromboembolic events and may constitute an indication for prophylactic filter placement.
These are:
1. Patients with DVT who are about to undergo surgery (lower-extremity
orthopedic surgery, major abdominal surgery, neurosurgery)
2. Patients with chronic pulmonary hypertension and a marginal cardiopulmonary
reserve
3. Patients with cancer
4. Trauma patients
The records of 32 cancer patients who were treated with heparin and warfarin for
thromboembolic disease were reviewed in a study published in 1981 that concluded that
standard techniques for anticoagulation were reported to be neither safe nor effective in this
population. Sixteen patients experienced 21 different hemorrhagic complications. Eight
patients had major hemorrhages that led to cessation of therapy or death. Six of 32 patients
had PE while receiving anticoagulants. It was suggested that venous interruption could be
a safer and more effective method of prophylaxis against PE in cancer patients (27). This
conclusion was disputed by the American College of Chest Physicians Consensus
Committee on Pulmonary Embolism (28), which stated that the case for the routine use of
caval filters in patients with cancer and DVT or PE was not supported.
Patients withsevere trauma are at riskof VTE. In many such patients,anticoagulation
is contraindicated on the basis of an unacceptably high risk of hemorrhage.
Other conservative methods, such as foot pumps and compression devices may not
adequately prevent DVT. Examples of patients in this category include; patients with
severe head injury and prolonged ventilator dependence, major abdominal or pelvic
penetrating injury, spinal cord injury with or without paralysis, severe head injury with
multiple lower extremity fractures and pelvic fracture with or without lower
extremity fracture.
A case-controled study on caval filters in trauma patients was reported in 1996.
The results indicated that vena cava filters may have reduced the incidence of PE in
multiple trauma patients, that mortality from PE had been reduced as a result of caval
filtration and that overall mortality was noted to be reduced. The study was not adjusted for
confounding factors and not validated in an independent set of patients. It was set in
a tertiary center in the United States. There were 120 patients (mean age 42 years, 63%
male). Forty patients were multiply injured and had survived more than 48 hours, with three
or more risk factors for PE, compared with 80 retrospective matched controls. Patients were
excluded if they were younger than 56 years, or had an injury score of !16. All patients
had VTE prophylaxis (antiembolism—TED stockings, plus or minus heparin). As a non
randomized trial, it is likely that the benefits of caval filters may have been overestimated.
The PE mortality was high, i.e., around 60% of cases, compared to the more commonly
quoted rate of around 2.5%. Also, the filter group in this study were older, had less severe
injuries and were immobilized for longer, all of which would comprise important
confounding variables.
A review of 4093 titles yielded 73 articles for meta-analysis of prevention of
VTE after injury (29). A random-effects model was used for all pooled results. Study
quality was evaluated by previously published quality scores. The incidence of DVT
and PE reported in the included studies varied widely. The pooled rates were 11.8% for
DVT and 1.5% for PE. Only a few randomized controled trials evaluated the methods
of VTE prophylaxis among trauma patients, and combining their data was considered
difficult because of different designs and differences in the preventive methods used.
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The quality of most studies was considered low. Meta-analysis showed no evidence that
low-dose heparin, mechanical prophylaxis, or low-molecular-weight heparin were more
effective than either no prophylaxis or each other. However, the 95% confidence
intervals of many of the comparisons were wide; therefore, a clinically important
difference may exist. The review concluded that the trauma literature on VTE
prophylaxis provided inconsistent data and highlighted a need for a large high-quality,
multicenter trial that could provide definitive answers. In Part II of this two-part review
(30), the role of caval filters was analyzed. The same methodology was employed as in
Part I of the review. It was noted that spinal fractures and spinal-cord injuries increased
the risk of DVT two-fold and three-fold respectively. Patients with DVT were
approximately nine years older than those without DVT. No specific cut-off point for
increased risk could be established because data could not be combined across studies.
Patients with prophylactically placed vena cava filters had a lower incidence of PE
(0.2%) compared with concurrently managed patients without caval filtration (1.5%) or
historical controls without caval filters (5.8%). The results report on uncontrolled
studies with observational design; nevertheless, the authors concluded that placement of
a caval filter in selected trauma cases may decrease the incidence of PE. The need for
future trials was again emphasized.
THE USE OF CAVAL FILTERS OUTSIDE OF THE TRAUMA SETTING:
THE EVIDENCE BASE
Girard and associates performed a systematic review of the literature in an attempt to
clarify the indications for filter placement (31). A systematic MEDLINE search produced
a total of 568 references with abstracts between 1975 and 2000 inclusively. Each reference
was analysed to predetermined criteria. A similar search was undertaken for heparin
and thromboembolism.
The annual number of publications ranged from one in 1976 to 42 in 1994 and 1998.
