Inferior Vena Caval Filters: A Solution Resulting in a Problem

By: Fellowship-trained Vascular/Interventional Radiologist

BACKGROUND:

Inferior Vena Caval Filters (IVCF) have been used in clinical practice since the 1970s.  They are designed to prevent the migration of blood clots from the deep veins of the legs (Deep venous thrombosis / DVT) that could get trapped in the blood vessels of the lungs (Pulmonary Embolism / PE).

The published figures for the annual incidence of diagnosed episodes of DVT  range from 48-206 per 100,000 people. This roughly translates into 130,000-550,000 new DVT diagnoses annually in the United States.  DVT can result in multiple long-term morbidities, with PE being the worst acute complication. There are an estimated 600,000 cases of PE per year in the US, which if untreated, result in a mortality rate of 30%.

DIAGNOSTIC AND TREATMENT OPTIONS:

First-line screening for DVT is doppler ultrasound.  Evaluation for PE utilizes a specialized CT scan protocol.  Alternatively, radioactive tracers can be introduced into both the blood stream and inhaled, to allow detection of mismatched lung aeration and blood flow. Most hospitals have accessibility to both noninvasive diagnostic options for diagnosis of PE.

Once the diagnosis of DVT/PE is made, treatment planning and future prevention requires careful evaluation of the patient, their risk factors, and medical history.
Standard therapies include:

• Observation/no therapy
• In-hospital intravenous blood thinners (used to bridge the patient to outpatient therapy)
• Subcutaneous injectable blood thinners (short or long-term)
• Oral blood thinners (long-term)

Important to note is that blood thinners do not cure DVT or PE, they merely prevent blood clots that are present from getting larger.  The risk for clot migration exists regardless of blood thinner therapy. In addition, there is a sizable subset of patients who are not candidates for blood thinners, who also require evaluation for IVC Filter placement.

Patients who may qualify for an IVCF:

• DVT/PE with contraindication to anticoagulation therapy (e.g. active internal or high risk for bleeding)
• Complication of anticoagulation therapy in anticoagulated patients requiring temporary or permanent cessation of treatment
• Recurrent DVT or PE on therapeutic levels of blood thinners
• Free-floating intravenous thrombus
• Prophylaxis
• Patients with DVT who are about to undergo high risk surgery
• Chronic pulmonary hypertension with marginal cardiopulmonary reserve
• Malignancy
• Multi-organ trauma

INFERIOR VENA CAVAL FILTERS:

For over four decades, surgical or mechanical inferior vena caval interruption has been utilized in the management of DVT with the goal of PE prevention.  IVCF reduce the risk of clinically significant PE at least five-fold.  Thus, while this risk is not reduced to zero, it is significantly decreased.  The risk of fatal PE is reduced to negligible levels.

As technologies have advanced, newer IVCF have been developed that can be implanted and subsequently retrieved within a pre-specified manufacturer-approved timeframe.  If necessary, or if attempted removal is unsuccessful, IVCF can be left in place as a permanent device.

CONTROVERSY:

Recent reports demonstrate the ever-growing use of IVCF.  Approximately  259,000 IVC filters will be implanted in 2012, compared to 167,000 in 2007. Obviously, the number of complications will only increase.

Per the FDA (August, 2008): “Since 2005, the FDA has received 921 device adverse event reports involving IVC filters, of which 328 involved device migration, 146 involved embolizations (detachment of device components), 70 involved perforation of the IVC, and 56 involved filter fracture. Some of these events led to adverse clinical outcomes in patients…FDA encourages all physicians involved in the treatment and follow-up of IVC filter recipients to consider the risks and benefits of filter removal for each patient. If a patient has a retrievable IVC filter that should be removed based on his or her individual risk/benefit profile, the primary care physician and/or those providing ongoing patient care should refer the patient for IVC filter removal when feasible and clinically indicated. ”

The FDA communication came on the heels of a retrospective, single center report about the rate of filter fracture and migration in the number of patients that underwent placement of one specific manufacturer’s IVCFs.  Although not a well-designed study from a medical research perspective, this article underscores the potential for long-term complication of IVCF, especially in the population that may only have a short-term need.

While an overall low percentage of IVCF could cause clinical complications if left in place for too long, it is imperative that physicians ordering and placing IVCF aggressively monitor these patients and identify when the benefit of IVCF with regards to PE prevention is outweighed by the risk.

Potential medico-legal areas include:

1. Lack of patient follow-up after implantation of IVCF
2. Complications as a result of implanted IVCF which should have been considered for removal prior to the adverse event