What Is an IVC Filter and How Does it Work?
Blood flows through the body delivering oxygen in the process. The system works amazingly well to keep us alive, however, the body’s survival mechanism can also present dangers to an individual.
Blood clots can form when a blood vessel is damaged, which may occur in an accident where trauma is delivered to the body.
In that case, blood platelets rush to the site of damage and cling to each other to form a plug to stop any leakage. Adding to the platelets are clotting factors that also race to the scene forming a long strand of fibrin. Along with the platelets they form a nice Band-Aid of sorts to plug any cuts.
The blood clotting process can also be sparked by the presence of cholesterol plaques in the arteries. They can mimic a break in the vessel and the clotting process starts. If the waxy plaque breaks apart from the artery, a heart attack or stroke can occur.
Not just cholesterol, but an irregular heartbeat, such as atrial fibrillation, can cause blood to move slowly or pool. This condition also signals platelets to form and clot in preparation for survival.
You may have heard of people developing deep vein thrombosis (DVT) on an airplane flight. It occurs during periods of inactivity when a blood clots forms in the legs, arms or pelvis. That clot can travel to the lungs from the legs or even to other parts of the body.
A pulmonary embolism (PE) develops in the artery to the lungs. Both are clots and are called a thrombosis.
The Centers for Disease Control and Prevention (CDC) reports as many as 60,000 to 100,000 Americans die every year from DVT or PE. Ten to 30 percent will die within one month of diagnosis. Often sudden death is the first symptom in about one-quarter of patients with pulmonary embolism.
One half of people with DVT will have long-term complications, according to the CDC, and about one-third of patients with DVT/ PE will have a recurrence within ten years. So finding a treatment and soon is imperative to prevent a blood clot from growing.
The first treatment is an image to determine the location of the blood clot. Imaging may include an angiogram, MRI, CT scan, ultrasound or chest x-ray.
After imaging, blood thinners are given. Anticoagulants (blood thinners) will prevent a new blood clot from forming. Medications such as clot dissolvers will encourage the clot to dissolve more quickly. A very large clot may have to be removed through a catheter that threads through your blood vessels.
Another method to trap a blood clot and prevent it from entering the lungs involves a vein filter.
An IVC filter is implanted in the main artery in the body, the inferior vena cava or IVC. The newer generation of IVC filters is made of nitinol, which is a metal alloy of nickel and titanium. Nitinol is increasingly being used by the medical device industry because it is elastic yet retains its thermal shape memory, in other words, it will restore to a predetermined shape upon heating or under pressure.
Resembling a spider with long legs or struts, the IVC filter acts like a cage intended to capture blood clots before they reach the lungs causing a pulmonary embolism (PE) or the heart causing a heart attack.
The IVC filter will be placed, usually by an interventional radiologist or vascular surgeon, into the inferior vena cava which runs from your legs to the right side of the heart. A small incision is made, usually in the jugular vein or the groin. Once in place, the IVC filter traps blood clots not unlike a filter used in your car or home.
An IVC filter may be used if an anticoagulant drug doesn’t work or the patient cannot take the drug. It is not considered to be a first-line treatment but only used if other treatments have failed or are contraindicated.
Use of IVCs has increased rapidly in the last three decade. For example, in 1979, the Food and Drug Administration (FDA) reports only 2,000 IVC filters were used. Today about 250,000 are implanted every year.
There are two types of IVC filters – those that remain in the body permanently and those that are intended to be removed once the patient is no longer in danger of a pulmonary embolism.
Initially, it was thought that the IVC filters may stay implanted in a patient indefinitely but that thinking is slowly evolving due to serious complications. According to the FDA, doctors should “consider removing the filter as soon as protection from pulmonary embolism is no longer needed.”
Removal is like the implantation. In this case a dye is injected around the device while a catheter is inserted in the vein. It grabs the hook at the top end of the filter and pulls it through the sheath and out of the body. In an ideal world there are no complications, but in the real world complications can arise.
If the filter is tilted or attached to the vena cava wall, to tissues or organs, it can be nearly impossible to remove. The removal hook is placed in the placement area through a sheath but any additional tissue may not be able to be retracted through the sheath.
The FDA is concerned that the filters are not always removed when they should be. As a result, some long-term risks have become apparent such as device migration, filter fracture, embolization, perforation of the IVC and difficulty removing the filter.
The following companies make an IVC filter – Cook Medical makes the Tulip and Cook Celect; C.R. Bard makes the Bard Recovery and the Bard G2 IVC filter; Gunther, Boston Scientific, Crux, Rafael, ALN, Angiotech and B. Braun all make IVC filters.
The IVC filter, like more than 90 percent of medical devices, was approved under the Food and Drug Administration’s 510(k) process, which basically relies on the company for safety assurances. The FDA “approval” is actually a “clearance to sell” under 510(k). The agency does not require clinical trials to be submitted before the clearance, though many companies do submit such information voluntarily.
The vena cava filters are considered a class II medical device indicating moderate risk, despite the fact that they may be permanently implanted.
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