Some vena cava filters are prone to break apart and cause emboli themselves, according to an Archives of Internal Medicine study. Meanwhile, the FDA is expressing concern that too many devices are being left in patients after the threat of embolism has passed.

Researchers at a single institution examined some 80 patients who had received either Bard Recovery vena cava filters or a later model, the Bard G2. They found strut fractures and embolization in 25% of the Recovery recipients, and in 12% of G2 recipients. Some patients had life-threatening cardiac symptoms, including ventricular tachycardia and tamponade.

The journal’s editor expresses shock that the FDA classified the filters with other Class II devices — such as mercury thermometers. She estimates that “more than 7000 Americans may now be carrying a fractured G2 filter.”

In keeping with the researchers’ and editor’s call for more scrutiny of these devices, the FDA says it is studying the issue further.