Retrospective clinical series (nZ189) represented exactly one-third (33.3%) of all
publications, with only 59 series reporting on R100 patients, and 90 series reporting on
!50 patients. Case reports (nZ180) represented nearly one-third of the literature
(31.7%). Animal studies (nZ38) and in vitro work (nZ35) represented 12.9% of the
literature. Prospective series accounted for only 7.4% of the literature. Among prospective
studies, only 16 series (2.8% of the entire library) included R100 patients, and there was
only one randomized controled trial, representing 0.02% of the library. Among the 16
prospective studies, nine series were partial and/or updated reports from the same authors
and/or on the same patients. There were 26 clinical series reporting mainly or exclusively
on prophylactic IVC interruption in trauma or major orthopedic surgery patients, all
originating from the United States. Only one of these was a prospective series of O100
patients. Sixty of the 568 references (10.6%) reported on temporary filters, with only one
prospective series of R100 patients. The annual number of publications ranged from
one article in 1985 to 10 articles in 1995.
By comparison, 531 references concerning heparin therapy in DVT were found,
and of those, two-hundred and fifty-two articles (47.7%) reported randomized controled
trials.
In 1998, Decousus et al. published the only randomized trial of vena cava filters in
the prevention of PE to date (32). This was an unblinded concealed randomized trial
without intention-to-treat and took over three and a half years to complete in 44 centers
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in France. Four-hundred patients were randomized using a 2!2 factorial design to caval
filter or no caval filter and a LMWH (enoxaparin) or unfractionated heparin. The mean
age was 73 years (range 60–94 years), and 50% were male. Inclusion criteria were an acute
proximal deep vein thrombosis, diagnosed by venogram, in a patient considered to be at
high risk for PE. Four different types of caval filter were employed. These included the
titanium Greenfield, Bird’s Nest, LGM Vena Tech and Cardial (CR Bard). All were
placed within 48 hours of diagnosis. Ventilation-perfusion scans were performed at
baseline and after 8 to 12 days of anticoagulation. Vena cava filters were associated
with a significant decrease in the incidence of PE compared with anticoagulation alone
(1.1% versus 4.8%, pZ0.03) at 8 to 12 days of follow-up. After two years, however, this
difference was no longer statistically significant, although the trend favoured caval
filters (3.4% versus 6.3%, pZ0.16). Symptomatic PE occurred at a similar frequency in
both groups after three months (filter, 4%; no filter, 6%). Fatal emboli were more common
among patients treated solely with anticoagulation (0.5% vs. 2.5%). In contrast, vena cava
filters were associated with significantly more recurrent DVT than anticoagulation
alone (20.8% vs. 11.6%, pZ0.02). There was no difference in bleeding or overall
mortality. Sixteen of the 37 patients (43.2%) with vena cava filters who had recurrent
DVT also had IVC thrombosis (8% of the filter population).
The authors concluded that in high-risk patients with proximal DVT, the initial
beneficial effect of vena cava filters for the prevention of PE was counterbalanced by an
excess of recurrent deep-vein thrombosis, without any difference in mortality.
Clearly, vena cava filters in combination with standard anticoagulation do appear to
offer significantly more protection from PE than anticoagulation alone. This additional
protection, however, appeared to be short-lived and did not decrease overall mortality. In
addition, vena cava filters were associated with a higher incidence of recurrent DVT over
two years of follow-up.
Because almost all participants (94%) in this trial received anticoagulants for at least
three months, however, the outcomes of these patients cannot be generalized to the typical
patient with a filter who does not receive anticoagulation. A further limitation of the trial
includes lack of clarity in how high-risk patients were defined. It is also not clear whether
patients would have received only positive benefits if filters had been removed after a few
weeks, whether patients with thrombophilia would differ in terms of outcomes and
whether filters could be an alternative to anticoagulation. Lastly, the data presented at two
years reflect the all-cause mortality as the outcome measure of net clinical benefit, with
those deaths in the filter group attributable to hemorrhage, myocardial infarction,
respiratory failure and renal failure. Arguably, filter efficacy relates specifically to PE
mortality. The reduction in symptomatic PE at 2 years with a filter (pZ0.16) may not have
reached statistical significance because of the sample size. The study was originally
designed for 800 patients.
The Michigan Filter Registry contains data for a prospective cohort of 2188 patients
with a Greenfield filter (33). Data on the percutaneous stainless steel Greenfield were
extracted in order to compare outcomes with the titanium Greenfield filter. Since 1995,
600 percutaneous stainless steel Greenfield filters were placed in 599 patients. A one-year
mortality rate of 42% left 349 patients available for annual follow-up, and studies were
completed for 231 (66%). Periprocedural events occurred in 2.5% of cases with associated
morbidity in 1.5%. The rate of new PE was 2.6%, and vena caval patency was 98.3%.
