Pulmonary Embolism Support Group
By far the most common form of pulmonary embolism is a thromboembolism, which occurs when a blood clot, generally a venous thrombus, becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs. Symptoms may include difficulty breathing, pain during breathing, and more rarely circulatory instability and death.
http://circ.ahajournals.org/cgi/content/short/112/3/416
Historically there has not been a long enough collective experience with IVC filters to get an arm around other long-term risks such as fracture or migration.
The more I read-up on long-term IVC filter retention the more I wanted it out, but the radiologist who put it in hid from his patients, refused to remove it when pressed by my PCP (the guy probably did not know how), and by the time I fought it a few months the window of removal had passed.
http://stanfordhospital.org/newsEvents/newsReleases/2010/ivc-filter-removal-laser.html
http://stanfordhospital.org/profiles/frdActionServlet?choiceId=showClinicalTrial&&studyId=6416&fid=7234