An inferior vena cava filter is a type of vascular filter, a medical device that is
implanted by interventional radiologists or vascular surgeons into the inferior vena cava
to presumably prevent life-threatening pulmonary emboli. Their effectiveness and safety profile
is not well established, and in general, they are only recommended in some high-risk scenarios.
In 2012, the American College of Chest Physicians recommended IVC filters for those with contraindications
to anticoagulation who either have acute PE or acute proximal deep vein thrombosis.
Anticoagulation In those with initial acute proximal DVT or
acute PE who had IVC filters placed instead of anticoagulation, and who have their risk
of bleeding resolve, the American College of Chest Physicians suggested, in 2012, that
they receive a standard course of anticoagulation. While IVC filters are associated with a long
term risk of DVT, they are not, alone, reason enough to maintain extended anticoagulation.
Placement IVC filters are placed endovascularly, meaning
that they are inserted via the blood vessels. Historically, IVC filters were placed surgically,
but with modern filters that can be compressed into much thinner catheters, access to the
venous system can be obtained via the femoral vein, the internal jugular vein or the arm
veins with one design. Choice of route depends mainly on the number and location of any blood
clot within the venous system. To place the filter, a catheter is guided into the IVC
using fluoroscopic guidance, then the filter is pushed through the catheter and deployed
into the desired location, usually just below the junction of the IVC and the lowest renal
vein. Review of prior cross-sectional imaging or
a venogram of the IVC is performed before deploying the filter to assess for potential
anatomic variations, thrombi within the IVC, or areas of stenoses, as well as to estimate
the diameter of the IVC. Rarely, ultrasound-guided placement is preferred in the setting of contrast
allergy, renal insufficiency, and when patient immobility is desired. The size of the IVC
may affect which filter is deployed, as some are approved to accommodate larger cavae.
There are situations where the filter is placed above the renal veins. Also, if there is duplication
of the IVC, the filter is placed above the confluence of the two IVCs or a filter can
be placed within each IVC. Indications for use
While the ability to retrieve a filter does exist for many models, it cannot be guaranteed
that all cases of filter placement will allow for, or be indicated for retrieval. Thus,
the requirements and indications for permanent placement of filters is used to decide on
when to use both permanent and temporary IVC filters.
Long-term risk factors must be considered as well, to include life expectancy of more
than six months following insertion, and the ability of the patient to comply with anticoagulation
therapy. The decision to use a filter that is temporary vs permanent basically is tied
to the expected duration of time that protection is needed to prevent Pulmonary Emboli from
passing to the heart and lungs. One such guideline is outlined below:
Contraindications to anticoagulation; e.g. a patient with DVT or PE who has another condition
that puts them at risk of bleeding, such as a recent bleed into the brain, or a patient
about to undergo major surgery Short Term Risk of PE/Short Term contraindication
of anticoagulation: Usually merits a retrievable filter
Uncertain Risk of PE and/or lack of control for anticoagulation: Usually results in permanent
filters for long term management Long Term Risk of PE/Recurrent PE/Recurrent
DVT: Permanent Filter Indication Categories
While many studies have been done on the efficacy of Vena Cava filters, there still have not
been any major studies done on the actual placement and removal of the filters regarding
standard guidelines. Which is why the Society of Interventional Radiology created a multidisciplinary
panel that developed the following guidelines to see if someone qualifies for implantation:
Absolute Indications These are patients that should strongly consider
having IVC filter placement, as they are at greatest risk of pulmonary embolus.
Proven VTE: Venous thromboembolism and contraindication or complication due to anticoagulation therapy
Recurrent VTE: Despite adequate anticoagulation therapy
Relative Indications This is a maybe category; normally it represents
patients who could benefit from an IVC filter, but may be just fine without one as well.
Proven VTE: High risk of contraindication or complication to arise during anticoagulation
thearpy Large, free-floating proximal DVT's
Poor Compliance: INR levels are not stable, not taking medicine as directed
Thrombolysis: Iliocaval DVT's, which are emboli in the Illiac region
Prophylactic Indications These are usually very controversial reasons
to do an IVC filter, and most radiologists and doctors generally will not recommend an
IVC filter if other options are available instead.
No VTE: Anticoagulation therapy is not possible Transient risk of VTE: Trauma, surgical procedures
or medical conditions Other Indications
Bariatric Patients: Undergoing surgery for weight control, only if BMI greater than 55,
previous history of DVT/PE, hypercoagulable state, chronic venous insufficiency, truncal
obesity or contraindication to anticoagulation therapy.
Indications for Removing IVC Filter There is no current published data confirming
the benefit of removing an IVC. Because of this, the Society of Interventional Radiology
created a multidisciplinary panel that developed the following guidelines to see if someone
qualifies for removal: No need for Permanent filter: Remove temporary
Low risk of Significant PE: Continued anticoagulation is working, remove temporary
No Expected Near-Term high risk PE: Continuation of anticoagulation therapy, remove temporary
Life expectancy of more than six months: Remove temporary
Ability to retrieve the filter: No complications, no tear probability, no trauma probability,
if so, remove temporary Patient/Guardian agrees: Fully consented,
fully informed, if so, remove temporary Side effects
The main function of a vena cava filter is to prevent death from massive pulmonary emboli.
Long-term clinical follow-up studies have shown that this is accomplished in 96% of
cases having a standard stainless-steel Greenfield filter.
FDA Communication The FDA has recently released an Initial Communication
on the Risk and Adverse events associated with Long Term use of an inferior vena cava
filter. Over a period of about 5 years, they identify 921 events. While not the majority
of cases, that number still represents a statistical significance of the use of long-term IVCs.
