Retrieval analysis of clinical explanted vena cava filters.

Vena cava filters are the most commonly used mechanical devices to prevent pulmonary embolism. A retrievable permanent filter has been available since 1999. That has allowed the direct study of thrombi captured in humans and the punctual interaction of blood and device at long and short term. Through traditional histologic methods, captured thrombi and the tissues formed around the filter were observed. An innovative environmental scanning electron microscopy technique allowed detection of micro- and nanosized foreign bodies inside thrombi and tissues, and chemical analysis could be carried out by means of energy dispersive spectroscopy. All specimens contained different quantities of foreign debris ranging from few tens of microns to 50 nanometers; their chemistry was not homogeneous when patients were compared, and also differed considerably within the same filter. The constant presence of debris deeply embedded in all thrombi observed may mean that they are the cause that triggered the formation of those thrombi as a result of the interaction between foreign bodies and blood components.