The combined rate of new VTE was 12.5%. Left-sided femoral vein placements increased
to 20%, and the major indication for filter placement had become for prophylaxis (46%).
It was concluded that the ease of use and favorable patient outcomes for the percutaneous
stainless steel Greenfield have resulted in more frequent placement for prophylactic
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indications. This registry provides important data and is notable for its size but is limited in
a number of ways. It reflects a heterogeneous population, i.e., prophylactic use has doubled
since 1993, follow-up imaging comprised ultrasound in many cases and outcomes were
“indeterminate” in 35 cases. Twenty percent of the original retrospective study data which
were subsequently incorporated into the registry was missing (34). In common with many
registries, it is likely that the results were largely self-audited and this is known to be
notoriously unreliable (35).
To a clinician seeking reliable information about the indications for IVC
interruption, the overall quality of the abundant literature is disappointing, in
contradistinction to the publications pertaining to heparin and VTE. Reliable evidence
is still available on the technique and safety profile of IVC interruption, despite the lack of
randomized trials, through large retrospective and prospective series. However, regarding
indications for use, careful systematic reviews have been unable to provide evidence-
based guidelines. Future randomized trials may focus on the trauma setting and on
prophylactic use. There are ethical concerns with the randomization of patients who have
contraindication to, or failure of, anticoagulant therapy to treatment with anticoagulants.
Furthermore there are logistical issues; the only published randomized trial took 3.5 years
in 44 centers. However, until results of future randomized trials and subsequent
recommendations become available, literature reviews about IVC interruption will remain
narrative at best, and many, if not most, indications for filter placement will remain
a matter of opinion.
Lastly, there is much industry support for the use of caval filters and a number of
clinicians involved in the Vena Cava Filter Consensus Committee have highlighted
competitive interests. Even with respect to randomized trials it is known that industry-
funded endeavours are more likely to be associated with statistically significant
pro-industry findings, both in medical trials and surgical interventions (36).
CLINICAL CONTROVERSIES CONCERNING VENA CAVA FILTERS
Many areas of clinical uncertainty have been highlighted above. The use of caval filtration
in free-floating iliofemoral thrombus, the use of filters in specific settings such as cancer
or trauma and the use of temporary or retrievable filters are all relatively controversial.
Many of these areas of uncertainty would be best addressed by means of robust well-
designed and preferably randomized trials.
Other specific questions remain unanswered.
The Use of Adjuvant Anticoagulation
It is not clear if anticoagulation is necessary after caval filtration. Many investigators
recommend routine anticoagulation after vena cava filter placement (37). However, little
data are available to support the utility of this practice. Several case-series have attempted
to address this issue. None of these investigators were able to demonstrate any benefit of
anticoagulation and the retrospective, unrandomized nature of the studies as well as the
limited duration and intensity of anticoagulation used in some of the studies suggest that
randomized comparisons will be necessary to resolve this issue.
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Comparative Efficacy of Filters and Anticoagulation
The comparative efficacy of caval filters relative to anticoagulation is unclear. The
randomized trial of Decousus suggested that filters may provide additional short-term
benefit against PE in anticoagulated patients. An unrandomized retrospective series found
no significant differences in recurrence rate or lower extremity symptoms between patients
treated with anticoagulation and in those in who filters were placed (38). The significant
design flaws of this small study mean that larger randomized trials will be necessary to
address this issue.
Suprarenal Placement of Caval Filters
The general recommended placement site for caval filters is in the infrarenal portion of the
vena cava. This reflects concern about the possibility of caval thrombosis precipitating
acute renal failure as a result of renal vein extension of thrombus following suprarenal
placement. On occasion, infrarenal placement is impossible. Six studies, including 187
patients in total, highlight this subset of patients (37). All but one study utilized the
Greenfield filter exclusively (39–44). Mean follow-up was 70 months. PE occurred in 6%
(7 of 112) and venous insufficiency developed in 75% (55 of 73). Although IVC
thrombosis was diagnosed in 3.6% (4 of 112), no evidence of significant renal morbidity
was noted.
Compared with infrarenal placement, suprarenal filters appear to be associated with
a higher rate of PE and venous insufficiency. These differences could reflect differences in
study population rather than site of filter placement. Previous PE and malignancy was
more common in those studies evaluating suprarenal placement, suggesting that this study
population was at particularly high risk of thrombotic events and venous stasis (41). More
work will be required to clarify the safety and efficacy of suprarenal deployment.
Superior Vena Cava Filters
Data on superior vena cava filtration (SVC) are scarce and the literature is limited to case
reports, a single small case series (45–50) and a report of a retrievable filter placed in the
SVC and successfully retrieved (51). To date the reported results are mixed, with some
patients remaining asymptomatic and others developing SVC thrombosis. Larger series
and longer follow-up will be required before any meaningful comment can be made on the
safety and efficacy of SVC filters.