Of these IVC filter side effects, 328 involved device migration, 146 involved embolizations
after detachment of device components, 70 involved perforation of the IVC, and 56 involved
filter fracture. Much of the medical community believes that this large number of adverse
events is related to the heart filter remaining in place for longer than necessary.
Common issues relating to failure, to include death include:
Device-associated morbidity Device migration
Filter embolization Filter fracture
Insertion-site thrombosis Perforation of the vena cava
Recurrent DVT Recurrent PE
Thrombotic complications Vena cava thrombosis
Less Common Adverse Reactions While these side effects are not common, many
do report issues stemming from the placement and complication of the IVC while inside of
the body. 9% delayed filter penetration of the IVC greater
than 3 mm Parts of filter broke off in 2%
Caval filter migrated to heart or pulmonary artery
Numerous small published articles and case studies report describe similar issues to
the above. Most notably: Filter fracture: Broken struts migrate to
retroperitoneum, requiring exploration. Perforation into the duodenum: Resulting in
severe diarrhea and weight loss. Arterial hemorrhage: Requires surgery to avoid
death. Misplaced Filter: Causes pericardiac tamponade
requiring surgery under cardiopulmonary bypass. Filter Migration to Right Atrium: Resulting
in acute myocardial infarction. Filter Lodged in Heart: Causes life-threatening
arrhythmia and often requires Pace Makers to resolve condition.
Heart Migration: Requires surgery to remove IVC from heart.
Sudden Death: Caused by the filter migrating to an active region in the heart.
Migration of Filter to Chest: Requires surgery. Perforation of filter strut into small-bowel:
Requires surgery to repair perforation. Even though the cases above are the exception,
and not the rule, most radiologists object to doing prophylactic filter insertions in
patients who do not have thromboembolic diseases. For the most part, whenever possible, interventional
radiologists would rather start the patient on anticoagulants than use an IVC, even if
requested or referred via a doctor. IVC filter composition, MRI dangers and effects
While most IVC filters are made of non-ferromagnetic materials, there are a few types that are
weakly ferromagnetic. Accordingly, IVC filters fall under the MRI Safe and MRI Conditional
categories depending mostly on type of material used during construction. Rarely will one
find an MRI Not Safe IVC filter, as most of the steel, and other ferromagnetic material
devices have been discontinued via the FDA. IVC filters are attached to the vena cava
via hooks on their ends. Some are compression springs, which compress outward onto the side
wall of the vena cava; however, they still have small hooks that retain their location.
These hooks aid in the anchoring and healing process, as they allow the tissues to 'ingrow'
around them, securing the IVC in place. It is unlikely, then, after 4 to 6 weeks of healing,
that an MRI of 1.5 tesla, up to 3 tesla, will cause any level of dislodging to occur for
the IVC filter. Studies of MR examination of both animals
and humans, with implanted IVC filters, have not reported complications or symptomatic
filter displacement. Several animal studies have even used “real-time”
MR for the placement of IVC filters to check for rotation, sheering, and other artifacts.
As part of the 'routing' survey for MRI studies, patients who have IVC filters will often need
verification from the doctor, or medical records, to state that the IVC is safe for the MRI.
Most patients with weakly or non-safe ferromagnetic implants will be given a card, which they
keep on their person at all time, that can help isolate if it is safe to do an MRI.
For patients who have been denied MRI scans for safety reasons, doctors usually recommend
the CT scan with contrast as an alternative. Labeling and recommendations
Most IVC filters that have been tested have been labeled as “MR safe”; the remainder
of IVC filters that have been tested are “MR conditional.” Patients who have been treated
with nonferromagnetic IVC filters can undergo MR examination any time after filter implantation.
In patients who have been treated with a weakly ferromagnetic IVC filter, it is advised that
the patient wait at least six weeks before undergoing an MR examination, unless there
is a strong clinical indication to perform the MR examination sooner after implantation,
and as long as there is no reason to suspect that the device is not positioned properly
or that it is not firmly in place. Most studies of IVC filters have generally been conducted
at 1.5 Tesla or less, although many IVC filters have now been evaluated at 3 tesla and deemed
acceptable for MR examination. Retrieval
The concept of a removable IVC filter was first thought up in 1967 However, it was not
until 2003 and 2004 that the United States Food and Drug Administration drafted regulations
and requirements on creating devices that were fit for retrieval from the vena cava
And still, even while the FDA did approve of the models and designs, it wasn't until
2005 that the Society of Interventional Radiology convened a multidisciplinary conference to
address the clinical application of nonpermanent vena cava filters.
Retrievable filters are fitted with a device that allows them to be pulled back into a
catheter and removed from the body, often through the jugular vein. Prior to 2004, filters
that had been in the IVC for less than three weeks were considered suitable to attempt
retrieval, as filters that have been in place longer might have been overgrown by cells
from the IVC wall and there was an increased risk of IVC injury if the filter is dislodged.
Newer designs, and developments in techniques mean that some filters can now be left in
for prolonged periods and retrievals after a year are now being reported. This would
include the ALN, Bard G2 and G2x, Option, Tulip and Celect filters.
It is important to note that the clinical exam prior to the removal of the filter is
vital in understanding both the risk and pathophysiological effects removing the filter will have on the
patient. Doctors and medical professionals must consider several key factors.
History The IVC filter was developed by Lazar Greenfield.
References
Cited literature
Athanasoulis, Christopher A, MD. "Complications of Vena Cava Filters". Journal of Radiology.
3 188: 614–615. Retrieved 102012. External links
IVC filters - emedicine.com IVC filters - Medical College of Wisconsin
IVC filter - GPnotebook.co.uk history of Lazar Greenfield and his filter
- Invention & Technology Greenfield Filter Informational Website