Concerns are being raised about a medical device implanted in thousands of Americans at risk for blood clots.

At least 27 deaths have been linked to the Recovery filter, which is inserted into the largest vein in the body, NBC News reports.

Government records show 300 other non-fatal problems have also been reported with the Recovery, sold by C.R. Bard.

After the problems with the Recovery came to light, Bard hired public-relations company to help manage media attention and an outside doctor to conduct a confidential study, NBC News reports.

The consultant found the Recovery filter had higher rates of relative risk for death, filter fracture, and movement than all its competitors.

"Further investigation...is urgently warranted," the doctor wrote, according to the network.