An inferior vena cava (IVC) filter is a small medical device designed to prevent blood clots from traveling to the lungs, where they can cause a pulmonary embolism. It acts as a barrier, primarily for individuals at high risk when blood-thinning medications are unsuitable or ineffective.
The Inferior Vena Cava
The inferior vena cava (IVC) is the largest vein in the human body, playing a central role in the circulatory system. This large blood vessel is located in the abdomen, running along the right side of the vertebral column. Its primary function involves collecting deoxygenated blood from the lower extremities, the pelvis, and the abdominal organs.
The IVC forms from the joining of the right and left common iliac veins, typically around the level of the fifth lumbar vertebra in the lower back. From there, it ascends through the abdomen and passes through the diaphragm, a muscular structure that separates the chest from the abdomen, before emptying into the right atrium of the heart.
Precise Filter Location
An IVC filter is most commonly placed in the infrarenal position, meaning below the level where the renal veins connect to the IVC. This specific site is chosen from an anatomical perspective to allow blood flow from the kidneys to bypass the filter, ensuring renal function is not compromised.
While infrarenal placement is standard, alternative suprarenal placement, which is above the renal veins, may be considered in specific clinical scenarios. These situations include instances where a blood clot in the IVC extends above the renal veins or in cases like pregnancy where the expanding uterus might compress an infrarenal filter. The suprarenal IVC is typically wider and its diameter can vary more, making infrarenal placement generally preferred when possible.
Why Placement Matters
Precise placement of an IVC filter is crucial for its effectiveness in preventing pulmonary embolism. By strategically positioning the filter within the inferior vena cava, it is able to effectively trap blood clots migrating upwards from the lower extremities.
This strategic placement maximizes the filter’s ability to capture clots while minimizing interference with normal blood flow through the major vein. The infrarenal position, in particular, balances the need to intercept clots with the necessity of maintaining proper blood return from the kidneys. An accurately placed filter allows blood to flow around the trapped clot, enabling the body’s natural processes to break down the clot over time.
How IVC Filters Are Placed
The insertion of an IVC filter is a minimally invasive procedure, typically performed by an interventional radiologist. The procedure usually takes about an hour and involves accessing a large vein, most commonly the femoral vein in the groin or the jugular vein in the neck.
During the procedure, a thin, flexible tube called a catheter is inserted into the chosen access vein. Using real-time X-ray imaging, known as fluoroscopy, the healthcare provider guides the catheter through the venous system to the precise location within the inferior vena cava. Once the catheter is in position, the collapsed IVC filter is deployed, expanding to fit securely against the walls of the vein.