It is believed that, every year, between 350,000 and 600,000 people in this country develop a VTE (venous thromboembolism). Those patients who have a DVT (deep vein thrombosis) are at a higher risk of developing a PE (pulmonary embolism). In fact, in a recent study, it was found that some 40% of patients that present with a DVT also had a PE. When a DVT is treated, the goal is to stop it from growing larger and to avoid embolization. Anticoagulant medication is the recommended form of treatment by the American College of Chest Physicians (ACCP). However, this is not always suitable treatment. If someone is allergic to anticoagulants, if they have recently experienced trauma, bleeding or surgery, or if they continue to develop DTVs despite the medication. In those cases, an IVC (inferior vena cava) filter may be considered.

A Brief History of IVC Filters

The first conceptual model of the IVC filter to prevent PE was developed by Trousseau in 1868. However, the first successful surgery was completed in 1959 by Bottini. In 1967, the first Mobin-Uddin filter was introduced and this was actually the very first mechanical filter. This means that the filter is able to trap the DVT, thereby ensuring it does not travel to the lungs.

As medical science advanced, so did IVC filters. Today, there are two main types. The first is the permanent filter and the second is the removable one. Removable filters can be either temporary or retrievable. A temporary model is attached to a catheter, which means it has to be removed as soon as possible in order to prevent infections. Retrievable filters, meanwhile, can be left in the body but their original design is to be removed eventually. Unfortunately, research has shown that many of these devices fail in some way or another, causing more damage to the patient.

Some Key Points to Know About the IVC Filter

• There is very little evidence that suggests using an IVC filter is beneficial for DVT treatment.
• Official guidelines state that an IVC filter should only be used if anticoagulant medication is not successful.
• Not enough data exists to see whether IVC filters are beneficial in the management of recurrent VTE or PE, ilio-caval thrombus and more.
• Retrievable IVC filters are preferred if the patient has a temporary contraindication to anticoagulant medication.
• If contraindication to anticoagulant medication is no longer present, the IVC filter should be taken out and medication should be resumed.

It is a known fact that IVC filters can lead to significant complications. Many of these complications get worse over time. Filter thrombosis is one of those complications. Essentially, a thrombus will end up directly in the filter, which either arose locally or originated distally. Unfortunately, it is not always possible to tell what the source is. Having knowledge of this is vital and goes above and beyond a theoretical implication. If it is a local thrombus, it is likely that it is a result of the IVC filter. However, if the thrombus is in the leg, it could point to the filter actually doing its job properly. The incidence of IVC filter thrombosis is said to be between 5% and 30%.

Symptoms of IVC Filter Thrombosis

Filter thrombosis is the most unwanted long term side effect of the IVC filter. If it happens, blood flow from the lower extremities is not as good anymore. However, not all patients actually present with symptoms. If they do have symptoms, it tends to be swelling, ulceration and heaviness of the leg. Unfortunately, this can develop into severe post-phlebitic syndrome. Common symptoms include back pain and other symptoms that could point to a variety of other issues as well. A consequence of filter thrombosis is phlegmasia cerulea dolens.

A review looked into the monitoring after IVC filter insertion. This looked at 1158 patients between 1975 and 2010. The study showed that, on average, after 39.9 months, 21% of people experienced a leg edema, while 5.4% experienced ulcers.

This is not the only problem with filter thrombosis. The other main problem is pulmonary embolism (PE), which is the very thing that IVC filters are trying to prevent. If a thrombus is caught within an IVC filter, it can lead to the filter arms retracting. When this happens, a new tract is formed and a thrombus can pass through this. Alternatively, a blood clot could appear above the filter site, which could also lead to a PE.

There is evidence to suggest that other consequences of thrombosis also exist. For instance, a blood clot could enter the renal vein, leading to renal dysfunction. It may also travel to the lumbar veins and cause congestion of the spinal cord. This, in turn, could lead to anything from weakness of the lower extremities to full paralysis.

Risk Factors Associated with IVC Filter Thrombosis

The list of publications in relation to IVC filters and thrombosis is extensive. Despite this, however, there is still not a lot known about the actual risk factors that could lead to a thrombosis. This is because most of the studies are retrospective. Additionally, most are related to a particular type of IVC filter that is used in a group of patients that is non-homogeneous. Although these difficulties are real, a number of risk factors are now suggested. These are:

1. Filter design, which is most likely the most important of the factors that could lead to thrombosis. Unfortunately, there are not enough head to head comparisons between the different types of filters. As a result, the data comes from single filter studies. It is believed, however, that double basked design filters like Trapease and Optease carry more risk.

2. Filter retention is also an issue. The longer it is in place, the higher the chance that a thrombosis will develop. It is known that there are differences here between the various types of filters, with some filters being more likely to lead to thrombosis.

3. Hypercoagulability is believed to be an IVC filter risk for thrombosis. However, being able to determine this with a degree of certainty is difficult, as it would only be possible if all other risk factors have been dismissed. These risk factors include such things as acquired factors and congenital factors.

4. IVC filter thrombosis in cancer patients. There is a claim that cancer patients have experienced some of the worst consequences of IVC filter thrombosis. It has not been possible to verify these claims yet, although it certainly is true that IVC filters on cancer patients are being studied in greater detail.

Anticoagulants and IVC Filter Thrombosis

There is some debate going on about the effect of long term anticoagulant medication use for people who have an IVC filter. Some circumstantial evidence does suggest that anticoagulants should be prescribed if it possible to do so. This stems from two pieces of data.

1. PREPIC 2 data, which suggests that there is no link between the amount of thormbi in patients whether they had are had not taken anticoagulants after having an IVC filter.
2. Retrospective data that uses case by case reviews. This data suggests that using anticoagulants could reduce the chance of developing thrombosis by as much as 50%.

It is very difficult, therefore, to draw accurate conclusions. This is also due to the fact that, naturally, there is prospective data. It is probable that treating patients with anticoagulants after they have had an IVC filter inserted will not be harmful. However, many physicians will only do so if they have reason to believe anticoagulants may be needed for other conditions.

Treating IVC Filter Thrombosis

It may come as some surprise that some patients who develop IVC filter thrombosis do not need any treatment. This is because many have an asymptomatic thrombosis. In these cases, regular blood flow is likely to be achieved thanks to collaterals. However, if a patient presents with symptoms, they should also be offered treatment.

Treating an IVC filter thrombosis will generally start with anticoagulant medication if possible. There has been a small study that showed that propagation of thormbus did not change whether or not patients received anticoagulants. The second step would be to assess whether the filter can be retrieved. If it can, particularly after sufficient anticoagulant medication has been applied and the thrombus regresses, this should be considered. In many cases, prescribing anticoagulant medication isn’t enough to solve the problem and some sort of intervention will be required. Some physicians will use a catheter IVC filter through thrombolysis and others prefer angioplasty. Optionally, physicians may choose to place a stent, but this is generally only done once the largest part of the vena cava is clear of any blood clots.

Additional Resources:

Inferior vena cava filter thrombosis: a review of current concepts, evidence, and approach to management
Inferior Vena Cava Filters for Recurrent Thrombosis
Management of the Thrombosed Filter-Bearing Inferior Vena Cava
A review of inferior vena cava filter thrombosis
Indications and complications associated with inferior vena cava filters