Assessment of Risk and Benefit of Anticoagulation for Venous
Thromboembolic Disease
In order to fully appraise the utility of caval filters, an informed decision regarding their use
must necessarily include a consideration of the relative risks and benefits of anticoagulation.
As highlighted above, there is a wealth of reliable evidence in the form of randomized trials
of anticoagulation in VTE which involve thousands of patients worldwide. The rate of
symptomatic recurrent thrombosis is 3% over two to four years of surveillance for patients
on long-term therapy (52,53). Major hemorrhage may be defined as one resulting in
retroperitoneal or intracranial bleeding, requiring blood transfusion or reducing baseline
hemoglobin by 2 g/dl. During heparin therapy, 3% of patients (range: 0–7%) will suffer
major hemorrhage as will 2% to 5% of patients on subsequent warfarin therapy (54,55). In
patients on warfarin therapy,for an indefinite period, major bleeding has been noted in 8.3%
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after 4 years offollow-up (53). The risk factors for hemorrhage include duration of therapy,
recent surgery or trauma, age over 65 years, concomitant aspirin therapy, renal or hepatic
insufficiency, previous gastrointestinal bleeding, alcohol abuse, higher intensity therapy,
and, in some studies, malignant disease and female gender (54,55). Clearly these factors
would notconstitute absolute contraindications, although many clinicians would hesitate to
anticoagulate a patient with recent central nervous system trauma or hemorrhage, active
hemorrhage, significant thrombocytopenia (less than 50,000/ml), cerebral metastases or
a recent large embolic stroke (56–58). The evidence-base for this strategy is limited but
anecdotal case reports and series suggest that anticoagulation is probably sufficiently
hazardous that vena cava filters should be considered for patients with VTE in
these situations.
KEY POINTS
† The evidence base for the use of caval filters is relatively limited.
† There are substantial variations in practice between the United States, the United
Kingdom and mainland Europe with respect to numbers of caval filters placed.
This may reflect clinical uncertainty, the influence of reimbursement and/or the
threat of litigation.
† Caval filters may reduce early PE mortality but there is no reduction in all-cause
mortality at two years in a population who also have adjuvant anticoagulation.
† In a population who are also treated with anticoagulation, the use of caval filters
may be associated with an increase in recurrent DVT.
† There are no randomized trials to support the use of caval filters for the most
widely accepted indications (documented failure of and absolute contra-
indication to, anticoagulation) and it is doubtful that an Ethics Committee or
Institutional Review Board will support trials in this area.
† The use of caval filters per se in trauma settings is increasing rapidly and the
practice would benefit from supporting randomized trial evidence.
† The latest generation of retrievable filters can be retrieved after extended periods
and may protect the patient from PE during high-risk periods, e.g., post-
operatively, while avoiding the longer-term risks associated with extended
placement.
† The practice of retrievable filter placement in trauma or perioperative settings
would benefit from evidence from robust trials.
† Many controversies exist regarding optimal management of patients with VTE
using caval filters including the use of adjuvant anticoagulation therapy (dose
and duration of therapy), suprarenal placement and SVC placement and the use
of filters for free-floating thrombus.
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SECTION D: VARICOSE VEINS
18
Etiology and Pathophysiology
of Varicose Veins
Jonathan Golledge
School of Medicine, James Cook University, Townsville, Queensland, Australia
INTRODUCTION
Review of published studies on varicose veins is hampered by the variety of methods used
to assess, define and classify the condition. The definition of varicose veins used in a given
study is often not stated or varies, making comparison from one publication to another
impossible. The CEAP classification states that “varicose veins are palpable, dilated
subcutaneous veins usually larger than 4 mm” (1). Not surprisingly, studies of the
prevalence of varicose veins have produced markedly disparate findings, with figures
varying from 4.5% to 57% (2). The mechanism(s) responsible for their development are
incompletely understood, however, a number of theories of etiology have been suggested
with varying degrees of clinical and pathological evidence. The suggested theories have to
explain in some form the findings from studies of varicose vein epidemiology, imaging
and pathology.
RISK FACTORS FOR VARICOSE VEINS
Most studies suggest that varicose veins are more common in women, older sub-groups
and following multiple pregnancies (2). There is little evidence to support other suggested
risk factors for varicose veins, including life style factors (3).
DUPLEX FINDINGS IN VARICOSE VEINS
Superficial venous reflux (retrograde flow across a valve of O0.5 sec) is detectable in
individuals without prominent superficial lower limb veins (14% in one study) (4). The
incidence of reflux is higher in patients with obviously dilated veins (77%) but not
invariably present in those with varicose veins (87%) (4). The site of reflux can be
anywhere along the great or small saphenous veins and frequently is located at a valve
distal to the sapheno–femoral or sapheno–popliteal junctions. For example, Labropoulos
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